Air Traffic Management Concept Baseline Definition - The Boeing ...

Air Traffic Management
Concept Baseline Definition
Prepared by
Boeing Commercial Airplane Group
NEXTOR Report # RR-97-3
October 31, 1997
Aslaug Haraldsdottir, Principal Investigator
Monica S. Alcabin
Alvin H. Burgemeister
Charles G. Lindsey
Nigel J. Makins
Robert W. Schwab
Arek Shakarian
William D. Shontz
Marissa K. Singleton
Paul A. van Tulder
Anthony W. Warren

Preface
This report documents research undertaken by the National Center of Excellence for
Aviation Operations Research, under Federal Aviation Administration Research Grant
Number 96-C-001. This document has not been reviewed by the Federal Aviation
Administration (FAA). Any opinions expressed herein do not necessarily reflect those of
the FAA or the U.S. Department of Transportation.
This document consists of the ATM Concept Baseline Definition, which incorporates
material from the NAS Stakeholders Needs report prepared as a separate volume. The
NAS Stakeholders Needs report should be viewed as an adjunct to this volume, and is
included as part of Boeing’s submission under NEXTOR Contract #DTFA03-97-00004,
Subagreement #SA1636JB.
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Executive Summary
This report presents an operational concept for the U.S. National Airspace System (NAS)
through the year 2015, including a transition path from the current system. This concept
was developed by Boeing Commercial Airplane Group for NASA’s Advanced Air
Transportation Technologies (AATT) program, under subcontract with NEXTOR
(National Center of Excellence for Aviation Operations Research).
The operational concept presented here is aimed at driving research to support preliminary
design decisions for the NAS, which will produce top level technical and human factors
requirements to achieve the system mission. Detailed concept validation research must
then be performed, where technology and human factors will be combined with economic
evaluation of concept components to fully define the operational concept and architecture.
Thus, the concept presented here, although well supported by rationale as to what might
be feasible in the next two decades, must be subjected to critical analysis and validation.
A companion report presents the results of a survey of NAS stakeholder needs, conducted
May-August 1997, which details stakeholders’ concerns about terminal area capacity and
access to airspace through 2015. Stakeholders also expressed the need to maintain or
improve safety in the NAS, and a need for increased emphasis on human factors research.
This report discusses the various factors that can force change in the NAS, and develops a
rationale for considering traffic growth as the primary driver for the ATM operational
concept. The NAS mission goals are defined in terms of safety, capacity and efficiency,
and a scenario is presented that predicts NAS traffic gridlock by 2006, where the terminal
area will be the primary choke point. If not averted, this will make current airline hubbing
operations infeasible, lead to escalation of operating costs and constrain economic growth.
This scenario is used as the basis for the operational concept, and high density operations
are emphasized in the report.
Highlights of the concept evolution presented in this report are:
1. Airspace will be configured to support a certain density of operation, ranging from
high to low, through dynamic partitioning.
2. Access to airspace will be based on the required system performance for the airspace
operation. A given aircraft will be qualified to a maximum Required System
Performance (RSP) level in which it can operate. RSP is developed by considering
ATM-related safety through an analysis of collision risk for the overall separation
assurance function.
3. A uniform CNS infrastructure performance is assumed to be provided throughout the
NAS, except for Category II-III landing and surface operations.
4. High density separation services will be provided neither by procedural nor radar
separation, but by a new precision form of separation assurance. This will allow
system throughput to be maximized where shared precision trajectory intent and a
universal time reference are assumed.
5. Low density separation services will be provided in other airspace, where user freedom
to select and modify the flight trajectory is allowed.
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6. Separation responsibility will remain shared between air traffic services and flight
crews. In high density operations the airplane will provide a separation monitoring
function.
The report discusses the human factors issues that lie at the heart of most of the proposed
system modernization initiatives, and makes recommendations regarding the nature and
extent of the human factors involvement in the system evolution. A detailed overview of
current and emerging communication, navigation and surveillance technologies is included
in the report, along with an overview of aviation weather technology.
The current lack of consensus in the industry on the details of the NAS modernization
path are discussed in the report. The need for a disciplined systems engineering approach
to the NAS evolution is detailed, with a particular focus on preliminary design activity that
is essential to focus the effort on the critical mission needs. The report calls for a
collaborative development and validation of the operational concept, and of the system
architecture, to ensure consideration of total system performance and minimize political
risk.
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Table of Contents
1 Introduction..................................................................................................................1
1.1 Objectives..............................................................................................................1
1.2 Context..................................................................................................................2
1.3 Scope.....................................................................................................................2
1.4 Report Overview....................................................................................................3
2 The NAS ATM System Development Process...............................................................5
2.1 Air Traffic System Modernization Mandate............................................................5
2.2 Consensus Future System Development Needs.......................................................6
2.3 Systems Engineering and Preliminary Design..........................................................6
3 The ATM System Functional Structure .......................................................................26
3.1 Air Traffic Management Objectives......................................................................26
3.2 A Functional View of the Current Concept...........................................................28
3.3 A Functional View of the Proposed Concept........................................................35
3.4 Proposed CNS/ATM Technology Improvements..................................................42
3.5 Airspace and Airways...........................................................................................42
3.6 Airports ...............................................................................................................43
3.7 Flight Service Stations .........................................................................................44
4 Human Factors ...........................................................................................................45
4.1 The Search For Greater Throughput And The Demands On The Human ..............45
4.2 The Role Of Human Factors In Enabling Change .................................................45
4.3 Human Factors Issues Affecting Tactical Control .................................................48
5 Available and Emerging Technology ...........................................................................55
5.1 Introduction.........................................................................................................55
5.2 Communication....................................................................................................65
5.3 Navigation ...........................................................................................................75
5.4 Surveillance .........................................................................................................80
5.5 Aviation Weather.................................................................................................87
6 ATM Concept Baseline.............................................................................................102
6.1 Concept Transition Methodology .......................................................................102
6.2 Capacity Driven Concept Baseline......................................................................106
6.3 Concept Validation Needs..................................................................................114
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7 NAS Concept Evaluation..........................................................................................116
7.1 Global Scenarios ................................................................................................116
7.2 Implications of Global Scenarios on System Transition Paths .............................119
7.3 Comparison with the FAA and RTCA Operational Concepts..............................120
8 Conclusions and Recommendations...........................................................................122
8.1 Conclusions .......................................................................................................122
8.2 Recommendations..............................................................................................122
8.3 Research Needs to Support the 2015 Concept....................................................123
Acknowledgments .......................................................................................................129
Bibliography ................................................................................................................130
Appendix A. Technology Inventory ............................................................................136
Appendix B. Global Scenario Issue Texts....................................................................149
Appendix C. Comparison of FAA 2005 and RTCA Users 2005 Operational Concepts 161
Appendix D. Transition Database................................................................................173
Appendix E. Constraints Model ..................................................................................183
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List of Figures
2.1 System Development Process
2.2 Requirements, Concepts, and Architecture
2.3 World Airplane Capacity Requirements (1997-2016)
2.4 User Needs Categories
2.5 American Airlines NAS Study Validated with Actual Delay Data
2.6 American Airlines NAS Study Results: Current NAS Delay Variance and Minutes
2.7 American Airlines NAS Study Results: Average Air Delay per Flight
2.8 Growth in Operations, Safety Rate & Frequency of Accidents (1980-2015)
2.9 Hull Loss Accidents (1982-92) for U.S. and Canada vs. Latin America
2.10 Primary System Agents
2.11 System Performance and Separations
2.12 The CAFT Analysis Process
2.13 Distribution of Airport Delay by Weather and Duration
2.14 Economic Modeling Process
3.1 The Air Traffic Management System
3.2 Air Traffic Management System Functional Structure
3.3 AOC and The Flight Planning Function
3.4 CFMU and the Flow Planning Function
3.5 Cockpit Crew and the Guidance and Navigation Function
3.6 The Separation Assurance Loop
3.7 Separation Standard and Performance Factors
3.8 Dense Terminal Airspace and CNS/ATM Technologies
3.9 Overview of Proposed CNS/ATM Technologies
5.1 Generic System Configuration for the Exchange of Air/Ground Information
5.2 Voice Communication
5.3 ACARS Communication
5.4 FANS-1 Communication
5.5 ATN Communication
5.6 Interfacility Communication
5.7 Navigation Functionality Overview
5.8 Area Navigation Capabilities for Departure Procedures
5.9 Reduced Separation Between Parallel Ocean Tracks
5.10 Airport Surface Surveillance Evolution Path
5.11 Terminal Area Surveillance Evolution Path
5.12 En Route Surveillance Evolution Path
5.13 Oceanic/Remote Area Surveillance Evolution Path
5.14 Functional Areas of Aviation Weather
5.15 Aviation Weather Observation Function
5.16 Aviation Weather Analysis Function
5.17 Aviation Weather Forecasting Function
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5.18 Aviation Weather Dissemination Function
6.1 Airspace Operating Phases
6.2 Capacity and Efficiency as a Function of Airspace Operating Phases
6.3 Final Approach Throughput Performance Factors
6.4 CNS/ATM Transition Logic Diagram Template
6.5 CNS/ATM Transition Logic for Flow Management
6.6 CNS/ATM Transition Logic for En Route and Terminal Area
6.7 CNS/ATM Transition Logic for the Arrival Transition Phase
6.8 CNS/ATM Transition for the Final Approach and Initial Departure Phase
6.9 CNS/ATM Transition for the Airport Surface
8.1 Preliminary Design Tools
viii

Acronyms
AAS
AATT
ACARS
ACP
ADF
ADF
ADS
ADS-B
AEEC
AERA
AFN
AFTN
AGFS
AGL
AIDC
AIV
ALPA
AMASS
AMSS
ANP
AOC
AOPA
ARSR
ARTCC
ASAS
ASDE
ASOS
ASR
ATA
ATC
ATIS
ATM
ATN
ATS
ATS
ATSMHS
AVOSS
AWC
AWIPS
AWOS
AWR
CAFT
CDM
CDTI
Advanced Automation System
Advanced Air Transportation Technology
ARINC Communications Addressing and Reporting System
Actual Communication Performance
Airline Dispatchers Federation
Automated Direction Finder
Automatic Dependent Surveillance
Automatic Dependent Surveillance-Broadcast
Airlines Electronic Engineering Committee
Automated En Route ATC
ATS Facilities Notification
Aeronautical Fixed Telecommunication Network
Aviation Gridded Forecast System
Above Ground Level
ATS Interfacility Data Communication
Aviation Impact Variables
Air Line Pilots Association
Airport Movement Area Safety System
Aeronautical Mobile Satellite System
Actual Navigation Performance
Airline Operational Control
Aircraft Owners and Pilots Association
Air Route Surveillance Radar
Air Route Traffic Control Center
Airborne Separation Assurance Systems
Airport Surface Detection Equipment
Automated Surface Observation System
Airport Surveillance Radar
Air Transport Association
Air Traffic Control
Automated Terminal Information System
Air Traffic Management
Aeronautical Telecommunication Network
Air Transportation System
Air Traffic Services
ATS Message Handling Service
Aviation Vortex Spacing System
Aviation Weather Center
Advanced Weather Information Processing Systems
Automated Weather Observation System
Aviation Weather Research
CNS/ATM Focused Team
Collaborative Decision Making
Cockpit Display of Traffic Information
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CDTW
CFIT
CFMU
CMA
CNS
CONUS
CPC
CPDLC
CSMA
CTAS
CWSU
DGPS
DH
DME
DOD
DOT
DSR
EATCHIP
EATMS
EGPWS
ETMS
FAA
FANS
FIR
FMC
FMS
FSL
FSS
GA
GAMA
GDP
GLS
GNSS
GPS
GPWS
HAI
IATA
ICAO
ICP
IFR
ILS
IMC
IRS
ITWS
Cockpit Display of Traffic and Weather Information
Controlled Flight Into Terrain
Central Flow Management Unit
Context Management Application
Communication Navigation Surveillance
Continental United States
Controller/Pilot Communications
Controller-Pilot Data Link Communication
Collision Sense Multiple Access
Center-TRACON Automation System
Center Weather Service Unit
Differential Global Positioning System
Decision Height
Distance Measuring Equipment
Department of Defense
Department of Transportation
Display System Replacement
European Air Traffic Control Harmonization and Integration
Programme
European Air Traffic Management System
Enhanced Ground Proximity Warning System
Enhanced Traffic Management System
Federal Aviation Administration
Future Air Navigation System
Flight Information Region
Flight Management Computer
Flight Management System
Forecast Systems Laboratory (NOAA)
Flight Service Stations
General Aviation
General Aviation Manufacturers Association
Gross Domestic Product
GPS Landing System
Global Navigation Satellite System
Global Positioning System
Ground Proximity Warning System
Helicopter Association International
International Air Transport Association
International Civil Aviation Organization
Installed Communication Performance
Instrument Flight Rules
Instrument Landing System
Instrument Meteorological Conditions
Inertial Reference System
Integrated Terminal Weather System
x

KIAS
LAAS
LAHSO
LLWAS
MAC
MCP
MDCRS
MLS
MMR
MNPS
MSAW
MU
NADIN
NAS
NASA
NATCA
NBAA
NCAR
NCARC
NCEP
NDB
NEXTOR
NOAA
NOTAM
NRP
NWP
NWS
OAG
ODAPS
PDT
PRM
PTT
RAA
RASS
RCP
RESCOMS
RGCSP
RMP
RNAV
RNP
RPM
RSP
RTA
RUC
RVR
Knots Indicated Air Speed
Local Area Augmentation System
Land and Hold Short Operations
Low Level Wind Shear Avoidance System
Medium Access Control
Mode Control Panel
Meteorological Data Collection and Reporting System
Microwave Landing System
Multi-Mode Receiver
Minimum Navigation Performance Standard
Minimum Safe Altitude Warning
Management Unit
National Airspace Data Interchange Network
National Airspace System
National Aeronautics and Space Administration
National Air Traffic Controllers Association
National Business Aviation Association
National Center for Atmospheric Research
National Civil Aviation Review Commission
National Center for Environmental Prediction
Non-Directional Beacon
National Center of Excellence for Aviation Operations Research
National Oceanic and Atmospheric Administration
Notice to Airmen
National Route Program
Numerical Weather Prediction
National Weather Service
Official Airline Guide
Oceanic Display and Planning System
Product Development Team (FAA)
Precision Runway Monitor
Push-To-Talk
Regional Airline Association
Radio Acoustic Sounding Systems
Required Communication Performance
Regional Scale Combined Observation and Modeling Systems
Required General Concept of Separation Panel (ICAO)
Required Monitoring Performance
Area Navigation
Required Navigation Performance
Revenue Passenger Miles
Required System Performance
Required Time of Arrival
Rapid Update Cycle
Runway Visual Range
xi

RVSM
RWP
SATCOM
SELCAL
SIDS
SSR
STARS
STARS
SUA
TACAN
TCAS
TDWR
TIS
TMA
TMU
TRACON
TWDL
TWEB
VDR
VHF
VMC
VOR
WAAS
WARP
WPDN
Reduced Vertical Separation Minima
Radar Wind Profilers
Satellite Communications
Selective Calling
Standard Instrument Departures
Secondary Surveillance Radar
Standard Approach Procedures
Standard Terminal Replacement System
Special Use Airspace
Tactical Air Navigation
Traffic Alert and Collision Avoidance System
Terminal Doppler Weather Radar
Traffic Information Services
Terminal Maneuvering Area
Traffic Management Unit
Terminal Radar Approach Control
Two-Way Data Link
Transcribed Weather Broadcast
VHF Data Radio
Very High Frequency
Visual Meteorological Conditions
Very High Frequency Omnidirectional Range
Wide Area Augmentation System
Weather and Radar Processor
Wind Profiler Demonstration Network
xii

1 Introduction
This report presents an operational concept for the U.S. National Airspace System (NAS)
through the year 2015, including a transition path from the current system. This concept
was developed by Boeing Commercial Airplane Group for NASA’s Advanced Air
Transportation Technologies (AATT) program, under subcontract with NEXTOR
(National Center of Excellence for Aviation Operations Research). The contract was
awarded as part of Milestone 1.0.0 of the AATT program, which will provide a baseline
air traffic management (ATM) operational concept to guide the program’s research
efforts.
The Boeing team worked actively with NASA experts, the Federal Aviation
Administration (FAA) Air Traffic Operational Concept Development Team and NEXTOR
faculty members from MIT and UC Berkeley during the six month contract period.
1.1 Objectives
The primary objective of this work was to define and document the probable evolution of
the NAS through the year 2015, based on current FAA and industry activity and the ATM
system mission. This evolution path, stated in the form of an operational concept, was to
provide part of a road map to guide AATT program research.
In order to achieve this objective, the team undertook the following tasks:
• Collect and document NAS stakeholder needs and expectations for the system in terms
of safety, capacity and efficiency.
• Identify the primary driving forces affecting the NAS modernization, along with the
most important constraints placed upon the system.
• Establish a probable baseline operational concept for 2015 and at least one feasible
transition path to that future concept.
• Provide insight for AATT planning that will allow the program to achieve a certain
level of robustness with respect to NAS modernization uncertainty.
The last task, that of providing insight into NAS modernization uncertainty, is perhaps the
most important one currently, due to the lack of the industry’s clear vision of the desired
end state and transition path. The following are the major factors contributing to the
uncertainty:
• Political climate
• System size and complexity
• Diversity of users
• Safety criticality
• Human operators in demanding roles
• Reliance on rapidly developing tehnology
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To cope with this uncertainty, the modernization must continue to be driven by a clear
statement of system mission and goals, and guided by an operational concept that strives
to achieve those goals.
1.2 Context
This work was performed with knowledge of a variety of related completed or ongoing
efforts. The primary related activities were the following:
• FAA Air Traffic Operational Concept Definition team, formed in January 1997, and
chartered with defining a concept for a target completion date of 2005.
• RTCA Task Force 3, whose Free Flight Report, published in 1995, along with
ongoing RTCA Free Flight follow-on work, includes the recent definition of an
operational concept for users of the NAS.
• FAA NAS Architecture Working Group had published Version 1.5 and 2.0 of the
architecture through 2012 when the team started work, and industry comments on it
had been published as V2.5. Some preliminary data on V3.0 was made available to the
team, but considerable uncertainty still remains.
• The Flight 2000 initiative was launched in early 1997, and the team kept up-to-date on
the program as much as possible. Again, uncertainty remains regarding program
funding and details of the final program plan.
• Eurocontrol had published its European Air Traffic Management System (EATMS)
Operational Concept V1.0, and the team had a number of other sources of information
available to keep abreast of developments in Europe. The pending changes in the
Eurocontrol charter seem likely to lead to an increased emphasis within the
organization on capacity issues in Europe’s terminal areas, and thus the U.S. and
European ATM concepts may see more convergence in the near future.
During this period the FAA budget constraints have continued to hamper the architecture
definition efforts. This, along with substantial difficulties in FAA’s recent system
development and procurement efforts produce considerable volatility in the NAS
modernization plan. Some of these difficulties can be traced to a lack of a clear business
case for most of the current modernization initiatives, and a lack of consensus among
users on many of the implementation details.
1.3 Scope
The operational concept presented here is aimed at driving research to support preliminary
design decisions for the NAS, which will produce top level technical and human factors
requirements to achieve the system mission. Detailed concept validation research must
then be performed, where technology and human factors are combined with economic
evaluation of concept components to fully define the operational concept and architecture.
Thus, the concept presented here, although well supported by rationale as to what might
be feasible in the next two decades, must be subjected to critical analysis and validation.
This process will inevitably lead to concept refinement, perhaps enabled by currently
2

unknown technology, and thus the concept will evolve to continue to reflect the current
state and the system mission.
This operational concept is for the Continental U.S. (CONUS) and the adjacent oceanic
areas, with primary focus on the domestic radar environment where NASA’s research
efforts are concentrated. The focus is on services and functions directly involved with
planning and operating flights in the CONUS. System components such as the airport
ground side, airway facilities operation and airline operations are not treated in any detail.
These are equally important to the operation of the total system, and must be considered
in their own right along with the ATM operational concept.
1.4 Report Overview
A capacity-driven operational concept developed by the team is summarized in Section
6.2, with supporting detail on improvements needed in the various ATM functions
presented in Sections 3.3 and 3.4. An operational concept must be clearly driven by stated
mission goals, and Section 2 presents the predicted traffic growth scenario that the team
chose as the primary driver for change in this operational concept.
Section 2 also discusses the current lack of consensus in the industry on the details of the
NAS modernization path. Section 2.3 addresses the need for a disciplined systems
engineering approach to the NAS modernization, and in particular the current lack of
preliminary design activity that is required to focus the effort on achieving the critical
mission needs.
Section 3 presents a view of the functional structure of the ATM system as it exists today,
and the fundamental system objectives of capacity, safety and efficiency. The primary
system functions are presented in the context of these objectives, using a representation
that illustrates the levels of flow planning in the system and of plan execution through
separation assurance and navigation. Section 3.3 and 3.4 discuss the improvements that
the team believes are needed in the system to achieve the capacity and safety objectives
stated in Section 2, with primary focus on the separation assurance function.
Sections 4 and 5 present the human factors issues and the technology performance
parameters that must be taken into account throughout the system development process.
The concept presented here is aimed at safely increasing traffic density in the system, and
this will have a substantial impact on the separation assurance function, where safety is
maintained and where human operator performance is a key issue. Section 4 discusses the
human factors issues in some detail, and Section 5 follows with an overview of the current
and emerging technologies available to support the concept.
Section 6 discusses the methodology that the team employed in synthesizing the
operational concept, which is then presented in the form of transition paths for the various
operating phases in Section 6.2. Each step in the transition path is described briefly to
relate technology to a proposed operational improvement. Section 6.3 details the concept
validation process that is needed to ensure that a concept fulfills the mission requirements
and to drive successful system design, build and installation.
3

Section 7 contains a discussion of various global scenarios that can affect the future NAS
operational concept, and the potential implications on the system transition path. In
addition, Section 7.3 gives a brief summary of how this operational concept compares
with the concepts developed by the FAA and RTCA earlier this year, with more detail
presented in Appendix C.
Conclusions and recommendations are presented in Section 8, including some fundamental
research directions the team believes must be addressed for an operational concept that
satisfies the system mission through 2015.
The survey of NAS stakeholder needs that was conducted as part of this effort is
presented in a separate document. A summary of the findings of the stakeholder survey is
presented in Section 2, along with additional material that supports the stakeholders’
general concern about traffic growth and the ability to operate efficiently in the NAS
through 2015.
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2 The NAS ATM System Development Process
This section establishes the context for the development of an operational concept and
future system architecture to achieve the long-range needs of the air transportation
system. The argument advanced in this section is that the industry needs to move from
historic, reactive approaches to system modernization, and to begin the systematic
development of a new NAS system using the principles of systems engineering. The
industry needs to focus on the systems analysis or preliminary design phase of a system
development to exercise broad trade studies, to examine new concepts of operation in
response to critical air transportation mission needs, to derive technical performance
requirements and evaluate human performance abilities in support of mission needs, and to
provide analysis tools for evaluating economic consequences of alternative transition paths
into the future.
2.1 Air Traffic System Modernization Mandate
Increasingly, the industry is faced with a sense of urgency regarding the modernization of
the air traffic control (ATC) system. The age of systems such as ARTS make it difficult to
continue to acquire spare parts, while the personnel qualified to maintain these old systems
are retiring. At the same time, there is a lack of a mandate for change. The diverse
interests of the FAA’s users makes a consensus regarding the future needs of the system
difficult. Michael S. Nolan (Nolan, 1994) describes the genesis of Project Beacon: “It
was apparent that the air traffic control system in the United States had been constructed
haphazardly in response to situations instead of in anticipation of them.” This statement
characterizes the state of system development as well today as in 1961.
The most recent systematic attempt at system modernization was the NAS Plan of 1981
(U.S. FAA, 1981). The initiative of FAA’s administrator J. Lynn Helms planned a
systematic upgrading of the navigation, communication, surveillance, weather and ATC
infrastructure. The driving premise for this modernization, and the economic justification,
was based on the concept of remote maintenance, which would sharply reduce O&M
costs. Unfortunately, many of the key elements of the NAS Plan failed to come to
fruition. The microwave landing system (MLS) program, the Mode S data link, the
Advanced Automation System, the Oceanic Display and Planning System (ODAPS), all
ended in failure to achieve full operational usefulness. Where improvements were
realized, they were often less than completely successful. En route computers were
upgraded, but with no new software.
Today the FAA F&E organization is developing a new system architecture. The hope is
that this architecture will become the blueprint for modernization. But while there is much
definition of technology features of the new architecture, there is a lack of agreement
about the fundamental measures of what will constitute a successful air traffic
infrastructure, both for the near-term and twenty years into the future, across the range of
diverse user needs.
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2.2 Consensus Future System Development Needs
The FAA’s R,E&D Advisory Committee met in Washington in September (U.S. FAA,
1997) to recommend research needs for the FAA to facilitate system modernization. High
priority recommendations centered on the need for improved system development
methods with emphasis on systems engineering, software engineering and human factors.
Other issues which received numerous citations included programmatic and management
concerns, emphasis on information technologies, need to provide enhanced levels of
system capacity, safety and security. Finally, the group agreed that a key priority is the
need for credible investment analysis. The systems engineering, software engineering and
human factors issues form the core of the discussion on system modernization, which
provides the framework for the following discussions on concept of operations, human
factors and technology assessment, and transition planning and system alternatives
evaluation. These preliminary design activities are key to the establishment of a system
architecture and the associated research needs, which supports the needed air
transportation needs of capacity, safety and efficiency of operation for the next twenty
years.
Another issue central to the discussions of the R,E&D Advisory Committee was the lack
of a mandate for system modernization. The airlines, military, general aviation (GA) and
business segment of the industry often disagree on specific technology decisions, as well
as policy issues. The concern is that the industry lacks agreement on the high level
objectives of system modernization and the mission needs of the system, which should
drive the technical requirements, concept of operation and system architecture. The
approach identified in this section focuses on the preliminary design phase of the system
development life cycle, and the need to clearly identify the long range mission needs of the
system. It also examines tools and methods to allocate requirements to subsystems, assign
functions to system agents and evaluate the performance objectives over the twenty year
life of the system.
2.3 Systems Engineering and Preliminary Design
Figure 2.1 summarizes the system engineering steps which divide the life cycle of a major
system development into phases: definition of requirements and objectives, analysis of
functions and operations, definition of system architecture, design of the system and
subsystem elements, production of the system elements, integration of the system in the
laboratory of integration and validation testing, certification, and system operation and
maintenance. The discipline of the systems engineering process is vital to the successful
completion of an airplane development program, where a large team of thousands of
engineers must work a complex, real-time, human-in-the-loop, safety critical system
development to produce and certify a system integrating subsystems containing hundreds
of thousands of line of code and a system architecture of data busses linking hundreds of
‘Line Replaceable Units’ of differing criticality. The development of a major ATC system
upgrade may be an order of magnitude more complex, because it shares the safety
criticality and human-in-the-loop real-time nature of the airplane development, and further
requires that the existing system remain operational while supporting transition to the new
system.
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System Requirements & Objectives
Validation
Functional & Operational Analysis
System Architecture & Allocation
Verification
System Design & Development
System Integration & Testing
In-Service
Reports
System Operation & Maintenance
Figure 2.1 System Development Process
The first three steps of Figure 2.1 belong to what is designated preliminary design in the
airframe development process. At the airplane level, the preliminary design process may
be conducted over a period of a year or two to establish a baseline production go-ahead
configuration. The purpose of the preliminary design phase is to evaluate a broad range of
airplane configurations over a large set of potential customer needs (typically payload
range studies among various city-pairs) to identify the design mission needs of the
production go-ahead configuration. This configuration is also the business case basis for
negotiations with the customers on sales.
Figure 2.2 summarizes the Boeing concept of the preliminary design process for the
development of air traffic management systems and components. The approach consists
of development of traffic demand scenarios, performance of a mission analysis based on
evaluating high level system capacity, safety and efficiency objectives, allocation of
operational requirements to subsystem technical requirements, and evaluation of
technologies, human factors, and economic factors in defining system transitions from the
current operating state to the future concept.
2.3.1 Scenario Planning and System Demand as ‘Driver’
The preliminary design process begins with the development of traffic demand scenarios.
These scenarios are, in turn, premised on economic, geopolitical, airline business and other
factors which may dictate fundamental changes in the operation of the future air
transportation system. The objective of the scenario-based planning approach is the
identification of a system whose operation is not necessarily optimized for a specific end
state, but is robust when evaluated against a range of possible future states of the world.
7

Traffic
Demand
Scenarios
Alternative
Operational
Concepts
Mission Requirements
•Stakeholder Objectives
•Safety Constraints
Goals
• Safety
• Capacity
• Efficiency
Concept Development
•Enroute
• Term/Surface
•Aircraft
Revise
Concept
Synthesis
System Design
and Implementation
Required
Performance
Analysis
RSP:
• RCP, RNP, RMP
• Operational
Improvements
Human Factors
and Operations
Available and
Emerging
Technologies
Concept Evaluation
• Technology Alternatives
• Safety Analysis
• Economic Analysis
Revise
Performance
Metrics
System Development
and Integration
•Architecture
• Simulation
• Prototyping
Decision
Concept Definition
ATM System
Specs
Evaluaton
Figure 2.2 Requirements, Concepts, and Architecture
The analysis of risk and the various forms of uncertainty which can influence system
development is summarized here. In this instance, risk may be defined as the chance that
predictions of future requirements will be significantly in error or that measures to
accommodate growth will be unsuccessful. Major elements of risk can be found in the
technical area, in politics, in regulation and in pressure on the stakeholders. Planning
major changes over so extended a period carries a great deal of risk and there are many
variables which must be taken into account. There are several possible scenarios:
• Traffic growth projections for the future may be too conservative, and growth may
exceed expectations. Such initiatives may also result in growth in unexpected areas
increasing the uncertainty associated with regional change.
• Traffic growth may not meet expectations, which are based on expected passenger
demand, in turn dependent on economic growth assumptions.
• Traffic growth is normally assumed to be linear with time, whereas regional change
may be much greater in some markets than others or the nature of the growth (pointto-point
versus hub-and-spoke service) may change.
The following material summarizes technical, political, regulatory and stakeholder risk.
Technical Risk
• The pace of technological advancement may render solutions under development
obsolete even before they are implemented. Users are aware that some of the
8

technologies needed for initial transition steps may need to be replaced or augmented
if expected air transportation system (ATS) changes are to occur later, and benefits are
to be realized. Users may delay implementation of enhancements, allowing delays to
grow, in turn reducing demand.
• Future operational concepts rely on the benefits (ultimately financial) to be realized
through the use of technological and procedural changes, many of which are currently
theoretical. Some of these postulated solutions may be shown to be impractical or
even impossible.
• The technological and operational solutions may work but expected benefits
may not be realized.
• The solutions may be too costly, resulting in failure to achieve the critical mass
of users.
• It may prove to be impossible to make technological advances which meet the
diverse requirements of users and regulators.
• The global aviation community may find it impossible to arrive at common
technological and operational solutions resulting in excessive cost of full
implementation.
• System and operating standards are developed, to a large degree, by volunteer bodies
which meet only on an occasional basis. Such an approach results in slow
development of standards and consequent delays in development of hardware,
software and procedures.
• Telecommunications developments like video conferencing could find higher
acceptance as alternatives to business travel, traditionally a source of high profits for
airlines. Business aviation radio bands might also be taken over by
telecommunications interests.
Political Risk
• Sub-regional implementations of Future Air Navigation System (FANS) (e.g.
FANSTAR) could spur the industry into a more aggressive approach to the transition
process.
• Restricted funding of Civil Aviation Authority or privatized service provider programs
might delay the airlines’ ability to realize benefits from new technologies, which would
result in increased delays and less growth.
• The funding of ground infrastructure improvement might be delayed or accelerated
changing the economic benefit picture for users.
• The trend toward charging system users more directly for services will change airline
profitability pictures and/or increase ticket prices or even discourage general aviation
proliferation.
9

• National or international conflict discourages discretionary travel. Regions in which
maximum traffic growth are expected (CIS, China, Africa) are the most volatile
politically and thus more vulnerable to the effects of unrest.
• Changes in diplomatic relations between or among countries may accelerate or delay
implementation of more efficient routes.
• Ratification of bilateral agreements (or failure to ratify) may affect international
frequencies.
• Different technological or procedural solutions may be adopted by different countries
or blocs, resulting in escalated cost of compliance.
Regulatory Risk
• Communities located under flight paths or close to busy airports may take legal action
to block improvements to airports.
• New concepts of operations must be developed and accepted by regulatory agencies
before new technologies and operational procedures can be developed.
• Certification periods might be further stretched by unresponsive regulatory authorities,
increasing costs and rendering solutions obsolete before implementation.
Stakeholder Risk
• It has been widely publicized that by the year 2015, if air transport safety standards
cannot be improved there will be one hull loss globally per week. The perception of
worsening safety may mean that passengers will be less eager to fly.
• If system capacity cannot keep pace with demand, resulting delays may also reduce
passenger demand.
• Labor action is likely to have only negative effects since it usually results in increased
airline costs and diminishes the traveling public’s confidence in the system.
• Oil prices directly and significantly affect airline costs and fluctuations in the prices
beyond those expected could affect growth. Airlines could absorb increases, reducing
profits and thus delaying investment in technology, and/or increases could be passed
on to passengers through increased ticket prices, reducing demand. Reduced prices
could also be passed on to passengers, increasing demand.
• Political unrest and forms of fundamentalism have been carried to the more stable
areas of the world in the form of terrorism. The threat of terrorist action against the
air transportation system (e.g. the recent revelation that GPS jammers are now
available on the open market), successful attacks or even suspicions that an attack has
occurred (e.g. TWA Flight 800) have an immediate effect on passenger demand which
can affect airline finances for years afterward.
• All users want to invest the minimum possible, at no risk, with a return on investment,
within one to two years. It may not be possible to develop transitional steps which
allow these aims to be met.
10

• The goals of various users are so diverse that it may prove to be impossible to reach
equitable solutions, resulting in dilution of benefits.
• Airlines may block improvements for competitive reasons.
Scenarios for evaluation of the mission must exercise as many of the key risk areas as
possible. Also, the transition evaluation process must address risk as a key element in the
evaluation of system alternatives.
The development of a comprehensive set of future scenarios is beyond the scope of the
current contract activity, but this report presents an initial list of issues from which global
scenarios for evaluation can be synthesized. These scenario factors are summarized in
Appendix B, Global Scenarios. From various government, industry, and private
documented studies, a sample or collage of texts was assembled from which a single world
scenario was constructed. In particular, this subtask broaches a range of general ATM
issues, although by no means exhaustive, which highlight potential limitations, costs,
constraints, and assumptions which may be of importance to the modus operandi of the
envisioned NAS future. To help the development of such a global scenario, six general
categories were used:
1. Economics/Markets (E),
2. Organizational/Institutional/Operational (O),
3. Technological/Scientific (T),
4. Social/Political (S),
5. Environmental (ENV), and
6. Human-centered/System-centered (H).
A brief description of each broad category follows:
Economics/Markets (E)
This category reviews the best estimates and forecasts for future air traffic growth and
demand figures including a few corresponding issues associated with increased air traffic.
Organizational/Institutional/Operational (O)
Under this category a select sample of issues such as workload, organizational structure
and culture, and operational considerations were collated.
Technological/Scientific (T)
The increasingly technoscientific NAS operational infrastructure introduces a number of
potential pitfalls as well as promises. Issues related to widely utilized computer and
information technology-based support and automation are captured by this category.
Social/Political (S)
In a growing global context of air traffic flows, this category aims to present some of the
potential political and social issues which may impact future operations.
11

Environmental (ENV)
This category focuses on possible constraints stemming from tougher future environmental
regulations.
Human-centered/System-centered (A)
The human/system related issues such as human-centered ATM design and structure are
presented under this category.
The above broad categories support a more specific issues list, itself composed of a
collage of texts drawn from the various documented sources. This helps to structure the
top level issues in meaningful sets of issues which inform the scenario writing process. It
should be noted that the list below is structured and generally ordered beginning at the top
with the broader, more external issues first (e.g. environmental, changing international
relationships, et. al.) following with more internal issues towards the bottom(e.g. airport
capacity, FAA organizational culture and workforce et. al.). This helps to continuously
contextualize the many interrelated issues considered in this scenario. The 13 global
scenario issues are:
Issue # 1: Air traffic growth and demand: twenty year outlook
Issue # 2 : Some limitations of future ATM concepts
Issue # 3: Changing international relationships
Issue # 4: FAA funding reform
Issue # 5: Environmental considerations
Issue # 6: Air travel and alternatives
Issue # 7: GPS and satellite-based navigation
Issue # 8: ATC systems architecture
Issue # 9: Ground handling
Issue # 10: Airport capacity
Issue # 11: Management of special use airspace
Issue # 12: Airport safety
Issue # 13: FAA organizational culture and workforce
Section 7.1 presents the single global scenario and Appendix B contains the above issues
list as well as the referenced texts from which the scenario was constructed.
The approach in this section identifies traffic demand as the single most critical ‘driver’ of
future air traffic system needs. The approach relates the future capacity, safety and
efficiency needs of the system to assumed traffic growth. The Boeing Current Market
Outlook (Boeing, 1997) summarizes the expected growth in air transport to the year
2015 (Figure 2.3). The balance of this section focuses on economic issues and their
impact on the demand scenarios for evaluation. The CMO indicates that about two-thirds
of world air travel growth is derived from economic growth. Thus economic
12

considerations are key to evaluating future scenarios, but an extensive evaluation needs to
consider all of the elements reviewed in Appendix B, Global Scenarios.
Figure 2.3 World Airplane Capacity Requirement (1997-2016)
The traffic forecasting process begins with a regional analysis of gross domestic product
(GDP) and travel share. World GDP rates are assumed to grow between 2 and 3% per
year for mature economies. GDP rise accounts for about two-thirds of world air travel
growth. Regional differentiation is considerable. From 1997 to 2006 China and Hong
Kong are assumed to grow at 7.4% annually, while Western Europe grows at 2.4% and
North America at 2.3%.
Key assumptions include declining yield and resultant fare changes, the use of flight
frequencies in competitive markets, the influence of globalization and world trade and the
differentiation of markets by stage length. With these various assumptions, GDP change
can be related to travel demand, stated in terms of revenue passenger miles (RPMs) and
then to operations counts. Regional flows can be translated into projected schedules, with
further assumptions. Ten and twenty year forecasts are produced. Key assumptions
stated in the CMO are: gross domestic product and increased value drive air travel,
relaxation of airline industry regulation allows increased competition, market forces
increasingly determine airline routes, airplane selection and the composition of the world
fleet, and air traffic control systems and airport capacities respond to demand.
2.3.2 Analysis of Future System Capacity, Safety and Efficiency Needs
The traffic demand defined in the previous paragraph is used to drive an analysis of the
system mission. A high level statement of mission requirements includes safety, capacity
and efficiency goals for all system stakeholders. The goals are stated in terms of metrics
against which all proposed operational concepts can be evaluated.
The mission analysis quantifies the predicted traffic demand for the period in which the
operational concept is expected to be in use. This demand is derived from stakeholder
13

usiness objectives of growth (capacity), efficiency, affordability, and safety, identifying
and accounting for the possible effects of constraints that may limit the achievement of any
particular objective. The stakeholders often have competing objectives, and a viable
operational concept will include a reasonable compromise among these objectives to
reduce political risk to system implementation.
A part of this study has included the conduct of a stakeholder survey of future system
needs. This survey is provided as a separate document, NAS Stakeholder Needs. Stakeholders
interviewed were: Air Transport Association (ATA), Regional Airline Association
(RAA), National Business Aviation Association (NBAA), General Aviation Manufacturers
Association (GAMA), Aircraft Owners and Pilots Association (AOPA), Helicopter
Association International (HAI), Department of Defense (DOD), Airports Council
International - North America (ACI-NA), Air Line Pilots Association (ALPA), National
Air Traffic Controllers Association (NATCA), and Airline Dispatchers Federation (ADF).
The document identifies a wide-ranging number of stakeholder issues. These are grouped
into potential system metrics of capacity, efficiency, safety, affordability, and access and
tallied by number of responses across all the interviewed groups in Figure 2.4.
Capacity
Need Category
Efficiency
Safety
Affordability
Access
0 5 10 15 20 25 30
Tally
Figure 2.4 User Needs Categories
This study has identified relevant industry activities that provide the basis for the
beginnings of the air transportation system mission needs analysis necessary for
establishing system requirements which drive system architecture definition. The focus is
on the capacity, safety and efficiency needs, which are the primary focus of the air carrier
segment, but mission needs analysis needs to encompass all of the stakeholders’ high level
objectives and future system needs, as part of the consensus development process.
Affordability is addressed as part of the evaluation phase and discussed in Section 2.3.6,
Transition Planning and Tradeoff Analysis.
American Airlines (AA) and Sabre Decision Technologies (SDT) have conducted an NAS
simulation of the air carrier operations for the next twenty years to examine the system
capacity needs over time. The simulation study summarized here is documented in the
14

Free Flight White Paper on System Capacity (Chew, 1997). The objective of the study
was the identification of a ‘critical’ year when the airline hub operating integrity threshold
is reached. The American Airline NAS study uses the 1996 Official Airline Guide (OAG)
as the starting point for analysis, representing over 18,000 flights per day.
100.00%
90.00%
Actual
Simulation - AA
Percent of Flights Within
80.00%
70.00%
60.00%
50.00%
40.00%
30.00%
20.00%
10.00%
0.00%
2
4
6
8
10
12
14
16
18
20
22
Delay in Minutes
24
26
28
30
32
>33
Figure 2.5 American Airlines NAS Study Validated with Actual Delay Data
A simulation was conducted representing the jet traffic operating over 4,000 routes among
the 50 busiest U.S. airports. An annualized traffic growth of 2.3% was assumed, based on
a 4% growth in passenger enplanements. These values are consistent with FAA and
Boeing 1996 market outlook estimates. Current NAS separation standards were
estimated at 7 nm en route, 2 nm in the terminal area and between 1.9 and 4.5 nm for
wake vortex avoidance. Figure 2.5 indicates the model output compared with observed
American Airlines data on system delay. The comparison shows that the 1996 simulation
data agrees well with empirical results.
The analysis examines the change in the average delay system wide, with growth in traffic,
as well as the growth in the percentage of flights which experience more than 15 minutes
of delay in the system. The 15 minute delay figure is considered key to maintaining hub
integrity and provides a good indicator as to the hub viability. The simulation results in
Figure 2.6 indicate that the 15 minute delay statistic grows faster than the average delay
value. American’s study indicates delay problems in the NAS will become significant by
the 2005 to 2007 time frame.
15

The next step in the analysis was to postulate several system improvements: reduced en
route separations from 7 nm to 3 nm, reduced terminal area separations from 4 nm to 2
nm, reduced wake vortex separations from 4.5 to 1.9 nm down to a range of 2.5 to 1.5
nm, and the addition of departure runways. The postulated system enhancements
provided system growth for 20 to 25 years from the 1996 base. Figure 2.7 shows the
reduction in the system-wide delay with the postulated enhancements.
8
7
Average Delay in Minutes
Percentage of Flights With More Than 15 Minutes of Delay
7.17%
8.00%
7.00%
6
6.00%
5.45%
5
5.00%
4
4.14%
4.00%
3.6
3
2.93%
3.1
3.00%
2
1
1.1
0.45%
1.3
0.61%
1.4
0.80%
1.6
1.09%
1.8
1.61%
2.11%
2.0
0
0.00%
1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016
Figure 2.6 American Airlines NAS Study Results: Current NAS Delay Variance and
Minutes
Future traffic demand affects safety and efficiency requirements in the future National
Airspace System, just as it does capacity needs. A recent analysis by the Safety
organization of the Boeing Commercial Airplane Group (Higgins, 1997) considers the
impact of increasing operations, with a flat safety rate (number of fatal or hull loss
accidents per million departures) projected into the future. Figure 2.8 shows the growth
in operations, the extrapolated safety rate and the consequent predicted frequency of
accidents.
2.3
2.7
2.00%
1.00%
16

4.5
4.3
4
3.7
Current NAS
Future NAS
3.5
3.3
3
Delays in Minutes
2.5
2
1.5
1.4
1.6
1.7
1.9
2.2
2.5
2.8
1
1.2
0.5
0.4
0.4
0.5
0.5
0.5
0.5
0.6
0.6
0.7
0.7
0.7
0.9
0
1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020 2022 2024 2026
Year
Figure 2.7 American Airlines NAS Study Results: Average Air Delay Per Flight
50
45
40
35
30
25
20
15
10
Improvement areas:
• Lessons learned
• Regulations
• Airplanes
• Flight operations
• Maintenance
• Air traffic management
• Infrastructure
Hull loss accidents
per year
Airplanes in service
23,100
11,060
1996 2015
Millions of departures
5
0
Hull loss accident rate
1965 1975 1985 1995 2005 2015
Year
Figure 2.8 Growth in Operations, Safety Rate, and Frequency of Accidents (1980-2015)
The worldwide accident analysis shows the substantial variation in accident rate by region
of the world. The U.S. has the safest and most efficient air transportation system in the
17

world. By region of the world the civilian air transport accident rate (accidents per million
departures) is:
Africa 10.7
Asia & Pacific Islands 2.6
China 4.2
Japan 0.8
Europe 0.8
Latin America and Caribbean 4.5
Middle East 2.0
Oceania 0.3
USA & Canada 0.5
Data indicating the primary factor causing accidents is found in Figure 2.9, in this case
comparing causal factors between the U.S./Canada and Latin America. ATC is cited for
hull loss accidents between 1982 and 1992 in 19% of the cases in the U.S. and 14% of
Latin American hull loss accidents.
Crew 7
66%
86%
Airline6
53%
53%
Airplane5
10%
37%
Maintenance4
ATC3
6%
19%
14%
24%
United States and Canada
Latin America and Caribbean
Airport2
19%
18%
Weather1
2%
7%
0 10 20 30 40 50 60 70 80 90
0 10 20 30 40 50 60 70 80 90 100
Percentage of accidents with group prevention strategies
70 U.S. and Canadian accidents
51 Latin American accidents
1580 U.S. and Canadian fatalities
1711 Latin American fatalities
Figure 2.9 Hull Loss Accidents (1982-1992) for U.S. and Canada vs. Latin America
The last issue of the system performance factors is efficiency. We define efficiency as the
cost, or degree to which the current or future system penalizes the airplane operations,
versus a minimal (or optimal) cost. Factors which are contained in the efficiency costs
include: route circuitry, other procedural restrictions such as special use airspace
prohibitions, and flight delay, often due to inadequate airport or airspace capacity. An
ATA study was performed on the base year of 1993 to examine these infrastructurerelated
costs. The ATA assessment was that the current system operation costs $4 billion
annually over best operation. United Airline estimated they incur costs of $670 million
annually (Cotton, 1994). These costs will increase with traffic loads, and that the delay-
18

elated component will increase with exponential growth, especially as potential saturation
is approached. A key cost avoidance issue is the magnitude of the unimproved system
user costs in ten or twenty years.
The above analysis considered the operational costs in the current system against a closeto-ideal
operation (no flight delays, no excess routing and other procedural restrictions,
access to optimal flight levels). The inefficiency costs in the present system were thus
quantified. Another issue which also needs to be addressed is the cost of services
provided by the FAA to the users of the system. In many parts of the world, user charges
for ATC and navigation services are a recognized (and fast-growing) component of the
airline direct operating cost structure. The International Air Transport Association
(IATA) recently reported that a “concerted effort to improve operational efficiency,
reflected in airline profits of US$4 billion on international scheduled services by IATA
members last year. The same improvement ... is not reflected in airport and airspace
management operations. ... Pointing to a 36 percent improvement in capacity between
1991 and 1995, coupled with a 30 rise in costs, the airlines say that airport charges have
risen by 48 per cent and en route charges 75 per cent.” (Jane’s Airport Review, 1997)
In the U.S., the ticket tax currently masks the impact of ATC system operational efficiency
on airline productivity. But changes in the funding basis for the agency, as recommended
in the National Civil Aviation Review Commission (NCARC) report (NCARC, 1997)
portend a much higher level of user awareness and concern on the ATC system
effectiveness.
2.3.3 Operational Concept: System Agents and Functional Allocation
Figure 2.10 summarizes at a high level the primary system agents involved in the daily
planning and execution of flights in the system. The left side of the figure shows the air
traffic planning element, the Traffic Flow Management System, and its agent, the Traffic
Flow Manager. The Traffic Flow Management System can be further partitioned into the
national level (Central Flow Control Facility at Washington Dulles), center level and
airport level elements. These people and their system determine the daily schedule
demand for resources (airport and airspace) and restrict or constrain flight, as deemed
necessary, consistent with safety of flight, controller workload, etc. The airline planning
counterpart is the dispatcher and the in-flight control agents, parts of the Airline
Operational Control (AOC) system.
On the flight execution side (right side of the figure), the sector controllers, planning and
execution, provide the separation assurance function of ATC between instrument flight
rules (IFR) flights in the system. The execution controller is in very high frequency (VHF)
radio contact with the flight crew, providing flight plan amendments, as necessary, for
separation assurance.
Section 3 describes, at a functional level, the complex interrelationships among the
planning and execution elements, and how the system efficiency, capacity (as measured by
throughput) and safety measures are supported. The system operational concept is
fundamentally the assignment of roles and responsibilities to system agents and to their
automation support systems. As the future mission needs of the air traffic system are
19

defined and quantified, a critical question to be asked is: how must the roles and
responsibilities be changed to assure the maximum likelihood that the future mission needs
will be met
Traffic Flow
Management
S ystem
T raffic
Manager
Sector
Controller
Controller
Decision
Support
S ystem
ATC
Airline
Airline
Operational
C ontrol
S ystem
Dispatcher
Work
System
Flight
Crew
Flight
Management
System
Figure 2.10 Primary System Agents
The basic air traffic management services of the system include: air traffic control, air
traffic flow management, airspace management, flight information services, navigation
services and search and rescue. We have assumed, in the mission analysis, that satisfaction
of system demand is the key driver on system modernization needs. Central to the air
traffic control function is separation assurance. Separation minima, as enforced between
IFR flights, are the primary determinants of the realized safety and theoretical throughput
of a given air traffic system. The correct sizing of the long term system needs is a central
modernization issue. Section 3 of this report examines implications of operating roles and
responsibilities, given the postulated system needs, and focuses on research issues central
to the development of a system whose capacity, safety, efficiency and productivity levels
meet projected user needs over the system life.
2.3.4 System Technical Requirements
Boeing believes that the separation assurance function is key to realizing fundamental
system capacity and safety long range needs. In support of this thesis, Boeing has
postulated a concept, Required System Performance (RSP), intended to characterize
airspace and/or aircraft operating in airspace, and the level of separation service
applicable.
In 1996, a white paper was prepared for the RTCA Technical Management Committee on
RSP (Nakamura and Schwab, 1996). This paper was endorsed by the RTCA group, and
was the basis for the coordinated development of RSP across several existing RTCA
20

Special Committees. The paper, with minor modifications, was also submitted to the
International Civil Aviation Organization (ICAO) Separation Panel meeting later in 1996.
The paper states that the definition of required air navigation system performance should
encompass navigation, communications and monitoring (or surveillance) performance and
provide a related, high level characterization of the air navigation environment, RSP. The
thesis of the paper is that RSP is best characterized by the traditional airspace attribute of
separation minima. The paper asserts that the concept of separation minima is the primary
airspace performance determinant.
As indicated in Figure 2.11, for procedural environments, this separation standard is
primarily related to navigation performance. In radar environments, however, with direct
controller-pilot voice communications, each of the communications, navigation and
surveillance (or monitoring) factors becomes important in a complex interaction of aircraft
navigation, air-ground communications, radar surveillance and air traffic service-airplane
interaction. Thus the concept of RSP necessarily contains elements of navigation,
communications and surveillance performance. These RSP components establish the basis
for an environment in which operational access approval is explicitly performance-based,
in place of current practice in which the basis of approval is indirect and implicitly related
to capability, based on equipage sets including navigation sensors used.
95%
Navigation
Performance
(nm)
20
16
12
8
Procedural Environments
Oceanic Base Operation
NATS MNPS
Proposed RNP 4
Standard
RNP 4 with Proven
Containment Standard
RADAR Standard
4
100 80 60 40 20 0
LATERAL SEPARATION MINIMA (nm)
Figure 2.11 System Performance and Separations
A key element to the successful definition of system performance is that the rare- and nonnormal
system performance will fundamentally drive system safety-related performance.
Thus, required navigation performance (RNP) must address 95% accuracy for navigation
availability and navigation system integrity level supported. Similarly, for communications
and monitoring, the normal, rare-normal, and non-normal (both detected and undetected
failure rates) must be specified, to insure system design that will support the future mission
capacity, safety and efficiency levels.
21

The RSP model described above relates the system level performance (capacity and safety)
to the sub-system performance elements for communications, navigation and surveillance
(CNS). Additionally, in an intervention ATC environment such as radar, models and
safety assessment techniques are needed to determine the impact of human performance,
together with decision support performance and CNS element performance on system
performance levels.
In Section 3 of this document, a first-cut system separation model is developed, identifying
the separation functions into: detection, response and response frequency considerations.
These provide the basis for the allocation of performance objectives to subsystem
elements, and the quantification of expected safety and system throughput levels.
2.3.5 Technology and Human Factors Analysis
A vital issue to the development of a successful new air traffic system is ensuring that
human performance capabilities and responsibilities are respected as new technologies are
deployed. The safety criticality of the system magnifies the importance of the need to
respect human performance and capabilities. Especially, in the preliminary design phase of
program development, we lack tools and methods for examining the issues of functions
and task design and allocation, and thus are unable to clearly determine which are best
done by humans and those activities which are best automated.
A number of issues explored in Section 4 of this report identify the need for developing a
comprehensive, integrated description of human behavior (both physical and cognitive) in
the system; consideration of human performance capabilities and limitations, starting at
concept definition; the need for human factors support through implementation, including
education and training requirements for transition and maintenance of new systems; and
the need to consider the entire range of possible operating condition in assessing human
performance. Specific domain issues include dependency on decision support systems;
situational awareness; and intent. Other issues identified include the need for structure
while maximizing throughput, and the problems with shared responsibility.
Current and planned technology elements are cataloged in Section 5. They are described
in terms of their potential application to air traffic services; their constituent performance,
and their expected system level, installed performance. These technologies can be
compared with the allocated technical requirements in order to trade-off the costs and
benefits of the alternatives.
2.3.6 Transition Planning and Tradeoff Analyses
A critical element of air traffic services planning is the determination of workable system
transition steps. To assess the tradeoffs of technology and operational changes, it is
necessary to develop tools and methods which organize airspace changes into workable
transitions.
The CNS/ATM Focused Team (CAFT) is a group of airlines, airframe manufacturers, and
service providers. The CAFT process is aimed at making credible investment analyses of
alternative system transitions. The analysis process is summarized in Figure 2.12. The
tools used in this process includes: (1) cost databases and forecasting tools, (2) a capacity-
22

efficiency-constraints model that identifies key elements of the system affecting system
performance, (3) transition logic diagrams linking operational improvements, technology
solutions, and benefit mechanisms in phased steps, and (4) economic modeling that
assesses the costs, benefits, and risks of the improvements to industry and all stakeholders.
Regional Priorities: The process begins with an examination of regional priorities
resulting from assessing current system operational effectiveness. As an example of the
regional priority of an airline, consider Figure 2.13 which presents the distribution of
airport delay by weather and duration. Thunderstorms cause the largest percentage of
delay for longer duration events at 20 major U.S. airports. As the duration increases, so
does an airline’s operational difficulty and disruption of schedule. This kind of data
indicates relative impact of airport operations disruptions by cause of disruption.
Constraints Analysis Model: The next part of the process is the constraints analysis
modeling, an example of which is presented in detail in Section 6.3. The primary factors
that affect throughput in the various phases of the aircraft’s flight through the system are:
gate, apron, taxiway, runway, initial climb/final approach, vectoring, standard instrument
departures (SID) and standard terminal arrival routes (STAR), and en route operations.
Constraints modeling can be performed for system safety, capacity, efficiency, or
productivity. The methodology allows examination of the economic, technological, and
operational implications of the complex interrelationships among demand, capacity, and
delay.
Regional
Growth Constraints
& Operational Costs
Regional
Priorities
Constraints
Analysis
Performance
Factors
Benefit Mechanisms,
Operational Transitions,
and Enablers
Costs,
Timing,
Benefits,
Risks
Economic
Modeling
- Market Forecasts
- ATA/IATA/NASA ATC Cost Studies
- System Performance Measurement
- Airport Capacity Studies
Regional Plans
FreeFlight (U.S.)
EATCHIP
IATA
Independent
Recommended
Changes to
Plans
Figure 2.12 The CAFT Analysis Process
23

60%
50%
40%
All Durations
> Fifteen Minutes
30%
20%
10%
0%
Thunderstorms Fog Visibility
Figure 2.13 Distribution of Airport Delay by Weather and Duration
Source: Weber, M. et al (1991)
With no capacity for growth, the system will adapt in some less than optimal way.
Examples include (1) schedules spread from desired peak times, (2) aircraft size increases
more rapidly than desired, (3) ability to compete with frequency is limited, (4) slot
constraints increase, (5) smaller cities lose service, (6) delays increase, (7) block times
increase, and (8) other transportation modes become more competitive. Each of these
adaptation mechanisms has an associated cost. Ultimately, any adaptation the system is
forced to take because of a lack of capacity causes ‘waste’, increasing the cost of air
travel. Constraints on the system limit the ability of carriers to compete freely. Some
carriers may lose the ability to respond competitively to the marketplace.
Transition Analysis Model: The constraints model is used as a template for determining
specific technology initiatives by phase of flight and by benefit category. A time-phased
approach, considering short- and long-term technologies, is then applied to determine the
phasing of technology for an airspace region of interest. The procedures and technologies
must be in place in each transition phase for throughput to increase. This modeling process
provides the basis for a systematic evaluation of alternative technologies. It also supports
the development of ATM operational concepts. The output of these phased technologies
provides an input to an economic model evaluation. Each transition has potential user
benefits, costs, timing, and risk elements that can be evaluated in the economic modeling.
These can be used as the basis of the performance of the technology and procedural
tradeoff studies that need to be conducted. Depending on the results of the mission
analysis, transitions can be developed, based on capacity, safety, efficiency or productivity
needs. Detailed NAS future capacity transitions, for each of the operating phases, are
provided in Section 6 of this report.
Economic Modeling: The development of economic models is the last step in the CAFT
process. These models evaluate costs, benefits, timing, and risk for each phase of
transition. For a given phase, the return on investment is evaluated for each technical
solution for each alternative. Figure 2.14 illustrates the typical steps in the development of
an economic model.
24

• Problem Statement
• Alternatives
• Assum ptions
Assess
Investm ent &
Operations
Cost Impact
Cost Inform ation
Assess
Risk &
Resolution Time
Convert
Benefit
Mechanisms
to $
Benefit Inform ation
Analyze
Model
Outputs
Probability of Success
Develop
Rules for
Modeling
Benefits
Phasing of Benefits
Recommended
Changes to Plans
Figure 2.14 Economic Modeling Process
25

3 The ATM System Functional Structure
This section discusses the primary functions involved in air traffic management and
presents a framework through which their performance can be related to the system
metrics of capacity, efficiency and safety. A top level functional structure for air traffic
management is presented in Section 3.2, along with a discussion of current roles and
responsibilities of system agents. Section 3.2 takes a close look at flow management and
traffic separation, and at the performance factors that combine to provide a safe minimum
separation standard for a given operation. Section 3.3 details the technical and operational
changes that are likely to be needed to support the system capacity, efficiency and safety
goals for 2015. Section 3.4 presents an overview of the CNS/ATM technologies that are
likely to be needed to support the new operational concept. Section 3.5 discusses the
airspace implications of the proposed operational improvements, Section 3.6 discusses
airport impact, and Section 3.7 takes a brief look at Flight Service Stations.
3.1 Air Traffic Management Objectives
The air traffic management component of the NAS is a very complex system whose
primary objective is to safely and efficiently accommodate the demand for flight through
U.S. airspace. Figure 3.1 illustrates a top level view of the system, showing air traffic
demand as the primary input, traffic flow as the output, disturbances as unwanted inputs,
and capacity as the system resource that allows traffic to flow.
Capacity
Disturbances
Traffic Demand
Air Traffic
Flow Management
Process
Traffic Flow
Figure 3.1 The Air Traffic Management System
System capacity in this report is used to denote the theoretical maximum flow rate
supported by the separation standard. Throughput is the rate of flow that is realized in
operation, which is never more than the system capacity, and often considerably less due
to the need to accommodate operational uncertainty and disturbances without
compromising safety. Efficiency is a measure of how close the real operation is to
achieving ideal flight, which is influenced partly by the balance between capacity and
demand, and partly by airspace restrictions such as special use airspace.
The primary capacity objective is to maximize flow rate, up to the actual traffic demand.
This goal is challenging due to several factors:
26

• The highly peaked nature of air traffic demand, caused by passenger desired
travel times and airline hubbing operations
• The diversity of aircraft performance capabilities
• Competing objectives among system stakeholders
The primary safety objective of air traffic management is to assure safe separation between
aircraft (and ground vehicles) on the airport surface and in the airspace. The system
efficiency objective is to minimize the cost of operating flights through the system, both
under normal conditions, and in the face of disruptions due to weather or other causes.
3.1.1 Capacity and Safety
The capacity of the air traffic management system is fundamentally bounded by the
separation standards in effect for the airspace. Thompson (1997) reviews the history of the
development of airspace separation standards and states that the standards for radar
controlled airspace have evolved slowly and are not based on a formal model of collision
risk. By contrast, the separation standards in MNPS airspace in the North Atlantic were
developed through use of a collision risk model developed by Reich (1966). Reich’s
model takes into account only the aircraft’s guidance and navigation error characteristics,
due to the absence of air traffic surveillance in oceanic airspace. The model includes a
parameter that defines collision risk, and the use of the model involves a decision to accept
a certain value for this risk parameter.
System capacity, and therefore throughput, are bound up in the definition of separation
standards, and thus to accommodate the demand for growth in the NAS through 2015 it is
fundamentally important that a rational approach to separation standards development be
put in place. Risk management is at the heart of this process, which must find an
acceptable balance between collision risk and airspace throughput through a clear
definition of a collision risk parameter for controlled airspace.
The process of establishing separation standards must include a model of the nominal
system performance, along with failure modes and effects, all of which combine to provide
a certain probability of spatial overlap of pairs of aircraft. The factors that contribute to
the performance of the separation assurance function are discussed in more detail in
Section 3.2.6.
3.1.2 Throughput and Efficiency
It is important to consider the relationship between throughput and efficiency in the
current system. There is a need on part of system users to retain a certain level of
flexibility in routing to achieve an efficient operation. But, when considering that current
separation assurance methods are fundamentally based on a controller’s highly tuned
knowledge of a sector and its fixed path geometry, it becomes apparent that flexibility
could have a negative impact on airspace throughput. In addition, a controller handles
more aircraft by assuming that pilots stick to their assigned trajectories with a high
probability.
27

Thus, in effect, flexibility is restricted in the system today to gain capacity and/or
controller productivity. In the future system, it is conceivable that a better balance could
be found between throughput and efficiency, but this balance will depend on limitations of
human and technology performance, of which the human performance is the more difficult
issue. This is discussed in more detail in Section 4.3.3 from the human factors point of
view. To guide the design decisions regarding throughput and efficiency, the system
developers must continue to keep in mind the fundamental system mission of providing
sufficient traffic throughput.
3.2 A Functional View of the Current Concept
3.2.1 Throughput and Safety
System throughput is a measure of the realized flow through the system in a given time
period. Whereas separation standards are established through an analysis of collision risk,
throughput is dependent on the controller’s ability to accommodate traffic demand in the
face of uncertainty and disturbances. Periods when demand exceeds capacity in parts of
the system can cause an increase in collision risk, and it is important to include functions in
the system that prevent such overload. In the NAS operation this is done through flow
planning, where a planning horizon of 24 hours is both feasible and appropriate given the
daily traffic demand cycle.
3.2.2 Levels of Flow Planning in the System
The traffic flow planning function is complicated by the fact that the system is subject to a
variety of sources of uncertainty. The three most important ones for the daily plan are:
• Weather prediction uncertainty, which affect primarily the arrival phase of
flights through airport arrival rates.
• Aircraft pushback readiness due to a variety of factors in aircraft turnaround at
the gate, which affects primarily the departure phase of flights.
• NAS equipment status, which can affect any phase of flight.
The uncertainty inherent in the daily flow plan often results in situations where the plan is
out of phase with the unfolding situation, leading to possible overloads or wasted capacity.
To deal with the uncertainty, the system could:
• Reduce the uncertainty level (difficult, but progress is being made)
• Provide plenty of room to safely absorb the uncertainty (wasteful)
• Modify the plan dynamically to manage the situation as it unfolds
The last option, to modify the plan dynamically, is what the NAS is evolving toward in an
effort to achieve an acceptable balance between throughput and safety. Thus the NAS
includes several levels of planning:
• National and regional flow planning
• Facility-level flow planning
28

• Sector-level flow planning
Each level has a certain planning time horizon and range of possible planning actions, as
will be discussed in detail in Section 3.2.4 and 3.2.5.
3.2.3 Levels of Plan Execution in the System
Flight and flow plans in the system are executed through a number of functions, the
primary ones being:
• Aircraft guidance and navigation
• Separation assurance
• Aircraft on-board collision avoidance
The execution functions are discussed in detail in 3.2.4 and 6.
3.2.4 Functional Structure
Figure 3.2 shows the functional structure of the air traffic management system in terms of
functions directly affecting the process that links real-time traffic demand with actual flight
through NAS airspace.
Weather
Flight
Planning
Filed
Flight
Plans
Flight
Schedule
Schedule of
Capacities
National
Flow
Planning
hrs - day
Planning
Approved
Flight
Plans Facility
Flow
Planning
hrs
Planned
Flow
Rates
Desired
Sector
Loads
Sector
Traffic
Planning
5-20 min
Clearance
Requests
Approved
Handoffs
Negotiate
Handoffs
Sector
Traffic
Control
5 min
Clearance
Requests
Execution
AOC
Vectors
Aircraft Aircraft State
Guidance and
Clearances Navigation
< 5 min
Traffic
Sensor
Airline CFMU TMU D-side R-side
Real State
Plan/Intent
Measurement
Requests
AC State
Sensor
Pilot
Other Aircraft
States
Efficiency
Throughput
Safety
Increasing Criticality Level
Figure 3.2 Air Traffic Management System Functional Structure
The diagram in Figure 3.2 illustrates the processes and information flow that make up the
traffic planning and separation assurance functions of the system. Figure 3.2 is only one of
many possible cross sections through a very large and complex system and hides a
considerable amount of detail, but is conceptually valid and useful to serve this discussion
of system safety, capacity and efficiency . It is also important to note that Figure 3.2 is an
29

idealized diagram of a system that is very adaptable due to the predominant presence of
human operators, and in which assignment of functions to agents is dynamic.
Figure 3.2 illustrates the path, starting at the left, from a desired flight schedule and a
weather forecast, through filed flight plans, to real aircraft movement on the extreme right.
Each block in the diagram indicates a function that is performed in the system today, and
the arrows denote either real aircraft state, communication of a plan or intent,
measurements or requests. The functions can be divided roughly into planning and
execution, with a substantial overlap in the sector controller team.
The diagram indicates the approximate planning time horizons for each function, ranging
from a day for national flow planning to minutes or seconds for the aircraft guidance and
navigation. The actual time horizons employed by system operators vary greatly
depending on the airspace and traffic levels, but the numbers in Figure 3.2 are reasonable
for most components of the NAS.
An approximate analogy to the current assignment of functions to agents is shown in the
figure through reference to the R-side (radar) and D-side (data) controllers, Traffic Flow
Management (TMU) positions and Central Flow Management (CFMU). The separation
assurance function is here considered to be assigned to the sector controller team, using a
radar display and flight plan information, with the aircraft crew as a collision avoidance
backup, through visual observation of traffic and through the Traffic Alert and Collision
Avoidance System (TCAS).
It is worth noting that the criticality level of the system functions increases from left to
right on the diagram. Criticality level is fundamentally important in all discussions about
required performance to support a function, and for the level of attention to human
factors that a function requires. Section 3.2.6 discusses the execution loop and separation
standards in more detail.
Figure 3.2 illustrates how uncertainty is accommodated through several levels of replanning
in the system. Traffic situation data feedback to the planning levels is a weekness
in the system today, and therefore there is not an ability to update the flow plan
comprehensively across facilities or regions.
To relate back to the system objectives, Figure 3.2 illustrates that safety is the primary
responsibility of the aircraft, with separation assurance assistance from the sector
controller. System throughput is maintained primarily by the execution loop, with
assistance through overload protection from the planning functions. Efficiency is worked
primarily by the flow planning functions, through negotiations of flight plans, with
assistance from the execution loop through in-flight rerouting.
3.2.5 Flight and Flow Planning
Figure 3.2 illustrates how the functions that make up air traffic management are connected
in an overall process to allow safe and efficient traffic flow through the NAS. The agents
that perform the flight and flow planning functions are:
• Airline operational control and/or dispatch
30

• Flow managers
Figure 3.3 shows the flight planning function, performed by AOC, local dispatch, or an
individual pilot. Airline operational control agents and dispatchers have detailed
knowledge of their airline’s business objectives and the nature of the airline’s operation,
much of which cannot be shared with outside agents for competitive reasons. In addition,
their operational objectives can change so rapidly that it may not be practical to express
them in much detail to outside organizations. Thus, it is necessary in today’s business
climate to allow each operator to make some of the decisions that influence the efficiency
of their daily operation.
Weather Forecast
(Airline) Schedule
Available Fleet
Flight
Planning
Airline Operational Control
Flight Plans
Technical performance parameters:
• prediction time horizon: hrs - day
• prediction time resolution: 15 mins
• spatial resolution: airports
Figure 3.3 AOC and the Flight Planning Function
Figure 3.4 shows the national flow planning function, which is assigned to central flow
managers. This function originated as a safety net to protect the sector controller team,
but has a large impact on operator efficiency through its interaction with the operator’s
flight planning activity. In addition, due to the competition between operators that is
inherent in operating in an overloaded system, there is a need for arbitration, and this is a
natural role for the flow management agent. The art is to manage effectively, while
allowing the individual agents sufficient room to optimize their operation, and this is the
objective of the Collaborative Decision Making (CDM) initiative, as discussed in Section
3.3.9.
3.2.6 Separation Assurance and Technical Performance
Figure 3.5 shows the guidance and navigation function, which is performed by the cockpit
crew. The cockpit crew has the most detailed and up-to-date knowledge of their aircraft
performance ability, and of the immediate environment in which the aircraft is being
operated. In addition, the crew is the only agent that has control of the aircraft. In
today’s operational environment, the cockpit crew has very limited information about
weather or traffic conditions ahead of it, and therefore must rely on assistance from other
system agents for medium to long term flight planning. It is interesting to note, though,
that the cockpit crew must maintain a planning horizon, often shared with AOC, ranging
from the duration of the flight (hours) to immediate control action (seconds). In this sense
the crew has a unique responsibility among the agents listed above, and herein arises the
31

question of where to put the emphasis for the cockpit, in light of the increased ability to
provide information through datalink.
Weather Forecast
Flight Plans (OAG)
Airport Arrival Rates
Sector Capacities
National
Flow
Planning
Central Flow Management
Departure Delays
Technical performance parameters:
• prediction time horizon: hrs - day
• prediction time resolution: 15 mins
• spatial resolution: airports, sectors
Figure 3.4 CFMU and the Flow Planning Function
Weather
NAS Status
FMS Trajectory
Aircraft Position
Clearances
Nearby Traffic
Guidance
and
Navigation
Cockpit Crew
Aircraft Position
Clearance Requests
Technical performance parameters:
• prediction time horizon: < 1 min - duration of flight
• prediction time resolution: 1 sec
• spatial resolution: ANP level
Figure 3.5 Cockpit Crew and the Guidance and Navigation Function
The sector controller team performs the function of separation assurance, which as
illustrated in Figure 3.2 can be divided into two functions, sector traffic planning and
traffic control. Depending on traffic complexity and volume, the sector controller team is
anywhere from one to four or five persons, with a variety of active and backup roles.
Section 4 provides considerable detail on the current nature of this function, and the issues
that face the industry regarding potential future changes to roles and responsibilities. It is
clear that the performance, both normal and non-normal, of the separation function is at
the heart of any discussion about system throughput, and thus the focus in this report is on
this critical inner loop in the system.
Figure 3.6 illustrates the separation assurance loop, with additional detail showing the
primary sub-functions in the loop. The sector planning function’s primary objective is to
manage the intervention rate in the sector, i.e. the number of potential conflict situations
the sector controller may need to process. The set of flight plans inbound and inside the
sector can be considered the primary data input to this function, along with the real-time
32

traffic situation as it currently affects the sector controller’s workload. The sector planner
may also need to assist the controller with clearance requests from aircraft that he cannot
immediately process. Thus, the sector planner function helps manage the sector controller
workload, and is therefore the primary agent in managing exposure to collision risk.
Planned
Flow
Rates
Desired
Sector
Loads
Flight Plan Management
Conflict Prediction
Sector
Planning
Clearance
Requests
Approved
Handoffs
Negotiate
Handoffs
Sector
Control
5-20 min 5 min
Clearance
Requests
Conformance Monitoring
Vectors
Detection
Intervention
Clearances
Flight Replanning
Conformance
Collision Avoidance
Aircraft
flight duration
to
< 5 min
AOC
Aircraft State
AC Position
AC Velocity
AC State
Sensor
Traffic
Sensor
Other Aircraft
States
Figure 3.6 The Separation Assurance Loop
The sector controller in today’s radar control operation is the only traffic management
agent that communicates directly with the aircraft. The functions performed by the sector
controller are conformance monitoring and short-term conflict detection and intervention,
along with receiving, granting or rejecting route modification requests from the aircraft.
This function directly affects the performance of detection and intervention of conflicts.
Detection performance depends on the accuracy of the aircraft state sensor, the display
resolution and update rate, and the controller’s ability to predict the aircraft trajectory into
the future. Intervention performance involves the decision to act on a potential conflict,
and the communication of the action to the cockpit crew, which then must intervene and
change the flight path. The sector controller is thus a critical component of detection and
intervention, and today’s system has very limited backup for failures in either the
performance of the function or in the surveillance and communication equipment the
function relies on.
The cockpit crew is responsible for guidance and navigation according to an agreed upon
flight plan, along with replanning for reasons of safety, efficiency or passenger comfort.
The cockpit crew contributes to the performance of the intervention function through its
response to ATC vectors. The crew also has a safety responsibility to monitor and avoid
other aircraft in its immediate vicinity, either visually or through TCAS. This is currently a
limited safety backup for the sector controller’s separation assurance. In addition,
separation assurance is transferred to the cockpit crew in some well defined scenarios to
increase throughput or efficiency (e.g., visual approaches or oceanic in-trail climb).
33

Figure 3.7 illustrates how intervention rate, intervention and detection combine in an
overall separation assurance function, and lists the performance factors involved in each
component. Nakamura and Schwab (1996) propose a framework where the performance
of each of these fundamental factors is combined in an overall Required System
Performance parameter, which is then directly related to a minimum allowable separation
between aircraft. The navigation function performance has been formalized through the
definition of Required Navigation Performance, as described in the RTCA Special
Committee 181 document DO-236 (RTCA, 1997). RNP includes a definition of accuracy,
integrity and availability levels, which are functions of navigation sensors and their
sources, cockpit-crew interface design and pilot performance. To compose an overall
performance index (RSP) for the separation assurance function, consideration must be
given to Required Communication Performance (RCP) and Required Monitoring
Performance (RMP), along with an additional potential metric relating to the performance
of the traffic planning function that manages intervention rate.
Resource-Constrained
Effective
Theoretical Effective Resource-Constrained
Intervention Rate
Intervention Detection
RNP, RMP, RCP RMP, RCP RMP
Display
Weather
Medium-Term Intent
Data Controller
Comm: g/g
Pilot
Flow Rates
Airspace Complexity
Sensor
Display
Short-Term Intent
Controller
Comm: a/g
Pilot
Closure Rate
Sensor
Display
Controller
Pilot
Required Element Performance
RxP = f (sensors, decision support, human)
Required System Performance sets the Separation Standard
RSP = g ( RCP, RMP, RNP )
Figure 3.7 Separation Standard and Performance Factors
The operational concept presented in this report is centered on needed increases in NAS
capacity to accommodate the predicted growth in traffic demand through 2015. The
system operational enhancements that make up the concept are centered around changes
in the performance of the separation assurance and navigation functions depicted in Figure
3.7, since these are the primary influences on system capacity. The phasing that is
suggested in Section 3.3, and described in Section 6.2, is one where the intervention rate
performance is worked first, then the intervention performance, and finally the core
detection function. The rationale for this phasing is twofold:
• There is capacity to be gained by reducing the spacing buffers inserted in today’s
operation above the minimum separation standard, to account for uncertainty in sector
traffic planning.
34

• It is probable that the process of reducing separation standards from current radar
separations will be slow, and a great many interrelated factors will have to be worked.
Sections 4 and 5 detail the human factors and technology performance issues involved in
the system development process, and Section 8 contains a list of the primary research
topics that the team has identified to support this concept.
3.3 A Functional View of the Proposed Concept
3.3.1 Airspace Characteristics: High Vs. Low Traffic Density
The operational concept presented here treats traffic density as the characteristic that
determines what operational improvements are suggested for a particular airspace. Given
that this concept is primarily concerned with capacity improvements, high density airspace
is the primary concern here. Based on the discussion in Section 3.1.2 regarding capacity
and routing flexibility, it will be assumed here that throughput has priority, and that
flexibility will be allowed to the extent that it does not detract from full utilization of
system capacity. Low density airspace allows more flexibility to optimize operator
efficiency, and thus the concept includes operational improvements to this end. If it is
found to be necessary to restrict traffic flexibility to maintain acceptable throughput, then
this must be the overriding concern.
Traffic density in the NAS is highest in terminal areas around large airports, or where
many airports are located in close proximity. Most en route airspace in the NAS can be
considered low density from the point of view of installed CNS technologies. There are,
however, areas such as the northeast corridor that have very high density en route traffic,
complicated by climbing and descending traffic to airports below. Sections 3.3.2-8 detail
the operational improvements proposed in this concept for the range of airspace density
found in the CONUS.
3.3.2 Throughput in Dense Terminal Airspace
For dense terminal airspace, capacity and throughput are the primary concern, and the
discussion in Section 3.2 is the basis for the concept. The operational enhancements that
are proposed in this concept are as follows, prioritized in the order in which they are
presented:
1. Reduce intervention rate, and the associated spacing buffers applied above the
basic separation minimum. This will be achieved through the following
improvements:
1.1. Precision 4-dimensional (3-D space, plus time) guidance and navigation,
based on area navigation (RNAV) capability, vertical guidance and a
common and accurate time source. This will effect an improvement in
trajectory planning and conformance by suitably equipped aircraft, and thus
contribute to a lower intervention rate.
1.2. Precision sequencing and spacing of arriving and departing aircraft through
improvements in the sector and/or facility planning functions. Inherent in
35

this improvement will be the same time source as onboard the aircraft,
knowledge of key aircraft performance parameters and better wind
information. Automation aids to process this information and calculate
trajectory predictions will be required, along with tools to assist in
optimizing arrival and departure sequences.
1.3. Air/ground data link to exchange trajectory and weather information will
be required to take full advantage of navigation and sequencing
capabilities. Careful consideration must be given to who the agents in the
data link exchange should be, because the improved navigation, sequencing
and spacing functions may allow much less reliance on ATC vectors, and
thus the nature of the communications may be shifting away from
execution and toward medium-term planning. Thus, it may be that AOC
will take on a more active role in decisions regarding aircraft sequencing
priority, and that the flow manager or sector planner will need to
communicate directly with AOC or the aircraft through data link.
2. Improved intervention performance. This may allow further reduction in spacing
buffers, and will help set the stage for eventual reductions in separation standards.
The following performance factors must be addressed:
2.1. More reliable clearance delivery. This refers to a lower error rate in
communicating clearances to aircraft, which may be achieved partly
through the use of data link and partly through a lower intervention rate
due to improved planning and conformance described in item 1.1.
2.2. Improved intervention response time. This may be enabled by data link,
given appropriate controller and crew interfaces that allow quicker
execution onboard, and where frequency congestion can be alleviated. The
improved planning and conformance described in item 1 may also result in
an a higher probability that the sector controller issues clearances in a
timely manner.
2.3. More accurate prediction of time-to-go in a conflict situation. The
improvements in trajectory prediction and conformance described in item 1,
combined with automation that provides estimated time-to-go, may result
in lower false alarm rates and thus reduced spacing buffers.
3. Improved conflict detection, coupled with the improvements in items 1 and 2,
should allow reductions in separation standards in dense terminal airspace. The
following factors must be considered for improvement:
3.1. Tracking of radar surveillance data. Current NAS tracker has substantial
lag in detecting aircraft maneuvers. Newer Kalman filter-based multiradar
trackers could improve detection performance considerably.
3.2. Precision position and velocity information from on-board navigation
sensors could further improve performance. In particular, an independent
velocity measurement would support improved short-term trajectory
prediction and reduce the lag in detecting maneuvers.
36

3.3. Event-based trajectory deviation reporting from the aircraft could allow a
reasonable compromise between position update frequency and the need to
detect maneuvers or blunders in tightly space traffic scenarios.
3.4. Short-term conflict alerting tools for the sector controller would reduce the
probability of missed detection of true conflicts.
The improvements listed in items 1-3 above pertain primarily to the nominal system
performance enhancements that may be required to support growth through 2015.
Section 3.3.4 details the associated non-normal performance requirements from the point
of view of simultaneously maintaining or improving safety in dense terminal airspace.
3.3.3 Efficiency in Dense Terminal Airspace
It is conceivable that high throughput in terminal areas can be maintained with some room
for operators to optimize efficiency. This points to the concept of dynamic planning for
fleet and flight management, to improve individual or bank efficiency, which would be
based on the following operational improvements:
1. Hub schedule updates to maximize passenger throughput.
2. Trajectory negotiation and intent information sharing through data link.
3. Precision 4D navigation to maintain conformance with trajectory plan.
4. Precision sequencing and spacing to aid in maintaining throughput.
As discussed in more detail in Section 4, there are substantial unresolved issues regarding
the effect of trajectory flexibility and reliance on automation on human performance,
particularly in non-normal conditions. The above list therefore would need to be subjected
to substantial concept validation studies before feasibility is proven.
3.3.4 Safety in Dense Terminal Airspace
The criticality of the detection and intervention functions will lead to a requirement for
very high availability and integrity levels, as traffic spacing is reduced in dense terminal
areas. It is unlikely that the current functional and CNS architecture will be sufficient to
achieve the total system certification and commissioning criteria associated with reduced
separations, and thus the following enhancements may be required:
1. Nominal performance parameters, such as accuracy and latency, will be improved as
detailed in 3.4.2-3.
2. Establish the level of criticality through risk analysis. It is clear that safety
improvements through risk reduction with the lower separations will require higher
availability and integrity of the total system.
3. High availability of function may require independent redundancy in communication,
navigation and surveillance, and in the separation assurance function element. This
may imply independent voice and data link channels, independent navigation sources
and two independent surveillance data sources.
37

4. High integrity of function may require an external monitor to detect failures. This,
taken with item 3, points to the potential of the aircraft acting as the redundant backup
for the primary separation function, which resides with the sector controller team.
3.3.5 Separation Assurance and CNS/ATM Technologies
Figure 3.8 illustrates where some of the technologies under consideration for the NAS
would be applied in the separation assurance loop for dense terminal airspace.
AOC
Desired
Hub
Schedule
Planned
Flow
Rates
Desired
Sector
Loads
Sector
Traffic
Planning
Clearance
Requests
Approved
Trajectories
Negotiate
Trajectories
Sequencing Automation
Trajectory Planner
Voice
Sector
Traffic
Control
Conflict Alert
Time to Alarm
CPDLC
Clearances
Vectors
Voice
CPDLC
AOC
Aircraft
Guidance and
Navigation
Precision 4D Nav
ADS-B, CDTI
ACARS
Aircraft State
ADS-A, ADS-B
AC State
Sensor
Traffic
Sensor
Other Aircraft
States
Other Aircraft
States
Figure 3.8 Dense Terminal Airspace and CNS/ATM Technologies.
3.3.6 Efficiency in Low Density Airspace
In low density airspace, be it terminal area or en route, users should be allowed to fly
preferred trajectories to the extent possible without compromising safety or throughput.
This increased flexibility in trajectories will, however, carry with it:
1. Increased reliance on automation tools to predict and resolve traffic conflicts. This
remains an open area for research and concept validation.
2. Substantial changes in traffic flow patterns both daily and hourly, therefore separation
assurance agents need to move with the flow. In current operation sectors are split or
combined during the day as traffic loads change, but their geometry and the airways
within them remain fixed. As discussed in Section 4 this is a fundamental premise for
today’s air traffic control methods. A complete airspace redesign for a facility or a
38

egion takes on the order of years to complete, including training of controllers and
reprogramming of automation equipment. Thus, dynamic flexible routing calls for an
enormous change in the way separation assurance is performed.
3. Criticality of function will drive required performance levels and the feasible
architecture. The issues are identical to those discussed in 3.3.4, but must be applied
to a different set of automation tools.
3.3.7 Transition from Low to High Density Airspace
This operation refers primarily to the entry of aircraft into high density terminal airspace
from low density en route areas, where routing flexibility is assumed. The primary
objective must be the maximum throughput of the airport, with hub or individual flight
efficiency as the secondary objective. The following operational characteristics are
suggested:
1. Structure is applied over a larger area as density increases, up to 200 nm radius or
more during peak traffic hours, and down to 10 nm radius during off peak hours.
2. Multiple terminal area entry points are defined, using reduced spacing based on
improvements discussed in Sections 3.3.2-5. This will help avoid long in-trail traffic
patterns that are wasteful of airspace and reduce opportunity for user preferences.
3. Data communication is used to negotiate trajectories into the terminal area, either
between the aircraft and traffic planner, or AOC to traffic planner with uplink to
aircraft through Controller-Pilot Data Link Communications (CPDLC).
4. Terminal area entry times are used to allocate arrival slots, and aircraft are responsible
to meet those times to ensure expedient handling.
5. Arrival and departure flows are coordinated.
3.3.8 Extended Terminal Areas
This refers to complex terminal areas with multiple airports, and even to entire regions
such as the northeast corridor. The following characteristics are suggested:
1. Traffic flow planning is coordinated regionally across airports and en route centers.
2. Arrival and departure management is coordinated.
3. Airport configuration management is improved.
4. Surface routing and scheduling are coordinated with TMA plan.
5. Precision 4D navigation is applied.
6. Data link for 4D trajectory information exchange is in place.
7. Precision sequencing and spacing is performed.
8. Departure time uncertainty for short-haul flights must be accommodated in the plan.
39

3.3.9 National Flow Management
3.3.9.1 Planning for Operator Efficiency and Overload Protection
As illustrated in Figure 3.2, efficiency and overload protection are the dual objectives of
flight and flow planning. The figure also illustrates how the system operation goes from a
plan to execution, through a sequence of functions that must be coordinated to form a
seamless and effective operation. Figure 3.2 illustrates how information and control
authority flows through the system, and when considering overall system flow
management it is crucial to maintain a whole system view to ensure a sound system
design.
3.3.9.2 Time Horizons and Coordination
Flow planning is fundamentally concerned with balancing the need to plan ahead against
the inherent uncertainty in predicting the future. From the aircraft’s point of view there
are two distinct periods involved in the flight:
• The period before departure, used for planning, checking and loading, subject to
considerable uncertainty, but a wide range of decision options is available.
• The period while airborne, where safe flight is the primary concern, uncertainty level is
low, and only a limited range of decision options remain.
Correspondingly, for flow managers to work effectively with flight planners, they should
have a wide range of routing and scheduling options available for aircraft prior to
departure, and it is reasonable to assume that this implies the function is at the national
level. However, as soon as the aircraft is ready for push-back, and can be fit into a
departure sequence, the primary concern of the corresponding flow planning function must
be safe flight. There is still a need to replan flows to accommodate in-flight operational
uncertainty, but immediate flight safety must always be the priority.
The NAS currently operates its central flow planning function with a large level of
uncertainty due to lack of real-time schedule updates from Official Airline Guide (OAG)
operators, and no predictive knowledge of any other flight plans. This leads to poor
overload protection, i.e. strains the separation assurance resources, and also leads to
periods of poor capacity utilization whith resources at times idle. Section 3.3.9.3
discusses the requirements to achieve performance improvements through more complete
real-time data flow. Section 3.3.9.4 discusses the efficiency gains that may be achievable
through collaborative decision making during the flight planning phase.
The problem of accommodating in-flight operational uncertainty through replanning
involves the following primary question:
• What is the extent of the replanning need (flight and hub optimization, and
disturbances due to weather, aircraft emergency, conflict resolution, etc.), after the
information flow and decision making structure at the national level have been
optimized
40

The answer to this question is likely to vary, primarily due to weather phenomena, and so
the system may need to accommodate dynamically a range of options:
• A large level of replanning need implies a flow management mechanism with a larger
scope (time and space), i.e. closer to a national or regional level. This might be caused
by major weather phenomena moving through the system.
• A limited need for replanning could be handled in a more distributed manner, i.e. at
facility or sector level. This is likely to be the ‘normal day’ scenario, when severe
weather is not a factor.
The frequency of occurrence, associated operational costs, or safety implications of these
options should determine the emphasis in the eventual system design. Section 8.3
discusses the research efforts needed to perform the high level trades involved in the
overall flow management strategy.
3.3.9.3 Information Flow
The thrust of the current initiative to improve information flow between users and the
central flow management facility is focused on the following four areas, as described in the
operational concept document for ATM-AOC information exchange (RTCA, 1997):
• Current operators, with published OAG schedules, will provide real-time schedule
updates to central flow, including flight cancellations, diversions and other decisions
made by the operator in response to major disruptions.
• Central flow management will include more users in the gate-hold program, in an
effort to reduce the uncertainty associated with non-OAG traffic demand in the
system.
• Common weather forecast information will be made available for all users and flow
managers, in an effort to build consensus on traffic initiatives.
• NAS status information will be made available to users, to the extent to which it
affects traffic flow through the system.
3.3.9.4 Collaborative Decision Making
This initiative, as described in the RTCA Task Force 3 Report on Free Flight (1995), is
focused on giving system users more freedom to make decisions in response to traffic flow
restrictions. This is essential to reduce the cost of major disruptions in system throughput.
The primary components of the initiative are:
• Users manage response to delay, after an overall delay allocation from central flow.
This involves the user allocating arrival/departure time to individual aircraft in their
fleet, or opting to re-route around congestion areas.
41

• Central flow management will continue to act as an arbitrator to allocate resources
fairly, and to help users expedite their flight planning.
3.4 Proposed CNS/ATM Technology Improvements
Figure 3.9 illustrates the primary technologies that are being proposed as the basis for the
NAS modernization through 2015.
3.5 Airspace and Airways
The NAS is currently operating at a throughput that is very close to saturation in many of
the busiest terminal areas. In areas such as the northeast corridor, the upper airspace has
also become quite congested. The concept presented here introduces step-by-step
improvements in the system for increased throughput, where initially no major new
technology will be required. However, as the system moves beyond the first steps in the
transition, the implication is that higher performance levels will be required to achieve
higher density operations where they are needed.
As the system transitions to support increased throughput, there will be substantial impact
on NAS airspace, including RSP levels to support operation at a given density level. RSP
will imply end-to-end performance, i.e. aircraft, communication, navigation, surveillance
and air traffic management. Thus, for a given airspace or operation, each system element
will be required to perform at a certain level to ensure system performance.
Airspace performance requirements should be imposed based the nature of the traffic that
will be accommodated in that airspace. High density traffic during peaks at hub airports
will require high performance levels, whereas off-peak traffic at those hubs, and traffic in
low density areas can be accommodated at a lower performance level. Thus, airspace
performance requirements can vary during the day, depending on traffic demand. How
best to manage such requirements must be resolved through careful analysis of user needs
and of what is feasible in an operational system. In the end, some of the decisions
regarding required airspace performance levels will have to be made at the policy level,
where a reasonable compromise between potentially competing objectives must be found.
42

Flight
Schedule
Flight
Planning
Filed
Flight
Plans
NASWIS
Weather
NAS Status
Schedule of
Capacities
National
Flow
Planning
hrs - day
AOCNET
CDM
Delay Est.
Approved
Flight
Plans
Planning
Facility
Flow
Planning
hrs
CTAS
SMA
Planned
Flow
Rates
Desired
Sector
Loads
Sector
Traffic
Planning
5-20 min
UPR
URET
CTAS
SMA
CPDLC
Approved
Handoffs
Negotiate
Handoffs
Clearance
Requests
Traffic
Control
5 min
CTAS
ATN
Radar Net
Voice
CPDLC
Clearances
Vectors
Voice
AC State
Sensor
Tracker
ADS-A
ADS-B
Execution
AOC
Aircraft
Guidance and
Navigation
< 5 min
Traffic
Sensor
ADS-B
CDTI
ACARS
Other Aircraft
States
Aircraft State
Figure 3.9 Overview of Proposed CNS/ATM Technologies
3.6 Airports
The throughput growth requirements presented in Section 2 imply a need for additional
runways in the system, and it is likely that this will have to be met both at existing hubs
and at other airports. As presented in the NAS Stakeholder Needs report that
accompanies this document, the system users are unanimous in their concern about
continuing access to airports, given that it is becoming increasingly difficult to get
approval for any new runway construction.
Airport construction and operational cost is a fundamental issue where economic growth
vs. shorter term business objectives must be carefully weighed. As detailed in the NAS
Stakeholder Needs report, the NBAA expressed concern about continued economical
access to smaller airports, because their members see this as essential for the growth of
small business outside the major population centers.
Another issue of interest is the potential introduction of new types of air transport vehicles
into the NAS. The current development of a civil tiltrotor aircraft is an example, where a
new aircraft user class could potentially contribute to the growth in system capacity. In
the case of the tiltrotor, one proposed scenario is that a portion of the current small jet
transport market could be served with tiltrotor aircraft, that would operate independently
into and out of heliport facilities at hub airports. This might bring added throughput
without the need for major new runway construction, but would instead require other
changes in both airspace and airport facilities. The viability of this concept will ultimately
be determined based on economics, where the seat-mile cost will drive the potential
market share, but some policy level decision may have to be made regarding the needed
infrastructure investment.
43

3.7 Flight Service Stations
The NAS Stakeholder Needs document details the concerns of the NAS users that rely on
Flight Service Stations for information needed during flight planning. This concern is
focused on flight safety related to weather conditions, and to airspace access through
flight plan filing. It must be kept in mind that the safety concern is supported by existing
data on accident rates, and it is probable that improvements in content and presentation of
weather information at Flight Service Stations would reduce the accident rate in this
segment of the system. The cost is probably the primary issue here, and there is an
immediate need for innovative economical solutions for this system component.
44

4 Human Factors
This section addresses some of the major thrusts in the role human factors must play in
enabling increases to the throughput of the ATM system. The primary focus of Section 4
is on human factors roles and issues in increasing throughput in the terminal area.
However, the basic thrust of human factors involvement as well as the issues addressed
apply throughout the ATM system. Section 4.1 frames the top level issues. Section 4.2
describes areas where human factors involvement in the system research, development,
design and implementation process should be improved. Section 4.3 raises some key
human factors issues that require research and development to avoid the unwanted sideeffects
that tend to develop from technically focused initiatives.
4.1 The Search For Greater Throughput And The Demands On The Human
Automation will always be beneficial: the data obtained in experiments
employing fine grained performance and workload measurements indicate that
many ‘tools’ will not be used as predicted or even at all, especially under high
task loading conditions.
(Jorna, 1997)
The current ATM system is a large, complex, almost organic system with human
interactions as the glue that holds it all together. Controllers and pilots manipulate and
manage complex subsystems in real time. They also manage the inherent risks, within
these subsystems, through being adaptive and flexible in times of critical circumstances.
These factors tend to make the development and design of new systems very complex.
The fact that the system has both tightly coupled and loosely coupled components further
complicates the task of defining, designing, and implementing changes which will increase
the throughput of the system and protect safety levels. It is this need for increased
capacity that is driving the need for change. If the American Airlines forecast (Chew,
1997) of impending severe throughput limitations in terminal airspace is valid, then change
must occur in the entire system. Since humans play central roles within this system, it can
be reasoned that a major drive for increased throughput will also drive a requirement for
major changes in the roles of the humans in the system and consequently in the tasks they
perform.
Human factors input is a key element in determining the way that changes to the human
role should best be managed in order to achieve increased capacity without suffering the
unwanted side effects that could adversely affect safety.
4.2 The Role Of Human Factors In Enabling Change
Before actual changes can be discussed or determined it is essential to have an appropriate
framework for the process of research, development, design and implementation itself.
Combined with this system development process there is a need to identify and
incorporate the right skills and knowledge into a team.
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4.2.1 Baseline Data Of Human Roles
In order to have a reasonable level of confidence in the successful evolution towards a
system that achieves the capacity goals stated in Section 2, there is a need for a
comprehensive, integrated description of human behavior (both physical and cognitive) in
the system. The description would serve as a baseline against which to compare proposed
changes to the system. Such a baseline provides by far the most cost effective way of
estimating potential impact of proposed change before the costly process of prototype
development and testing is undertaken. The valuable framework that such a database can
provide should not be underestimated.
An excellent review of human factors research relevant to various aspects of air traffic
control has recently been published by the National Research council’s Panel on Human
Factors in Air Traffic Control (Wickens, 1997). Many of the references in this work
provide pieces of the puzzle of human behavior in the ATM system. The work of the
Panel is probably the first comprehensive step in providing a knowledge base for human
behavior in the ATM system. The next part of that team’s work should add greatly to a
knowledge base.
The availability of both the database and knowledge base should provide a powerful tool
for focusing the development and assessment of decision support tools.
4.2.2 Involvement Of Human Factors From Concept Development Through Final
Design
The role of human factors in system development must not be confined to that of
modifying the results of earlier design decisions to ensure user acceptability. Failure to
consider human performance capabilities and limitations from the very beginning of
concept definition can lead to inappropriate design and serious compromises in system
productivity and even safety. Human factors specialists must be full members of
interdisciplinary development and design teams from the start of the development cycle, so
that both the strengths and weaknesses of the human subsystem can be adequately
accommodated in the final design.
The design team should include the design engineers and end user personnel as well as the
human factors specialists; the latter often play a mediating role between designer and user.
The emphasis here on inclusion of end user personnel is important. However, there is a
need to ensure that the end users are well versed in the principles and skills used by the
other team disciplines. These end users tend to become untypical because of their
involvement in the development process, thus there is a need for regular reviews involving
more typical end users.
The multi-disciplinary design teams should work closely through the entire spectrum of
development tasks from concept development and function analysis/allocation through
preliminary design and prototype development and system evaluation with special
emphasis on human performance testing. Section 4.2.3 discusses the involvement of the
team beyond this point, but it cannot be too strongly emphasized that human factors
specialists should be full members of such teams from the beginning of their existence.
46

4.2.3 Human Factors Support For Implementation, Education, And Training
The involvement of human factors should continue beyond the design stage into the
implementation process. There is a tendency to allow modifications to the final design to
be made by the end user to facilitate implementation. This needs to be carefully controlled
by involving human factors and end users together. It is very easy to lose some or much of
the effectiveness of the original design concept through misinformed or uninformed final
design modifications choices which can lead to loss of efficiency, and possibly have safety
implications.
New systems require fully developed implementation plans which include educating the
users on the logic, capabilities, and rationale of the new system operation as well as its
role in the overall ATM system. The operators of a system will tend to look upon changes
in system design as extensions or refinements of current practice and may fail to
understand the need for new and different tasks and procedures to realize productivity and
safety. This need for education and training was one of the main conclusions of the PD1
simulation report (Eurocontrol (1997), PHARE Development simulation 1). The
education process is in addition to the typical training that operators will receive with the
introduction of new equipment or procedures. The baseline data, described earlier in
Section 4.2.1, will be invaluable in supporting the development of the implementation plan
for new equipment and procedures.
Without a positive and proactive education and training program there is likely to be
considerable transfer of old attitudes and working methods, often referred to as negative
transfer. In developing the implementation plan, very careful attention must be paid to the
potential for transfer of habits used to accomplish tasks under the old system which, if
applied with the new system, would seriously compromise efficiency; but more
importantly safety. Such negative transfer is most often evident when operators are under
considerable stress. Again, the baseline database will provide an effective tool in the
identification of potential negative transfer.
4.2.4 Designing To Support Human Performance Across The Entire Range Of
System Operating Conditions
The air traffic domain is comprised of many complex subsystems, it is subject to the
vagaries of the weather, it is also operated by many different individual humans each
having their own slight differences in behavior as well as each being prone to error or
misjudgment. The net effect is a system with many minor disturbances and potential
exceptions, the majority of which never develop into reportable incidents - because of the
influence of the adaptive human being. There are also the rare-normal and abnormal
conditions which develop, but with much less frequency.
It is critical when designing decision support systems to include the capability to explicitly
present to the operator the limits of the system with respect to operating conditions.
The operator cannot be left to guess or assume system status and shortcomings under
specific conditions when asked to step in and perform manually what the system has
heretofore been accomplishing automatically. This issue will be treated in more detail
when discussing the issue of decision support systems in Section 4.3.1.
47

Capturing the range of normal, rare-normal, and abnormal conditions is itself difficult.
The baseline database must do this for the operations as they occur today. Controllers and
other end users must be key members of the team which develops this database. In fact, a
number of end users from very different ATC environments should participate and review
the database to ensure adequate capture of operating conditions.
4.3 Human Factors Issues Affecting Tactical Control
This section identifies the major human factors issues that have an impact on the search for
increased capacity in the tactical domain of the air traffic management system.
The terminal and tower domains are probably the most dynamic parts of the air traffic
control environment. They are both time- and safety-critical, and the central role of the
human in these domains is both skill- and practice-critical. These environments are
managed by many individual controllers, all in the very exposed situation of having no
immediate support for their tasks. This is because in tower and terminal control there is
not usually a second controller working in close contact (like the ‘D’ side of en route).
Thus the controller is a potential single point failure which, when combined with the single
VHF radio channel for communications, makes for a high level of risk in the event of a
failure in either of these two subsystems. The pressure on the controllers and pilots in this
environment has a greater significance when taking into account the nature of terminal and
tower operations. It is here that most rare-normal situations occur involving aircraft
failures, pilot errors or weather effects. This is also where separation standards are used
as the target separation distances to achieve maximum throughput. Allowing a little extra
separation reduces throughput, while a judgmental error the other way causes a loss in the
safety separation. In addition, there is always the potential for an aircraft to suffer some
form of technical problem. The terminal and tower environments are thus very difficult
domains in which to implement change and the challenge must not be underestimated.
Sections 4.3.1 - 4 attempt to frame the specific human factor issues that affect increasing
throughput in the terminal airspace. These issues were raised earlier within Section 3.4.
The issues of one section tend to be influenced by issues in other sections. This is the
nature of the system, complex and interconnected with adaptive, reasoning humans in a
key role.
4.3.1 Decision Support Systems
The term ‘decision support’ covers many different types and levels of computerized
support or guidance to the human operator. The main issues associated with decision
support are the growing dependency that tends to occur and the effect that the support
could have on the ability to maintain situational awareness.
Whatever the nature of the support system, it is clear that controllers and pilots respond in
a very similar way to other living organisms by developing a growing dependency on the
support. This growing dependency has been described in various sources and has a major
impact on the way that human roles should develop within air traffic control systems.
48

“System designers, regulators, and operators should recognize that over-reliance
(on automation) happens and should understand its antecedent conditions and
consequences”
(Parasurman, 1997)
This dependency can be expected to grow not only as a function of time and confidence
in the system, but it can also be expected to grow as a function of lack of knowledge of
how the system functions without the presence of that support. Thus, new (relatively
naive) operators who do not have the same skill and experience base as the existing
operators, can be expected to display dependency quicker than operators who have this
pre-support experience. Growing dependency has implications on how the system copes
with failures, errors and exceptions. Therefore it is essential that such dependency is
accounted for not only in the development, design and implementation stages but also
during the certification procedures where issues of availability, reliability and redundancy
are raised.
The second issue to be raised about decision support systems is how they affect the
operator’s ability to maintain the necessary level of situational awareness. A key aspect of
situational awareness is the ability to identify when intervention is necessary and then
intervene as required.
Controllers formulate a ‘tactical plan’ which is constantly being executed and modified in
real time. This tactical plan is their baseline for actions within their domain of
responsibility. The plan demands that certain information is accessed and processed in a
timely manner. If the necessary information is not available, then this absence is itself a
trigger to change tactics. Thus triggers to tactical actions can be derived from the absence
or presence of information. This knowledge of what should be present, but is not, would
have to be explicit in the support tool design; lack of required information requires some
form of ‘flag’.
The whole aspect of situational awareness, what it is, where it comes from, what
information is needed when (in order to support it), is still not adequately understood. To
place decision support systems into such a domain of incomplete knowledge is an action
that should be treated with great caution.
Most aspects of these two issues can be addressed using a series of questions about the
proposed new process or tool:
• Has the level of expected dependency on the new support tool by new operators been
identified
• What is its availability - how often is it prone to fail
• What is its reliability - what are the situations when its output is highly variable
• What online checks are being made on its reliability - are these continuous or periodic
• Is it the human operator that verifies the output If so, is this operator capable of
making those reliability checks
49

• What are the back-up procedures to take into account failure, degradation or
inappropriate outputs
• What verification procedures are used to ensure required availability of back-up
systems/procedures
• Are these back-up systems and procedures available, online and well practiced
• What is the certainty that any necessary human intervention skills are of the
appropriate level of proficiency and availability - does this change with time and
population structure - how is this tested and how frequently
There needs to be more research in the whole area of decision support tools, and how they
are subject to growing dependency and affect the maintenance of appropriate situational
awareness.
4.3.2 Intent
There are several issues surrounding the content and availability of intent information that
have an impact on the effectiveness of decision support systems and have major
implications requiring human factors consideration.
The main issues are:
• Where is the knowledge of the intentions of each aircraft and of the tactical controller
Is it in the Flight Management Computer (FMC) or other computer or is it in
someone’s head
• How accurate and reliable are these intentions
• How long are they valid
• How can these intentions be made available to the decision support system in order to
allow it to function with the best quality data available
• How can the system be kept updated or informed when disturbances occur that
demand rapid re-planning on the part of both pilots and controller
‘Intent’ is the description of how the future is most likely to unfold, and in it there is an
attempt to shape the future. Thus intent involves elements of both prediction and predetermination.
Airborne technology has developed to a state that is allowing prediction of
the future, from the individual aircraft’s point of view, to be realized with a fairly high
degree of certainty. This high level of certainty is the result of the FMC’s working to
ensure that predictions come true; the FMC ensures conformance; the future state(s) is/are
constraints that should be achieved.
Intent is not confined to the aircraft and its plan; it is also an important aspect of the
controller’s method of managing a domain of responsibility. The controller’s intent is an
extension forward in time of the dynamics of the current situation, identifying where
modifications will be necessary to maintain safety and achieve pilots’ requested profiles.
The air traffic control system functions principally through the action of the controller
combining all the individual pilot intents with his/her own intent into an overall plan,
50

arbitrating wherever intents conflict. The intent information then becomes a constraint to
which each pilot and the controller attempt to conform. Controllers that talk of ‘having
the picture’ are referring to knowing not only both the current status and intent, but also
of having a plan for the future. They are fully aware of the situation.
The controller’s intent currently tends to exist only in the head of the controller. Groundbased
decision support systems need to have knowledge of the controller’s intent in order
to support the execution of the ‘tactical plan’. These issues are made more difficult to
resolve within the terminal and tower domains by the nature of the operations in those
domains. Terminal and tower are very time-critical and tend to have both a high
mechanical task loading as well as a high cognitive loading. This places extreme demands
on decision support systems for the terminal environment both in terms of task loading
and situational awareness.
Thus there are major issues surrounding the requirements for a better understanding of
registering intent:
• How to get intent into the system
• How to ensure its validity
• How to update it or declare it invalid
There is another set of issues surrounding the possibility of using some decision support
system to create its own plan, thus resolving human input problems. The main issue in this
approach is how to inform the operator about the system’s plan, (especially if the human is
the back-up system).
Decision support systems will have limited effect unless they have knowledge of both the
pilots’ and controller’s intentions. It is the sharing of intention and then the formulation of
a plan that are key elements in achieving greater throughput whilst maintaining or
improving safety.
4.3.3 Using Structure To Maximize Throughput
The usual response of controllers, when the demand for throughput increases, is to impose
some structure as to how traffic flows through their domain of responsibility. This has
been raised as a possible strategy for maximizing throughput in Section 3.4.7. The
imposition of various restrictions, in a structured form, is an attempt to control the
complexity which results from having many pilots each with different requirements. As
traffic load increases, the controller tends to move from a mode of processing individual
requests to one of restricting individual aircraft so that they fit into a certain structure.
A number of options are available:
1. The structure can be predetermined and accessible to the pilots for planning; e.g.,
Airways, SID’s, STAR’s, or
2. It can be predetermined but not available to the pilots; e.g., letters of agreement
between air traffic control facilities on the use of flight levels or routes, or
51

3. It can consist of predetermined actions based on group or individual experience and
not published anywhere, and can be as extreme as stopping all departures from a
particular airport if a sector becomes dangerously overloaded.
There are major differences in the controller’s cognitive workload between allowing
aircraft to fly in a non-airways system, searching for conflicts as the traffic levels grow,
using novel strategies for each situation, versus that of enforcing structure and limiting
conflicts to particular, well-defined points where pre-determined strategies can be utilized
to resolve them.
The current strategy for reducing the cognitive workload on controllers when predicting
conflicts is to restrict traffic to conform to a particular structure. In this way, the cognitive
load per aircraft can be reduced so that the overall level (resulting from the total traffic)
remains at a manageable level.
The degree of detail on each aircraft’s passage through a domain of responsibility, which
the controller must retain, can be reduced using this structuring technique. If all aircraft
are on individual routes and profiles, then the removal of all structure and constraints from
the ATC system may well reduce the actual incidence of conflicts. However, although the
incidence of actual conflict may be reduced, there would probably be an increase in the
controller’s cognitive load because of the demand for more detail on each individual flight
in order to detect potential conflicts.
It is important to keep in mind that the primary role of the controller is to detect and
resolve potential conflicts, before they become actual conflicts. The act of tactical planning
and its constant revision reflect this responsibility. (See Section 6.4 for a discussion on
how to reduce the workload of searching for potential conflicts).
This issue is most obvious in terminal airspace where, due to the uncertainty of aircraft
performance in the vertical plane and the lack of good quality intent information currently
available, there are many more potential conflicts than for aircraft in a more stable cruise
environment. This aspect of detecting potential conflicts and understanding the heuristics
for determining what is a potential conflict are important aspects when establishing fast
time simulations to forecast the effects of different airspace organizations. It is the
potential conflict that creates workload for the controller, and in any situation where
aircraft are climbing and/or descending towards each other there is a need to manage the
uncertainty of these potential conflicts by close monitoring and probably positive
intervention until the situation becomes certain.
How controllers assess and manage uncertainty needs to be clearly understood before
schemes that involve removal or modification of some of the structures used to manage
uncertainty are implemented. Human factors knowledge needs to be used in determining
the impact of airspace structure on capacity, and the requirements for support for the
controller’s cognitive workload in a system that has less structure than at present.
4.3.4 Sharing Responsibility
Responsibility for separation assurance is usually vested in the controller except for very
specific situations (i.e. during visual meteorological conditions (VMC) when limited
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aircraft-to-aircraft separation responsibility can be delegated to the pilots concerned).
Controllers assess how all the aircraft are flowing through a sector or area of
responsibility, working out where adding structure (perhaps in the form of temporary
restrictions) will reduce the incidence of conflicts. When conflicts do occur, there is a
balancing of the needs of the individual aircraft and an attempt to confine the side effects
of any resolution maneuver to as few aircraft as possible. The controller, in any conflict
resolution strategy, balances the demands of each aircraft against the needs of all the
aircraft that are implicated. As discussed in Section 4.3.2, controllers impose structure
during dense traffic scenarios in order to reduce the incidence of conflicts. This is a
stabilizing and throughput maximizing strategy. The controller acts as arbiter where there
is a conflict of interest, but does not have time to discuss the resolution strategy.
Is it possible to transfer separation assurance to the pilots in the terminal area to achieve
VMC-type separation distances in instrument meteorological conditions (IMC) and
thereby increase runway utilization
The terminal area encompasses the most demanding phases of flight for pilots: approach
and departure. Taking on the additional role of separation assurance would have the
potential of considerably increasing that workload in IMC. In the event of any on-board
difficulty, pilot workload would rise, probably necessitating a reduction of overall tasks.
It is also probable that in order to achieve the goal of safe and stable flight the first task to
be off-loaded would be the separation assurance task. The transfer of such a responsibility
back to the controller would have to be explicit in order for each party to be aware of the
extent of changes in his/her responsibility. Such a sudden transfer at a time of already high
pilot workload could also lead to a situation of higher than acceptable risk. The aircraft is
already experiencing difficulty, and the intent information required as input to any decision
support system may be rapidly changing without either the system or the controller being
aware of the extent of these changes. In additional, separation standards associated with
airborne separation assurance concepts might be less than those which an unsupported
controller could sustain. Thus the controller is presented with a situation where the
appropriate separation does not exist for ground-based separation. In this context, the
system is potentially fail-dangerous.
By going through this type of failure mode analysis, it is clear that if separation assurance
is shared with the flight deck in order to achieve reduced separation standards, then
adequate redundancy must be provided to prevent the immediate reversion to control by
an unsupported controller on the ground. This points to a need for consideration of some
critical human factors issues on the flight deck, not the least of which is a major potential
shift in pilot roles, tasks and operating procedures. There seems little likelihood that pilots
will be able to support aircraft-based separation in potentially high workload scenarios
without the integration into the cockpit of major decision support systems. In such a
scenario human factors issues which are raised, both in the cockpit and at the controller’s
workstation, should be examined without delay.
The other issue connected with the sharing of responsibility is that of ensuring that actions
chosen by pilots as resolution strategies do not cause other conflicts. There is a need to
constrain the possible range of strategies commensurate with traffic conditions.
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It is probable, in light traffic conditions, that certain conflicts could be delegated to pilots
to resolve without maneuver restriction. But in heavy traffic conditions, restrictions would
need to be imposed on available strategies in order to prevent a ripple effect on other
aircraft. Once again, unless significant information and suitable support systems are
provided to the pilot, the initiative for limiting maneuvers must be provided by someone
with an overview of the situation. It is likely that the controller must continue to provide
such oversight. In this case, the expectation of aircraft-based separation in anything but
the least dense traffic scenarios must be seriously questioned.
Any issue that affects the roles of pilots or controllers as well as the tasks they perform to
execute those roles needs to have the human factors issues carefully considered in order to
prevent unwanted side effects.
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5 Available and Emerging Technology
5.1 Introduction
5.1.1 System Performance
To achieve reduced airplane separations in part requires a formal definition of system
performance that encompasses improved communications, navigation and surveillance
performance. In addition, a formal characterization is required of the airspace environment
(e.g., airspace configuration, traffic characteristics, available functionality, procedures
definitions) for both nominal and rare-normal performance (e.g., failure modes, temporary
constraints such as weather, etc.).
Experience has shown the need for a formal definition of system performance. For
example, more precise departure and approach paths and direct routings for improved
airspace operations were expected with the introduction of area navigation technology
such as that introduced in the initial 757/67 aircraft fielded in 1982. A more complete
characterization of systems capabilities and features (i.e., the airplane operating
environment and air traffic infrastructure) since 1982 has led to incremental step benefits.
Total system performance characterization of the primary variables enables the higher level
of performance and closer permitted separation.
The proposed definitions of the required performance components for navigation,
communication and surveillance are summarized in the following paragraphs. RNP has
been adopted by the ICAO Required General Concept of Separation Panel (RGCSP) and
All-Weather Operations Panel (AWOP), implemented in the Boeing 737, 747, 777 models
(757/767 will be certified in early 1998), and is ready for initial operational approval. RCP
and Required Monitoring Performance (RMP) are in various stages of development.
These performance definitions can be combined in many ways to support the reduction of
buffer regions in airplane separation. However, the identification of Required System
Performance must find a practical set of CNS capabilities that address operational needs in
a way that provides intended efficiency while maintaining or increasing safety. To
illustrate the objective of RSP, one can conceive a protection volume around the airplane,
whose size depends on the dimensions of the combined communication, navigation,
surveillance performance, and synthesizes into an RSP performance characterization.
5.1.2 Communication Performance
Airplane communication requirements for each phase of flight are a function of the
controller-pilot communication needs. These vary greatly with traffic complexity and
density, the weather conditions, the controller’s needs to issue clearances and vector the
airplane or simply to establish contact with the crew.
Increased communication performance will be provided through air/ground data link
communications integrated into the Aeronautical Telecommunication Network (ATN) to
complement the current voice communications means. This evolution to more data
communications together with increased flexibility in the use of communication
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technology will enable the use of the several available links depending upon the most
efficient communication pathway. The pathway chosen will be transparent to the user, but
will be affected by aircraft location, message type, message criticality, and pathway
availability.
The draft document on RCP (RTCA, 1997) establishes the end-to-end requirements for
the communication component of the CNS/ATM operating environment. The following
paragraphs provide further details of the RCP concept.
5.1.2.1 Required Communication Performance Concept
Required Communication Performance is a statement of the operational communication
performance delay, integrity and availability necessary for flight within a defined airspace,
or for an aircraft to perform a specified operation or procedure. Figure 5.1 illustrates a
generic system configuration for the exchange of air/ground information. An RCP is
determined by cognizant authorities in consideration of environmental factors such as
target levels of safety, separations, flight operation standards, and hazards associated with
the airspace or procedure.
ATS Facility
Data
To
User
Aircraft
Aircraft
System
End
System
Air/Ground
Networks
Ground/Ground
Networks
ATS System
End
System
Data
To
User
Voice
Voice
Figure 5.1 Generic System Configuration For The Exchange Of Air/Ground Information
As RCP evolves to its formal definition, it will define the communication performance of
the individual components (i.e., the aircraft subsystem, the air/ground networks, the
ground/ground networks and the ATS subsystem) on an end-to-end basis, both for Voice
and Data communications. The requirements must be stated in technology independent
terms and, to a degree, independent of architecture, in order to accommodate alternative
technologies and architectures.
5.1.2.2 Installed Communication Performance
Installed communication performance (ICP) is a statement of the aggregate performance
of a given communication system, as depicted in Figure 5.1, and the service arrangements
and levels that have been arranged for with air/ground service providers. ICP is expressed
in the same terms and with the same parameters as RCP. The total user-to-user ICP T is a
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function of all the ICPs of elements between the users (i.e., communications elements
between a pilot and a controller). Once ICP T is determined, it can be compared against a
specific RCP to determine if the RCP is met.
Determination of ICP T is part of the process of gaining operational approval for the given
RCP airspace or operation. ICP is inherently tied to one or more specific technologies. It
is the term used to describe the performance of the particular communication path as
certified by the cognizant authority. ICP can be associated with a given aircraft because it
is strongly influenced by the aircraft’s equipage and the communication support
arrangements that have been made for it.
5.1.2.3 Actual Communication Performance
Actual communication performance (ACP) is an observation of the dynamic operational
communication capability of the same communication elements as was used for the
determination of ICP. ACP is expressed in the same terms and parameters as are RCP and
ICP, but at a given instant may differ from the ICP of a particular path. ACP can be
determined by monitoring the communication path or by monitoring the current condition
of the elements of the path. It is recognized that various cognizant authorities may wish to
specify the necessary reactions of the airspace manager and flight crew when ACP differs
from ICP.
5.1.3 Navigation Performance
Airplane navigation requirements for each phase of flight are a function of airplane
separation requirements. The separation of aircraft and obstacles also provides
requirements especially in the approach/landing phase. A high degree of confidence in the
aircraft staying within a specified volume of airspace is needed to establish separation
standards. The dimensions of this volume are based on the probability of the aircraft
navigation system performance not exceeding a specified error. However, airplane
separation criteria established by the FAA also account for the availability and limitations
of communications, and surveillance services, as well as operational factors (e.g., the
crew/autopilot’s use of the navigation information to control the airplane position) in
addition to navigation requirements.
The increased equipment accuracy and world wide coverage of new systems based on
Global Positioning System (GPS) navigation will greatly improve operations because of
the performance limitations of ground aids. This is achieved in large part by providing
increased integrity monitoring and more reliability. As navigation evolves to satellite based
aids, consideration of additional failure modes will have to be considered. These and
potentially more sophisticated crew alerting schemes will keep driving new requirements
as applications evolve. Cost considerations may become driving factors, but minimizing
the impact on crew interfaces as a fundamental design philosophy will help as will the
potential use of navigation technology developed for the mass market.
RTCA’s document DO-236, “Minimum Aviation System Performance Standards:
Required Navigation Performance for Area Navigation” (RTCA, 1997) establishes the
requirements for the airborne navigation component of the CNS/ATM operating
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environment. These standards will be used by the service providers and users to obtain
operational benefits and may be used to varying degrees depending on the operating
environment. The following paragraphs provide further details of the RNP concept and
the examples in paragraph 5.3 illustrate potential or proposed applications of the RNP
MASPS.
5.1.3.1 Required Navigation Performance Concept
RNP is a statement of the navigation performance accuracy, integrity, continuity and
availability necessary for operations within a defined airspace. Boeing’s implementations
of RNP focuses on horizontal applications and specify the accuracy, integrity and
availability of navigation signals and availability of navigation equipment requirements for
a defined airspace (Leslie, R.S. (1996) and Tarlton, T. (1995)).
The RNP concept introduces the containment surfaces to define requirements beyond
accuracy and provide assurance of navigation performance. It defines a region around the
desired airplane path that can be defined, and that the probability that the airplane does not
remain within that region can be bounded. The containment integrity and containment
continuity requirements define the allowable probabilities of certain types of failures for
the navigation system. In particular, the integrity requirement limits the probability of a
malfunction of the navigation system which causes the cross-track component of the total
system error to exceed the cross-track containment limit associated with the current RNP
without annunciation. The continuity requirement limits the probability of the loss of
function, which occurs when the system indicates that it is no longer able to meet the
containment integrity requirement. The containment surface width is typically set at two
times RNP (i.e., the airplane will be located within two times RNP of the FMC estimated
position). The containment surface ties this performance measure to the airspace
environment and has direct operational implications for flight path, separation minima and
obstacle clearance surfaces criteria.
5.1.3.2 Actual Navigation Performance
Actual Navigation Performance (ANP) is the actual estimated navigation system accuracy
with associated integrity for the current FMC position. It is expressed in terms of nautical
miles and represents a radius of a circle centered around the computed position where the
probability of the aircraft being inside the circle is 95%.
The computed accuracy, ANP, is displayed to the crew as ACTUAL (navigation
performance), and annunciation is provided if ANP (ACTUAL) does not comply with the
containment integrity requirement of the current RNP.
5.1.4 Surveillance Performance
5.1.4.1 Required Monitoring Performance
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A key concept in the definition of future ATM systems is that of Required Monitoring
Performance (RMP). The term ‘Monitoring Performance’ refers to capabilities of an
airspace user to monitor other users and be monitored by other users to a level sufficient
for participation of the user in specified strategic and tactical operations requiring
surveillance, conflict assessment, separation assurance, conformance, and/or collision
avoidance functions. RMP is intended to characterize aircraft path prediction capability
and received accuracy, integrity, continuity of service, and availability of a monitoring
system for a given volume of airspace and/or phase of operation.
Aircraft path prediction is a key function for airspace management and monitoring.
Aircraft path prediction capability is defined by a position uncertainty volume as a function
of prediction time over a specified look ahead interval. Monitoring integrity (assurance of
accurate, reliable information), where there is availability of service, must be defined
consistent with desired airspace operations. Continuity of service and availability also
must be defined consistent with desired airspace usage. Development of these concepts is
currently in progress by various standards organizations.
5.1.4.2 Surveillance System Objectives
Surveillance is a key function for airspace management and supports both tactical
separation assurance of aircraft and strategic planning of traffic flows. The primary
objective of the surveillance function is to support the following types of airspace
management functions:
• Short Term Separation Assurance
The surveillance function provides current aircraft state information on controller displays
and as inputs to separation automation functions, i.e. the short term Conflict Alert system
for detecting immediate path conflicts, and the Minimum Safe Altitude Warning (MSAW)
system for detecting potential flight into terrain. In addition, future automation functions
may require inputs for path lateral and vertical conformance monitoring and for automated
checking of path intent versus path clearances.
• Medium Term Separation Assurance
The surveillance function currently provides state information for sector-based airspace
planning and load management. In the future, additional automation functions such as
Medium Term (~ 20 min. lookahead) Conflict Probe may be used to detect and resolve
potential airspace conflicts, enhancing the productivity of ATC centers. These automation
functions will probably require enhanced surveillance in order to provide accurate and
reliable path predictions for medium term lookahead periods.
• Medium Term Airspace Planning
In the future, the surveillance function must support medium term flow planning and
airport arrival/departure management in congested hubs and other areas where traffic
loads can lead to flow inefficiencies and saturation of airspace throughput. Automation
tools such as the Center-TRACON Automation System (CTAS) arrival manager and
proposed dynamic sectorization tools will require higher levels of surveillance
performance if safety and capacity goals are to be achieved as traffic demand increases.
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• Strategic/Long Term Planning and Flow Management
One of the goals for the future flow management system is to transition from a departure
managed system to an arrival managed system of flow management. One enabling
technology for strategic management of airport arrival slots is accurate 4D prediction of
flight paths from takeoff to arrival at airport metering fixes. The surveillance function
supports strategic flow management by providing accurate state and intent information for
long term path predictions. Similarly, en route traffic flow control automation such as
dynamic sectorization requires accurate path predictions for sector load analysis and flow
management.
5.1.4.3 Current Radar-Based Surveillance System Performance
The current NAS uses a variety of radar systems to supply surveillance data for surface,
terminal, and en route airspace management. On the airspace surface, current generation
Airport Surface Detection Equipment (ASDE-3) primary radars are being installed at
major hub airports to provide surface surveillance and incursion alerting. In the terminal
airspace of most medium and large capacity airports, surveillance data is provided by an
Airport Surveillance Radar (ASR) primary radar which provides position reporting on a
periodic scan basis, supplemented by a co-located Secondary Surveillance Radar (SSR)
which provides aircraft identification, altitude, and backup position reporting. Smaller
airports may only have access to an SSR radar, or may have no surveillance capability
other than that provided by voice reporting and tower controllers. En route airspace uses
a networked system of Air Route Surveillance Radars (ARSR) which provide continuous
monitoring of aircraft flying in domestic airspace above ~ 9,000 feet altitude. Each radar
is networked to one or more Air Route Traffic Control Centers (ARTCC) to provide
continuous monitoring of aircraft across NAS managed airspace. Considerable
redundancy is built into the en route surveillance system in that ARSR sensors are
positioned to achieve at least dual radar coverage throughout NAS managed airspace, and
in addition a co-located SSR provides identification, altitude and position reporting along
with that of the primary ARSR radars.
Current terminal area surveillance is provided by a mix of ASR -7,8,9 primary radars and
Air Traffic Control Beacon Interrogator (ATCBI - 3,4,5) and Mode S secondary radars.
The older generation analog ASR-7 radars are more than 30 years old and are being
replaced by modern ASR-9 radars or the near term ASR-11 radar. The last-generation
ASR-8 radars are also analog radars which are being upgraded to ASR-8D digital radars
to perform surveillance equivalent to that of the current generation ASR-9 radars. The
ATCBI-3,4,5 are older SSR radars which are being replaced by modern Mode S radars or
the near term ATCBI-6 which is a monopulse SSR with limited Mode S functionality.
(The ASR-9s for major hub airports are paired with Mode S radars, and the ASR-11s will
be paired with ATCBI-6 secondary radars.) These radars are designed to support ranges
of at least 60 nm around each airport, and to scan at a rate of about one report per five
second interval. The individual radars have a detection capability exceeding 98 percent,
and a system availability exceeding 0.999 in low altitude terminal airspace. The modern
radars have azimuth accuracies on the order of one milliradian rms, which means that the
position reports of aircraft within terminal range are accurate to 0.1 nm or better. By
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contrast, the older radars have azimuth accuracies on the order of three milliradians which
means that the cross-range components of position reports have much greater uncertainty
and aircraft tracking is significantly less precise.
Current en route surveillance is provided by a mix of ARSR-1,2,3,4 primary radars with
co-located ATCBI and Mode S secondary radars. The ARSR-1,2 radars are very old
analog radars and must be decommissioned in the near term as they are very expensive to
maintain. The ARSR-4 radars are the current generation systems which are being
deployed paired with Mode S secondaries along the U.S. coast lines and international
borders, and the ARSR-3 radars will be given service life extensions to maintain service
over the next 20 years. These radars are designed to provide line-of-sight (~ 250 nm
range) capability and to scan at a rate of about one report per 12 second interval. The
detection probability and accuracies are similar to those of the terminal radars. This means
that position reports at ranges on the order of 150 nm or more are considerably less
accurate than those for terminal surveillance, and as a consequence of the report accuracy
and lower data rate, en route tracking and data report quality are much lower for en route
surveillance. This is one of the reasons that horizontal separation standards are much
larger in en route airspace.
NAS Surveillance System Limitations and Deficiencies
Surveillance system performance today is characterized by the radar sensors available, the
tracking and data fusion software in the ATC centers, and the display automation used for
tactical control. In the terminal area, the modern ASR and monopulse SSR sensors
produce high quality position data for determining aircraft state and identity, and the older
less capable sensors are in the process of being replaced. Similarly, most of the processing
and display limitations of the current ARTS system may be overcome with the
replacement STARS automation system. A primary architectural problem, however, is the
low connectivity of radars in the terminal area. This leads to an expensive system, since
every airport with ATC facilities needs a source of surveillance data. One of the goals of
the future system is to reduce the number of radars in each urban area to provide dual
surveillance coverage of all major airports (for functional redundancy in case of system
failures), and at least single coverage of other airports by networked distribution of
surveillance data to ATC fusion nodes. These goals are annunciated in the NAS
Architecture V2.0 (U.S. FAA,1996).
By contrast, current NAS en route surveillance is characterized by a number of problem
areas. The accuracy and usefulness of aircraft state data is greatly limited by the use of
legacy tracking and display software. This results in fair to poor velocity estimates with
considerable noise variations from scan to scan, and in large tracker lag errors (~ 30 to 60
second lag errors during turn maneuvers). Moreover, the use of the ‘radar mosaic’
concept for switching from one primary sensor source to another as the aircraft traverses
across mosaic boundaries leads to track state ‘jumping’ as the tracker shifts from one
sensor source to another. In addition to these implementation problems, the current
surveillance system does not provide flight path intent data for path conformance
monitoring, and provides only limited coverage at low altitudes and in mountainous
terrain. The implementation problems of the current system can be largely overcome by
use of modern multi-sensor tracking and data fusion software, which compensates for
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deterministic sensor errors such as azimuth bias errors, and enables dynamic blending of
the most appropriate data for aircraft state estimation. (A surveillance ‘server’ concept is
advocated in NAS Architecture Versions 2.0-3.0, which would network multiple terminal
and en route sensors into common data fusion nodes, and distribute the global track data
to appropriate ATM facilities, requesting users, and to external fusion nodes.)
5.1.4.4 Surveillance System Performance Metrics
Within the regions where surveillance coverage is available, the primary metrics for the
surveillance function are accuracy, availability, integrity and latency. (Continuity of
function and reception probability are also of interest, but are usually treated within the
scope of the above metrics.) Although individual sensors or subsystems may have
individual or characteristic performance, it is the end system performance metrics which
are of significance for the users of surveillance data. For path prediction analysis, for
example, both position and velocity performance is significant for determining the overall
prediction errors for a given lookahead period. We summarize these metrics and future
requirements in this section.
Accuracy Metrics
The accuracy metrics in the current system are most often driven by user requirements for
separation assurance. In the terminal area, where this function involves vectoring and
altitude level-off controls, the greatest need is for relative accuracy measures, i.e.
monitoring the current aircraft states versus the currently active clearance. Typical
relative position accuracy of modern radars in the terminal area is under 0.1 nm and is
adequate for current means of separation assurance. The future use of RNP routings on
the order of RNP-0.3 for SIDs, STARs, and non-precision approach, and the potential use
of operational concepts to increase throughput may lead to requirements for substantially
higher accuracy and dynamic reporting of path intent. Part of this requirement will be for
absolute accuracy, since bias errors between the flight navigation system and the
surveillance system may appear as path conformance violations to ground controllers, and
part of this requirement will be for more precise velocity states for faster detection and
resolution of route conformance and clearance errors.
The accuracy metrics for surveillance performance in transition and en route airspace are
driven by several needs including conflict detection, separation assurance and sector load
planning. Operational concepts such as the use of medium term conflict probe will require
much better tracking than is available with current legacy systems. Earlier studies
(Warren, 1996) have shown the need for much reduced lags in tracking of maneuvering
aircraft, and in achieving steady state velocity errors on the order of 5 knots rms.
Similarly, the use of operational concepts to achieve reduced separation standards, and the
future use of RNP-1 routings may lead to requirements for substantially better tracking
accuracy than is achievable with currently fielded systems.
Availability Metrics
Since active surveillance is essential for safely separating aircraft at the separation
standards currently used in the NAS, the desired levels of system availability are on the
order of 0.99999 or better (RTCA, 1997, MASPS on Automatic Dependent Surveillance-
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Broadcast (ADS-B), V6.0). Individual radar sensors can support availability on the order
of 0.999. However, to achieve the overall system level availability, dual surveillance
coverage is usually required. This is currently not a problem at high altitudes since dual
radar coverage or better is available throughout the NAS. At low altitudes, and in the
terminal maneuvering areas this requirement is difficult to achieve and an availability of
0.999 is currently considered acceptable, except at the major hub airports. This level of
availability is probably adequate for future systems, except that traffic growth may extend
the need for higher availability in more terminal areas. Continuity of function is often
included in the availability metrics and in future system planning considerations.
Integrity Metrics
Integrity is usually measured in terms of undetected errors in surveillance system outputs.
Desired system level integrity is on the order of one undetected error in 10 7 scans/output
reports. At the sensor level, clutter detections and fruit replies can lead to large
spontaneous errors at much higher rates. The tracking and data fusion software typically
provides the added integrity to achieve the desired system level performance. Future
systems will probably require equivalent integrity, although the use of multi-sensor
processing and integrity checking could yield higher integrity than current systems.
Latency Metrics
Latency is a measure of the acceptable delay between successive surveillance reports on
the average or at a specified probability level. (For example, with en route radars the
probability of reception per scan is on the order of 98%, and the latency between
successive scans is 12 seconds at the 98% probability level.) This metric is typically
specified by a stressing application such as separation assurance at a typical range between
the aircraft being tracked and the tracking sensor. For close range applications such as
parallel approach monitoring and collision avoidance, a typical latency requirement is a
one second report updating at a 95 to 99 percent probability of reception. For other
applications latency requirements increase with separation range and size of minimum
separation standards, e.g. latency may be 15 minutes with ~95% reception probability for
an oceanic ADS system supporting horizontal separation standards on the order of 30
miles. This does not include transmission latency, which is a measure of the time delay in
actually receiving the report at the data fusion center, or latency error, which is a measure
of the time stamping error associated with a surveillance report. These metrics are also
useful in quantifying system performance.
5.1.5 Aviation Weather Performance
Weather has a major impact on the safety, efficiency, and capacity of aviation operations.
Accidents and incidents continue to be caused by adverse weather. Runway acceptance
rates and other capacity metrics are reduced in IMC. According to some studies, 40-65
percent of delays that affect U.S. domestic airlines are caused by adverse weather, at
annual direct costs ranging from $4-5B per year (Evans, 1995). In addition, passengers
are inconvenienced by flight delays and cancellations or diversions due to weather, and are
uncomfortable when turbulence is encountered during a flight. The expected future
growth in air traffic will only exacerbate all these conditions, imposing constraints on the
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ability of the airlines to meet growing demand while improving safety and efficiency.
Boeing has recently launched an Aviation Weather Study to collect and document
information on the affect of aviation weather on the domestic and international ATM
system (Lindsey, 1997). An important component of this effort is to develop an
understanding of user requirements for aviation weather information, and then to assess
how well the current and planned aviation weather system will meet those needs. Section
5.5 presents some of the preliminary findings from this project regarding the operational
aspects of current and future aviation weather technologies.
Recently, the National Research Council released a report describing the results of its
review of the domestic aviation weather system (NRC, 1995). Some of the key findings
and recommendations from that study related to the performance of weather technologies
included:
• Some of the measurements provided by automated weather observing systems are not
always reliable, especially observations of ceiling and visibility measurements. More
human observers are needed at key facilities to ensure that erroneous data are not
disseminated to pilots and controllers.
• Aircraft observations of winds and temperatures provided by the Meteorological Data
Collection and Reporting System have improved forecast accuracy, and its use should
be expanded and more carriers encouraged to participate.
• New weather technologies coming online now and in the near term are producing
much larger data sets than previously available. New data management and analysis
technologies, such as the Aviation Gridded Forecast System, are needed to manage
and distribute this information.
• The accuracy and timeliness of short-term ‘nowcasts’ and longer term forecasts of
weather conditions in the terminal area and en route environments need to be
improved. Additional research is required to improve current weather forecasting
tools and to develop new technologies.
• Many of the negative impacts of weather on the aviation system are regional rather
than global problems. Regional solutions should be sought where they will be most
effective (Alaska is a key area identified by the NRC where this recommendation
should be followed).
• Interactive computer graphics workstations and graphical images depicting current and
expected weather conditions are becoming the tools of choice for analyzing and
disseminating weather information to users. Efforts are needed to standardize the
information provided by these systems so that all users benefit from shared situational
awareness. Controllers in particular should be given critical weather information in
formats that improves their situational awareness without increasing their workload.
Such information could significantly improve the efficiency of the air traffic control
system while improving safety standards at the same time.
• The limited capabilities of current cockpit displays and communications links are the
largest technical constraint on disseminating weather information to pilots. Research
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is needed to develop cockpit display systems and communications systems that will
provide weather information to pilots in as an efficient and timely manner as possible.
Human factors issues and crew workload considerations must be addressed early in
this process.
The NRC study addressed many areas of concern related to the aviation weather system,
but it did not specifically investigate some of the near term and far term performance
requirements for aviation weather technologies to support CNS/ATM systems. For
example, accurate 3D meteorological information will be needed for CTAS and conflict
probe trajectory calculations, and for the wake vortex separation prediction system being
developed by NASA. The data sets needed for these tools will be generated from analyses
of current surface and aloft conditions and forecasts of future conditions. The accuracy,
precision, and completeness of the meteorological information must be quantified, and the
sensitivity of CNS/ATM tools to errors in the data need to be determined. Information is
also needed on the amounts and types of additional data, especially upper-air data, that
will be required to ensure the success of these technologies.
Most weather impacts on today’s ATM system are associated with bad weather, especially
in the terminal area when adverse weather creates inefficiencies that lead to capacity
reductions at the busiest airports. Thus, most aviation weather technology deployments
already made or planned for the near term focus on improving the quality and timeliness of
weather information for instrument meteorological conditions. However, for the far term
the focus will need to shift to improving the quality of aviation weather information under
all weather conditions, including what would normally be considered fair weather, i.e.,
visual meteorological conditions. This is because the day-to-day success of Free Flight
and new CNS/ATM technologies like CTAS will depend in part on the quality of the
observed and predicted meteorological information that these technologies will need.
5.2 Communication
5.2.1 Air/Ground Communication
Air/ground communication provides for the transfer of information between the aircraft
and a ground entity. The ground entity may be an air traffic control facility, an airline
operations center or another source of required information, such as an airport which
prepares an Automated Terminal Information System (ATIS) message.
Air/air communication is a special case of air/ground communication. The primary use of
air/air communication is monitoring the party line of other air/ground communications.
Certain operations, such as operations at uncontrolled airfields, require transmission-inthe-blind.
That is, the pilot reports his position and intent to any and all aircraft near that
airport without addressing a specific aircraft or expecting a reply. In addition, flight crews
directly communicate between aircraft, such as in oceanic airspace.
Communication functionality may be described in three layers of service. The
Application layer provides standard formats for efficient transfer of information. In voice
communication, this consists of standard phrases and reporting procedures which have
evolved over time and are specified in documents such as FAA Order 7110.65, Air Traffic
65

Control, and the Aeronautical Information Manual (U.S. FAA, 1997). The next layer is
the Protocol layer, which provides the conventions or rules for communication. The third
layer is the Media layer, which connects communicating nodes together by radio
frequencies or wires.
5.2.1.1 Voice
Voice air/ground communication has evolved from early tube-type avionics transmitters
and receivers to modern 760-channel very high frequency (VHF) transceivers and satellite
communication (SATCOM). As shown in Figure 5.2, voice communication provides both
air traffic services (ATS) and AOC services. Air traffic services includes ATC voice
procedures, waypoint reports, and ATIS broadcast information. Although waypoint
reports are actually a subset of ATC voice procedures, they are shown here as a placeholder
for the ADS function which will be described in the data communication section.
ATIS broadcast is shown here as a representative of a broader group broadcast services,
including transcribed weather broadcast (TWEB), Automated Weather Observation
System (AWOS), and Automated Surface Observation System (ASOS) on very high
frequency omnidirectional range (VOR) and non-directional beacon (NDB) audio
channels.
Two-way voice traffic on VHF or HF radio is performed as half-duplex; that is, one party
transmits, then the other party responds using the same channel. The speaker presses a
transmit button to gain access to the channel; hence the term push-to-talk (PTT). In
theory, an ATC controller is the owner of any channel assigned to ATC but in fact channel
access is equal for all users. Many operations, including oceanic VHF, the emergency
channel (121.5 MHz), and Multicom, have no ATC participant who can be said to own
the channel.
Since there are many users potentially requiring access to the channel, a verbal Medium
Access Control (MAC) protocol has evolved. The pilot or controller listens for a break in
the communications, presses the transmit button, and speaks the message. If a response is
not received in a timely manner, the sender assumes that a collision happened or some
other problem prevented the person at the other end from responding and the transmission
is repeated. This is essentially the same logic as the Collision Sense Multiple Access
(CSMA) normally attributed to digital data protocols. The individual messages may be
considered packets of information.
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ATC
Voice
Procedures
Waypoint
Reports
AOC
Voice
Procedures
ATIS
Broadcast
SELCAL
Voice
PTT
SATCOM HF VHF
VOR
Audio
Figure 5.2 Voice Communication
For those channels where the probability of receiving a call is sufficiently small (e.g., AOC
channels) or the normal channel noise is quite high (e.g., HF voice) a tone selective calling
(SELCAL) system is provided to indicate to the pilot that a call addressed to his aircraft
has been received. He can then turn up the receive audio and respond.
SATCOM does not use the PTT protocol. SATCOM provides a service which has more
in common with conventional or cellular telephone service. A telephone number is
entered into a control/display device in the aircraft or at the ground station. When a
‘send’ button is pressed a connection is established between the airplane and the ground
and an annunciator is activated at the other end. When the call is received a duplex voice
path is activated, allowing simultaneous talk in both directions. Since air time is relatively
expensive the connection is maintained only while active conversation is required, then the
call is terminated.
VHF radio is the preferred medium whenever the aircraft is within line-of-sight of a
ground station. When within range, VHF signal quality is generally good to excellent.
There are 760 channels to choose from, spaced 25 KHz apart. Some European countries
will soon activate VHF channels 8.33 KHz apart, allowing up to three times as many
channels to choose from, but the FAA has no plans to use this capability.
HF radio is the normal communication medium for oceanic and remote areas not covered
by VHF. Unlike VHF, HF communication is normally indirect, i.e., a radio operator
actually talks with the flight crew, then communicates with the ATC controller by text
(teletype). This is because of the unique skills required to communicate in the noise and
fading signal of HF and the need to choose communication frequency based on time of day
and ionospheric condition. A phone patch can be arranged if the controller and pilot need
to talk directly.
SATCOM service is generally available whenever at least one satellite is within line-ofsight
of the aircraft. The current satellite service, called Aeronautical Mobile Satellite
Service (AMSS) by ICAO, is currently provided by Inmarsat. Since the satellites are
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geostationary, they orbit over the equator at an altitude such that they appear stationary to
a ground observer. Therefore, the satellite appears near the horizon to an aircraft flying at
a high latitude. There are four Inmarsat locations (Atlantic Ocean East, Atlantic Ocean
West, Indian Ocean, and Pacific Ocean), so coverage extends nearest the poles directly
north (or south) of each satellite location.
Voice broadcast is provided in the VHF communications band for ATIS, ASOS, and
AWOS. TWEB is available on some VOR and NDB stations. Some countries also
provide ATIS on a VOR frequency instead of a VHF communications frequency.
5.2.1.2 ACARS
Voice communication can provide direct communication from a person’s brain, through
his voice, to the brain of another person. Data communication, on the other hand, has the
capability to communicate from a computer to another computer. This allows
communication of important data without human intervention. On the other hand, text
messages can be presented by the computer to the pilot and controller, which can
communicate some information more efficiently and accurately than voice. The
advantages are improved communication accuracy and a potential reduction in workload.
ARINC Communications Addressing and Reporting System (ACARS) was developed by
the airline industry nearly 20 years ago to support their AOC needs. Most of the
communication requirements of the federal regulations are met by ACARS. The
Out/Off/On/In reports, which were the first messages of ACARS, have been supplemented
by a wide variety of messages, conveying information both to and from the airplane. For
instance, some airlines regularly send flight plans to their airplanes for direct loading into
the FMC. Onboard maintenance computers can automatically send reports to the ground
at a specific point in the flight, in case of a detected fault, or in response to a ground
request. The airlines are continuing to expand the functionality of ACARS with additional
message formats.
As seen in Figure 5.3, ACARS is also used for air traffic services communication. The
FAA provides pre-departure clearances for about 40 of the major airports. This is not a
direct ATC-to-airplane service, but rather has used some existing capabilities to provide
this service. ARINC receives the departure clearances from the FAA for contracting
airlines and delivers them to the airline. The airline in turn forwards the clearance to the
designated airplane. Although this is generally considered an ACARS service, the airline
can use any appropriate means, such as delivering a printout to the cockpit, to get the
clearance to the airplane. The FAA is in the process of installing digital ATIS in a number
of towers at major airports, which will allow the flight crew to request and receive the
current ATIS information by ACARS. Like pre-departure clearances, the FAA version of
ATIS is unique to the FAA.
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CPC = Controller
Pilot Communications
CPC
Waypoint
Reports
ATIS
&
PDC
AOC
ATIS & PDC
(FAA)
PDC = Pre-Departure
Clearance
ACARS
ACARS = Aircraft Communication
Addressing & Reporting System
SATCOM HF VHF
Figure 5.3 ACARS Communication
The Airlines Electronic Engineering Committee (AEEC), who specified ACARS, has
defined a series of ATC messages and recommended their use to the various authorities
which desire to provide air traffic services via ACARS. These messages, defined in
ARINC Specification 623 (ARINC, 1994), include departure clearances, ATIS, waypoint
position reports (for oceanic use), and a series of simple controller/pilot communications
(CPC). The CPC messages were added to the specification to support the NOW
communications the FAA has been considering. A few European airports have
implemented services using the pre-departure clearance and ATIS messages.
ACARS was developed in the era of teletype services and networks, which are based on
character-oriented protocols. As a result, all ACARS messages are restricted to those
which can be conveyed by upper-case alphabetic characters, numbers, and a very limited
set of punctuation marks. The air/ground message format is received by ARINC at its
processor in Annapolis and translated into the airline ground/ground protocol and then
forwarded to its destination. An uplink is similarly translated into the ACARS protocol.
ACARS was originally developed for use with VHF radio. The airplane installation
includes an ACARS Management Unit (MU), which is connected to a conventional VHF
communications radio by audio lines, transmit and data mode discretes, and a tuning bus.
Modulation is 2.4 Kbps minimum shift key, which can be achieved by normal AM double
sideband modulation of the radio frequency with the audio from a modem in the MU.
Received signals can be similarly demodulated and sent to the modem as audio signals.
A new modulation standard for VHF ACARS has been proposed, which is differentially
encoded 8-phase shift keying. The bit rate will be 31.5 Kbps. This modulation method
will require direct digital modulation of the radio frequency signal, so the audio interface
to an external modem will not be possible. A VHF Data Radio (VDR) has been specified,
but is not yet in production, to provide the new modulation functionality. A digital data
bus will be used to connect the MU and the VDR.
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The 2.4 Kbps and 31.5 Kbps described above are the raw bit rates in the signal-in-space.
The available user bit rate is decreased by message overhead and is inversely proportional
to the number of stations sharing a VHF channel. A single channel (frequency) is used
across most of the U.S. and up to three additional channels may be available in high
density airport areas. Therefore, if 14 aircraft and two ground stations are within line-ofsight
of each other on one frequency, the average long term bit rate for each will be 2400 /
16 = 150 bps.
The ACARS specification has been expanded to provide SATCOM and HF media
connections. The VHF-unique protocol is stripped off and the remaining characters are
encapsulated in a SATCOM or HF protocol data unit for transmission. The ACARS MU,
the SATCOM data unit, and the HF data unit or radio are connected together with digital
data busses.
The raw bit rate of 10.5 Kbps has been mentioned for SATCOM. Although this bit rate is
available for providing a dedicated circuit for SATCOM voice, as described earlier, data
link protocols depend a packet service, which is multiplexed among multiple users. A bit
rate of 300 bps is a more reasonable value.
HF data radio has automatically-selected bit rates of 300, 600, 1200, and 1800 bps. The
bit rate is chosen based on the channel real time propagation characteristics, such as noise
and fading. Experience has shown that the bit rate is normally 600 bps. An estimated ten
aircraft can share a channel, providing an average bit rate of 60 bps per aircraft.
5.2.1.3 FANS-1
The set of data link services provided in a FANS-1 airplane is shown in Figure 5.4. The
ACARS protocol and the air/ground media are identical to those described above.
Communication between the controller and the pilot is provided by Two-Way Data Link
(TWDL), as described in RTCA Document DO-219 (RTCA,1993). This application has
been commonly called Controller-Pilot Data Link Communications (CPDLC) which, as
described below, is the formal name for the ATN application which provides the
equivalent functionality.
Position and intent reporting is provided by the Automatic Dependent Surveillance
function. Although there is an equivalent RTCA document, the specification produced by
AEEC, ARINC 745, was used for this implementation (ARINC, 1993). The ground
system requests a ‘contract’ with the aircraft, specifying the reporting period for basic and
supplemental data to be transmitted. The contract can also specify a set of events, such as
altitude deviation, which will also cause a report to be transmitted.
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TWDL = Two-Way
Data Link
CPDLC = Controller
Pilot Data Link Comm.
TWDL
(CPDLC)
ADS
AOC
ADS = Automatic
Dependent Surveillance
ACF = ACARS
Convergence Function
ACF
AFN = ATS Facilities
Notification
AFN
ACARS
SATCOM HF VHF
Figure 5.4 FANS-1 Communication
The AOC functionality is generally the same as described above. It includes the normal
collection of airline-defined functions and messages. The FANS-1 installation also
includes direct interface to the FMC to support uplink and downlink of a large number of
FMC-hosted parameters, including flight plans. Although this functionality was previously
available, this is the first time it has been installed in an entire fleet of airplanes.
ADS and TWDL were both intended to be used over the ATN, so they were designed as
bit-oriented applications. Since ACARS can only accept character-oriented messages, an
ACARS Convergence Function has been specified to convert bit-oriented messaged to
character-oriented format for transmission and to convert received messages back to bitoriented
format. This is done by taking each nibble (four bits) of the bit string and
expressing it as a hexadecimal character (0...9, A...F). A 16-bit cyclic redundancy check is
calculated on the original bit string and the four characters representing the result are
appended to the character string calculated for the message. The reverse procedure is
performed at the receiving end.
An additional function was required to send and receive messages, in ACARS character
format, to find the necessary addresses for communicating in the FANS-1 environment
and to communicate function availability at the two ends (e.g., an ATS ground station that
can send and receive TWDL but not ADS). This function is called the ATS Facilities
Notification (AFN) function.
The FANS-1 functionality was first demonstrated in the South Pacific, for flights between
the Los Angeles and San Francisco to Sydney, Australia and Auckland, New Zealand. Air
traffic control uses TWDL replaces HF voice communication for regular pilot/controller
dialog. Position reports by HF voice (about every 40 minutes) have been replaced by
periodic (about every 15 minutes) ADS reports or by position reports using TWDL for
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those Flight Information Regions (FIRs) which don’t yet have ADS at the controller
workstations. The reliability of these data link applications over SATCOM has been
proven. The operational procedures are in the process of being formalized, which will
allow the airlines and ATC agencies to gain benefit from the investments that were made.
FANS-1 equipment and operations are being established along other oceanic and remote
routes which currently use non-radar procedures for ATC. Although FANS-1 has been
considered for en route and terminal operations, the relatively poor latency of the ACARS
network and human factors challenges on the ground and in the cockpit have slowed those
developments.
5.2.1.4 ATN
ICAO has been developing the network and applications of ATN for a number of years.
The ATN Standards and Recommended Practices (SARPs) have been accepted by ICAO
and are in the process of final publication. Unofficial but complete and correct electronic
copies are available on electronic file servers (French Ministry of Transport, 1996). The
functions of ATN are illustrated in Figure 5.5.
CPDLC ADS FIS AOC
FIS = Flight Information
Services
CMA = Context
Management
Application
CMA
ATN
GateLink
SATCOM HF VHF
Mode S
Figure 5.5 ATN Communication
The air/ground applications of ATN which have been defined are CPDLC, ADS, FIS, and
CMA. CPDLC is a refined version of the TWDL/CPDLC function described above for
FANS-1. Lessons learned in the implementation and operation of FANS-1 have been
applied to the ATN version of CPDLC. In addition, the international ATC operational
community has evolved some new concepts and phrases since RTCA document DO-219
was written, which have been incorporated in the ATN CPDLC specification.
ADS has similarly been improved based on lessons learned from implementation and
operation of FANS-1. The most obvious change is the addition of more event triggers to
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the ATN ADS specification. This will allow a greater reliance on aircraft-detected
deviation from the planned flight to initiate reports and less dependence on periodic
reports and controller detection of those deviations. This will allow the periodic reports
to be less frequent, resulting in more efficient use of radio bandwidth with equal or better
conformance monitoring.
Flight Information Services (FIS) is a collector for a potential group of applications, such
as weather and Notice to Airmen (NOTAM) reporting. At this time, the only function
which has been defined is ATIS. FIS may be described as an ‘inverted ADS’ in that the
aircraft can request a contract with a ground-based database for specific information. For
instance, an aircraft may ask for the arrival ATIS information for a specific airport, with
the contract specifying that an update be sent to the aircraft whenever the information is
modified. This would allow the aircraft to maintain current ATIS information with no
further pilot intervention.
Context Management Application (CMA) is functionally equivalent to the AFN function
of FANS-1. The aircraft and ground share information about function and version
availability for each of the applications. The intent is that future versions of the
applications will be backward compatible, allowing the applications to down-mode to a
lower version to maintain compatibility with their peer at the other end.
The ATN protocol consists of a family of protocols derived from those specified by the
International Standards Organization. The protocol family is partitioned into seven layers
of functionality, called the Open Systems Interconnection.
The key protocols of ATN are found in the Network layer. The movement of data
packets is performed by the Connection-Less Network Protocol. The exchange of routing
data to ensure that the packets get forwarded to their destination is performed by the
Inter-Domain Routing Protocol. Other members of the protocol support the functionality
provided by these two protocols.
The primary media for ATN are the same as for FANS-1, that is, VHF, SATCOM, and
HF. The subnetwork protocols for these three media are different from those in an
ACARS environment in that they are optimized to support the bit-oriented network
protocol data units which they convey. In addition, a couple of other media have been
proposed for ATN.
Mode S data link was proposed as a medium early on in the development of ATN.
Although some European countries continue to plan for Mode S data link, the FAA has
removed Mode S data link from their plans, in favor of VHF.
When the aircraft is parked at the gate, on the open ramp, or in a hangar, an umbilical
cable may prove to be a more efficient way to convey data to and from the aircraft. This
would save precious radio bandwidth for mobile aircraft, which have no choice but to use
radio frequencies, and would allow a larger bandwidth than is technically feasible over
available radio bands. The Gatelink concept has been proposed to fill this need. The
current definition is based on the 100 Mbps Fiber Distributed Data Interface network.
Gatelink has not been implemented in other than prototype so it may change if, and when,
it is finally built.
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5.2.2 Ground/Ground Communication
In addition to the air/ground communication described above, communication among
ATC facilities and between ATC and AOC facilities is important to CNS/ATM. Much of
the communication internal to the NAS is conducted on FAA-specified systems that do
not necessarily conform to international standards. Communication between the NAS and
the ATC systems of other countries either conform to ICAO and other international
standards or is based on a bilateral agreement between the U.S. and a specific adjacent
country. Figure 5.6 illustrates the general overview of ground/ground voice and data
communication.
AIDC
ATSMHS
AFTN
Telephone
AIDC = ATS
Interfacility Data
Communication
AFTN = Aeronautical
Fixed Telecommunication
Network
ATN
ATSMHS = ATS
Message Handling
Services
NADIN II
NADIN = National
Airspace Data
Interchange Network
PTN = Public
Telephone Network
PTN
FAA Lines
Figure 5.6 Interfacility Communication
5.2.2.1 Voice
The primary communication between ATC facilities and between AOC and ATC is via
telephone. Voice switching centers at ATC facilities provide automated dialing and
connection through either dedicated FAA circuits or through the public telephone
network.
5.2.2.2 Current Data
Data is communicated among centers, TRACON’s, towers, and Flight Service Stations
over a dedicated packet switched network called National Airspace Data Interchange
Network (NADIN). Data include flight plans and transfer-of-control information between
host computers.
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The airlines and the FAA have recently established AOCNET to provide a means of
sending messages between the AOC center and the NAS primarily the central flow facility.
5.2.2.3 ATN
ATN provides not only air/ground communication but also ground/ground
communication. Two applications have been developed for ground/ground service. ATS
Interfacility Data Communication (AIDC) provides direct real-time messaging between
controllers, similar to CPDLC between pilots and controllers.
The second ATN ground/ground application is ATS Message Handling Service
(ATSMHS). Based on the X.400 Message Handling Service (e-mail) developed by the
International Telegraph and Telephone Consultative Committee, ATSMHS provides a
store-and-forward messaging service that is appropriate for sending flight plans and other
information that is unnecessary to send in real time.
5.3 Navigation
5.3.1 Navigation Functionality
The navigation functionality provides position determination, flight plan management,
guidance and control, display and system control, and fault configuration management.
Navigation functionality may be described in three layers of services (see Figure 5.7). The
Controls and Displays layer provides the interfaces between the flight crew and the
airplane systems. These include:
1. The Mode Control Panel, which provides coordinated control of the FMC, FD/AP and
altitude alert functions
2. The Electronic Flight Instruments’ Primary Flight Displays, which displays the flight
mode annunciation, and airspeed, attitude, altitude, vertical speed, and heading
indications
3. The Horizontal Situation Indicator, which displays flight path orientation and guidance
cues (bugs) on airspeed and Engine Pressure Ratio
4. The Control Display Unit, which enters the desired lateral and vertical flight plan
information into the FMC and displays the waypoints and path constraints stored
within the navigation database.
The processor layer integrates data from the air data, inertial reference, radio navigation,
engine and fuel sensors, navigation, performance and flight plan databases, and crewentered
data to navigate the airplane. The sensors layer provides the airplane state data
(i.e., position, velocity, acceleration, attitude) and navigation and guidance information.
This includes radio navigation sensors, such as Instrument Landing System (ILS) Glide
Slope and Localizer receivers or equivalent Microwave Landing System (MLS), Distance
Measuring Equipment (DME) or equivalent tactical air navigation (TACAN), Global
Positioning System (GPS), Inertial Reference System (IRS), Very-high frequency Omni
Range (VOR) receiver, Automated Direction Finder (ADF) and the air data sensors (pitot
static and temperature probes, angle of attack, etc.).
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Early navigation systems (i.e., direction finders and four-course low frequency ranges)
developed around determining the position of the aircraft to avoid obstacles and arrive
safely at a destination. In those days, navigation needed navaid-to-navaid operation for
airplane position fixing and to allow procedural control of airplane separation. This
established the U.S. route structures (i.e.,Victor and Jet Airways). The success of these
navigation systems (with increasingly more accurate position determination in different
phases of flight) led to the trend of minimizing aircraft track excursions. With this trend,
navigation systems were able to combine navigation data from several sources to optimize
the intended track and increase operational accuracy. The resulting Area Navigation
(RNAV) capability is able to better utilize resources (e.g., fuel and time). This capability is
implemented in the Flight Management Systems (FMS) where the system controls the
airplane path along a stored trajectory and enables RNAV operations on any desired flight
path within the coverage of station-referenced navigation aids or within the performance
limits of self-contained aids.
Electronic
Flight
Instruments
Control
Display
Unit
Secondary
Flight
Instruments
Mode
Control
Panel
Flight
Plan
Nav/Perf
Data Base
Area
Navigation
Autopilot
Flight Director
Air
Data
GPS DME/TACAN VOR IRS ILS/MLS
ADF
(NDB)
Pitot
Static
Figure 5.7 Navigation Functionality Overview
The FMS provides the crew both lateral and vertical flight path guidance cues along
predefined procedures or can fly the airplane in an automated flight mode. Thus, by
combining the navigation systems developed over the decades, incremental operational
benefits have been obtained since the late 1980s in all phases of flight. New capabilities
introduced in the 1990s, based on GPS technology, have allowed a further increase in
accuracy or overall performance. These performance enhancements are the basis for the
many new applications proposed by the user. The most promising of these are illustrated
in the following paragraphs.
5.3.2 Terminal Area Navigation
Terminal area routes provide access to the en route structure for departing airplanes (SID)
and routing to enter and execute the approach (STAR) and landing phase for arriving
airplanes. The procedures are stored in the navigation database and are selectable from a
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menu associated with the airport of interest. Terminal navigation is typically characterized
by moderate to high traffic densities, converging routes, and transitions in flight altitudes
that require narrow route widths. The routes are typically within the coverage of radio
navigation aids (VOR and DME/TACAN, ADF) which provide increased navigation
performance over self contained aids (i.e., IRS). Navigation while flying along a SID or
STAR may be to procedure-tuned navaids or to optimally selected navaids. Independent
surveillance is generally available to assist ATC in monitoring airplanes independently
from the ground.
The standard FMS RNAV capability provides guidance cues to the crew along predefined
procedures as illustrated on the left of Figure 5.8. It maximizes the crew’s situational
awareness through MAP/Horizontal Situation Displays in the cockpit and allows the crew
to manage its workload. In addition the system allows aircraft to consistently and
precisely fly along the predefined path such as departure or approach and landing paths.
Standard FMS Area
Nav. Departure
Flight Path
Flight Path
RNP
FMS/RNP
Flight Path
Obstacle
(or Protected Airspace)
Departure
Waypoint
Figure 5.8 Area Navigation Capabilities For Departure Procedures
With the advent of GPS and the RNP concept, significant improvements in accuracy and
availability over VOR/DME RNAV systems is obtained with lateral accuracies of 0.2 to
0.3 nm achievable in coupled flight. Coupled vertical accuracy can be justified to near
Category 1 minima. This is illustrated on the right in Figure 5.8. The RNP function
provides flight phase dependent performance with assurance provided by the containment
region around the flight path and navigation performance alerting to the crew, enabling
access to sites with natural or man-made fixtures around them. The best example of this
capability is the Alaska Airlines FMS-based departure and arrival procedures at Juneau,
Alaska. Other examples include the Eagle County Departure out of Vail, Colorado, and
the San Francisco Quiet Bridge Approach, all FMS-based procedures developed jointly by
the FAA and Air Transport Association Task Force.
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The ability to design FMS approaches or departures based on RNP containment enables
potential economic benefits by allowing access to runways which do not have a precision
approach in use, or which require special RNAV procedures to ensure separation.
Access to these runways can provide benefits in terms of: reduced delays, on ground or
while airborne; avoided diversions; reduced fuel load requirements for dispatch; increased
payload and reduced communications between the controller and the pilot.
5.3.3 Oceanic /En Route Navigation
Oceanic navigation requires very large separations because of the limited navigation
performance of the inertial reference systems or long range navigation systems, and the
lack of independent surveillance capability other than infrequent voice position reports.
The IRS is typically characterized by a linear accuracy decay of 1.5 to 2 nm/hr. Oceanic
routes are typically fixed or wind optimized tracks between key city pairs where the tracks
are repositioned based on the latest wind forecasts. The routes are typically structured
around a main track (optimum wind/minimum time track) and a number of parallel tracks
on either side to accommodate the predicted traffic. Traffic flow is primarily
unidirectional because of the time difference between continents and the airline customers
arrival time preferences.
The procedural separations applied in this environment are dominated by the navigation
performance, and yield operations where 20 nm (95%) navigation systems are separated
by 100 nm and 12.6 nm (95%) systems are separated by 60 nm (see also Figure 2.10). It is
proposed to reduce the large separation to 30 nm based on the containment concept of
RNP as illustrated in Figure 5.9 below. An RNP 4 capability (i.e., a 4 nm 95% accuracy
threshold) together with high availability has been proposed to achieve this reduced
separation. The required high availability is provided by the onboard integrity monitoring
techniques that allow the use of GPS with high accuracy during many satellite
constellation outages (which are a function of satellite geometry and pseudorange noise)
and eliminates the need to frequently revert to less accurate means of navigation. An
aircraft meeting the RNP will remain within the 8 nm lateral containment limit with a
predefined level of confidence. As an initial implementation, a ‘safety buffer’ of 14 nm is
proposed to account for less frequent blunders. This buffer can be reduced, perhaps
eliminated, when other CNS elements provides suitable assurance of containment region
conformance (e.g., data link, ADS) and operational experience confirms that navigation
containment removes most of the sources of large excursion risk.
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8.0 NM
4.0 NM
POPP
PLMN
14.0 NM
30.0 NM
PLWX
4.0 NM
8.0 NM
PWVG
Defined Path
RNP 95% Threshold
Containment Threshold
Figure 5.9 Reduced Separation Between Parallel Oceanic Tracks
In this context, the containment applies to the lateral position of the aircraft. In the future,
the time and vertical components will be added, to provide a four dimensional containment
surface that can be used to support full user-preferred trajectories in four dimensional
flight. In fact, a Required Time of Arrival (RTA) function is already available on several
FMSs, specified as a time at which to reach a waypoint. The first application for this
function could help the crossing of oceanic tracks. This initial RTA function is part of the
FMS performance prediction computation and requires further development to integrate it
with the RNP concept. The ability to design oceanic track procedures based on RNP
containment enables potential economic benefits by allowing more airplanes to fly the
minimum time track along the optimal wind, by reducing fuel burn and fuel reserves.
En route navigation has not benefited to the same extend from the GPS capability and still
uses the basic short-range aid to navigation in the U.S., VOR or VOR/DME. Some new
or recently upgraded airplanes include GPS sensors, typically to provide operational
benefits in other than the en route environment or in areas lacking the VOR/DME
infrastructure. When using the IRS, an approved external navaid must be used to monitor
its performance. Air carrier operators use these navaids, while other operators have
historically used Loran-C and OMEGA. GA airplanes and smaller operators do benefit
from the GPS capability because of its lower acquisition cost.
The VOR/DME navaid forms the basis for the international air navigation system. Over
time it has proven to be safe and adequate, as well as currently representing a large
investment in ground/airborne equipment by both users, governments and institutions
worldwide. At present, almost all commonly traveled U.S. domestic routes are covered
by Jet Routes or Victor Airways supported by the VOR/DME navaid. However, the
VOR/DME system performance is limited so that route width in the domestic phase of
flight varies from 16 to 8 nm at best. The FAA is developing a Wide Area Augmentation
System (WAAS) to increase GPS performance (i.e., primarily integrity and availability, but
also accuracy), as well as a means to phase out land-based navigation aids and reduce
maintenance costs. Introduction of the FMS has freed the airplane from the constraints of
flying fixed routes over navaids and opened up new airspace. FMS-enabled Direct Routes
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(i.e., Great Circle tracks) have been introduced progressively to save fuel and time by
avoiding the inherent detours of fixed routes (e.g., National Route Program and random
routes/User Preferred Trajectories). Fixed track routings have been retained where the
traffic distribution must be kept simple and/or the number of crossing points in a sector
kept well defined.
5.3.4 Landing and Surface Operations
The ILS navigation aids (i.e., localizer and glide slope) provides lateral (from 25 nm out)
and vertical guidance (from 10 nm out) to the runway. Marker beacons or DME navaids
indicate the distance to the runway threshold. Precision Approach Minimums range from
CAT I to CAT III operations as a function of Decision Height (DH) and Runway Visual
Range (RVR). CAT I requires 200 feet DH and 1800 to 2400 feet RVR minima
depending on lighting system and airplane speed category, CAT III requires a DH between
0 and 50 feet and an RVR from not less than 700 feet (CAT IIIA) to not less than 150
feet (CAT IIIB). The ILS performance is limited in some areas by FM frequency
interference, in-band congestion, and siting limitations (an ILS site requires the
surrounding terrain to be flat so that signal characteristics are not distorted). Hence, the
Microwave Landing System was developed to the same performance requirements as ILS.
The FAA’s MLS development contract ran into production problems in the late 1980s and
was later canceled. It has been replaced with the Local Area Augmentation System
(LAAS) program which is a GPS-based landing system augmented with ground
augmentation aids. LAAS performance will include coverage for multiple runways or
airports in a regions. Airplane avionics are being developed to carry a Multi-Mode
Receiver (MMR) able to interface the crew controls and displays with one of several
receivers, either ILS, MLS or GPS Landing System (GLS).
5.4 Surveillance
5.4.1 Summary of Surveillance Evolution
The current surveillance system is based on the use of redundant primary and secondary
(beacon) radars. The role that ground based radars play may be gradually diminished as
GPS-based ADS 1 systems become available. The evolution to next generation
surveillance is complicated by interoperability and compatibility with current systems in
use. Two principles which limit available options for next generation systems are:
• Compatibility with current secondary radar systems, i.e. Mode A/ C/ S
• Interoperability with current TCAS collision avoidance systems and next generation
Cockpit Display of Traffic Information (CDTI)-based air/air surveillance and situation
awareness
1 In this section ADS is referred to in a generic sense rather than as a specific implementation. In this sense,
Mode-S Specific Services, Mode-S extended squitter broadcast and contract based ADS as defined by RTCA
DO-212 represent specific implementations of ADS technology.
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The near future will probably see a mix of radar and ADS technologies which will be
integrated and fused at the major ATC centers, providing high integrity and high accuracy
surveillance based on multiple sensor inputs.
The value that ADS methodology adds to surveillance is not limited to radar monitoring
capability, however. With ADS it is possible to downlink extended surveillance
information related to aircraft intent, and other data such as current winds aloft which are
useful for predicting aircraft paths. The ability to fly flexible routings, for example, may
depend on knowing validated and accurate path intent, as well as the ability to monitor
current position and velocity states.
The value of ADS broadcast (ADS-B) for air/air surveillance and airborne separation
assurance is yet to be evaluated. However, this technology will certainly play a role in
areas where radar surveillance is uneconomic or not feasible. Dual mode CDTI/TCAS
systems will be in use in the near future for oceanic and remote area applications such as
In-Trail Climb/Descent and for increased safety in non-radar airspace. CDTI will also play
a role in the congested terminal areas of major hub airports providing additional safety and
operational capabilities for equipped aircraft, as discussed in Sections 3 and 6.
The sections below summarize the evolution of surveillance for surface, terminal area, en
route, and oceanic operations. The emphasis of these sections is on the evolution of
air/ground surveillance since the primary responsibility for separation assurance will
remain with ground-based systems in the near term evolution of the NAS airspace system.
A possible evolution path for air/air surveillance and CDTI is then summarized.
5.4.2 Airport Surface Surveillance
Airport surface surveillance includes monitoring and display of the movements of all
vehicles on controlled areas such as taxiways and runways, and providing sensor inputs for
surface movement and incursion alert automation systems. Figure 5.10 shows the
probable evolution of surface surveillance from current radar-based monitoring systems to
multi-sensor radar/ADS-B systems. The dotted arrows in the figure denote evolutionary
upgrade paths, while the solid line arrows denote inputs from sensors to automation
systems. The older generation of ASDE-2 radars is currently being phased out and newer
generation ASDE-3 primary radars are being installed at 40 of the biggest hub airports in
the U.S. The ASDE-3 display system will then be upgraded by Airport Movement Area
Safety System (AMASS) software for automated incursion alert. Two major problems
with the ASDE-3 systems are the cost of installing and maintaining the radars, and the lack
of aircraft/vehicle ID for surface movement, guidance & control. At the larger hub
airports, ADS-B systems will be integrated with the ASDE radars to provide
aircraft/vehicle ID, and to provide a backup sensor for radar failures. At smaller airports,
ADS-B ground systems will provide a less expensive means of surface surveillance for
equipped aircraft and surface vehicles. The AMASS automation software will evolve into
Surface Movement Guidance and Control Systems, for comprehensive surface guidance &
control to maximize airport capacity during peak periods, while maintaining adequate
safety for airport surface operations.
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ASDE-2
Radar
* 1960’s Era
Radar
ASDE-3
Radar
* Modern
Radar
ADS-B
* GPS
Incursion
Alerting
Surface Movement
Guidance & Alerting
(SMGCS)
Legend
System Transition
Sensor
Automation
Application
CDTI
* Airport Map
& Vehicle
Tower
Displays
Figure 5.10 Airport Surface Surveillance Evolution Path
ADS-B data may also be used aboard equipped aircraft to display surface traffic and
airport features on a plan view CDTI display optimized to surface operations. This would
provide the air crew with redundant monitoring of potential incursions for increased safety
and surface situation awareness.
5.4.3 Enhanced Terminal Area Surveillance
Terminal area surveillance with today's radar-based technology and automation system
consists of tracking and display of position and velocity states and aircraft ID for all
aircraft operating within 60 nm of the airport surveillance radars. Figure 5.11 illustrates
that future terminal area systems may evolve in several ways to provide enhanced terminal
surveillance. One of the major changes will be the evolution of multi-sensor tracking
systems for integrating data inputs from multiple radar systems and from ADS-B equipped
aircraft to derive the most accurate and robust tracking of current aircraft states obtainable
from multiple data sources. Even without ADS inputs, the use of multiple radar sensor
blending has been shown to greatly improve the quality of aircraft tracking for advanced
automation systems such as CTAS, and area-wide conflict probe (Hunter, 1996 &
Warren, 1994). These systems need high quality velocity estimates with accurate steady
state tracking and rapid response to aircraft maneuvers, which is attainable with state of
the art multi-sensor tracking systems. The advent of ADS-B equipped aircraft will also
require multi-sensor tracking to blend radar and ADS-B sensor inputs.
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ASR/SSR
Radar
Terminal
Automation
Short
Arrival/
Term
Departure
Separation Managers
ASR/SSR
Radar
Multi-Sensor
Tracking
Path Predictions
(20 min lookahead)
ADS-B
* GPS Squitters
* 1990’s Era
Automation
CDTI
ADS / ADS-B
* Winds Aloft
* Future Waypoints
* Event Reports
Figure 5.11 Terminal Area Surveillance Evolution Path
A second major change is that surveillance will evolve to include any data inputs that can
be used for improved path predictions. This will include radar and ADS-B measurements
of current position and velocity, information on current flight plan and path intent, and
data related to winds aloft along the intended path. The current ADS systems for oceanic
use recognize the need for such extended surveillance, and explicitly include downlink of
winds aloft and future waypoints for more accurate tactical and strategic path prediction.
With current ground-based systems, 3-4 minute path predictions are generated for conflict
alert, based on current estimates of aircraft position and velocity. Automation systems
such as CTAS and regional conflict probe require 20-30 min. predictions of aircraft path,
and thus require much more extensive data fusion of wind, tracker states, and path intent
to achieve high quality path predictions. In this regard, ADS systems can play a unique
role not feasible with current surveillance systems, i.e. transmitting aircraft intent,
including the generation of event messages when path intent changes.
It is technically feasible to transmit extended surveillance data such as waypoint intent
using either ADS-B or ADS-A selective addressing. However, such data is unlikely to be
of interest to the general population of air and ground users capable of receiving ADS-B
messages. Thus, the current thinking is that extended surveillance data such as future
waypoints and winds aloft will be obtained using selectively addressed ADS. In any event,
the terminal areas of busy hubs need dynamic flight intent updating to support future
operational concepts such as departure and arrival automation and dynamic selection of
SID and STAR routing options.
The use of ADS-B data for air/air surveillance and CDTI applications such as aids to
visual approaches and visual acquisition of traffic is also important for increased safety and
capacity in the future CNS/ATM system. Although separation assurance and flow
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management functions will primarily remain with ground-based systems, cooperative
air/ground use of CDTI capability can be a valuable supplement for reducing separation
standards and increasing traffic throughput during arrival and departure rushes.
5.4.4 Enhanced En Route Surveillance
Today's en route surveillance system is based on primary and secondary radar systems
which are nearing the end of their economic life, and on 1960's era automation software
which is obsolete by today's standards. Both the radar sensors and the tracking software
need to be replaced to support flexible routings and advanced ATM initiatives. Figure
5.12 illustrates the likely evolution path for en route surveillance in NAS airspace. The
current plan is to decommission the older radar systems, extend the networking of radar
sensors to include terminal radars to reduce the need for replacing en route radars, and to
replace the older beacon radars with modern monopulse SSR or Mode S sensors.
The current Mosaic-based en route tracking system will also be replaced by multi-sensor
tracking software, greatly enhancing the quality, accuracy, and flexibility of the en route
tracking function. Recent studies (Hunter, 1996) have graphically demonstrated the
performance problems associated with using Mosaic-based trackers for advanced ATM
automation systems such as CTAS. It is essential that multi-sensor tracker software be
developed and implemented in the mid-term NAS architecture in order to support midterm
CNS/ATM initiatives such as direct path routings with reduced separation standards.
The use of Mode S extended squitter for en route air/ground ADS-B surveillance is
problematic in the near and mid-term due to insufficient reception range with low cost
omni antennas. Eventually, ADS-B listening stations will probably be added to the ground
infrastructure to perform enhanced en route surveillance for equipped users, and to back
up the conventional en route surveillance infrastructure. In the mid-term transition period
when ADS-B avionics become available for air/air and terminal applications, a possible
transition solution for enhanced surveillance is to use the Mode S interrogation capability
to obtain ADS-B equivalent information during each scan of the Mode S radar. Figure
5.12 shows that such ADS capability is highly desired for evolution of flexible routings
and advanced ATM automation.
As in the terminal area, extended surveillance is also needed to predict aircraft trajectories
for nominal 20 minute Conflict Probe and other ATM applications en route. Although
enhanced radar tracking and more frequently updated wind forecasts may be used in the
near term to support advanced ATM automation, ADS transmission of path intent and real
time monitoring of aircraft states for path conformance are seen as essential evolution
steps to achieve increased capacity and efficiency in the future CNS/ATM system.
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ASR/SSR
Radar
Mosaic Based
(Host) Tracker
* Arrival Metering
* Conflict Probe
Mode-S/ Monopulse
Secondary Radar
Multi-Sensor
Tracking
Path Predictions
(20 min lookahead)
* 1990’s Era
Automation
ADS-B /
Mode-S
ADS-B / Listening
Stations
Short Term
Separation
ADS /
ADS-B
* 2005 Era Sensors * Future Waypoints
Figure 5.12 En Route Surveillance Evolution Path
5.4.5 Enhanced Oceanic and Remote Area Surveillance
Today’s methodology for non-radar procedural separation involves the use of HF or VHF
voice reporting at fixed latitudes in oceanic airspace or at intermediate waypoints in
remote area routings. The older airspace automation systems are relatively primitive
compared to those for radar-based ATC and are still based on the use of flight strips for
flight following. This technology is being supplanted by next generation FANS systems
with ADS-based surveillance, data link and satellite-based voice communications, and
GPS-based navigation for oceanic and transcontinental routings. The main driving forces
for implementation of this technology are to increase capacity in procedural airspace and
to provide more optimal wind routes and altitudes for increased flight efficiency. This
evolution is shown in Figure 5.13. At the same time, there is a great need for increased
safety in many areas of the world such as Africa and undeveloped areas of Asia. In the
near term, TCAS is being mandated in some of these areas to provide increased safety for
avoiding mid-air collisions. The probable next evolution for capacity and safety in these
areas is the implementation of dual CDTI/TCAS systems using both ADS-B and TCAS
sensors. In the near term, such systems will be developed for applications such as in-trail
climb/descent for enhanced oceanic operations. In the far term, the dual use of both ADS
and CDTI technology will give enhanced situation awareness to both ground-based
controllers for traffic planning and separation assurance, and to the air crew for enhanced
tactical maneuvering in low density, remote areas. The evolution to ADS-based ground
surveillance and ADS-B based air/air surveillance will probably enable reduced separation
standards on the order of 15 nm horizontal minimums for equipped aircraft, based on
redundant ground and air surveillance systems and separation assurance capability.
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HF / VHF
Voice Reporting
ADS / CPDLC
DATALINK
ADS -B / TCAS
SENSOR
FIRST
GENERATION
OCEANIC
AUTOMATION
ENHANCED
OCEANIC
AUTOMATION
* 1990’s Era
Automation
CDTI / TCAS
SEPARATION
ASSURANCE
FLIGHT PLANNING/
REROUTING
PROBLEM
RESOLUTION
Figure 5.13 Oceanic/Remote Area Surveillance Evolution Path
The widespread use of ADS-B and CDTI technology for separation assurance may first
occur in oceanic airspace. In essence, the oceanic centers would provide strategic
planning and separation services for such aircraft, and the flight crews of equipped aircraft
would provide short term separation services for limited tactical encounters such as track
crossings. For reduced separation standards, both aircraft involved in an encounter will
need to be ADS or ADS-B equipped.
5.4.6 Enhanced Air/air Surveillance and CDTI Evolution
Although there are many potential applications for CDTI, a phased implementation of
ADS-B/CDTI equipage is envisioned, since user benefits depend on the percentage of
ADS-B equipped aircraft for each application. A few of the more noteworthy applications
and their possible role in the evolution of CDTI are briefly described below.
The near term applications of CDTI are for proposed functions such as in-trail climb, intrail
stationkeeping, enhanced visual approaches, and on-board monitoring of closely
spaced parallel approaches. These functions may be viewed as extensions of existing
TCAS avionics and display systems. However, the TCAS systems were designed for
collision avoidance and were never intended for such applications. From a user
perspective, however, TCAS systems are expensive avionics which serve a limited, though
important function. There is great interest in extending the functionality of such
equipment. One likely group of users transitioning to ADS-B may be the TCAS users
who have already invested in Mode S transponders, TCAS processors and cockpit
displays. Moreover, widespread ADS-B equipage by TCAS users may justify
development of increased performance TCAS systems with lower false alarm rates and
more accurate detection and display of intruder aircraft.
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Another group of users which can benefit from ADS-B and CDTI equipage are the non-
TCAS aircraft which fly in high density terminal airspace and need a lower cost system for
conflict avoidance and visual acquisition of traffic. Although TCAS-I was originally
intended for such users, equipage costs have proved prohibitive for most GA and military
users. However, a transition problem exists for potential CDTI users since user equipage
may not be cost effective unless a substantial portion of the airspace population is visible.
The likely transition solution is the implementation of Traffic Information Services (TIS)
which would transmit ground-based surveillance data to airborne users. Eventually, as
ADS-B systems are mandated in such airspace, the TIS services can be replaced with
ADS-B surveillance as a primary source of CDTI input data.
The last application to be mentioned is the use of ADS-B and CDTI technology for
cooperative Airborne Separation Assurance Systems (ASAS). The concept of operation
is cooperative since responsibility for separation assurance is primarily a ground function
as in the current system, except that during limited time encounters between two aircraft,
responsibility for monitoring and assuring safe separation can be transferred to properly
equipped and certified air crew. The motivation for this mode of operation is the ability to
fly User Preferred Trajectories, including user specified routing, speed, and cruise altitudes
for most economic flight operations. Such operations may lead to an increased number of
encounters, however, compared with current operational procedures. Controller
workload may be kept within acceptable bounds by transferring separation assurance to
the air crew, who can perform separation monitoring during close proximity encounters
and activate conflict avoidance maneuvers whenever a potential loss of separation is
detected.
5.5 Aviation Weather
Operational aviation weather services are provided by the FAA, the National Weather
Service (NWS), and the private sector. Research and development of aviation weather
technologies is conducted by the FAA, the National Oceanic and Atmospheric
Administration (NOAA), NASA, the MIT Lincoln Laboratory, and the National Center
for Atmospheric Research (NCAR). The operational and research functions performed by
these organizations can be broken down into four areas:
• Observations
• Analysis
• Forecasting
• Dissemination
Figure 5.14 illustrates the functional relationships between these four areas. Observations
are used to prepare analyses of current weather, which in turn are used to prepare
forecasts of expected conditions. Forecast products usually include gridded data fields,
which must themselves be analyzed. Finally, the analysis and forecast products are passed
to the users via the dissemination process.
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Dissemination
Forecasting
Analysis
Observations
Figure 5.14 Functional Areas Of Aviation Weather
The NWS operates much of the meteorological observing network, and it prepares
weather analyses and forecasts at the National Center for Environmental Prediction
(NCEP) and the Aviation Weather Center (AWC). The NWS distributes weather
information to users electronically via land-based networks and satellite communications
systems and by voice. The FAA also collects weather information, including surface
observations in the terminal area and radar observations of storm locations and intensity.
NWS meteorologists working in the Center Weather Service Units (CWSU) at each
ARTCC, in the Central Flow Weather Service Unit, and at Flight Service Stations (FSS)
provide analysis and forecasting services for their FAA colleagues, and produce weather
information that is then relayed to controllers and pilots. A few of the major airlines have
their own meteorological centers, but most receive their weather information from the
NWS and/or private sector providers of weather information.
Observations of current meteorological conditions are collected at airports and at other
sites located throughout the country and offshore. These include surface and upper-air
observations of winds, temperature, pressure, moisture, precipitation, cloud type and
amount, radar reflectivity, and soil and water temperature, among others. These data are
used to prepare objective analyses of current weather conditions that affect aviation
operations, referred to as Aviation Impact Variables (AIV’s). Examples of AIV’s include
ceiling and visibility, precipitation, icing conditions, winds aloft, runway winds, and
turbulence.
Objective analyses also provide initial and boundary conditions for numerical weather
prediction (NWP) models and other forecasting tools. Weather conditions are forecasted
on time frames as short as 30-60 minutes (referred to as ‘nowcasts’) to as long as several
days. Nowcasts provide useful information for managing air traffic flows into and out of
terminal areas, and for providing information to support tactical decision making, e.g.,
vectoring aircraft around hazardous weather. For aviation applications, the longer-range
forecast periods of greatest interest are probably in the 3-24 hour time frame. These
forecasts support strategic planning and decision making by providing information that
helps planners and air traffic managers coordinate aircraft and airport operations. Once
the weather analyses and forecasts are prepared, the information must be distributed to
users in a timely manner. Weather information is highly perishable, so that the technology
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and human factor elements in all four of these areas must work together effectively and
efficiently.
5.5.1 Observations
Weather observations for aviation applications are collected by the NWS, FAA, and the
airlines themselves, via the Meteorological Data Collection and Reporting System
(MDCRS). Meteorological data used in the aviation weather system can be broken down
into four broad categories, which include:
• Surface observations of present weather, such as winds, temperatures, pressure and
altimeter setting, atmospheric water vapor, precipitation, visibility, and cloud cover.
• Upper-air observations of winds, temperatures, pressure, and water vapor.
• Weather radar reflectivity data showing storm location, intensity, and motion; and
Doppler radar observations of near-surface and upper-air winds.
• Visible and infrared satellite imagery of cloud location, motion, and temperature; and
water vapor imagery showing upper-air circulation patterns.
Historically, most operational aviation weather systems have been operated in a standalone
mode, that is, there has been little or no integration of the data into systems that
directly supported aviation operations (the Low Level Wind Shear Avoidance System,
LLWAS, is an exception). This paradigm is finally changing. The Lincoln Laboratory is
developing and testing algorithms to detect gust fronts and measure microburst intensities
with Doppler radar, and to present this information to controllers along with other
aviation-related information via the Integrated Terminal Weather System (ITWS) (Evans
and Ducot, 1997). Likewise, the Aviation Vortex Spacing System (AVOSS) program at
NASA’s Langley Research Center is developing an operational wake vortex separation
tool, which will likely require surface and upper-air meteorological data from a network of
sensors that are not currently being used at airports (Hinton, 1997). These kinds of
technologies hold much promise for improving the safety, efficiency, and capacity of the
ATM system. They will also expand requirements for observations in the airport and en
route environments, and they will require research into instrument and system
performance metrics, human factors engineering, and operator training issues.
Figure 5.15 identifies the major instrument systems used in the four categories of
observations mentioned above. The following sections describe the different types of
weather observing systems currently in use or planned for the near term, and indicate areas
where new technologies are needed to support weather requirements for the future ATM
system.
5.5.1.1 Surface Observations
Surface measurements are made with a combination of in-situ and remote sensing systems.
The NWS is completing its deployment of the Automated Surface Observing System
(ASOS), and the FAA is completing the network of Automated Weather Observing
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Systems (AWOS). These systems are complementary, but perform somewhat different
functions. The ASOS was intended to be a complete surface meteorological observing
station that would replace human observers. ASOS systems are deployed at airports but
also in a much broader weather observing network around the country. Problems have
emerged with some of the ASOS sensors, particularly the visibility package, which have
prevented the ASOS from achieving the goal to eliminate human observers. Work
continues on these problems, but the likelihood of their success is not known at this time.
Human observations of some critical aviation impact variables will likely be needed for the
foreseeable future (National Research Council, 1995). The AWOS is designed strictly as a
terminal weather information system. It was not intended to eliminate human observers,
but it does provide certified observations of ceiling, visibility, altimeter setting, wind
speed, and wind direction. It too has been criticized for providing misleading aviation
weather information, especially ceiling observations.
Specific information on the performance of the sensors on the ASOS and AWOS was not
available at the time of this writing. However, it is reasonable to expect that the accuracy
of the sensors is adequate for most current and expected analytical and modeling
applications. The notable exception is that the visibility and present weather sensors have
been criticized for giving inaccurate and misleading information under some circumstances
(NRC, 1995). An important issue for the success of future improvements in aviation
weather information is likely to be increasing the spatial density of measurements to
provide improved coverage of key weather parameters. When completed, the ASOS
network will consist of over 850 units and the AWOS network will consist of 160 units
located at airports that do not otherwise provide certified weather information. (Some
state governments have also purchased AWOS systems.) These two surface monitoring
systems will likely go forward for a decade or longer as the primary surface observing
systems used for aviation weather.
Other sources of surface data are used for aviation weather, primarily to support tactical
decision making. For example, the FAA operates sensors that measure runway visual
range (RVR). Errors in automated RVR systems (and ASOS and AWOS visibility
measurements) deployed to date suggest that near term improvements in visibility
measurement technologies could improve the efficiency of airport operations. The FAA
also operates the LLWAS, a network of tower-mounted anemometers that is supposed to
detect potentially hazardous wind shear and microburst conditions at the airport.
However, concerns over the efficacy of LLWAS data have sometimes lead controllers to
ignore LLWAS warnings. This was apparently the case during the 1994 crash of a USAir
MD-80 at Charlotte-Douglas airport (NRC, 1995) during a microburst event. In the near
term, improvements in wind shear algorithms and/or the use of more Doppler radar
information could improve safety conditions in the terminal area. There is also a national
network of lightning detection sensors that show where cloud-to-ground lightning strikes
are occurring.
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ASOS
AWOS
TDWR
NEXRAD
Surface
Upper-Air
Rawin
Profiler
LLWAS
MDCRS
Observations
ASR-9
Weather
Radar
Satellite
NEXRAD
TDWR
Figure 5.15 Aviation Weather Observation Function
5.5.1.2 Upper-Air Observations
Adequate upper-air meteorological data are critical to the aviation weather system, and
this is an area where additional resources and technology development in the near term
and far term could produce significant improvements in aviation weather information. The
primary source of upper-air data comes from the NWS’s network of rawinsonde
observations. Radio wind soundings are made by weather balloons that carry aloft a small
instrument package called a radiosonde. The radiosonde measures atmospheric pressure,
temperature, and moisture as it ascends, which are used to calculate altitude. Radio
direction finding techniques or navaid-based tracking systems follow the motion of the
balloon, from which winds aloft are computed. The accuracy of the thermodynamic
sensors is generally good (a few percent), while rms errors in winds aloft are typically 1-3
m/s. Sounding systems expected to become available in the near term will use GPS to
track balloon position, which should improve the accuracy of altitude data and may
significantly improve the quality of upper-air wind information. GPS radiosondes have not
yet come into widespread use because of their cost relative to conventional radiosondes,
but this situation is expected to improve over the next few years.
In the U.S., two soundings are made each day, one at 00 UTC (1900 EST) and the other
at 1200 UTC (0700 EST), at approximately 80 stations in the CONUS, Alaska, and
Hawaii. The data are used to analyze weather patterns on constant pressure surfaces and
aloft winds at constant flight levels, and to initialize NWP models. The meteorological
community is virtually unanimous in its opinion that increasing the spatial and temporal
density of upper-air data would significantly improve weather forecasts, but due to budget
constraints there are no plans to expand the rawinsonde network. The current network is
probably just barely adequate to characterize synoptic-scale weather features (fronts,
locations of high and low pressure centers, etc.), but much of the weather that affects
aviation occurs on the mesoscale, e.g., connective storms. The current rawinsonde
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network does not provide adequate spatial or temporal resolution to monitor the
atmospheric environment on this scale, and the accuracy of weather forecasts suffers as a
result. The absence of upper-air data in the oceanic domain also seriously degrades the
performance of NWP models, especially of forecasts issued for coastal areas and of aloft
conditions expected during intercontinental flight operations.
To compensate for the lack of data coverage in inland areas, networks of Doppler radars
are being used to provide supplementary upper-air observations. Three categories of
radars are currently providing upper-air information. These include the WSR-88D
(NEXRAD) Doppler weather radar, the Terminal Doppler Weather Radar (TDWR), and
Doppler radar wind profilers (RWP), which can be equipped with radio acoustic sounding
systems (RASS) for temperature profiling. When fully deployed, the NWS and DOD will
operate a nationwide network of 138 NEXRAD radars, and the FAA will operate TDWRs
in 34 terminal areas. Both of these radar systems measure near-surface winds in storm
environments, and provide vertical profiles of winds in the clear air during periods when
hazardous weather conditions are not occurring.
The only operational RWP network providing upper-air data for aviation analysis and
forecasting applications is the Wind Profiler Demonstration Network (WPDN) operated
by NOAA’s Forecast Systems Laboratory (FSL). This network of 404-MHz radars
provides continuous measurements of upper-air winds through much of the troposphere.
There are 32 profilers in the WPDN, most located in the midwest. The WPDN has been
operational for almost a decade, but has been threatened with elimination because the
radar frequency interferes with search and rescue satellite operations. Plans are being
considered to convert the WPDN to 449 MHz and to expand the network into the
Caribbean and Alaska. In the near term, maintaining and expanding the WPDN would
likely benefit aviation weather information by providing enhanced spatial and temporal
resolution of aloft winds. For example, RWP data in the TRACON area could improve
the quality of aircraft trajectories calculated by the CTAS system. In addition, there are
now some semi-permanent networks of so-called ‘boundary layer’ RWP and RASS that
operate near 1 GHz and provide continuous observations of winds and temperatures in the
first 1-3 km of the atmosphere. The usefulness of data from these instruments in aviation
weather applications has not yet been explored to any degree. In the near term, the impact
of RWP data from boundary layer profilers on CNS/ATM technologies like CTAS should
be investigated.
The quality of Doppler radar wind data has been the subject of several studies in recent
years. There is no way to determine the absolute accuracy of these instruments, since the
data can not be compared to absolutely known values or reference standards in the same
way that surface sensors can be checked. Based on recent intercomparison studies, the
accuracy of Doppler radar wind data is on the order of ±1.0 m/s on a vector component
basis, with rms errors of about 2.0-2.5 m/s. The completeness of Doppler radar wind data
depends on atmospheric conditions. Higher temperatures and humidities generally
produce good data recovery, while cold, dry conditions limit data availability. All three
Doppler radar system also suffer from contamination from biological targets, especially
migrating birds (Wilzak et al., 1994). Migrating birds often appear in Doppler radar data
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sets as legitimate atmospheric data, when in fact the data actually indicate the direction
and speed of the birds’ flight. Work is progressing on developing improved signal
processing algorithms to correct these errors and to improve the quality of radar-derived
wind information. This is an area that warrants careful attention and additional research in
the near term to ensure the long term future success of aviation weather technologies that
rely on radar wind data.
Another important source of upper-air meteorological data that has been evolving over the
last few years are the wind and temperature measurements being provided by aircraft
equipped with the MDCRS. Some MDCRS aircraft are also being equipped with
humidity sensors. Sensitivity studies indicate that the aircraft data are improving the
quality and accuracy of NWS forecasts. If more aircraft measurements become available
in the near term, further improvements can likely be expected. The benefits to be gained
from adding relative humidity measurements to more MDCRS aircraft should also be
evaluated, especially for improving predictions of convective activity in the terminal area.
One drawback to current aircraft-based data is that most of the observations are being
collected along a limited number of fixed routes, so that horizontal and vertical gradients
in atmospheric conditions are not well resolved. Under Free Flight rules, allowing
operators to fly preferred routes with aircraft equipped with MDCRS capability will help
improve this situation. Sensitivity studies will be useful that show the density of aircraft
measurements that are needed to see statistically significant improvements in forecast
accuracy.
In the far term, new approaches to collecting upper-air data may be needed to achieve
significant improvements in aviation weather information. Data over the oceanic domain
is especially important. Options for collecting upper-air observations over the oceans
include:
• Expanded MDCRS observations
• “Dropsondes” from commercial and military aircraft
• Space-based remote sensing systems, such as Doppler lidar (light detection and
ranging) systems
• Aircraft-mounted Doppler radar systems
• Remotely piloted vehicles with radiosonde-type capabilities
• Radar wind profilers located on islands and ships of opportunity
Each of these technologies is probably technically feasible, but the cost to develop and
deploy them needs to be studied carefully and evaluated in terms of their expected impact
on the quality of aviation weather information.
5.5.1.3 Weather Radar Observations
The reflectivity data acquired by the NEXRAD and TDWR systems gives an indication of
the location, intensity, and amount of precipitation being generated by a storm system.
These data are displayed in the form of color-coded mosaics projected on a plan view of
the radar’s area of coverage. This information allows meteorologists to track the
development and motion of potentially hazardous weather. The NEXRAD is capable of
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observing weather out to about 200 miles from the radar site. The TDWR’s range is
about 50-60 miles. In addition to these stand-alone meteorological radars, the ASR-9
surveillance radar has been equipped with weather sensing capabilities to detect
precipitation and track storm motion. Some of this information can be depicted on a
controller’s display, although during heavy workloads controllers often turn off the
weather display. The planned deployment of the NEXRAD and TDWR networks is
nearly completed. New TDWRs could be installed at other airports, but information is not
available at this time on any plans to expand this network.
One drawback to this mixed network of weather radars is that not all users in the aviation
system are receiving the same information. The ARTCCs receive the NEXRAD
information, while the TRACONs receive the TDWR and ASR-9 data streams. Pilots
receive none of the ground-based data, but do have access to on-board weather radar
information. This means that during some meteorologically significant events, different
players in the ATM system are making decisions without the benefits of shared situational
awareness. This reduces the overall efficiency of the system and leads to capacity
reductions at busy airports during adverse weather. As discussed later, some new
technologies like ITWS that are scheduled to be deployed in the near term are designed to
eliminate some of these problems.
5.5.1.4 Satellite Data
Satellite imagery is not collected specifically for the aviation community, but rather as part
of the broader mission of the NWS to provide national and global coverage of
atmospheric conditions. Satellite imagery is used by meteorologists in the aviation
weather system to monitor storm development and motion and to help prepare forecasts.
5.5.2 Analysis
Analyses of weather data provide the link between observations and forecasts. They
consist of data sets and depictions of weather conditions over selected geographical areas
that are based on objective analyses of the available observations. Most operational
analyses used in the aviation weather system take the form of charts showing features such
as surface fronts, isobars, winds, locations of VFR and IFR conditions, upper-level flow
patterns, locations of troughs of low pressure and ridges of high pressure, and composites
of radar reflectivity. These charts are typically stand-alone two-dimensional images, which
may be produced in hard-copy form, or in computer graphical images that can be
manipulated and animated with appropriate software. They are often accompanied by
text-based messages that describe the salient features depicted in the analyses. Most of
these products are produced by the NWS and distributed to their field offices and FAA
personnel for interpretation and dissemination to controllers and pilots as appropriate.
Figure 5.16 shows the major components of the analysis process used in the aviation
weather system, which are described below.
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AWIPS/WFO-
Advanced
WARP
Analysis
Products
RUC
AGFS
Figure 5.16 Aviation Weather Analysis Function
The NWS has put a great deal of effort into developing a new generation of graphical
meteorological workstations and associated sub-systems, referred to as the Advanced
Weather Information Processing System (AWIPS). AWIPS is behind schedule by a few
years, mainly because of software problems. FSL is now working on a new version of the
software called ‘WFO-Advanced’, and the combined AWIPS/WFO-Advanced technology
is now expected to be deployed to NWS field offices over the next several years. When
finally implemented, AWIPS will allow meteorologists at NWS facilities to prepare multiimage,
animated mosaics of current and forecasted weather conditions, and to prepare
interactive weather alerts and warnings that can be immediately distributed to other users
and to the public. Initial results from field tests of these systems have indicated that they
will significantly improve the quality and timeliness of weather reporting and forecasting.
A full assessment of the performance of the AWIPS/WFO-Advanced systems cannot be
completed until more units are deployed and being used operationally.
The FAA is in the process of procuring its own version of a meteorological workstation,
referred to as the Weather and Radar Processor (WARP). WARP is designed to replace
the Meteorologist Weather Processor in the ARTCC’s. It is currently scheduled to be
deployed in the CWSUs and in the CWFSU at the central flow facility by the end of 1997.
WARP will allow a Center’s meteorologists to prepare mosaics of NEXRAD reflectivity
data and to overlay supporting weather information like lighting strike data, satellite
imagery, and gridded and graphical weather information. The system will allow CWSU
staff to prepare and distribute aviation weather products such as Center Weather
Advisories and Hazardous Weather Area outlines. In its initial ‘Stage 0’ implementation,
the WARP products will be available to CWSU and TMU personnel for briefing and
planning purposes. Future implementations of WARP (Stage 1, Stage 3), are designed to
allow weather displays to be presented to controllers. As is the case for AWIPS, this
technology ought to represent a significant step forward in the analysis and dissemination
of aviation weather information, but more work is needed to understand system
performance, human factors issues, and training requirements.
The role of the FAA weather operations staff in the centers and the TRACONs is to
interpret current weather information and forecasted conditions so that they can provide
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guidance to traffic managers and controllers on potential weather impacts on aviation
operations. Most of the actual data management, analysis and forecasting of weather
conditions is the responsibility of the NWS’s Aviation Weather Center. To assist AWC
meteorologists, FSL and NWS have been developing the Aviation Gridded Forecast
System (AGFS). The AGFS will consist of 3D gridded data sets of observed, analyzed,
and forecasted weather conditions that affect aviation. The AGFS includes software tools
that allow AWC meteorologists to prepare and distribute analyses of AIVs. More
information is needed on how the AGFS will be integrated into the analysis and
forecasting functions performed in the CWSUs and the TRACONs, and on the quality of
the gridded fields. However, a tool such as the AGFS will be needed to help manage and
provide quality control to the increasingly complex meteorological information being
produced by observing networks and analysis and forecasting tools.
5.5.3 Forecasting
The need for accurate forecasts of expected weather conditions in the terminal and en
route environments is becoming increasing acute as demand for system capacity increases.
Most aviation forecasting services are provided by the NWS through the Aviation
Weather Center, although some of the larger airlines have their own teams of
meteorologists who prepare forecasts for their areas of operation, and some private sector
firms also provide forecasting services. Figure 5.17 shows the major components of the
aviation weather forecasting system, which are described in this section.
Aviation
Weather Center
NCEP
NWP Models
Forecast
Products
ITWS
AVOSS
Figure 5.17 Aviation Weather Forecasting Function
NCEP operates a suite of numerical weather prediction models that produce forecasts of
gridded meteorological parameters that are analyzed to estimate the future locations of
storm systems, areas of precipitation, surface and aloft winds, and other conditions
affecting aviation operations. These models solve the so-called ‘primitive’ equations
describing the physics of the atmosphere, with varying degrees of sophistication in the use
of numerical integration techniques, turbulence closure schemes, hydrostatic versus nonhydrostatic
approximations, boundary conditions, horizontal and vertical resolution, and
so forth. Short-term forecasts out to 48 hours are performed using the Eta model, while
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longer-term domestic and international forecasts are made using codes such as the AVN
and MRF prognostic models. Forecasts are usually issued in three to six hour intervals for
periods as short as three hours to as long as several days. AWC meteorologists use these
forecast products and other available information to prepare Terminal Aerodrome
Forecasts for U.S. airports, and to prepare advisories and alerts for weather conditions
that may adversely affect aviation operations (e.g., SIGMETS and convective SIGMETs).
In their present forms, models like the Eta and its counterparts are best suited for
predicting the movement of synoptic scale meteorological features that affect the weather
over regions larger than individual terminal areas and on time scales longer than are
valuable for many aircraft operations. Thus, while these models are useful for general
large-scale weather prediction, they have not been optimized to meet the specific needs of
the aviation weather system. The FAA, NASA, MIT-LL, NOAA, and NCAR have been
working on several new technologies designed to provide aviation-specific forecasts.
FSL has developed an analysis and forecasting tool called the Mesoscale Analysis and
Prediction System, which has been recently implemented at NCEP as the Rapid Update
Cycle (RUC). The RUC combines objective analyses and short-term (less than 12 hr.)
prediction tools to prepare gridded data sets of surface and upper-air meteorological
conditions that affect aviation operations. The RUC is run at NCEP every three hours on
a 60-km grid covering the CONUS, and produces an analysis of current conditions and 3-
hourly forecasts out to 12 hours. An experimental 40 km version is being tested, and
plans call for going to finer horizontal resolutions in the future.
RUC products are currently being tested in new CNS/ATM and aviation weather
technologies. For example, the current implementation of CTAS uses the 3D RUC wind
fields to calculate aircraft descent trajectories. An important issue for the successful
application of RUC data in CNS technologies like CTAS, Conflict Probe, and other flight
management systems is the need for good information on the accuracy and repeatability of
RUC variables (e.g., rms errors in upper-air wind analyses and forecasts). For example,
some preliminary evaluations of RUC upper-air wind forecasts indicate that in the 0-1 hr.
time frame rms errors in vector winds may be on the order of 2-3 m/s, increasing to 5-7
m/s at the end of the RUC forecast period. Likewise, the sensitivity of CNS/ATM
technologies to uncertainties in RUC variables needs to be examined. More information is
also needed on how RUC data sets will be incorporated into the AGFS.
The ITWS is an analysis and prediction tool that is currently being developed by MIT-LL
for use in the terminal area. The ITWS ingests the RUC gridded wind fields, TDWR and
NEXRAD wind data, ASR-9 weather reflectivity data, MDCRS observations,
ASOS/AWOS and LLWAS data, and other available information. It analyses these data
to determine storm cell locations and movement, areas of precipitation, locations and
intensities of gust fronts and microbursts, low-level winds affecting runway operations,
locations of tornadoes, and other aviation impact variables. It predicts storm cell
movement and the locations of gust fronts at 10 minute and 20 minute intervals from the
analysis time. ITWS also produces three-dimensional gridded fields of winds on scales
varying from 2 km near the terminal area to 60 km at the outer extent of the ITWS
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domain, which generally extends to the outer boundaries of the TRACON and beyond into
Center airspace.
ITWS test beds are currently being evaluated at several large airports, including Dallas-
Fort Worth and Orlando. The FAA issued a contract in early 1997 to procure four
commercial systems, with an option to expand ITWS installations to 34 terminal areas that
cover 45 of the busiest airports in the U.S. by early in the next century. Initial reports of
the benefits of ITWS to users suggests that the technology can improve efficiency and
increase capacity during adverse weather (Evans and Ducot, 1997). Plans are also
underway to test the ITWS gridded wind fields in the CTAS system. Analyses of the
accuracy and uncertainties in ITWS products and their contribution to uncertainties in
CTAS trajectory calculations will be needed in the near term.
Another specialized analysis and prediction system under development is the AVOSS
wake vortex separation tool. The AVOSS will ingest surface and upper-air
meteorological data from a network of surface and upper-air sensors deployed around the
airport, and use these data to prepare predictions out to about 30 minutes of key
meteorological parameters that affect vortex decay and transport (e.g., vertical wind and
temperature profiles). These parameters will then be used to predict separation
requirements for aircraft pairs based on expected vortex intensity and location. NASA,
MIT-LL, the Volpe Transportation Center, and other organizations are participating in the
AVOSS program. Plans call for the first prototype operational system to be fielded in the
2000-2001 time frame, with deployments of operational systems completed by later in the
decade. The AVOSS will be a complex technology that will require careful evaluation and
testing. More information is needed on the interaction of an operational AVOSS system
with the ITWS technology and with other CNS/ATM technologies like CTAS and cockpit
displays of traffic and weather information (CDTW) (see Section 5.5.4).
The FAA is funding research and development efforts in several areas related to weather
impacts on aviation and the development of new aviation weather analysis and prediction
technologies. An Aviation Weather Research (AWR) program has been initiated within
FAA’s Office of Air Traffic Systems development, which is organized into eight Product
Development Teams (PDT). The research areas currently being explored by the AWR
include:
• Inflight Icing
• The AGFS
• Turbulence
• Convective Weather
• Weather Support For Ground De-Icing Decision Making
• Model Development And Enhancement
• NEXRAD Improvements
• Ceiling And Visibility
While some of these PDTs focus mainly on developing improved measurement methods,
most are directed at developing tools to improve the short-term prediction of AIVs. For
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example, the ceiling and visibility PDT is focused in part on developing and demonstrating
a forecast tool that will predict the time of burn-off of the marine stratus layer at San
Francisco International Airport. Such a tool would allow more efficient use of the
airport’s closely spaced parallel runways and increase airport capacity by allowing parallel
runway operations to begin sooner in the day than they currently do. However, the status
of funding for some of these efforts is uncertain. For example, work on the ceiling and
visibility PDT may be discontinued in 1998.
In the far term, improvements in aviation weather forecasts in the terminal area are likely
to come from improved numerical weather prediction methods, with the models being
driven by data collected from networks of surface and upper-air sensors deployed in the
region surrounding the airports. RESCOMS (Regional-Scale Combined Observation and
Modeling Systems) technologies should be investigated to determine the sensitivity of
model results to different densities of measurements and to uncertainties in observations.
Model configurations and data requirements would be established based on the
meteorological conditions that prevail in a terminal area. For example, RESCOMS
forecasting in the coastal and complex terrain setting of southern California might be best
performed by a hydrostatic NWP and a relatively dense network of surface and upper-air
wind and temperature sensors. Conversely, at Dallas-Fort Worth a RESCOMS system
would include ITWS technologies combined with a non-hydrostatic model able to simulate
convective storms. For en-route Free Flight operations, the RESCOMS concept could be
extended to Center airspace by the addition of more MDCRS data combined with other
supplemental upper-air observations from networks of wind profilers or rawinsondes.
In the near term, improving the absolute accuracy of forecasts of complex weather
systems like convective storms is an ambitious task. For example, to be effective for
strategic planning, the location of convective cells need to predicted to within 1-2 miles
and within tens of minutes of their actual position several hours in advance. Current and
likely near-term technologies will probably not meet this requirement. However,
improvements in weather prediction in the near term may be able to provide sufficiently
accurate estimates of the probability of such weather events to be useful in flight planning
operations. For example, American Airlines is supporting the development of a
forecasting system to allow it to make proactive operational decisions based on the
likelihood of weather impacts at its hub airports (Qualley, 1997). The usefulness of
probabilistic estimates of weather impacts on components of the aviation weather system
needs to be explored in more detail.
5.5.4 Dissemination
Aviation weather information is currently disseminated in the form of alphanumeric text
messages, graphical depictions of weather patterns, and audio recordings of current and
forecasted conditions. Communications systems for sending weather information to users
include dial-up and dedicated telephone lines, satellite broadcast, internet transmission,
and radio broadcast of data and voice messages. For the aviation community, weather
information is available from the AWC, the Direct User Access Services Service system,
manned and Automated Flight Service Stations, the CWSUs, and airline dispatch offices.
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An important issue for users of aviation weather products is that the information they need
must be presented in a way that is timely, efficient, easy to comprehend, and that allows
different users in different locations (controllers, pilots, airline dispatch, airport operators)
to develop a shared situational awareness of the weather conditions affecting flight
operations. In the current ATM system, these objectives have often been difficult to meet.
Traditional text-based messages are often difficult to decode and interpret, and do not
provide an integrated view of important weather conditions. TRACON and ARTCC
controllers are presented with different types and amounts of weather information, and
pilots have limited access to weather information other than that provided by their
onboard sensors (radar, winds, temperature) and visual observations. This has lead to
inefficiencies and capacity reductions at busy airports during adverse weather, which could
likely have been mitigated if the dissemination process was more effective.
To address these issues, increasingly the trend for distributing aviation weather
information is through the use of interactive graphical images produced by computer
workstations. The AWIPS/WFO-Advanced and WARP technologies are intended to meet
this need. Likewise the ITWS system is designed to provide interactive computergenerated
graphical images showing weather conditions and expected storm movement in
the terminal area. Figure 5.18 illustrates the various near term components of the
dissemination system for aviation weather information. If successful, these technologies
can provide CWSU personnel and controllers with similar types of information so that
they can make effective strategic and tactical decision and improve efficiency in the
terminal area and en route environment. Several issues need to be addressed to
understand if these technologies will be successful, including issues related to human
factors engineering, and requirements for training programs.
An important area beginning to receive attention is the dissemination of weather
information to the cockpit. In the far term, there may be good reasons to get ATC out of
the loop in disseminating weather information to pilots (NRC, 1995), and several types of
cockpit weather information systems are being investigated. For example, MIT-LL has
been testing the Terminal Weather Information for Pilots (TWIP) system, which provides
a simple alphanumeric and graphical depiction of ITWS data products to pilots via the
ACARS system (Campbell et al., 1995). Anecdotal evidence indicates that pilots receiving
TWIP messages during approaches to busy airports being impacted by convective weather
find them very useful.
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WARP
TWIP
ITWS
CWIN
Information
Dissemination
CDTW
DUATS
FSS/AFSS
Figure 5.18 Aviation Weather Dissemination Function
It is likely that there are a number of weather products that pilots would find useful,
especially to support strategic decision making during Free Flight operations and tactical
decision making in the terminal area. A CDTW system could facilitate flight management
decisions and improve safety in Free Flight operations, and it could serve as an interface to
needed data during final approach to airports equipped with an AVOSS. However, a
number of technical and logistical issues must be addressed to develop a successful
cockpit weather information system. Among these are understanding what kinds of
weather information are most useful to pilots during different phases of flight, addressing
human factors engineering and crew work load considerations, and developing suitable
communication links and weather product formats so that data transmissions to the
cockpit are timely and cost effective.
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6 ATM Concept Baseline
This section details the baseline concept developed in response to the mission needs
identified in Section 2. The capacity-driven concept in Section 6.2 is based on the
methodology developed as part of the CNS/ATM Focused Team (CAFT) process, initially
developed to evaluate the RTCA Task Force 3 planned evolution to Free Flight. The
overall methodology is introduced in Section 2.3.6, Transition Planning and Tradeoff
Analyses. This process has been applied to the Task Force 3 recommendations, the
Eurocontrol EATCHIP plan and the IATA regional CNS/ATM Plans. The complete
methodology is described in the paper on CNS/ATM Transitions from the 1997 CAFT
meeting (Allen et al, 1997).
6.1 Concept Transition Methodology
The baseline concept is developed by considering possible capacity transitions from
current to future operations. The transition analysis is based on the airspace phases and
performance factors of the constraints analysis model. The model divides a flight into six
operating phases, going from the departure gate to the arrival gate, as illustrated in Figure
6.1. Phase 1 is airspace and flight planning, which spans the other five regions. Phase 2 is
the airport surface, phase 3 is final approach and initial departure, and so on through the
en route, which is phase 6.
5
6
5
4
4
3
2 3
2
1
1 Airspace and Flight Planning 4 Approach/Departure Transition
2 Airport Surface
5 TMA Arrival / Departure
3 Final Approach / Initial Departure 6 En Route
Figure 6.1 Airspace Operating Phases
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Constraints modeling can be performed for system safety, capacity, efficiency or
productivity measures. The methodology allows examination of the technical and human
performance factors which potentially affect the airspace region.
The final approach and initial departure phases include the runway and refer to a phase in
which air traffic control interventions are minimal due to the nature of the aircraft
operation. The approach transition phase is operated differently depending on available
technology and traffic density. In busy airports this is generally where air traffic
controllers vector aircraft to merge traffic into properly spaced streams for final approach
and landing, while in low density operations it might be a single waypoint transition to the
next region. The Terminal Maneuvering Area (TMA) arrival/departure phase is generally
operated through published SID and STAR procedures. The en route phase encompasses
the remainder of the flight, including published transitions from SID to cruise and from
cruise to STAR. En route operations vary greatly by location, anywhere from oceanic
procedural control to dense traffic in radar controlled airspace. The differences in
operation can be characterized by levels of performance for the CNS components, as well
as by air traffic control automation support, topography, traffic flow patterns, airspace
availability and so on.
En Route
TMA
Arrival/Departure
Planning
AIRSIDE
CAPACITY/EFFICIENCY
FACTORS
Approach
Transition
Airport
Surface
Gate
Final Approach/
Initial Departure
Taxiway
Apron
Final
Approach
Initial
Departure
CONDITION:
LOCATION:
Figure 6.2 Capacity and Efficiency as a Function of Airspace Operating Phases
Using the six operating phases above, Figure 6.2 provides a graphical illustration of how
the capacity and efficiency of operations are aggregated across the various operating
phases. Overall system capacity and efficiency are complex functions of the type of
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operation in each of the phases, along with the interactions between them, which can also
be thought of as the ‘handoff’ from one air traffic control unit to another.
The air traffic management system capacity and efficiency depend on a large collection of
technological, procedural and environmental factors, all of which vary by geographical
location. Thus, when using the constraints model, it is necessary to note both location and
weather condition for which the analysis is being performed, as illustrated in the lower left
hand corner of Figure 6.2. The system operational element which is most constraining to
the operation will vary from region to region and, within a given region, from day to day.
In the U.S. domestic airspace, in good weather conditions, system capacity is usually
constrained in the final approach/initial departure phase. In marginal visual conditions, the
system may constrain in the approach transition region (at Chicago O’Hare and San
Francisco, for example). In instrument conditions (Cat I), the system is usually
constrained on final approach/initial departure, while in low visibility (Cat II-III)
conditions, the airport surface tends to constrain. When convective weather affects
terminal operations, the terminal arrival/departure corridors tend to saturate. In
procedural environments (such as oceanic regions) the en route system may constrain the
system throughput.
Each of the six phases illustrated in Figure 6.2 has its own set of performance factors,
some of which are unique to that phase, while others, such as communication and
navigation, are common throughout. All of the constraint factors for each of the
operational phases are summarized in Appendix E. Figure 6.3 illustrates the throughput
performance factors for the final approach phase. The figure shows navigation and
guidance performance as two of the factors that contribute to the throughput on final
approach, along with communication system performance. Accuracy, availability and
integrity are the determining factors for both, and, on final approach, signal interference of
the instrument landing system is an important factor. The surveillance element is broken
into two components, i.e. monitoring performance and control performance. Monitoring
performance here refers to the display of position and velocity information to the air traffic
controller, including the performance of a surveillance system such as radar or dependent
position reports. Control performance includes both controller and pilot, and includes any
automation aids such as a sequencing tool, blunder detection etc.
Other factors depicted in Figure 6.3 are important as well, wake vortex being perhaps the
dominant performance constraint in most instrument weather conditions. Runway
occupancy may become the dominant factor in extremely low visibility where pilots have
difficulty locating runway exits. In each case, when it has been determined that a phase of
flight such as final approach is the constraint on throughput, it is necessary to evaluate that
operation in detail, and the constraints model can be a valuable tool in focusing the
analysis.
The constraints model is used as a template for determining a set of technology iniatives
by operational phase to achieve a particular mission objective, for example, increased
throughput. A time-phased approach, considering short-, medium- and long-term
technology schedules and system needs, is derived.
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Figure 6.4 shows a template for illustrating phased improvements in the NAS driven by
the top-level stakeholder goals. The upper right corner identifies the Regional Plan
represented. Separate transition logic diagrams are created for capacity and efficiency,
and for each operational phase of the constraints analysis. A benefit mechanism is
identified for each diagram, with incremental phasing of operational enhancements.
Approach Configuration
- Approach Path Length
-
Other Runway Dependencies
- Runway Occupancy Factors
Airplane Performance
- Approach Speed
- Weight Class
- Braking Performance
- Gate Assignment
CONDITION:
LOCATION:
Wake Vortex
- Visibility
Final
Approach
Nav/Guidance Performance
- Accuracy
- Availability
- Integrity
- Gross Navig. Error Rate
Control Performance
- Finall Approach
Sequence
- Spacing Precision
- Go-around decision
- Blunder Detection &
Alarm
Monitoring Performance
- Availability
- Integrity
- Accuracy; Latency
Comm Performance
- Availability/Coverage
- Integrity
- Message Delivery
Performance
Figure 6.3 Final Approach Throughput Performance Factors
CNS/ATM Transition Logic Diagram
REGIONAL PLAN
Operational Phase Benefit Mechanism Capacity (Efficiency)
Regional Initiative
ENABLER
Operational
Enhancement
Phase 1
ENABLER
Regional Initiative
Regional Initiative
ENABLER
Operational
Enhancement
Phase 2
ENABLER
Initiative (Not in Regional Plan)
Regional Initiative
ENABLER
Operational
Enhancement
Phase 3
ENABLER
Initiative (Not in Regional Plan)
Figure 6.4 CNS/ATM Transition Logic Diagram Template
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6.2 Capacity Driven Concept Baseline
The sequence of transition steps presented here defines one of many possible paths that
the system operational concept and architecture could follow through the year 2015. This
particular path is constructed with the objective of achieving the capacity goals stated in
Section 2, using the team’s best judgment of what system enhancement steps could be
taken during this period with available and emerging CNS/ATM technologies. This
transition path, and most of the individual steps within it, have not been validated, and
thus the quantification of the system capacity impact cannot be estimated for each step.
Also, the baseline set of selected technologies will need to be subjected to requirements
validation and system tradeoffs. The transition path, however, is a reasonable baseline
from which to initiate the top level operational and technology trades that must be
performed for initial concept validation, followed by the detailed validation studies that
precede eventual implementation. Thus it supports the process presented in Figure 2.2,
namely the research and development that must be initiated now to move the system
successfully through 2015.
6.2.1 NAS Flow Management
Figure 6.5 shows the proposed concept transition path for national and local traffic flow
management. The diagram shows two parallel paths, one starting at the national level and
the other starting at the airport level. The two paths merge in the third transition step into
a coordinated traffic flow management system. The improvements implied in each
transition step are detailed below.
CNS/ATM Transition Logic Diagram
Planning (1)
NAS
Improved Throughput Capacity
Real-time
Info Exch.
EFM
–Flpl feedback
–Ration by sched
–Flexible delay program
–Schedule updates
–Collaborative Dec. Making
National
Improved
TFM
Collaborative
Traffic
Management
Dynamic
Density
Aircraft
Weather
Reports
Convective
Weather
Forecast
TFM Seq
Spacing
Tool
Data
Link
Coordinated
TFM System
Air Traffic
Mgmt System
Local/Airport
Enhanced
Arrival
Planning
Integrated
Airport Flow
Planning
EFM
–Config Mgmt Sys
–Departure Spacing Program
–Surface Traffic Automation
–Surface Movement Advisor
Figure 6.5 CNS/ATM Transition Logic for Flow Management
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National Level. Improved Traffic Flow Management
This step involves real-time information exchange between NAS users and central flow
management, focused primarily on automatic schedule updates from the airlines and timely
notification to airlines of flow management actions. Currently only OAG schedule and
historic routing is used in the ground-hold program.
National Level. Collaborative Traffic Management
This operational enhancement includes a collection of changes in flow management aimed
at giving users more flexibility in deciding how delay is allocated across their operation.
Delay will be allocated to operators according to their published schedule, and the
operator in turn allocates the delay to their individual flights. Where arrival airport
capacity is the constraint, emphasis will be on arrival airport schedule management and
away from departure gate-hold times. This will allow operators to minimize the overall
cost impact of delay on their operation by prioritizing flights according to issues such as
passenger and baggage connections.
Airport Level. Enhanced Arrival Planning
This enhancement step provides improved terminal area arrival flow planning, including
arrival runway load balancing, enhanced arrival sequencing and improved arrival flow replanning,
given a perturbation such as runway change or convective weather.
Airport Level. Integrated Airport Flow Planning
This enhancement step involves a group of airport traffic planning initiatives aimed at
integrating arrival and departure traffic, along with surface movements, into a coordinated
plan. This will include optimal airport balancing of arrival and departure resources and the
need for automation to support airport configuration management, including the
replanning from one configuration to another due to transients.
Coordinated Traffic Flow Management System
In this step flow planning at the national, regional and local level are brought together in a
coordinated system. The function allocation strategy to achieve this step, and the
technologies required are to be determined, but many of the relevant issues are brought
out in Section 3.3.
6.2.2 NAS En Route and Outer Terminal Area
Figure 6.6 shows the proposed concept transition path to achieve increased capacity in the
en route and TMA Arrival/Departure operating phases. The sequence of operational
improvement steps represented by the boxes, from top to bottom, address a reduction in
effective traffic spacing starting with airway spacing criteria, through reduction of
intervention rate and intervention buffers, to the eventual reduction in the basic separation
standard. The improvements implied by each box are described in detail below.
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Reduced Lateral Spacing For More Arrival And Departure Transition Routes
This enables closely spaced standard arrival and departure routes to fit additional traffic
streams within terminal area corridors. This will help avoid congestion over entry points
into terminal areas and reduce the need for in-trail traffic that backs up into en route
airspace. This enhancement will be most beneficial in terminal areas where airspace is
constrained due to proximate airports or special use airspace, or where severe weather
activity can prevent traffic flow through parts of the airspace.
Airspace design criteria have to be changed to enable this operational enhancement.
Those criteria are likely to be predicated on a level of navigation performance in the range
of RNP 1 to RNP 0.3, along with the corresponding surveillance performance. Airspace
will then have to be redesigned around airports where advantage can be taken of this
enhancement.
CNS/ATM Transition Logic Diagram
NAS
En Route (6) and TMA (5) Improved Throughput Capacity
Airspace
Criteria
RNP 1-
RNP0.3
Nav
Reduced Lateral Spacing
along Fixed Airways
RMP 1-
RMP0.3
Surv
Airspace
Design
Guidance
Path
Short
Term
C.A.
ADS-B
(A/G)
Data
Link
Wind and
Temp
CDTI
Monitor
& Backup
RVSM
Reduced Intervention
Rate Buffer
Reduced Intervention
Buffer
Reduced
Separation Standard
Radar
Trackers
RMP0.2
Surv
ADS-B
(A/A)
A/C Perf
Models
RNP0.2
Nav
TFM Seq
Spacing
Tool
Ground
Conformance
Monitor
Figure 6.6 CNS/ATM Transition Logic for En Route and Terminal Area
Reduced Intervention Rate Buffer
The intervention rate separation buffer is the outermost separation buffer discussed in
Figure 3.7, which is added to reduce the number of potential conflict situations in the
sector, and thus to limit sector controller workload. This is the role of the sector planning
function in Figure 3.6, and thus the enhancements proposed here relate to the performance
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of flight plan management and medium term conflict prediction functions. Improvements
in both the horizontal and vertical dimensions are included in this step, and the
implementation order is likely to be horizontal first because the technology is more mature
for horizontal than for vertical prediction accuracy, although the benefits of improved
vertical accuracy may be greater.
An improvement in medium term trajectory prediction will be needed to reduce the
uncertainty that the controller has today when predicting conflicts. This improvement will
be enabled by tracker enhancements that provide higher accuracy and lower latency, better
wind and temperature information, and a medium term conflict probe. The terminal area
will benefit from automation for more accurate sequencing and spacing of climbing and
descending traffic, which will require accurate aircraft performance models. Data link will
probably be required to exchange weather information, aircraft performance parameters,
and trajectory definition between the air and ground systems.
In addition to the above factors, a higher probability that the aircraft will follow its
intended path may be required, and this may involve implementation of 4D terminal area
navigation capability, and a common and accurate time source. Depending on the level of
criticality of the function, there may be a requirement for cockpit traffic situation
awareness through position broadcast, to provide redundancy of function.
Reduced Intervention Buffer
The intervention buffer is the spacing added above the minimum separation standard to
account for the time required for the sector controller to detect a conflict, decide on a
resolution, communicate it to the pilot, and for the pilot to act. This is the performance of
the reaction loop around the sector controller and aircraft illustrated in Figure 3.6.
To reduce the intervention buffer it is postulated here that data link would improve the
delivery time and integrity of communications from controller to pilot. A ground-based
conformance monitor is assumed that would alert the controller to aircraft deviations from
intended trajectory, and a short term conflict alert function is also assumed. Criticality
level is expected to be high, which will likely require an independent monitor function in
the aircraft through CDTI.
Reduced Separation Standards
This refers to both vertical and horizontal separation. Reduced Vertical Separation
Mimima (RVSM) in domestic airspace would likely be predicated on vertical path
following performance similar to what is required currently in the North Atlantic.
Horizontal separation is likely to require improvements in the surveillance sensors both for
en route and terminal areas, and better navigation performance. The detailed requirements
will have to be worked out through research, starting with the development of a risk
evaluation methodology that can be used to determine the influence of technology and
human factors on collision risk in radar controlled airspace.
6.2.3 NAS Approach/Departure Transition
Figure 6.7 shows the proposed concept transition path to achieve increased capacity in the
Arrival/Departure transition operating phases. The sequence of operational improvement
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steps represented by the boxes, from top to bottom, address a reduction in effective traffic
spacing starting with route spacing, intervention buffers, through reduction in the basic
separation standard. The improvements implied by each box are described in detail below.
Reduced Lateral Spacing For More Arrival And Departure Transitions
This enables closely spaced arrival and departure routes to fit additional traffic streams
within terminal area corridors. This enhancement will be most beneficial in terminal areas
where airspace is constrained due to proximate airports or Special Use Airspace.
Airspace design criteria have to be changed to enable this operational enhancement.
Those criteria are likely to be predicated on a level of navigation performance of RNP 0.3,
along with a corresponding surveillance performance. Airspace will then have to be
redesigned around airports where advantage can be taken of this enhancement.
CNS/ATM Transition Logic Diagram
NAS
Arr/Dep Trans (4) Improved Throughput Capacity
Close
Routes
Criteria
Final
Approach
Spacing
Tool
RNP0.3
Nav
Reduced Lateral Spacings:
More Arr & Dep Trans
Reduced Separation
Buffer (Ground Vectoring)
RMP 0.3
Surv
Airspace
Design
Radar
Trackers
TFM Seq
Spacing
Tool
RTA
Short
Term
C.A.
CDTI
Reduced Separation
Buffer (A/C Guidance)
RMP0.1
Surv
A/G Data
Link
ADS-B
(A/G)
Reduced Horizontal
Separation Standard
RNP0.1
Nav
Figure 6.7 CNS/ATM Transition Logic for the Arrival Transition Phase
Reduced Separation Buffer (Ground Vectoring)
This enhancement involves more accurate timing of aircraft delivery to the final approach
fix through more effective ATC vectors. The improvement will be enabled by better
trackers for trajectory prediction, automation tools for accurate traffic sequencing and
spacing, and automation support to generate accurate ATC vectors for final approach
spacing.
Reduced Separation Buffer (Aircraft Guidance)
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The component of the spacing buffer at the final approach fix that is contributed by the
aircraft guidance and navigation performance will be improved in this step. This will
involve the use of required time of arrival functionality with the appropriate performance
parameters, an accurate and common time source and data link to deliver clearances with
accurate timing information. In addition, short term conflict alert functionality may be
required to improve conformance monitoring.
Reduced Horizontal Separation Standard
In this operating phase it is normally spacing on final approach that determines the
separations applied. As seen in Figure 6.7 the concept includes a plan to reduce spacing
on final approach, and thus the approach transition phase may need corresponding
separation reductions. The improvement and enablers would be analogous to the last box
in Figure 6.6, with perhaps a need for further improvement in navigation and surveillance
performance.
6.2.4 NAS Final Approach
Figure 6.8 shows the proposed concept transition path to achieve increased capacity in the
Final Approach and Initial Departure operating phases. The chart shows two independent
enhancement paths, the one on the right centered on additional runways, the one on the
left centered on increased runway utilization. The improvements are described in detail
below.
CNS/ATM Transition Logic Diagram
NAS
Final App/Init Dep (3) Improved Throughput Capacity
TFM
Assignm.
Seq.
Increased Rwy.
Utililization
with current
technology
PRM
CRDA
AIP
Additional
Available
Runways
DGPS
Air to
Ground
ADS
Ground
Monitor
Reduction in
lateral separation
to 2500 ft
Wake
Vortex
Mitigation
Reduction in
longitudinal
separation to
3/2.5nm
Procedures
Procedures
CDTI
Air toAir
ADS
Reduction in
lateral separation
to 1000 ft
DGPS
Reduction in
longitudinal
separation to
2nm
ROT
Rollout /
Turnoff
Guidance
Figure 6.8 CNS/ATM Transition for the Final Approach and Initial Departure Phase
Additional Available Runways
This improvement involves a combination of new runways being built, and of existing
runways being made more available through development of instrument approaches.
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FAA’s Airport Improvement Program is the enabler for new runway construction, which
also may rely on new approaches to approach and procedure design to address airport
noise concerns. Existing FMS capabilities can be utilized to reduce both the spread and
the severity of noise impact, through tailored approach and departure procedures.
Experience at Frankfurt airport (Schadt and Rockel, 1996) has shown that by flying FMS
procedures instead of ATC vectors, neighborhood noise impact can be reduced
considerably.
Instrument approaches to a larger number of runways in the CONUS will be enabled by
differential GPS down to CAT III minima, and again the implementation relies on
procedure development for each airport.
Increased Runway Utilization with Current Technology
This improvement step involves the installation of existing technology where needed to
increase throughput of closely spaced parallel and converging runways in IMC. To fully
take advantage of the Precision Runway Monitor and Converging Runway Display Aid
technologies it may be necessary to include arrival and departure sequencing and spacing
automation.
Reduction in Lateral Separation to 2500 ft
This enhancement reduces further the minimum lateral separation between parallel
runways for independent operations. To assist with aircraft blunder detection, ADS
event-based position reporting and improved monitoring on the ground will be needed.
Precision missed approach guidance may also become an issue.
Reduction in Lateral Separation to 1000 ft
The reduction below 2500 ft between independent parallel runways in IMC is currently
being discussed in the context of airborne separation assurance through CDTI. Wake
vortex is also an issue here. This is an ambitious step, and the exact requirements will have
to be worked out carefully through further research.
Reduction in Longitudinal Separation to 3 or 2.5 nm
In IMC, the longitudinal separation on final approach is currently set by wake vortex
considerations, and therefore this enhancement step must address wake detection and
avoidance. This may be done through a combination of wake prediction/detection
technology and new procedures to mitigate risk.
Reduction in Longitudinal Separation to 2 nm
Further reduction in longitudinal spacing on final approach would address runway
occupancy and the need to ensure rapid braking and turnoff performance of the aircraft.
In low visibility this may require improved rollout and turnoff guidance, perhaps based on
differential GPS. Included here might be the possibility of allowing two aircraft on the
runway at the same time, if it can be ensured that the trailing aircraft has the required
braking performance to stop short.
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6.2.5 NAS Surface
Figure 6.9 shows the proposed concept transition path to achieve increased capacity on
the airport surface. The chart shows two independent enhancement paths, the one on the
right centered on low visibility operations, the one on the left centered on good VMC.
The improvements are described in detail below.
Additional Gates, Taxiways and Aprons
This enhancement will be needed along with any additional runways, or improved runway
utilization, to ensure that the airport surface does not become the constraining factor in
the operation. The Airport Improvement Program is the cornerstone for this
enhancement.
Reduced Schedule Uncertainty
This enhancement involves reducing variability of operations at major hubs during peaks,
so that arriving aircraft can get to a gate expediently, and thus avoid gridlock on taxiways
and apron areas. This will involve both more predictable aircraft turnaround time, and
better airport flow management, which should result in less schedule padding due to
variance in traffic related delay.
CNS/ATM Transition Logic Diagram NAS
Surface (2)
Improved Throughput Capacity
Good Visibility
Low Visibility
AIP
Additional
Gates, Taxiways
and Aprons
AMASS
ASDE
Improved Surface
Guidance
and Control
Lights
Reduce
Turnaround
Time
Reduce
Schedule
Uncertainty
Enhanced
Flow
Managmt
Surface
Guidance
Visual Throughput
in CAT IIIb
RNP 0.1
Surface
Traffic
Automation
Data Link
Improved Surface
Sequencing,
Scheduling and
Routing
RTA
ASDE
CDTI
Figure 6.9 CNS/ATM Transition for the Airport Surface.
Improved Surface Sequencing, Scheduling and Routing
This involves surface surveillance and automation to sequence, schedule and route aircraft
through the taxiway system more effectively.
Improved Surface Guidance and Control
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In extreme low visibility conditions it can be taxiway guidance and surface surveillance
that limit the airport’s throughput. This enhancement step would improve surface lighting
to guide the aircraft, and implement surveillance and runway incursion alerting for the
tower controller.
Visual Throughput in CAT IIIb
This enhancement would be enabled by all-weather surface operations guidance in the
aircraft, along with aircraft position information. Presentation of other aircraft position
may also be a requirement.
6.3 Concept Validation Needs
The system transitions presented in Section6.2 are constructed to achieve phased
reductions in traffic spacing in high density areas in the NAS. None of the steps presented
have been fully validated, although the initial improvements are well supported by
performance data, and the steps are subject to more uncertainty as we predict further into
the future.
Regardless of what transition steps the system will eventually go through, it is necessary to
follow a disciplined process of transition plan validation before system procurement
decisions are made. Figures 2.1 and 2.2 are top level illustrations of what this validation
process entails, in terms of sequence and content of the validation tasks.
The first three steps in Figure 2.1 constitute the system preliminary design phase, which
when applied to the air traffic management system development will include the following
tasks:
1. Considering the whole system, which improvement steps should be taken first, based
on considerations of potential benefits vs. estimated cost This task produces a
prioritized list of transition steps, and thus serves to focus further more detailed efforts
on the most important problems.
2. For each of the operating phases, what are the kinds of improvement steps that are
needed, and in what order should they be taken This step involves a look at available
and emerging technology, taken together with human factors feasibility issues, but
must remain at a high enough level to retain an overall system view.
3. For a particular improvement step in the plan produced in 1 and 2, derive the required
system performance, and allocate to the associated CNS/ATM elements. This
allocation, again, must includes human factors feasibility along with technology
performance.
4. Given the CNS/ATM performance requirements in 3, determine what combinations of
technology and procedures can be applied to achieve the improvement objectives.
This produces a list of alternatives for each transition step under consideration.
5. Determine which of the alternatives in 4 is the best option. This involves technology
and human factors feasibility, investment analysis, and implementation risk, and must
be considered in the context of the overall system architecture. Thus, the design
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trades involved in this step will result in functional allocation and system architecture
decisions for the end-to-end system improvements being considered.
Items 1 through 5 above will require appropriate analysis tools to properly resolve the
complex issues, and it is important for these issues to remain at an overall system level.
Thus, the tools employed must include only the necessary level of detail and carefully
constructed metrics. The team is concerned that this is currently a weakness in the NAS
modernization process. Specific research topics aimed at addressing this concern are
discussed in Section 8.3.
The detailed validation of operational concept elements (i.e. the transition steps in the
modernization plan) follows the preliminary design trades described above. This is an area
where much more emphasis has been placed in traditional system development, and thus
many of the required methods and tools are already available. The following items must
be included in the concept validation process:
• Normal, non-normal, and rare-normal performance of all system components must be
included throughout the process. This may currently be an area of weakness in ATM
systems development, where too much emphasis is placed on normal performance, and
disturbances and failure modes are considered only late in the development process.
• Technology must be prototyped, including human factors considerations, and
simulation analysis used to produce performance data and refine the system design.
• Concept validation involves demonstrating technical and human performance, and the
associated benefits and costs, against the metrics established in the preliminary design
phase.
• The validation process is iterative, may lead to a conclusion that a concept (and
associated technology) is not viable and must be either modified or abandoned.
• When the validation process is completed, and an investment case is made, the concept
moves into system design, build and install.
Of the three primary system development phases (preliminary design, concept validation
and design and implementation), the last is by far the most costly, and the first can be
performed at a relatively low cost by properly focusing the effort. Thus, it is possible to
avoid potentially costly procurement that fails to meet requirements with a reasonable
investment in preliminary system design.
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7 NAS Concept Evaluation
7.1 Global Scenarios
Scenario writing typically involves the juxtaposition of a number of alternative futures.
These constructed images of the future may range from ‘optimistic’ to ‘pessimistic’ as
they attempt to extrapolate current nominal trends with other likely and plausible futures.
In this section, only a single NAS scenario was constructed. This single global scenario is
based on a review of some relevant references structured by six major scenario categories
that capture the many facets of NAS operations subject to possible limitations, constraints,
modifications, and shifts regarding the future ATM system envisioned for 2015. Section
2.3.1 outlines the scenario building process, including a brief description of the 13 issue
categories which, along with the six major scenario categories, organize the selected texts
drawn from the several sources listed in the Bibliography. Appendix B contains the collage
of texts cited from the Bibliography. The following is a general scenario that provides a
spectrum of potential issues which may affect the future patterns of development of the
ATM infrastructure and operation.
First, according both FAA and Boeing references, the increase of air traffic domestically
and globally is estimated to grow from 1997 to 2016 by about 5% (Boeing CMO (1997),
p. 3). This expected growth will increase domestic aircraft operations in 2008 to 31.5
million relative to 1996 (24. 0 million) (U.S. FAA Aviation Forecasts (1997), p. I-14).
Coupled to this growing traffic is its effect on the workload levels at ARTCCs. The
forecasts indicate a workload increase at an annual rate of 1.8% from 1996 to 2008. This
increased workload means that FAA en route centers are expected to handle 50.2 million
IFR aircraft by 2008 (ibid, p. I-14).
The increased traffic flows require a substantial economic investment for all categories of
infrastructure including ATC/ATM systems, airports, and feeder roads, all of which will
require government financial support. These supports may be delayed since governments
may be cash-strapped (Booz, Allen & Hamilton (1995), p. 2-29). For example, future
funding for the FAA will fall far short of what the agency needs to provide even the
current level of services, since it is projected that a budget shortfall of $12 billion exists in
the near term or from fiscal year 1997 to 2002. Such deficits promote an unfolding
scenario of increased corporatization and privatization of basic ATM services with
uncertain consequences regarding economic, safety and regulatory issues (U.S. Congress
(1996), p. 9).
Political and economic related concerns in the international context may also conflict with
the sovereignty of states. Air transport authorities have become increasingly concerned
about the regulation of international air transport. The establishment of unified regional
economic markets has invoked concerns about adverse effects on the national airlines of
non-participating states (Booz, Allen & Hamilton (1995), p. 2-135). A major ICAO
meeting in 1994 concluded that “in view of the disparities in economic and competitive
situations there is no prospect in the near future for a global multilateral agreement in the
116

exchange of traffic rights.” (Donne (1995), pp. 47-49). Related potential disruptive issues
include global market access, where an open skies policy for international operations is not
yet considered feasible, especially when slot allocations are limited, foreign investment in
another sovereign state’s airlines raises ownership and control concerns, and the over 900
different taxes worldwide imposed on the industry creates an added economic burden on
airlines (ibid, pp. 50-51).
In the area of environmental considerations, the affect of world air transport has,
according to IATA, been less severe than other modes of transportation. However,
tougher standards are being proposed which may add to developmental costs incurred by
the airline industry (ibid, pp. 161-162).
The future affects of alternatives to air travel seem to be relatively secure. Various forms
of innovative electronic communication have been, and may well be in the future, less
severe than some reports have suggested. Video-conferencing, for example, seems to have
some impact on reductions in air traffic only during economic recessions when
businessmen forego travel expenses during these periods. From an efficiency point of
view, such high-tech communications and information technologies do not directly
compete with air travel (ibid, pp. 85-87).
A number of potential drawbacks exist, however, with the proposed GPS and satellitebased
navigation on the use of airspace. First, several ICAO member states have been
vocal in their reluctance to accept a GPS-based satellite navigation system, primarily
because GPS is U.S.-owned and currently managed by the DOD. They are also concerned
that the U.S. may unilaterally degrade the GPS signal accuracy for precision guidance
(Booz, Allen & Hamilton (1995), pp. 3-94, 3-95). Much work has been conducted by the
international community to develop and implement a GNSS, which may not include GPS
(ibid, p. 3-49). Moreover, uncertainties associated with GPS (and other) satellite-based
navigation include system availability and integrity especially crucial during precision
approaches in poor weather conditions (ibid, pp. 3-53, 3-58).
Not only the space segment poses potential constraints for the future ATC/ATM
operations in NAS or other airspace. The ATC architecture may itself be a source of
potential problems. If current software practices continue (such as heterogeneous
communications protocols and data formats, and multiple application languages), costly
software maintenance of the many (e.g. 54 operational ATC systems written in 53
programming languages) fragmented ATC systems would be the result in the future (U.S.
GAO AIMD-97-30 (1997), pp. 40-46). No FAA organization is responsible for the
problem of technical ATC architecture creating the potential proliferation of an
uncoordinated ATC software architecture development process affecting the future ATC
modernization effort (ibid, pp. 47-54).
The disruption and delay of traffic flow may also be generated from ground handling
processes. For example, due to increased mix of international passengers, delays may be
caused by increasing volume of visa processing. This could be especially acute in a
possible future of heightened political instabilities which would create stricter measures to
control the flow of immigrants and foreign travelers (Booz, Allen & Hamilton (1995), p.
148). Another future risk associated with ground handling concern health requirements of
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travelers. There are signs that debilitating or fatal diseases which have been eradicated in
many countries may be returning and have the potential for spreading through
international travel, and thereby causing further processing delays as health-related
documentation is reviewed at ports of entry. Also, outmoded and complicated inspections
negate the inherent advantage of speed offered by public air transport which may also add
to the cost of airline operation in excess of $100,000 per day (Donne (1995), p.149).
In addition to ground handling issues, the efficient operation of airports demands increased
airport capacity that could handle the projected 57% increase in passenger enplanements
between 1993 and 2005. Major investments will be needed to accommodate more
passengers and larger aircraft. A substantial increase in aircraft operations at a large hub
airport may warrant consideration of additional runways. However, the outlook for new
runways at major origin/destination airports is less promising. New runways are being
considered at only 5 of 13 large hub airports where more than two-thirds of traffic is
locally generated. The engineering and political obstacles are daunting to new runway
construction at these airports. It is projected that airfield congestion at major
origin/destination airports will continue to be one of the most difficult issues facing civil
aviation (U.S. FAA NPIAS (1995), pp. 29-30).
Efforts to increase future airspace capacity with Free Flight concepts may be stalled by
conflicts of Special Use Airspace issues. Although SUA serves the important safety
function of segregating hazardous activity from non-participating aircraft, civil users have
voiced concerns about whether SUA is being efficiently managed. By its location SUA can
limit air traffic to and from a particular location and thus has become a much more urgent
issue because of the aviation community’s movement toward Free Flight. Under a Free
Flight operating concept, the users of the system would have more freedom to select
preferred routes as long as such routes do not interfere with safety, capacity, and SUA
airspace. A key recommendation is the establishment of a real time system to notify
commercial users of SUA availability. At least two hours of minimum notice is suggested.
Such use of SUA could disrupt the visions of relatively unfettered Free Flight for the NAS
in 2015 (U.S. GAO RCED-97-106 (1997), p. 25).
Some potential airport safety problems may be anticipated under the emergence of the
new NAS. An example is when the acquisition, development, integration, and assimilation
of complex systems and technologies (which rarely are ‘off-the-shelf’) produce
unexpected outcomes, costs, and delays, such as was the case for the now defunct
Advanced Automation System (AAS). Currently being replaced by the Standard Terminal
Replacement System (STARS) which provides controllers in TRACONs with new
workstations and supporting computer systems, the AAS incurred schedule delays of up
to eight years with estimated increase in costs from $2.5 billion to $7.6 billion. FAA’s
schedule for STARS can also be jeopardized by scheduling conflicts with other
modernization efforts. For example, in September 1996, a study identified 12 potential
scheduling conflicts at the first 45 STARS sites. Safety issues surrounding airport
operations may also be associated with an unhealthy mix of newer digital and older nondigital
systems such as terminal surveillance radars (U.S. GAO RCED-97-51), pp. 3-4).
FAA’s organizational culture and workforce issues also may prove to be problematic in
the future in terms of safety, schedule delays, and project costs. As may be inferred from
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above, the agency’s organizational culture has been an underlying cause of the persistent
cost overruns, schedule delays, and performance shortfalls as exhibited, for example, in its
acquisition of major ATC systems. FAA officials have rushed into production before
completing development, testing, or evaluation of programs. Also, poor oversight has
caused acquisition problems in such projects as ODAPS and Mode S where the delivery of
the latter was delayed for five years (U.S. GAO RCED-96-159 (1996), pp. 22-29).
Moreover, an environment of control has been fostered by the agency’s hierarchical
structure where employees are not empowered to make needed management decisions.
Fewer than half reported that they had enough authority to make day-to-day decisions
about day-to-day problems. Also, poor coordination between FAA’s program offices and
field organizations has caused schedule delays as has been the case with the Terminal
Doppler Weather Radar, the Airport Surveillance Radar, and the Airport Surface
Detection Equipment (ibid, pp. 29-31). Finally, a study in 1994 showed that differences in
the organizational culture among FAA’s air traffic controllers, equipment technicians,
engineers, and divisional managers made communication difficult and limited coordination
efforts (ibid, pp. 32-33).
With respect to potential future issues regarding FAA’s workforce, the agency has
identified that for 1997 and 1998 their staffing needs will be met. However, it is uncertain
whether current sources can provide the controller candidates FAA will need through
2002. FAA officials have identified several impediments that hinder their ability to staff
ATC facilities at specified levels. The first is FAA headquarters’ practice of generally not
providing funds to relocate controllers until the end of the fiscal year, which causes
delayed controller moves and continued staffing imbalances. The second impediment is the
limited ability of regional officials to recruit controller candidates locally to fill vacancies at
ATC facilities. In addition, FAA regional officials also believe that limited hiring of new
controllers in recent years has hindered their ability to fill vacancies. Partly due to these
impediments, as of April 1996 about 53% of ATC facilities were not staffed at levels
specified by FAA’s staffing standards (U.S. GAO RCED-97-84 (1997), pp. 3-4.
7.2 Implications of Global Scenarios on System Transition Paths
The global scenario outlined in Section 7.1 suggests some of the possible ways that the
future transitional path of the NAS system in 2015 may be diverted from the generally
expected trajectory. The particular unfolding nature of these transitions may affect system
capacity, safety, and efficiency.
NAS system demand is primarily driven by general market and economic conditions. For
example, about 80% of the Gross Domestic Product (GDP) directly contributes to the
Revenue Passenger Miles (RPM). Moreover, political, social, and cultural realities, and
concomitant uncertainties, may also play a significant role in shaping the demand for
travel, in general, and air travel, in particular. To address future traffic demand, a sufficient
NAS system capacity must be provided. How the future NAS system capacity is realized,
however, is dependent on a number of parameters including airplane size, the mix of an
airline’s fleet, the nature and extent of operating in a hub and spoke configuration, and
other relevant issues such as airline deregulation and the impact of technological
developments and applications (e.g. ADS-B, CTAS). In terms of NAS capacity, an
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estimated 5% constant traffic growth requires that the NAS infrastructure and operational
capacity in 2015 is prepared to handle 2.4 times the current traffic flow rate. A successful
system transition toward this goal may likely be delayed given the range of technical,
economic, institutional, and political obstacles. From delays in ground handling due to
likely increases in processing foreign passengers, to delays in integrating the latest
software and other technological subsystems, the NAS may have insufficient capacity in
2015 to assimilate the projected growth rates in traffic. The estimated RNP levels may not
be viable (especially near terminal areas) for the stated period, as successfully integrating
the CNS/ATM technical operational infrastructure may be affected by potential ATC
architecture integration issues associated with complexity, functional redundancy, and
general compatibility of several software-laden technologies. The number of planned
runway construction projects at the 13 major hubs promises to constrain the capacity
needs in 2015. Of course, economic shortfalls can undercut needed improvements in
system capacity by underfunding specific technical projects (e.g. ASR-9 surveillance radar
installations) which directly contribute to enhancements in NAS capacity.
Given recent ATC developmental history, possible impacts on system safety may arise
from the emerging trend of multiple, uncoordinated, and fragmented technologies
producing an unsystematic array of incompatible technologies (e.g. several software
protocols) which may diminish presumed margins of safety. Also, the expected shortage of
trained air traffic controllers after 2002 may be detrimental to operational safety precisely
when traffic flow levels are expected to rise dramatically. In addition, possible conflicts
stemming from Special Use Airspace between the military and civilian interests may
introduce added risks in a regime of Free Flight envisioned for en route airspace. If a
minimum of two hour notification is needed to communicate the availability status of the
SUA, a decrease in operational safety may be expected due to possible communication
errors in the operational context of relative route flexibilities generated in a Free Flight
environment, which would require heightened ATC surveillance levels.
Possible setbacks from planned NAS efficiency may come from the inability of operators
to have unfettered airspace market access, or when limitations in slot allocations at many
airports is reached. This is due, in part, to concerns by sovereign states in protecting their
national interests. International competitive pressures may further exacerbate the efficient
traffic flows from one global region to another. The uncertainties regarding different
satellite-based CNS schemes may also cause operational inefficiencies as carriers may be
required to adapt to multiple modes of navigational aids, moving from GPS-based systems
to other non-U.S. developed navigational systems. Finally, potential inefficiencies may be
incurred due to possible degradations of satellite-based navigation signal availability or
continuity of function due to ionospheric scintillations and other potential sources of
errors. These effects would be especially severe during the approach and landing phases.
7.3 Comparison with the FAA and RTCA Operational Concepts
The concept presented in this report is built around the goal of increasing system capacity
in clearly defined transition steps. Additional system improvements to support increased
efficiency are also presented. This concept, as well as other long term ATM operational
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concepts under consideration for the NAS, will need to be validated against the mission
objectives as discussed in Section 6.
Appendix C contains a top level analysis that the team performed on the FAA and RTCA
operational concepts in June of this year. It appears that the FAA and RTCA concepts
assume a very similar technology basis as this report, with an operational emphasis that is
perhaps more on user flexibility than on system capacity, although this is not stated in
either document.
Many possible transition paths and a large array of technology can be applied to the NAS
modernization. An approach that is largely technology-driven has resulted in an emphasis
on new technology as the solution, but there is not yet an agreement on what the primary
problem is. The industry must clearly define what problem should be solved (i.e. state the
system mission), and use this statement to drive technical requirements with proper
inclusion of human factors, or run the risk of making a huge investment in a system that
does not fulfill the mission.
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8 Conclusions and Recommendations
8.1 Conclusions
1. The traffic growth predictions presented in Section 2 indicate that as early as 2006
the NAS will suffer serious traffic gridlock unless increased capacity is ensured.
The terminal area is predicted to be the primary choke point in the system, with
increasing congestion in some en route regions. This situation, if not addressed,
will cause airline hubbing operations to become difficult, if not infeasible, with
escalating costs which will constrain economic growth.
2. The current approach to NAS modernization will not accommodate the predicted
growth. This is primarily due to two factors:
• The pace of the modernization is too slow to respond to market needs.
• The system development process is inadequate, as it is largely technologydriven
to point solutions, without traceability to clearly defined mission
goals.
8.2 Recommendations
1. NAS capacity must be increased two to three fold through 2015. This is a
challenging task, technically and economically, and will involve a combination of
the following:
1.1. Additional runways will be needed, either at existing hub or reliever
airports or at new airports.
1.2. Higher traffic density in terminal areas and the most congested en route
regions will also be needed. The operational concept presented in this
report proposes to achieve this through a combination of the following:
1.2.1. Improvements in communications, navigation and surveillance
technology to support reduced separations. This will be aimed at
more accurate trajectory definition and execution, and better
position and intent information for the separation assurance
functions. A precision 4-D separation assurance framework,
distinct from procedural or radar control, will emerge.
1.2.2. Changes in the separation assurance functions to achieve the
capacity goals. This will involve decision support tools for
increased accuracy and productivity, along with an architecture that
supports the required criticality of function for separation
assurance.
1.2.3. Airspace configuration to support either high or low density
operations through dynamic partitioning. Access to airspace will be
based on aircraft capability, qualified to a maximum Required
System Performance (RSP) level in which the aircraft can operate.
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1.2.4. A coordinated traffic flow planning system that supports higher
capacity and efficiency. This will involve a careful definition of
roles for each flow planner and the information infrastructure
needed to support each function.
2. A major change is needed in the ATM system development process to ensure that
the modernization objectives will be achieved. The following issues must be
carefully considered:
2.1. All system elements will be affected, and thus a whole-systems approach
must be taken to ensure that benefits will be delivered.
2.2. A collaborative development approach must be adopted throughout the
modernization process to ensure inclusion of all system stakeholders.
2.3. The high level preliminary design trade examination must be done before
major concept and architecture decisions are made to ensure that the
system will achieve its mission - which includes total system productivity
and affordability.
2.4. Concept development and validation must incorporate human factors and
technology equally throughout the modernization effort.
2.5. The level of risk and criticality requirements for ground and air elements
must be understood and incorporated early in the development, to ensure
that the concept and architecture will be certifiable.
2.6. Interdisciplinary research and development teams are essential to ensuring
modernization success, due to the size and complexity of the system.
8.3 Research Needs to Support the 2015 Concept
This report has presented an operational concept baseline for the NAS through 2015, and
has devoted considerable attention to how a large scale system development such as the
NAS modernization should be approached. This section presents a list of research areas
where focused effort will be required to move from a concept into an operational system.
The list is not exhaustive and a considerable effort is required to develop a comprehensive
research and development plan, but this section attempts to highlight the most critical
research needs.
8.3.1 System Development Process
The following are the primary recommendations to address the shortcomings of the ATM
system development process:
1. System Performance Metrics. An overriding concern for the entire ATM system
development process is that efforts are not properly focused on clear goals. This is
partly due to a lack of consensus in the industry, but partly due to a lack of meaningful
metrics against which to measure success. Thus, from the point of view of managing
research and development, an immediate priority must be placed on the development
of a set of system performance metrics that directly relate to the system safety,
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capacity and efficiency goals. Deriving from these top level metrics will be a hierarchy
of metrics for measuring performance of system components, all of which need to be
defined to support the top level metrics.
2. Integration of Human Factors. There is a need to determine, in detail, the process
of how human factors can be incorporated into ATM system development, design,
integration and maintenance. The process should define both the nature and timing of
inputs. The plan for human factors involvement would then be available as guidelines
which could be used by decision makers in the system development process.
3. Role Definition. Focused and specific guidelines need to be produced on how to
determine and describe the eventual role of the humans in a system where the
functional allocation is to be human-centered. The kind of automation support
humans need will be identified by the requirements of the human role within the ATM
system. This activity must done as part of the operational concept definition phase of
system development and would be expected to identify very explicit research questions
that need to be answered as a part of preliminary design.
8.3.2 Research Tools Development
An integrated set of analysis and simulation tools needs to be developed, aimed at the
evaluation of preliminary design concepts for a selected U.S. high density air traffic area.
The tools must support the development of a transition plan from the current ATC
infrastructure to the future architecture and operation. This tool set will support the
identification of long range (up to 30 year) system capacity, safety and efficiency needs,
evaluation of alternative operational concepts, allocation of requirements to CNS and
ATM system elements, and evaluation of the safety, human performance suitability and
economics of alternative transition strategies.
A series of research tasks are needed for developing an operational performance baseline
of a high density air traffic services area. These tasks will establish traffic and
infrastructure forecasts, develop an integrated analysis tools set spanning overall system
operational modeling, technical CNS and ATM performance modeling, and economic
transition assessment. Also to be established is a database of technology (current and
emerging), as well as human performance tools and assessments. These tools and data
will be applied to the preliminary design and evaluation of the phased introduction of new
CNS/ATM technologies for high density traffic areas. A conceptual framework for this
set of preliminary design exploration tools is shown in Figure 8.1.
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Concepts Requirements Trades Evaluation
Operational
Baseline
Traffic and
Infrastructure
Forecast Models
Analysis Tools:
Operations
Investment Anal
Tech Reqmts
System Transition State 1
System Transition State 2
System Transition State 3
System Transition State 4
Technology
Schedule &
Performance Models
Human Perf
Models & Data
Figure 8.1 Preliminary Design Tools
8.3.3 Research on ATM Functions
Overall Performance of ATM Functions
1. Reduction of separation for higher throughput must be researched. The
relationship between safety and capacity must be quantified through a collision risk
model for what is the radar controlled environment in the current system. This risk
model will include the following primary components:
• Intervention rate buffer, which reflects protection against exposure to
potential conflicts in a sector, and is thus directly related to sector
controller workload.
• Intervention buffer, which reflects the time needed to determine that a
conflict is imminent, and to resolve it.
• Detection performance, which is directly related to the resolution and
accuracy of the surveillance sensor, and the situation display.
• Definition of criticality levels for each function and allocation or
requirements to subfunctions.
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• Definition of normal, non-normal and rare-normal conditions for each
operating phase in the ATM system, and accounting for these in the entire
process to ensure that systems will be certifiable.
2. The relationship between capacity and efficiency must be developed, including the
following primary components:
• Degree of structure needed to ensure throughput as contrasted with
routing flexibility to achieve efficient flight.
• Internal schedule flexibility for larger operators, and how collaborative
decision making can be incorporated in flow planning.
• Flow planning and separation assurance for improved routing flexibility.
Planning roles in the system must be coordinated and clearly defined.
3. Transitions from en route to high density terminal areas must be addressed. One
of the possible methods is to base a plan on required time of arrival at particular
points around the terminal areas. The need to perform conflict prediction and
resolution through possibly intermediate sectors is an issue.
4. Trajectory prediction accuracy and use of intent information for traffic planning
and separation assurance must be addressed, in the context of the collision risk
model discussed in item 1.
5. Flow planning in extended terminal areas and high density regions such as the
northeast corridor is a challenging topic and of considerable importance.
6. Surface automation and the overall coordination with terminal area airborne
operations must be examined.
7. The problem of wake vortex in a variety of situations (including approach,
departure, parallel approaches and airborne) is one of the largest challenges on the
road to increased capacity.
8.3.4 Human Factors Performance
The output from the following items could be in the form of contributions to both a
database and knowledge base. It may be possible to formulate either models or analysis
and development tools in specific instances.
1. Decision Support Systems:
The main issues identified in Section 4.3.1 were how controllers would become
dependent on decision support systems, how this dependency might affect
situational awareness, and what type of intervention skills may be necessary for
any rare-normal or abnormal events. Research should be focused at identifying the
relationship between dependency and situational awareness with specific emphasis
on determining the ability of the controller to:
• Identify when intervention is necessary
• Maintain the necessary skills to intervene.
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2. Intent:
The research area identified is the understanding of the nature and structure of the
controllers’ intent. There is a need to understand how their intent is translated into
a 4D action plan, how the plan is shaped by the need to delay execution of specific
actions, and how that action plan is modified in real time. This knowledge is basic
to determining how intent data could be entered into and used by a decision
support tool.
3. Structure to Maximize Throughput:
An understanding needs to be developed about how airspace structure is used to
reduce cognitive workload (intervention rate) and thus facilitate increased
capacity. The cognitive demands on the tactical controller were discussed in terms
of being affected by the need to identify potential conflicts. The task of
determining the potential for conflicts becomes more difficult in the terminal
environment due to the uncertainties in the profiles of climbing and descending
aircraft. Topics will include:
• Real time studies on the cognitive workload for distributed flight profiles
versus a more structured organization. The scenarios for this test must
include both high and low density traffic situations with the presence of
aircraft that do not respect clearance or suffer some failure (i.e., nonnormal
and rare-normal events).
• Fast time studies on the number of potential conflicts created in high and
low density airspace using a non-airway or free-routing organization.
4. Sharing Separation Assurance Responsibility:
Research associated with the sharing of the separation assurance task should focus
primarily on identifying the feasibility of ground and cockpit recovery procedures
involving transfer of control. Factors to address are requirements for independent
monitoring and the technologies needed to support such requirements.
8.3.5 Communication Research
In order to fully exploit the future capability of data link, the following research should be
undertaken:
1. Natural Language Information Flow Between the Aircraft and Control - The
current specifications for Controller/Pilot Data Link replicate exactly the standard
phrases specified in FAA Order 7110.65 and its ICAO equivalent document.
These documents have evolved over many years to ensure complete and
unambiguous verbal communication. They do not, however, represent the best
way of communicating when verbal communication is not the means. Research is
needed to define the best way to communication flight clearances and intent
independent of the means of expressing that information. Human factors research
must accompany this effort to ensure that the resulting natural language of air
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traffic control can be unambiguously conveyed to and from the humans at each end
of the communication process.
2. Natural Language Information Flow for Aircraft Access to Ground Data
Bases and for Ground Access to Aircraft State and Intent - The current
specifications for ADS and FIS are derived from their verbal counterparts.
Research is required to develop methods for requesting and sending information
that is independent of the constraints of verbal communication. The bandwidth
and latency constraints of air/ground communication media must be recognized in
this development, however.
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Acknowledgments
The Boeing team worked very closely with NASA personnel during the entire contract
period, and had numerous opportunities for professional exchange and to gain insight into
the technologies that are being developed within the AATT program.
The team also had an opportunity to work with the FAA Air Traffic Operational Concept
Development Team, which was formed at about the time this contract was being
established. The FAA’s first operational concept document draft was available to the
Boeing team before this contract was established, and the team received updates as they
became available. Team members also attended two FAA internal working meetings on
functional allocation and task analysis for the air traffic concept during the contract period,
and gained valuable insight into the details involved in the concept implementation.
The team was supported by NEXTOR faculty members for the duration of the contract,
and their expertise was valuable for various aspects of the concept. John R. Hansman,
MIT, served as Principal Investigator for NEXTOR. Hansman, along with Amedeo Odoni
of MIT, Adib Kanafani and Mark Hansen of UC Berkeley, provided consultation on a
number of technical issues. Their expertise contributed substantially to the concept
definition and its presentation.
For the NAS Stakeholder Needs survey, the team relied on the valuable time and ATM
system knowledge of 11 professional organizations: ACI-NA, ADF, ALPA, AOPA, ATA,
DoD, GAMA, HAI, NATCA, NBAA and RAA. The team is grateful for the time taken
by the experts in these organizations to provide the information requested in the
appropriate format, and for the valuable insight the team gained into the various aspects of
this large and complex system.
Last, but not least, the team was supported in its work by a number of experts within
Boeing, who contributed to the wide range of topics covered in this report. The primary
contributors, in addition to the authors listed, were Malcolm A. Coote, Nicholas Patrick,
George Boucek and Roger Nicholson. Unfailing support from the CNS/ATM Program
management team of James E. Templeman, Richard L. Wurdack, and David L. Allen, is
also gratefully appreciated. Information needs, along with persistent and much needed
editorial support was provided by Daniel B. Trefethen, and Christa M. Stafford cheerfully
ensured that team members always knew exactly where they were going and how to get
back again.
129

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133

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134

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Tech. 12:449-467.
135

Appendix A. Technology Inventory
A.1 Communication
The communication technology elements are shown in Tables A-1 through A-3. As
described in the body of this report, communication technology can be described as three
layers. Each lower layer provides certain communication services to the next layer above
it. The top, application, layer presents communication services to the flight crew or air
traffic controller through a set of control and display interfaces and by accessing and
servicing data bases hosted in the aircraft and controller workstation automation.
Table A-1 describes the applications which use communication paths to perform their
function. Table A-2 describes the communication protocols which operate over the
communication media and provide communication transport services to the
communication applications. Table A-3 describes the communication media which
connect the aircraft to the ground to support the communication functions.
Table A-1, Communication Applications, presents each application and describes key
characteristics about that application. The input column identifies the protocol technology
which is appropriate for that particular application. The output column identifies the user
of the communication service. The column marked “performance” describes the user
expectations of performance currently associated with this particular application and its
underlying protocol and medium. Greater performance may be required in the future to
support more critical functions (e.g., en route, terminal and ground operations.) The
availability column describes when the technology and its underlying protocol and medium
support is, or will be, available.
Table A-2, Communication Protocols, presents each protocol and describes key
characteristics about that protocol. The input column identifies the medium or other
protocol element that supports it. The output column identifies the application or other
protocol which uses the services provided by the protocol element. Note that ATN and
FANS-1 require certain mutually-supporting protocol elements, which are described in
Section 5.1 of the body of this document. The performance column identifies the
performance contribution or reduction which the protocol adds to the communication
path.
Table A-3, Communication Media, presents each radio or other medium which has been
used for aircraft/ground communication. Since the media represent the bottom of the
communication stack they do not have inputs but the column was retained for consistency.
The output column identifies the protocol elements which use the services of the medium.
There is a subnetwork protocol associated with all of the data link related media, in
addition to the protocol described in Table A-2. The performance column describes when
the medium is, or will be, available.
136

Table A-1
Communication Applications
Technology Elements Inputs Outputs Performance Availability
Controller-Pilot Data Link
Communications (CPDLC)
Automatic Dependent
Surveillance (ADS)
ATN, 622-ACF
ATN, 622-ACF
Flight Crew Interface, Flight
Management, Flight Data
Processor, Surveillance Data
Processor
Flight Crew Interface, Flight
Management, Flight Data
Processor, Surveillance Data
Processor
• latency:
oceanic operations < 1 minute
en route & terminal: near real time
• availability: non critical performance
• latency: < 1 minute
• event reporting rates:
oceanic 1/15 minutes,
en route 1/minute,
deviating from clearance: near real time
• availability: non critical performance
• non critical performance
Initial Operations
(1)
Initial Operations
(1)
Flight Information Service
(FIS)
ATN
Flight Crew Interface, Flight
Management
Plain Old ACARS (POA) ACARS Flight Crew Interface, Flight • latency: non critical performance Initial Operations
Messages
Management
• availability: non critical performance (2)
ARINC 623 ATS Data Link ACARS Flight Crew Interface, Flight • latency: < 1 minute
Initial Operations
Messages (623-ATS)
Management
• availability: non critical performance (3)
Controller-Pilot
SELCAL, Flight Deck Mics & Head • latency: near real time
Mature
Communications (FAA Order SATCOM voice Phones
• availability: critical - en route & terminal,
7110.65)
non critical oceanic & remote
ATIS VHF radio Flight Deck Head Phones • non critical performance Mature
AOC SELCAL Flight Deck Mics & Head • non critical performance
Mature
Phones
Notes:
(1) FANS-1 applications are in operational use in the South Pacific and elsewhere; ATN applications in prototype evaluation.
(2) FAA Pre-Departure Clearance (PDC) and digital ATIS.
(3) European Departure Clearance and digital ATIS.
137

Table A-2
Communication Protocols
Technology Elements Inputs Outputs Performance Availability
Context Management
Application (CMA)
ARINC 622 ACARS
Convergence Function (622-
ACF)
ARINC 622 ATS Facilities
Notification (622-AFN)
Aeronautical
Telecommunication Network
ATN
Flight Crew Interface, Flight
Management
ACARS CPDLC, ADS • transfer delay: minimal increase
• integrity: CRC check
ACARS
VDL, SATCOM Data 3,
HFDL Data 3, Mode S
DL, Gatelink
Flight Crew Interface, Flight • provides log-on functionality
Management
CPDLC, ADS, CMA, FIS • transfer delay: minimized by large # of
routing stations
see application
see application
see application
ACARS Routing VHF, SATCOM Data 2, 622-ACF, 622-AFN, 623- • transfer delay: increased by limited # of see application
HFDL Data 2
ATS, POA
routing stations
SELCAL HF radio, VHF radio FAA Order 7110.65, AOC Mature
138

Table A-3
Communication Media
Technology Elements Inputs Outputs Performance Availability
VHF Data Link (VDL) N/A ATN • transfer delay
• voice 250 msec
• data 1 sec (95%), 5 sec (99.9%)
• access delay: TBD
• hroughput: 31.5 Kbit/s (link)
• coverage: line of sight (200 nm)
VHF Radio N/A ACARS, SELCAL • near real time transfer delay
• freq. congestion dependent access delay
• availability: en route domestic/terminal primary
• coverage: line of sight (110-160 nm)
SATCOM N/A SATCOM voice • transfer delay
• congestion dependent access delay
ACARS - Data 2 • throughput: 9.6 - 4.8 Kbit/s data (link)
• availability: oceanic primary
ATN - Data 3 • coverage: satellite range (optimized at mid/low
latitudes)
HF radio N/A SELCAL • transfer delay
• congestion dependent access delay
• availability: oceanic primary
• coverage: line of sight + ionospheric skip
HF Data Link (HFDL) Data 2 N/A ACARS - Data 2 • transfer delay
• congestion dependent access delay
ATN - Data 3 • throughput: ~30 bits/s (airplane)
• availability: oceanic primary
• coverage: line of sight + ionospheric skip
Mode S DL N/A ATN • transfer delay: radar scan rate
• throughput: 300 bit/s uplink,
160 bit/s downlink (airplane)
• coverage: line of sight
VDL-based ACARS
maybe 1999
Mature
Initial Operations
Mature
Data 2 - 1998
Data 3 - TBD
TBD
139

Gatelink N/A ATN • coverage: at the gate
140

A.2 Navigation
The navigation technology elements are shown in Tables A-4 and A-5. Like the
communication elements, navigation can be described in layers. Sensors, described in
Table A-4, provide service in the form of raw data to processors or directly to displays.
Processors, described in Table A-5, in turn, manipulate the raw data and turn it into useful
information for displays and for control of aircraft. The controls and displays are very
aircraft-specific and therefore are not described here.
Table A-4, Navigation Sensors, lists the elements which sense either physical phenomena
about the aircraft state or radio signals. They can, in, turn be used to determine aircraft
state. The output column describes the user of the raw data and a short list of the
parameters which are available from this sensor. The performance column describes
accuracy, availability, area of coverage, and other key characteristics for each sensor. The
availability column describes the state of development of the sensor technology.
Table A-5, Navigation Processors, describes some of the processors of navigation data
typically found on aircraft. The inputs column describes the data sources which the
processor requires to performs its function. The outputs column describes the users of the
information generated by the processor. Performance, as mentioned for all processors, is
almost entirely dependent on the quality of the raw data supplied to the processor. All of
the processors identified are in current production and in use today. The navigation data
base, although identified here as a separate processor to better illustrate the functionality,
is normally a subfunction of the navigation processor it supports.
141

Table A-4
Navigation Sensors
Technology Elements Outputs Performance Availability
Inertial Reference Systems (IRSs)
Flight Guidance, Autopilot (2D position, Aircraft
Velocity, Acceleration, Attitude)
• Accuracy: 2 nmi per hour
• Availability: primary
• Coverage: global
VOR/DME Flight Guidance (2D position) • RNP 2.0
• Availability: primary
• Coverage: line of sight
DME/DME and Scanning DMEs Flight Guidance (2D position) • RNP 1.0
• Availability: primary
• Coverage: line of sight
GPS
Flight Guidance (3D position; time; integrity • RNP 1.0
limit)
• Coverage: global
GPS/WAAS
Flight Guidance (3D position; time; integrity
limit)
• RNP 0.1
• Availability: primary
• Coverage: regional
GPS/LAAS Autopilot (Final approach path deviation) • < RNP 0.1
• Availability: primary
• Coverage: local
ILS Autopilot (Final approach path deviation) • < RNP 0.1
• Availability: primary
• Coverage: local
MLS Autopilot (Final approach path deviation) • < RNP 0.1
• Availability: primary
• Coverage: local
Pitot and Static pressure
Flight Guidance, Air Data (altitude, vert. velocity,
airspeed)
• Availability: primary
• Coverage: global
mature
mature
mature
operational;
IOC 1998; Phase II
IOC 2002
Reqmts in
development
mature
Plans in Europe,
some operational
prototypes
mature
142

Table A-5
Navigation Processors
Processors Inputs Outputs Performance Operational
Availability
Navigation &
Guidance Computer
Navigation Sensors (position,
velocities, accelerations); Flight
Plan; Performance Plan
Flight Management; Flight Steering see sensor Mature
Autopilot Computer Flight Steering; Approach & Flight Guidance for Approach and Landing; see sensor Mature
Landing Path Deviation
Flight Control
Air Data Computer Pitot Static Flight Guidance (aircraft air mass parameters) see sensor Mature
Navigation Data Base
Flight Guidance (waypoint data; Radio Sensors
(frequencies for autotuning)
see sensor Mature
143

A.3 Surveillance Inventory
The surveillance system elements which are in place or proposed for the 2000-2015 time
period are summarized in Table A-6. There are a total of 12 rows which describe the
major systems comprising air-ground, air-air, and oceanic surveillance. The columns in
the table name the various surveillance elements and give a number of details on
performance characteristics and system availability. The table includes all the systems that
are currently deployed or proposed for regional deployment in future architecture plans,
and those which could be available in the time frame of interest to implement future
CNS/ATM systems.
Rows 1 and 2 in Table A-6 summarize the characteristics of current and emerging radar
technologies for air-ground surveillance. The specific systems in these rows, e.g. ASR-9,
are NAS deployed radars. The newest proposed radars shown are the ASR-11 primary
radar, the European Mode-S radar (POEMS) which features Downlink of Aircraft
Parameters (DAP) at each scan cycle, and the ATCBI-6 which is a monopulse SSR with
selective interrogation capability (Partial Mode-S capability).
Rows 3, 4, 5, and 6 are surveillance elements that describe various concepts for
processing and distributing surveillance data. The current generation systems embed the
Radar Data Processor (RDP) as a major element of current generation ATC automation.
The Surveillance Distribution Network (SDN) is a concept for networking terminal and en
route radars to ATC centers and other sensors such as ADS and ADS-B systems. In the
core areas in Europe this concept has been implemented using common surveillance
distribution protocols and appropriate ground based communication networks. The SDN
needs to be paired with appropriate Surveillance Data Processor (SDP) software which is
intended to blend multi-sensor inputs into common aircraft track files, i.e. the RDP in
current systems will probably be replaced in the NAS system with SDN and SDP systems.
Finally, the Surveillance Server System (SSS) is an advanced version of SDN and SDP
which distributes multi-sensor processed track files to any ATC, military, or other users of
track file data. This system will allow smaller airports and aircraft dispatch operations to
have access to the most current and accurate aircraft state information.
Row 7 describes the current TCAS system for collision avoidance. Although there is
research and standards development continuing beyond the capabilities shown here, there
are no specific regional plans or commitments to develop TCAS beyond version 7 at this
time, although this is feasible in the time frame of interest. A likely successor to TCAS II
would be a system using Mode-S extended squitters and Mode-S interrogation
capabilities.
Row 8 in Table A-6 describes Contract ADS. This type of sensor is primarily oriented for
oceanic and remote area - non-radar airspace. Many undeveloped areas are considering
the use of ADS surveillance as a lower cost alternative to traditional radar surveillance.
Rows 9 and 10 in Table A-6 describe ADS-Broadcast sensors for airborne surveillance
and ADS-B listening stations for air-ground reception and distribution of ADS-B data to
ground facilities. The two primary systems proposed for ADS-B implementation in this
time frame are the Mode-S extended squitter and the STDMA system which is being
144

standardized as VDL Mode-4. Both systems will require ground stations for air-ground
surveillance, and are being considered for reduced cost air-ground surveillance and for airair
applications such as collision avoidance and Cockpit Display of Traffic Information
(CDTI).
Row 11 in Table A-6 describes Mode-S Services. This sensor is a potential domestic form
of ADS that would use interrogation by the Mode-S radars to downlink surveillance data
such as aircraft position and velocity states and intent information. Mode-S Services is
complementary to extended squitter based ADS-B and is considered to be a transitional
system between the current radar systems and a fully integrated radar/ADS-B surveillance
system.
Row 12 in Table A-6 describes Traffic Information Services (TIS) or TIS broadcast. This
is the concept of transmitting ground based track information to equipped aircraft for
providing air-air surveillance on nearby aircraft. This type of service can be implemented
using the Mode-S interrogation band, or using another communication system such as
VDL Mode-4. This service is intended as a lower cost means of surveillance than TCAS
systems, and as a transitional or backup service to using ADS-B for air-air surveillance.
145

Table A-6
Surveillance Inventory
Surveillance System Inputs Outputs Performance Availability
Primary
Radar
Terminal Radars:
ASR - 4, 5, 6, 7, 8, 9, 11
En-Route Radars
ARSR - 1, 2, 3, 4
Surface Radars
ASDE - 2, 3
N/A
Aircraft Skin Report (r, r_dot,
az , t)
Six Level Weather (ASR - 9,
11)
Aircraft Height (ARSR - 4)
Terminal / En-Route Systems
Range Coverage ~ 60 / 250 nm
Detect Prob. ~ 0.98
Update Rate ~ 5 - 12 sec
Azimuth Accuracy ~ 2 mrad
Range Accuracy ~ 150 ft
Current systems mature
Replenish older primaries by 2002
(ASR - 4, 5, 6, 7, 8; ARSR - 1, 2;
ASDE - 2)
Secondary
Radar
Classical SSR
ATCBI - 3, 4, 5
Monopulse SSR
Mode-S, ATCBI - 6
Radar Data Processor (RDP)
Radar Tracker
Surveillance Distribution
Network (SDN)
N/A
Transponder Replies
Aircraft ID
Pressure Altitude (r , j , t)
Mode-S Data-Link
TIS Uplink
DAP Downlink
ADS Broadcast
Primary Radars Aircraft States
Secondary Radars Aircraft ID
Surveillance Position States
Distribution Network Velocity States
Primary Radars
Secondary Radars
ADS A/B Systems
Radar Data Processor
Surveillance Data Processor
Surveillance Server
Range Coverage ~ 150 - 250 nm
Detect Prob. ~ 0.99
Update Rate ~ 5 - 12 sec
Azimuth Accuracy
~ 3 mrad (classical)
~ 1 mrad (monopulse)
Time to Establish Tracks
Tracker Latency
Maneuver Response Time
Steady State Accuracy
Clutter / Fruit Rejection
Data Correlation Purity
RCP Performance Parms:
Throughput in bits/sec
Data Latency at 99% level
Integrity of Decoded Reports
Current systems mature
Replenish older systems by 2002
(ATCBI - 3, 4, 5)
Data Link pre-operational 1998
Data Link initial operations 2003
Current system and new systems in
development
ARTS (TRACON)
STARS (TRACON)
HOST (En-Route)
Pre-operational 2000
Initial operations 2001
146

Table A-6
Surveillance Inventory
Surveillance System Inputs Outputs Performance Availability
Surveillance Data Processor
(SDP)
Multi-Sensor Data Fusion
Surveillance Server System
(SSS)
Traffic Collision Avoidance
System (TCAS) - Sensor
Contract ADS (ADS-C)
(1)
ADS - Broadcast
Mode - S
STDMA
Primary Radars
Secondary Radars
Surveillance
Distribution Network
ADS A/B Systems
Aircraft States
Aircraft ID
Position States
Velocity States
Current Intent States
Primary Radars Aircraft Tracking
Secondary Radars Trajectory Prediction Services
Surveillance
Distribution Network
ADS A/B Systems
TCAS Squitters Intruder Track files:
Mode-S Address
Relative alt & alt-rate
Relative rnge & r-dot
Relative Bearing
Navigation DataBase
Air Data Parameters
FMS / RNAV Based
Aircraft States
Similar to ADS-C
ADS Reporting Svcs
Earth Ref. States
Air Ref. States
Flight Intent (2)
Meteo Reporting (2)
Earth Ref. States
Air Ref. States (3)
Flight Intent
RDP Metrics Plus Metrics for
Sensor Data Maintenance
Group Track Redundancy
Intent/ Clearance Checking
RDP Metrics Plus Metrics for
Sensor Data Maintenance
Group Track Redundancy
Intent/ Clearance Checking
TCAS Sensor Performance:
Range Coverage ~ 30+ nm
Detection Prob. > 0.9
Update Rate ~ 1 sec
Range / Alt. Accuracy ~ 25 ft
Comm Metrics as in SDN above
Surveillance Metrics Include
Report Update Rate
Maneuver Alerting
Conformance Alerting
Comm Metrics as in SDN above
ADS- Broadcast Rate
Spectrum Efficiency (4)
Range Coverage
Pre-operational 2003
STARS P3I
HOST Replacement
Initial operations 2005
Pre-operational 2006
Initial operations 2008
Current system mature
Version 7 upgrade in 1999
Pre-operational 1996
Initial operations 2000
Pre-operational 1996 (STDMA)
Initial operations 2004
147

Table A-6
Surveillance Inventory
Surveillance System Inputs Outputs Performance Availability
ADS - B Listening Stations
(5)
ADS - Broadcasts
Backup
Interrogations
Earth Ref. States
Air Ref. States (3)
Flight Intent
Mode - S Services (DAP) Similar to ADS-C Downlink via Mode-S Radars
ADS Reporting Svcs
Earth Ref. States
Air Ref. States
Flight Intent (2)
Meteo Reporting (2)
Traffic Information Services
(TIS,TIS-B)
Mode-S Radar
Tracks
Predicted Relative Position
States for CDTI / Traffic
Alerting
Notes:
(1) VHF / HF / SATCOM transmission media
(2) Outputs for strategic path predictions
(3) Air Reference States only broadcast as backup to Earth Reference States
(4) 1090 Mhz frequency shared with Mode-S radars and TCAS
(5) Proposed for Radar augmentation or system replacement
Range Coverage ~ 60 - 250 nm
Report Update Rate ~ 3 - 12 sec
Reception Prob. > 0.9
Near GPS Accuracies
Range, Detection Prob. & Update
Rate Equivalent to SSR
Message Content & Accuracies
Equivalent to Contract ADS
TIS Metrics Include:
Relative Range Coverage ~ 7 nm
Relative Altitude Cvg ~ 1200 ft
Range Resolution ~ 2 nm
Bearing Resolution ~ 6 deg
• Pre-operational 1996
(STDMA)
• Initial operations 2004
• Pre-operational 1999
• Initial operations 2003
• Pre-operational 1997
• Initial operations 1998
148

Appendix B. Global Scenario Issue Texts
The Global Scenario is based on 13 issues which were constructed to organize the
scenario writing found in section 7.1. These 13 issues emerged from a select reading from
a number of diverse government, industry, and other sources related to the future
operational configuration of the NAS. Below is a list of these 13 issues including the select
fragments of texts marked by their appropriate reference number and page. Also indicated
after each portion of text are six relevant broad scenario categories which are also
presented in section 2.3.1.. These categories are: 1) Economics/Markets (E), 2)
Organizational/Institutional/Operational (O), 3) Technological/Scientific (T), 4)
Social/Political (S), 5) Environmental (ENV), and 6) Human-centered/System-centered
(H). A brief description of each broad category follows:
Economics/Markets (E)
This category reviews the best estimates and forecasts for future air traffic growth and
demand figures including a few corresponding issues associated with increased air traffic.
Organizational/Institutional/Operational (O)
Under this category a select sample of issues such as workload, organizational structure
and culture, and operational considerations were collated.
Technological/Scientific (T)
The increasingly technoscientific NAS operational infrastructure introduces a number of
potential pitalls as well as promises. Issues related to widely utilized computer and
information technology based support and automation are captured by this category.
Social/Political (S)
In a growing global context of air traffic flows, this category aims to present some of the
potential political and social issues which may impact future operations.
Environmental (ENV)
This category focuses on possible constraints stemming from tougher future environmental
regulations.
Human-centered/System-centered (A)
The human/system related issues such as human-centered ATM design and structure are
presented under this category.
Issue # 1: Air Traffic Growth and Demand: Twenty Year Outlook
• Major projections for the twenty for the twenty-year period 1997-2016 are:
worldwide economic growth will average 3.2% per year.
traffic growth will average 4.9% per year.
149

cargo traffic will average 6.6% per year.
The world fleet will be 23,600 passenger and cargo jets in 2016.
The composition of the world fleet in 2016 will be:
69.1% single-aisle airplane.
23.5% intermediate-size airplanes.
7.4% 747-size or larger airplanes.
The total market potential for new commercial airplanes over the next twenty years is
16,160 airplanes, or an equivalent $1.1 trillion in 1996 us dollrs.
Airlines will take delivery of:
11,260 single-aisle airplanes.
3720 intermediate-size airplanes.
1180 747-size or larger airplanes. [Ref. 15, page 3] (E)
• Cooperative strategies, such as code sharing, concentrate traffic by serving the
customers of two airlines on a single airplane departure. Partners in the alliance can benefit
by accommodating the demand for frequency while enjoying the cost advantage of fewer
flights. However, cooperative strategies can also let airlines concentrate their traffic at
both ends of a city pair that would not warrant nonstop service by either airline alone. This
diverts traffic from existing pairs, increasing regional frequencies overall. Even in the same
city pair, alliances can increase competition. Large international markets where airlines
combine services are usually opened to additional competition as a prerequisite to the
alliance being permitted. Thus, traffic may actually end up divided among more
competitors or even competing alliances. [Ref. 15, page 25] (S), (E)
• Activity in the combined FAA and contract towered airports is projected to grow from
61.8 million operations in 1996 to 72.3 million in 2008, and increase of 1.3% annually.
The majority of this growth is expected to be the result of increased commercial aircraft
activity, which is forecast to increase from 24.0 million operations in 1996 to 31.5 million
in 2008, and increase of 2.3% annually. [Ref. 14, page I-14] (E)
• The workload of the air route traffic control centers is forecast to increase at an average
annual rate of 1.8% during the 12-year forecast period. in 2008, FAA en-route centers are
expected to handle 50.2 million IFR aircraft, up from 40.3 million in 1996. [Ref. 14, page
I-14] (O)
• U.S. commercial air carriers flew an estimated total of 12.3 million hours in 1996, up
from 12.0 million hours in 1995. Two aircraft categories for over three-fourths of total
airborne hours: two-engine narrowbody aircraft (65.2%) and three-engine narrowbody
(12.0%). In 2008, the number of hours is forecast to increase to 19.3 million, an average
annual increase of 3.8%. airborne hours are forecast to increase 2.8% in 1997 to 12.7
million, and 2.7% in 1998, to 13.0 million. [Ref. 14, page III-43] (E), (O)
150

Issue # 2: Some Limitations of Future Air Traffic Management and Concepts
• Capacity constraints in free flight systems will be restricted by runway operating time.
with the aircraft and runways in place today, it is conceivably possible to land or takeoff at
55 second intervals from a single runway. However, this is constrained by procedures that
at most airports, limit an arrival or departure to an interval of 90 to 120 seconds causing a
significant portion of the runway resource to be wasted. [Ref. 9, page 2-117] (O)
• For automation to be effective and satisfy minimum safety standards, it must meet the
needs of all system users. Flight crews have always benefited from HF attention, while
much less consideration has been given to HF aspects of ATC. With increased automation,
routine functions change from controlling to monitoring the systems. This alters the
demands placed on the controller. Monitoring is not the best function for most humans
because it tends to become monotonous and boring which leads to difficulties maintaining
an adequate state of alertness and awareness. [Ref. 9, page 3-18] (T), (O), (H)
• The issue of national and regional security is of fundamental concern to the design of
effective dual-use airspace and to policies and procedures that will permit the smooth and
instantaneous subjugation of airspace to the military in case of a national security threat.
satellite CNS poses some unique and challenging issues to ATC/ATM planners in this
regard. While it has been determined that surveillance is accurately performed by satellite
navigation augmented by ADS, it is not reasonable to assume that hostile aircraft will
cooperate. Some form of radar surveillance will be required and will be present in the
modernized ATC/ATM environment of the developed or developing country. During
peace time, the issue of special use airspace for training or exclusion zone purposes will
also complicate matters. [Ref. 9, page 2-134] (S), (T)
• The hundreds of billions of dollars needed for all categories of infrastructure including
ATC/ATM systems, airports, and feeder roads will compete largely in capital markets with
funds required for new aircraft. If government is a financial contributor to these
modernizations, lengthy delays can be expected, as most governments, LDCs or DCs, are
cash strapped...the most likely scenario unfolding will be the corporatization or
privatization of much of the ATC/ATM infrastructure. Government backed bond funding
can occur in a cycle tied to needs, as opposed to political agendas. [Ref. 9, page 2-29] (E)
• Internationally, several ICAO member states have been vocal in their reluctance to
accept a GPS-based satellite navigation system, primarily because GPS is U.S.-owned
system currently managed by the DOD. The international community has repeatedly
expressed concern that the United States may unilaterally decode to intentionally degrade
the current GPS-SPS accuracy or “dither” the SA signal at such a high rate so as to
preclude adequate precision guidance. This issue takes on additional significance when
member states begin to maintain transportation infrastructures that rely completely on
satellite-based navigation. From a European perspective, this apprehension has
understandably diminished a willingness to implement a GPS-based satellite navigation
system for critical safety and life operations. [Ref. 9, page 3-94-95] (S), (T)
• Although ATC is in principal an exercise in safety, it is also a means by which states can
control the sovereignty of their airspace as well as access to their economies. In recent
151

years, air transport authorities have become increasingly concerned about the interest
shown by anti-trust and competition law authorities in the regulation of international air
transport. The establishment of unified regional economic markets has also invoked
concerns about possible adverse effects on the national airlines of non-participating states.
[Ref., page 2-135] (S), (E)
Issue # 3: Changing International Relationships
• Conscious of the pressures for change, ICAO held a major worldwide air transport
conference in Montreal from November 23 to 6 December 1994...attended by more than
800 delegates from 137 ICAO contracting states and from close to 50 interested
international and national aviation organizations, the conference was the biggest and most
important international aviation meeting for 50 years...the most significant decision
emerging was on the controversial issue of multilateralism versus bilateralism. The
meeting accepted that those two concepts ‘can and do co-exist, and can each
accommodate different approaches to international air transport regulation’. But it also
affirmed that ‘in view of the disparities in economic and competitive situations there is no
prospect in the near future for a global multilateral agreement in the exchange of traffic
rights’. [Ref. 4, page 47-49] (S), (E)
• Sub-issues include:
Market Access: It was agreed that full global market access (‘open skies’) is not
feasible at this time, but the meeting supported the principle of ‘gradual,
progressive, orderly and safeguarded change’, with preferential treatment for
developing nations [Ref. 4, page 50]. (E)
Slot Allocations: Despite many criticisms, the existing voluntary airline system of
slot allocations was recognised as the only tried and tested system offering the
assurance of efficient utilisation of the limited resources available: until a better
system can be devised internationally, it seems likely to remain in operation, but
ICAO will continue to study the situation closely [Ref. 4, page 50]. (O), (E)
Airline Ownership and Control: For 50 years the industry has lived with the rule
that a country’s airlines must be owned or effectively controlled by interests based
in that country: there are pressures for this to be changed, so as to allow increased
foreign investment, but this will in turn raise questions concerning sovereignty and
international traffic rights. there was no consensus on this topic at the meeting, but
it was agreed that ICAO should study the situation, with a view of finding ways of
broadening the present criteria [Ref. 4, page 50]. (E), (S)
Taxation: With over 900 different taxes worldwide imposed on the industry, the
burden runs into many millions of dollars annually and is increasing, with the
industry now regarded by governments as a ‘cash cow’ for revenues unrelated to
152

aviation. it was agreed that ICAO’s existing policies on seeking exemption,
reduction and elimination of taxes on international air transport be continued. [Ref.
4, page 51] (S), (E)
Aero-Political Pressures: ...the multilateral/bilateral traffic rights debate,
especially where ‘fifth freedom’ is concerned...seems most likely to dominate aeropolitical
affairs...it is pointed out that where the U.S. is involved, many countries in
the region (Asia-Pacific) feel they have had an unfair deal ...described as
‘inequitable and antiquated bilaterals’, which has led to ‘damaging disputes’ with
such countries as Australia, Japan and Thailand, disrupting trade and travel.
Singapore feels that its own liberal attitude-‘Singapore’s skies are open to all U.S.
carriers’-is not fully reciprocated by the Americans....it is felt that the U.S. now
enjoys an unacceptable level of ‘fifth-freedom traffic’ which accounts for some
40% of the total air traffic in the Asia-Pacific region. [Ref. 4, page 79-80] (S),
(E)
Issue # 4: FAA Funding Reform
• Although the FAA’s budget grew significantly in the 1980’s, the years of growth in FAA
funding appear unlikely to continue...the FAA’s budget has been cut by $600 million over
the last few years. The FAA also has substantially reduced the number of employees and
eliminated many technology programs...funding for FAA is expected to continue to
decline in the foreseeable future because of spending reductions in transportation
programs proposed in the recent balanced budget resolution...because of efforts to balance
the federal budget, future funding will fall far short of what the FAA will need to provide
even the current level of services, and drastic cuts in services will need to be made if new
revenue is not found. The administration...projects an aggregate $12 billion shortfall in
FAA funding over the time period from fiscal year 1997 to fiscal year 2002. This projected
shortfall represents the difference between FAA’s stated need of $59 billion during that
period and an estimated budget cap of $47 billion...the year-to-year appropriations process
makes it difficult for the FAA to operate under a long-term capital investment plan. This
leads to reactive, near-term investment decisions by the FAA based on an artificially
imposed federal budget process, rather than on the basis of need or sound business
decisions. [Ref. 7, page 9] (O), (E)
Issue # 5: Environmental Considerations
• ...the impact of world air transport on the environment has been far less severe than
other modes of transportation in energy consumption, emissions, global warming, land
use, and noise. However, tougher standards are being proposed. IATA has argued...that
such new requirements would affect the development of new aircraft, which are currently
in their earliest conceptual stages, already appear to offer the prospect of substantial
environmental benefits in terms of fuel and emissions efficiency, but if tougher new
153

standards are introduced the expense involved could well make the development of such
aircraft impossible...IATA assessed the loss in fleet resale value as a result of introducing
any such new constraints at as much as $5bn to $10bn. [Ref. 4, page 161-162] (ENV),
(S)
• A European-sponsored committee declared that ‘eliminating aircraft congestion in the
air and on the ground is by far the most efficient way to reduce the impact of air transport
on the environment. It can and must be achieved as a matter of absolute priority.’
Moreover...the aerospace industry lobby is particularly concerned to insure that ICAO is
made well aware of the technical problems for the aerospace manufacturers which would
result from the recommendation of new (and more stringent) environmental regulations
for the aviation community. [Ref. 4, page 162] (ENV), (S), (T)
Issue # 6: Air Travel and Alternatives
• ...a corporate air travel survey by IATA’s market and economic analysis division appears
to indicate that the impact...of various forms of innovative electronic communications has
been, and may well be in the future, less severe that some reports have suggested...much
of the growth of video-conferencing over the past few years seems to have been due more
to the effects of recession, with businessmen cutting travel costs, than to any improvement
in business efficiency stemming from advanced electronic communications systems. [Ref.
4, page 85-87] (T)
Issue # 7: GPS and Satellite-based Navigation Issues
• ...while optimistic, the international aviation community continues to express trepidation
about investing preferentially in a satellite-based system that is currently controlled and
operated by U.S. DOD. Consequently, much work has been conducted by the
international community to develop and implement a GNSS, which may not include GPS.
Potential GNSS architectures may include the Russian Glonass, yet-to-be developed
private systems, or other satellite systems which may carry GNSS signals, such as those
proposed by the IRIDIUM consortium and Inmarsat. [Ref. 9, page 3-49] (S), (T)
• There are a number of GPS (and other satellite systems) navigational error sources
which are being addressed by various government, industry, and academic institutions.
These include: 1) Satellite Clock and Ephemeris errors, 2) Atmosperic related Ionosphere
and Troposphere errors, 3) Receiver Errors such as Multipath, Oscillator, Tracking Delay,
Noise, Filter Bias, 4) System Errors including Selective Availability and Geometry, and
other sources. Although alternate mitigation schemes are being proposed that minimize the
effects of these potential GPS-based navigation errors, the uncertainties associated with
system integrity and availability of satellite-based operations persist, in particular during
precision approach and landing (> Cat II, III) phases of flight. [Ref. 9, page 3-53-58] (T),
(O)
Issue # 8: ATC Systems Architecture
154

• IPT architecture efforts are limited and do not constitute an ATC-wide technical
architecture. [Ref. 5, page 40] (T)
• Heterogeneous communications protocol and data formats require expensive system
interfaces. [Ref. 5, page 45] (T)
• Myriad of application languages makes maintenance more costly and difficult (software
applications associated with 54 operational ATC systems have been written in 53
programming languages including 19 assembly languages). [Ref. 5, page 46] (T)
• Software maintenance is a significant FAA expense...the Host Computer System (HCS),
its backup - the Enhanced Direct Access Radar Channel (EDARC) and PAMRI
(Peripheral Adapter Module Replacement Item cost $63.6 million annually to maintain.
[Ref. 5, page 47] (T)
• Until a software sub-architecture is developed that is based on systematic analysis of the
needs of current and planned operating environments and defines the languages to be used
in developing ATC systems, FAA will continue to experience language proliferation...
[Ref. 5, page 47] (T)
• FAA...lacks an effective management structure for developing, maintenance, and
enforcing a technical ATC systems architecture. no organization in FAA is responsible for
technical ATC architecture...FAA has permitted a “hodge podge” of independent efforts
scattered across its ATC modernization organization to emerge with no central guidance
and coordination. [Ref. 5, page 54] (T), (O)
Issue # 9: Ground Handling
The Visa Problem: although several countries outside the EU have reached bilateral
agreements to dispense with visas, in many parts of the world they remain a vital element
of entry facilitation. there are no signs of any significant reduction in requirements in the
years ahead-if anything, in an unstable political world visa requirements will become
stricter, especially as measures to control illegal immigrants become tougher. [Ref. 4, page
148] (O), (S)
Health Requirements: ...in some parts of the world, debilitating or even potentially fatal
diseases are rife, and some which it had been thought had been eradicated, such as
smallpox, are returning. as a result, some countries are toughening their health
requirements-demanding, for example, to see certificates of vaccinations which in many
places have been ignored for years. It is thus incumbent upon every traveler to ensure that
his or her vaccinations and health documentation are in order. [Ref. 4, page 149] (S)
Inspections: ...IATA makes the point that complicated and outmoded inspections...negate
the inherent advantage of speed offered to the public by air transport...it cites one
example...where ‘ departure delays during peak hours at a major airport by excessive
inspection controls cost the airlines in excess of $100,000 per day’. [Ref. 4, page 149]
(O), (E)
155

Other ground handling problems include: ‘off-airport’ check-in, baggage handling et al. all
of these may produce delays and bottlenecks in the flow of air traffic. [Ref. 4, page 151-
155] (E), (O)
Issue # 10: Airport Capacity
• The forecast for a 57 % increase in passenger enplanements between 1993 and 2005
suggests that a major investment will be needed to expand terminals to accommodate
more passengers and larger aircraft...the increase in air carrier operations at medium hubs
will be accommodated by scheduling more flights for off-peak periods, attracting a portion
of general aviation activity to reliever airports, and developing new runways to increase
airfield capacity...a substantial increase in aircraft operations at a large hub airport may
warrant consideration of additional runways...the outlook for new runways at major
origin/destination airports is less promising...only 5 of 13 large hubs airports where more
than two-thirds of traffic is locally generated are actively considering new runways...the
engineering and political obstacles to new runway construction at these airports is
daunting...airfield congestion at major origin/destination airports ...will continue to be one
of the most difficult issues facing civil aviation [Ref. 13, page 29-30] (O), (E)
Issue # 11: Management of Special-Use Airspace
• Within the NAS, some airspace is designed for use by the DOD and other federal
agencies to carry out special research, testing, training...etc...non-participating aircraftboth
civil and military-may be restricted from flying into such areas. Although Special-Use
Airspace (SUA) serves the important safety function of segregating hazardous activity
from non-participating aircraft, civil users have voiced concerns about whether SUA is
being efficiently managed...by its location SUA can limit air traffic to and from a particular
location...SUA has become a much more urgent issue because of the aviation community’s
movement toward “free flight.” Under a “free flight” operating concept, the users of the
system would have more freedom to select preferred routes free of many of the current
restrictions as long as such routes do not interfere with safety, capacity, and SUA
airspace...a key recommendation from the task force (RTCA free flight) is the
establishment of a “real-time” system to notify commercial users of the availability of
SUA. FAA and airline officials...suggest... that at a minimum, airlines need 2 hours’ notice
to take advantage of SUA. [Ref. 10, page 25] (O)
Issue # 12: Airport Safety
• ...concerns about accelerating the entire modernization effort that focus on the
complexities of the technology and the integrity of FAA’s acquisition process....the
complexity of developing and acquiring new ATC technology-both hardware and
software-must be recognized...new ATC technology...is available “off-theshelf”...however,
FAA has found significant additional development efforts have been
needed to meet the agency’s requirements...two major contracts for systems-the Standard
156

Terminal Replacement System (STARS) and the Wide Area Augmentation System
(WAAS)-called for considerable development efforts. [Ref. 21, page 6-7] (T)
• STARS is an outgrowth of the troubled Advanced Automation System (AAS)
acquisition...the terminal segment of this system, known as Terminal Advanced
Automation System, would provide controllers in TRACONS with new workstations and
supporting computer systems. However, in June 1994, the FAA Administrator ordered a
major restructuring of the acquisition to solve long-standing schedule and cost problems.
These schedule delays were up to 8 years behind the original schedule, and estimated costs
had increased to $7.6 billion from the original $2.5 billion...FAA’s schedule for STARS
can be jeopardized by scheduling conflicts with other modernization efforts...in September
1996, the IPT identified 12 potential scheduling conflicts at the first 45 STARS
sites...another scheduling conflict involves terminal surveillance radars...many existing
surveillance radars are not digital, but STARS requires digital processing and
communications....there are also potential difficulties in developing STARS
software...[Ref. 20, page 3-4] (E), (O)
Issue # 13: FAA Organizational Culture and Workforce
FAA’s Organizational Culture
• FAA’s organizational culture has been an underlying cause of the persistent cost
overruns, schedule delays, and performance shortfalls in the agency’s acquisition of major
ATC systems. Weaknesses in ATC acquisitions stem from recurring shortcomings in the
agency’s mission focus, accountability, internal coordination, and adaptability. [Ref. 12,
page 22] (O)
• FAA officials rushed into production of ATC systems....cost, schedule, and performance
problems have resulted from excessive concurrency-beginning system production before
completing development, testing, or evaluation of programs. FAA has proceeded with
producing numerous systems, including Microwave Landing System (MLS), Mode S
radar, and Oceanic Display and Planning System (ODAPS), before critical performance
requirements had been met...[Ref. 12, page 24] (O)
• ...FAA concluded that because accountability for contract administration was not welldefined
or enforced, program officials were not encouraged to exercise strong oversight of
contractors...poor oversight...has caused acquisition problems in such projects as ODAPS,
Mode S, and AAS...the delivery of the first system (MODE S)...had been delayed by 5
years. [Ref. 12, page 28-29] (O)
• ...an environment of control...has been... fostered by the agency’s hierarchical
structure...employees are not empowered to make needed management decisions. This
lack of empowerment decreases their sense of ownership and responsibility, which...makes
them more reluctant to be held accountable for their decisions and actions....fewer than
half reported that they had enough authority to make day-to-day decisions about day-today
problems. [Ref. 12, page 29-30] (O), (H)
157

• Poor coordination between FAA’s program offices and filed organizations has caused
schedule delays. Although coordination between program offices and filed organizations is
necessary to ensure that sites suitable for installing ATC systems are acquired and
prepared, installations of the Terminal Doppler Weather Radar (TDWR), the Airport
Surveillance Radar (ASR-9), and the Airport Surface Detection Equipment (ASDE-3)
have all been delayed because of problems with putting these systems in the field....the
implementation of the final 10 ASR-9 radars was being delayed because planned sites were
not ready...similarly...FAA had to postpone TDWR’s implementation at 11 locations
because of the unavailability of sites and land acquisition problems. [Ref. 12, page 31]
(O), (T)
• A major limiting coordination among stakeholders in FAA’s acquisition of major
systems has been its organizational structure...OTA (Office of Technology Assessment)
noted (1994) that differences in the organizational culture among FAA’s air traffic
controllers, equipment technicians, engineers, and divisional managers made
communication difficult and limited coordination...[Ref. 12, page 32-33] (O)
FAA Workforce
• FAA has identified a sufficient number of controller candidates to meet its short-term
staffing needs in fiscal years 1997 and 1998. However, beyond fiscal year 1998, it is
uncertain whether current sources can provide the controller candidates FAA will need to
meet its hiring goals for fiscal years 1999 through 2002. The majority of available
candidates are controllers who were fired in 1981 and who FAA officials believe could be
eligible to retire within a few years of reemployment...[Ref. 11, page 3] (O), (S), (H)
• FAA officials identified several principal impediments that hinder their ability to staff
ATC facilities at specified levels. The first is FAA headquarters’ practice of generally not
providing funds to relocate controllers until the end of the fiscal year, which causes
delayed controller moves and continued staffing imbalances. The second impediment is the
limited ability of regional officials to recruit controller candidates locally to fill vacancies at
ATC facilities. In addition, FAA regional officials also believe that limited hiring of new
controllers in recent years has hindered their ability to fill vacancies. Partly due to these
impediments, as of April 1996 about 53% of ATC facilities were not staffed at levels
specified by FAA’s staffing standards...[Ref. 11, pages 3-4] (O), (S)
Selected References
1) Air Transport and The Environment, IATA, http://www.atag.org/atenvv/atenv.htm
2) The Economic Benefits of Air Transport, IATA,
http://www.atag.org/ecobat/ecobat.htm
3) Outlook for Air Transport to the Year 2003, ICAO Circular 252-AT/103, 1995
4) The Future of International Air Passenger Transport: Ito an Era of Dynamic Change,
Financial Times Management Report, Michael Donnel, 1995
158

5) Air Traffic Control: Complete and Enforced Architecture Needed for FAA Systems
Modernization, GAO/AIMD-97-30, February 1997
6) Proposal to Corporatize The Nation’s Air Traffic Control System, S. Hrg. 103-1016,
1995
7) Air Traffic Management System Performance Improvement Act of 1996, Report 104-
251, April 10, 1996
8) Air Traffic Control: Improved Cost Information Needed to Make Billion Dollar
Modernization Investment Decisions, GAO/AIMD-97-20, January 1997
9) Air Traffic Control and Air Traffic Management Systems: An Analysis of Policies,
Technologies, and Global Markets, Volume I, Booz . Allen & Hamilton, 1995
10) National Airspace System: Issues in Allocating Costs for Air Traffic Services to DOD
and Other Users, GAO/RCED-97-106, April 1997
11) Aviation Safety: Opportunities Exist for FAA to Refine the Controller Staffing
Process, GAO/RCED-97-84, April 1997
12) Aviation Acquisition: A Comprehensive Strategy Is Needed for Cultural Change at
FAA, GAO/RCED-96-159, August 1996
13) National Plan of Integrated Airport Systems (NPIAS) 1993-1997, FAA, April 1995
14) FAA Aviation Forecasts: Fiscal Years 1997-2008, FAA-APO-97-1, March 1997
15) 1997 Current Market Outlook, Boeing Airplane Marketing Group, March 1997
16) World Economic Outlook: 20 Year Extension, WEFA Group, 1997
17) EATMS Operational Concept Document (OCD), FCO.ET1.ST07.DEL01, January
1997
18) Meeting Europe’s Air Traffic Needs: The Role of Eatchip and Eurocontrol,
Eurocontrol 1996
19) In Search of the Future of Air traffic Control, IEEE Spectrum, August 1997
20) Air Traffic Control: Status of FAA’s Standard Terminal Automation Replacement
System Project, GAO/RCED-97-51, March 1997
21) Aviation Safety and Security: Challenges to Implementing the Recommendations of
the White House Commission on Aviation Safety and Security, GAO/T-RCED-97-90,
March 1997
22) Air Traffic Control: Better Guidance Needed for Deciding Where to Locate Facilities
and Equipment GAO/RCED-95-14, December 1994
23) Report on the Implementation of the Air Traffic Service Plan, MP 96W0000184, The
MITRE Corporation, August 1996
24) Status Report: Global Navigation Satellite System (GNSS) Augmentation Audit and
Cost Benefit Analysis, April 1997
159

25) Aviation Automation: The Search for a Human Centered Approach, Charles E.
Billings, LEA, 1997
160

Appendix C. Comparison of FAA 2005 and RTCA Users 2005 Operational
Concepts
The following matrix is an analysis of the main features of the two concept documents:
• An Evolutionary Operational Concept for Users of the National Airspace System
DRAFT v3.0 June23, 1997 prepared by the RTCA Select Committee on Free Flight.
• A Concept of Operations for the National Airspace System in 2005. Revision 1.3
June27, 1997. FAA.
The objective of the matrix is to focus on the attributes of the ATM System as described
for the year 2005 in those two documents. The matrix is a comparison of the two
different approaches to describing the functionality within the system. It identifies
similarities, differences, and gaps in the two descriptions.
An attempt was made to integrate this work with the European concept as produced by
Eurocontrol; European Air Traffic Management System Operational Concept Document
Issue 1.0 1 March 1997. This document is targeted at the year 2015 and is focused on the
process for identifying a Concept rather than on determining the functionality of the
system as it could exist. The comparison with the two previous documents was thus
abandoned due to this fundamental difference in the structure of the documents.
The two documents that are compared within this matrix have subsequently been revised.
This matrix is thus a statement of the situation as it existed in July 1997.
161

Flight
Planning
Overview
Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
FAA 2005 User 2005
NAS Wide Information system (interactive).
More accurate (real-time) data for traffic forecasting. More data
available for Users - helps flight planning.
Integrated information system.
Flight Object replaces flight plan.
NAS-Wide Information System and Interactive Flight Planning System give
Users access to real-time sharing of info. regarding NAS and system demand
Enhanced data set supports 4-D planning and certain preferences i.e. runway
Gaps
Differences
Key Aspects
VFR use ELT
Collaborative use of data improves traffic planning.
User provided daily schedule as baseline for planning traffic loading.
Automatic flight plan checking for constraints.
Additional information can be added to the plan during flight
Military can access info. on aircraft entering ADIZ Air Defense
Identification Zone.
Doesn’t cover benefits of changes other than providing User Preferred
routings.
Doesn’t offer any additional capacity.
Doesn’t refer to Flow Management.
More data, more accurate, updated in real-time, more accessible.
Cooperative decision making for traffic planning.
Refers to ability to update, when airborne, certain fields. This means
User accessible flight plan even when airborne.
VFR flights equipped with ELT (Emergency Locator Beacon).
Collaborative use of data improves traffic planning.
All Users have access to same information source.
Additional information can be added to the plan during flight
Refers to ability to update, when airborne, certain fields. This means User
accessible flight plan even when airborne.
162

Surface
Movement
Automation
requirements
Communication
requirements
Information
requirements
Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
FAA 2005 User 2005
Automation to identify vehicles on airport movement area
Automation to predict movement of all vehicles on airport movement area
Automation to provide conflict advisories on airport movement area
Automation to plan aircraft's movement from de-icing to takeoff without
stopping
Decision support systems to monitor and plan flow of surface traffic and Tower decision support system provided for DOD enabling exchange of
accommodate user preferences for runway and gate assignment taking information about environmental and operating conditions to coordinate local
into account current and projected congestion, runway loading, and air base operations.
environmental considerations
Dynamic planning of surface movement that includes balancing taxiway
demand and improves sequencing of aircraft to departure queue
Radio communications available
More users equipped for data link at more airports
Increased information sharing between users and service providers
Increased CDM between users and service providers
Improved information to the NAS-wide information system
More users equipped for data link at more airports
More data link messages for GA including clearance delivery, taxi instructions,
basic meteorological information, current weather maps
NAS-wide information system provides status of active and proposed flights
and NAS infrastructure
Increased automation of weather information (terminal weather radar,
automated weather observation systems, integrated terminal weather
systems that detect and predict hazardous weather, improved surface
detection equipment)
Continuous updating of aircraft flight for real-time planning
Real-time updates of taxi times
NAS-wide information system provides timely update of flight plan information
Tracking of all vehicles entering active movement areas
Service provider acquires all NOTAMS and meteorological information Airport information and weather provided over data link to more users at more
airports
163

Surface
Movement
Information
requirements
Separation
Assurance
Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
FAA 2005 User 2005
More data link messages for GA including clearance delivery, taxi instructions,
basic meteorological information, current weather maps
Automated ATIS message recorded for transmission over synthetic voice Automated ATIS message recorded for transmission over synthetic voice or
or digital data link
digital data link for DOD
Weather advisories automatically transmitted over synthetic voice or Weather conditions provided over data link to more users at more airports
digital data link
Taxi schedules automatically incorporate departure clearances, aircraft Taxi routes data linked to the cockpit. Aircraft receive positions of other aircraft
location, and aircraft type
on the airport surface.
Taxi clearances and instructions data linked to cockpit for DOD
Departure clearances that incorporate enhanced flight plan information
including pilot requested ascent and descent profiles and cruise speed and
altitude provided over data link
More data link messages for GA including clearance delivery, taxi instructions,
basic meteorological information, current weather maps
Surface movement information system provides environmental and
operational conditions and sends updates to NAS wide information
system; this information used for ATIS message
Surface movement information system and NAS-wide information system Aircraft coordinate with ATC regarding pushback and departure times.
interface with surface and airborne surveillance information, flight Pushback clearances include specific aircraft location, aircraft type, and
information, weather, and traffic management system
sequencing number.
Separation assurance by service provider through visual cues including Satellite-based surveillance broadcasts provide enhanced situation display of
enhanced situation displays and surface detection equipment that receive surrounding surface traffic to the pilot
and display the aircraft's broadcast of satellite navigation derived position
data
Pilots continue to rely on visual cues for separation assurance; some aircraft
equipped with moving map display in cockpit; some aircraft equipped with
conflict detection logic with moving map display
Cockpit display of position information from other aircraft.
ATC monitors aircraft movement and possible conflicts
164

Surface
Movement
Efficiency
Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
FAA 2005 User 2005
Ramp service providers sequence and meter aircraft movement at gates Ramp service providers sequence and meter aircraft movement at gates and
and ramp areas using situation displays that interface with decision ramp areas using situation displays that interface with decision support systems
support systems and control tower personnel
and control tower personnel
Service provider coordinates with airline ramp and airport operators to
efficiently sequence aircraft on the airport surface
Traffic flow service provider establishes initial taxi times based on
weather and airport configuration and adjust parameters as needed
Tower automation uses timely aircraft information from NAS-wide information
system to establish a realistic set of schedules for departures, arrivals, and
surface traffic
Traffic flow service provider coordinates with arrival/departure traffic
flow service provider
Reduced taxi occupancy times achieved through decision support systems Reduced taxi occupancy times achieved through decision su pport systems
Surveillance
Satellite-based surveillance broadcasts
Gaps
Doesn’t detail how runway occupancy could be increased.
Doesn’t detail how airfield capacity might be increased.
Doesn’t detail how runway occupancy could be increased.
Doesn’t detail how airfield capacity might be increased.
Differences Concentrates on ground systems Concentrates on air side
Key Aspects A lot of references to automation.
Concentrates on efficiency.
165

Arrivals/
Departures
Overview
Separation
assurance
Data processing
Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
FAA 2005 User 2005
Decision support systems assist service provider to assign runways and
merge/sequence traffic, based on accurate traffic projections and user
preferences.
Tools such as FMS, datalink, and satellite navigation allow route
flexibility by reducing voice communications and increasing
navigational precision.
Avionics fits allow an increasingly frequent transfer of responsibility
for separation assurance to the flight deck for some types of operations.
Pre-defined data link messages, such as altitude clearances and
frequency changes, are uplinked to an increasing number of equipped
aircraft. Voice communications between service providers and pilots
are thereby reduced, giving the service provider additional time for
planning functions that help accommodate increased traffic demand.
Enhanced ground-to-ground communications systems (both digital and
voice) that allow seamless coordination within and between facilities.
Disruption in departure and arrival traffic is minimized by improved
weather data and displays. These displays enhance safety and efficiency
by disclosing weather severity and location
Decision support systems help service providers to maintain situation
awareness, identify and resolve conflicts, and sequence and space
arrival traffic.
Separation assurance changes in the following areas: aircraft-to-aircraft
separation, aircraft-to-airspace and aircraft-to-terrain/obstruction
separation, and departure and arrival planning services
Aircraft-to-aircraft separation remains the responsibility of service
providers
All-weather pilot-pilot separation when deemed appropriate
Expanded data acquisition results from inputs by the flight deck, airline
operations center, service provider, and interfacing NAS systems
Accurate information on SUA status and planned usage is disseminated
automatically to the NAS-wide information system. Eliminating
numerous coordination calls normally required between facilities
Increased pilot situational awareness (ADS/CDTI)better weather and
navigation increases safety and efficiency of approaches/departures and leads
to better runway utilistation.
RNAV capabilities support user preferred arrival/departure routed,
climb/decent profiler, runway assignment.
CFIT more readily avoided using GPS nav and improved terrain database.
Reduced visual minima using specific points to allow easy visual acquisition
of traffic.
ABS-B/CDTI enable visual approaches where momentary loss of visual target
acquisition occurs.
ATIS info available via datalink.
Dat aavailable on surrounding traffic and w/x displayed on CDTI
166

Arrivals/
Departures
Automation/
decision support
Traffic Flow
Service
Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
FAA 2005 User 2005
Conflict detection and resolution functions consider arrival and
departure traffic throughout terminal airspace, separation at the
intersection of converging runways, separation between parallel
runways, and separation from ground vehicular traffic on the runways.
Tower, arrival/departure, and en route service providers have access to
identical tools and information regardless of facility
In the final portion of the arrival phase, decision support systems
facilitate the use of time-based metering to maximize airspace and
airport capacity.
Focus on establishing the parameters to be used by the support tools,
and the tools develop the plan.
service providers collaborate with users to resolve congestion problems
through adjustment of user schedules.
If scheduling inadequate, service providers work with the national
traffic management function to solicit user input concerning flow
constraints.
DoD
Equip with MMR’s. TCAS.
Gaps
Doesn’t refer to where increased capacity is coming from.
Differences Not much emphasis on RNAV capabilities or FMS approaches. Little emphasis on ground system.
Key Aspects Automation features highly.
No real assessment of where increased capacity will come from in a
critical part of the airspace.
Ground tools enhance final approach spacing - communication direct to pilot
who executes more flexible procedures.
167

Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
En-Route FAA 2005 User 2005
Overview
En route airspace structures and boundary restrictions are unconstrained
by communications and computer systems, and aircraft are no longer
required to fly directly between navaids along routes
Accommodation of User preferences for trajectories, schedule and flight
sequence - based on decision support tools for Conflict detection,
resolution and flow management.
Flexible airspace structure (Probably daily! Potentially several times
per day) adjustment of structure to meet predicted flows.
Route structure the exception not the rule.
Surveillance includes aircraft broadcast GNSS positions.
Automated inter/intra facility coordination and communications.
NAS Wide info. system continually updated.
Routine pilot - controller comms. via datalink.
Potential for separation minima to be reduced - dependent on aircraft
equipage.
Better w/x predictions available to all users (based on real-time
reporting).
Greater accommodation of user requests, including carrier preferences
on the sequencing of their arrival aircraft.
Facility boundaries are adjusted to accommodate dynamic changes in
airspace structure.
Accommodation of User preferences for trajectories, schedule and flight
sequence - based on decision support tools for Conflict detection, resolution
and flow management.
Flexible airspace structure (Probably daily! Potentially several times per day)
adjustment of structure to meet predicted flows.
Route structure the exception not the rule.
Surveillance includes aircraft broadcast GNSS positions.
Automated inter/intra facility coordination and communications.
NAS Wide info. system continually updated.
Routine pilot - controller comms. via datalink.
Better w/x predictions available to all users (based on real-time reporting).
Moving map displays - reduces CFIT.
Cross-border flight plan transfer (Mexico/Canada).
A/c not equipped for all services will retain current level of service.
Routes and procedures allow direct VFR flights through busy terminal areas
Datalinking of NAS status data in-flight where required
GNSS position used for surveillance drives enhanced conflict probing.
168

Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
En-Route FAA 2005 User 2005
Separation
assurance
Traffic Flow
Management
Gaps
Responsibility still with Service Provider.
Changes to separation assurance function a result of increased decision
support (conflict detection and resolution)..
Availability of flight data for all flights. Improvements in separating
controlled and uncontrolled flights and in VFR flight following service.
Separation from SUA - activity info. availability allows more efficient
planning of trajectories
New role - Coordination of the dynamic changes to airspace structure.
Better real-time information (airborne times) gives improved
capabilities for strategic management.
NAS info. available to all Users .
Problem solving to change structure/flows a collaborative process
involving Users.
Use Conflict Detection tools of en-route control but with longer time
horizon.
Doesn’t cover benefits.
Doesn’t talk of where capacity will come from. Doesn’t refer to
separation assurance being transferred to pilot.
Responsibility still with Service Provider.
Reduced horizontal separation standards - in form of time-based separation. -
provides more capacity.
CDTI for more GA a/c enhances safety.
Use of ground system enhanced conflict probe and alerting.
Doesn’t cover much of the Ground System.
Doesn’t refer to pilot taking over separation assurance role - even in specific
circumstances
Differences Covers Traffic Flow Management Doesn’t refer to Traffic Flow Management.
Covers international aspects of flight plan transfer.
Refers to VFR access to busy terminal airspace.
Key Aspects
Carrier preferences on the sequencing of their arrival aircraft
Flexible airspace structure. Route structure only for high density
periods. Facility boundaries are adjusted to accommodate dynamic
changes in airspace structure.
Automated inter/intra facility coordination and communication
functions.
Doesn’t refer to Free Flight. Doesn’t talk of separation assurance being vested
with pilot.
Refers to Ground Based Conflict Probe thus assumes separation assurance
remains with Service provider.
Covers international aspects of flight plan transfer
169

Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
Oceanic FAA 2005 User 2005
Airspace structure
Capacity increase
Conflict detection
and resolution
Separation
assurance
Trajectories flown instead of tracks facilitated by full surveillance,
better navigation tools, real time communications and automated data
exchange between pilot and controller via data link.
Reduced separation and dynamic management of route structures help
user formulate and request preferred flight profile.
Structure changes dynamically based on weather, demand and user
preferences.
If demand exceeds capacity, changes to airspace structure and
trajectories made dynamically.
Procedural changes in separation through improved infrastructure.
Oceanic separation minima massively reduced allowing corresponding
increase in traffic demand.
Real time position data and continuously updated trajectory projections
virtually eliminate manual control procedures in Oceanic airspace.
Improvements in navigation, communication and the use of surveillance
are paramount enablers of reduced separation.
Service providers strategic in providing these functions plus solutions
to traffic congestion and demand for user-defined trajectories using new
tools and procedures.
Service providers have same decision support tools available as en
route controllers
Separation standards and procedures are derived from radar control
techniques.
Service providers use tools to prevent aircraft entering restricted
airspace.
Aircraft crossing Air Defense boundaries reported to the military.
Decision support systems and traffic display similar to en route.
Separation standards may differ.
Environment creates opportunity for transfer of responsibility to the
pilot for specific operations.
CDTI creates pilot situational awareness of nearby traffic. Utilizes
aircraft broadcast of satellite-based position
Trajectories flown instead of tracks facilitated by full surveillance, better
navigation tools, real time communications and automated data exchange
between pilot and controller via data link.
User-preferred routes replace the oceanic track system.
Structure changes dynamically based on weather, demand and user
preferences.
Procedural changes in separation through improved infrastructure.
Vertical, longitudinal and lateral reductions in separation.
More precise monitoring of separation and conformance through surveillance.
Improvements in navigation, communication and the use of surveillance are
paramount enablers of reduced separation.
Service providers strategic in providing these functions plus solutions to
traffic congestion and demand for user-defined trajectories using new tools
and procedures.
Higher degree of cockpit responsibility necessitates appropriate support aids.
Decision support systems and traffic display similar to en route.
Higher degree of cockpit responsibility necessitates appropriate support aids.
Cockpit self-separation provides immediate situation assessment,
communications (i.e. air-to-air) and greatly reduced separation standards.
170

Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
Oceanic FAA 2005 User 2005
Separation
assurance
Communications
Surveillance
Interoperability
Pilots coordinate specific maneuvers with service provider using CDTI
to supplement ATC big picture.
ATC conflict probe supplements pilot support of climb, descent,
crossing and merging traffic.
Separation standards and procedures are derived from radar control
techniques.
Aircraft navigation using global satellite navigation system....improved
accuracy generates required safety for reduced separation standards.
SATCOM and electronic messaging allow more interactive and
dynamic environment, supporting cooperative activities among flight
crews, AOCs and service providers.
Rapid delivery of clearances by the service providers, and responses by
the flight deck, are achieved through increasingly common use of data
link.
Data link and expanded radio coverage provide direct air-to-ground
communications (both digital and voice).
Satellite navigation systems, and data link allow more accurate and
frequent traffic position updates.
Service providers use visual displays to monitor traffic situation in
oceanic airspace.
Harmonized NAS/ICAO oceanic system where data presented to service
provider in same/similar form.
Route and airspace flexibility is achieved as Oceanic airspace is
integrated into the global grid of named locations. This flexibility is
maximized through seamless coordination within and between
facilities.
Coordination/data exchange between sectors automated to increase
efficiency and productivity of service providers.
NAS oceanic service providers coordinate with their oceanic neighbors
to agree on a common set of rules and operational procedures for a
harmonized oceanic system.
Pilots coordinate specific maneuvers with service provider using CDTI to
supplement ATC big picture.
Improved inter- and intra-communication among air traffic service providers
and NAS users.
Harmonized NAS/ICAO oceanic system where data presented to service
provider in same/similar form.
171

Table C-1
Comparison of FAA 2005 and Users’ 2005 Operational Concepts
Oceanic FAA 2005 User 2005
Interoperability Differences between separation standards, data processing protocols
and other issues worked toward harmonized conclusion.
Dynamic changes in airspace structure and trajectories coordinated via
electronic data transfer nationally and internationally.
Daily airspace structure, alternatives to potential capacity problems and
management of traffic over fixes and through gateways coordinated
through international collaboration.
Flight planning Domestic and oceanic flight planning procedures identical.
Flight planning into non-US airspace evolves in concert with ICAO
procedures.
Overview Greatly reduced separation. Trajectories flown instead of tracks.
Dynamic changes in airspace structure.
Dynamic changes in trajectories.
Real time position data and communications create en-route-like Pilot gains responsibility for separation in some circumstances using CDTI.
environment. Same support tools provided.
Overview
Inter-sector, civil/military and international coordination via electronic Cooperation among service providers and users.
data exchange.
Conflict probe.
International harmonization.
Increasing use of data link.
Gaps
No reference to long-range communications other than satellite-based.
Differences
No recognition of dynamic re-routing.
No reference to flight planning.
No recognition of separation reduction in three dimensions.
Key Aspects International harmonization and coordination. Availability of ADS-B
Real-time surveillance and communication.
CDTI.
Reduced separation.
172

Appendix D. Transition Database
This appendix presents a database that captures the relationships between the operational
enhancement steps and the enablers in Figures 6.4-9.
The first column in the tables, Enabler Grouping Number, presents the number assigned to
the enabler grouping. All of the enablers start with a “NAS” for this operatonal concept
and are assigned a number as follows:
1.0 - Navigation
2.0 - Surveillance
3.0 - Airspace
4.0 - Communication
5.0 - ATM tools
6.0 - Weather
7.0 - Airport Enhancements
8.0 - Not modeled
9.0 - Enhanced Flow Management
The second column presents the name of the specific enabler and the third column,
presents the name of the enabler grouping. The fourth column, Capacity Benefit
Mechanism, presents the capacity benefit to be gained from the operational enhancement.
The fifth column, Reference Figure Number, provides the figure number in Section 6 in
which this enhancement appears. The sixth column, Capacity Operational Enhancement,
provides the operational enhancement to be gained from that specific enabler.
The ninth column, Source, provides the name of the document from which the enabler is
presented. In this table, the document used is the ATM Concept Baseline Report. Other
databases have been developed by the C/AFT for Free Flight, EATCHIP and IATA plans,
as discussed in Section 6.
173

Enabler
Grouping
Number
NAS7.0
NAS7.0
Enabler
Airport
Improvement
Program (AIP)
increase airport
capacity
Airport
Improvement
Program (AIP)
increase airport
capacity
Enabler
Grouping
Airport
Enhancements
Airport
Enhancements
NAS7.1 Lights Airport
Enhancements
NAS3.0
NAS3.0
NAS3.1
NAS3.1
Airspace
Criteria
Close Routes
Criteria
Airspace
Design
Airspace
Design
Airspace
Management
(ASM)
Airspace
Management
(ASM)
Airspace
Management
(ASM)
Airspace
Management
(ASM)
NAS3.2 Procedures Airspace
Management
(ASM)
Capacity
Benefit
Mechanism
Improved Final
Approach /
Initial
Departure
Throughput
Surface
Improved
Throughput
Surface
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Final App/Init
Departure
Improved
Throughput
NAS5.0 Guidance Path ATM Tools Enroute and
TMA
Improved
Throughput
Ref. Figure
Number
Table D-1
Transition Database
Capacity
Operational
Enhancement
6.8 Additional
Available
Runways
6.9 Good Visibility -
Additional
Gates, Taxiways
and Aprons
6.9 Low Visibility -
Improved
Surface
Guidance and
Control
6.6 Reduced Lateral
Spacings Along
Fixed Airways
6.7 Reduced Lateral
Spacings: More
Arr & Dep.
Transitions
6.6 Reduced Lateral
Spacings Along
Fixed Airways
6.7 Reduced Lateral
Spacings: More
Arr & Dep.
Transitions
6.8 Additional
available
runways
6.6 Reduced
Intervention Rate
Buffer
Associated
Initiatives
Target Date Source Cost Benefit
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
174

Enabler
Grouping
Number
NAS5.1
NAS5.1
NAS5.1
Enabler
TFM
Sequencing
Spacing Tool
TFM
Sequencing
Spacing Tool
TFM
Sequencing
Spacing Tool
Enabler
Grouping
ATM Tools
ATM Tools
ATM Tools
Capacity
Benefit
Mechanism
Arrival and
Departure
Transitions
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Planning
Improved
Throughput
NAS5.10 ROT ATM Tools Improved Final
Approach /
Initial
Departure
Throughput
NAS5.11
NAS5.12
NAS5.13
NAS5.14
NAS5.15
Rollout/Turnof
f Guidance
Ground
Conformance
Monitor
Aviation
Vortex Spacing
System
(AVOSS)
Surface Traffic
Automation
Dynamic
Density
ATM Tools
ATM Tools
ATM Tools
ATM Tools
ATM Tools
Improved Final
Approach /
Initial
Departure
Throughput
Enroute and
TMA
Improved
Throughput
Improved Final
Approach /
Initial
Departure
Throughput
Surface
Improved
Throughput
Planning
Improved
Throughput
Ref. Figure
Number
Table D-1
Transition Database
Capacity
Operational
Enhancement
6.7 Reduced
Separation
Buffer (Ground
Vectoring)
6.6 Reduced
Intervention Rate
Buffer
6.5 Local/Airport
Level Enhanced
Arrival Planning
6.8 IMC - Further
Reduction in
longitudinal
separation to
1000 feet
6.8 IMC - Further
Reduction in
longitudinal
separation to
1000 feet
6.6 Reduced
Intervention
Buffer
6.8 Reduction in
longitudinal
separation
6.9 Good Visibility -
Improved
Surface
Sequencing,
Scheduling, and
Routing
6.5 Coordinated
TFM System
Associated
Initiatives
Target Date Source Cost Benefit
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
175

Enabler
Grouping
Number
NAS5.16
NAS5.2
NAS5.3
NAS5.3
NAS5.4
NAS5.4
NAS5.5
Enabler
Air Traffic
Management
System
Aircraft
Performance
Models
CDTI Monitor
and Backup
CDTI Monitor
and Backup
Short Term
Conflict Alert
Short Term
Conflict Alert
Final Approach
Spacing Tool
Enabler
Grouping
ATM Tools
ATM Tools
ATM Tools
ATM Tools
ATM Tools
ATM Tools
ATM Tools
Capacity
Benefit
Mechanism
Planning
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
NAS5.6 PRM ATM Tools Improved Final
Approach /
Initial
Departure
Throughput
NAS5.7 CRDA ATM Tools Improved Final
Approach /
Initial
Departure
Throughput
Ref. Figure
Number
Table D-1
Transition Database
Capacity
Operational
Enhancement
6.5 Coordinated
TFM System
6.6 Reduced
Intervention Rate
Buffer
6.6 Reduced
Intervention
Buffer
6.7 Reduced Vertical
Separation
Standard
6.6 Reduced
Intervention
Buffer
6.7 Reduced
Separation
Buffer (Ground
Vectoring)
6.7 Reduced
Separation
Buffer (Ground
Vectoring)
6.8 IMC - Increased
Runway
Utilization (with
today's
technology)
6.8 IMC - Increased
Runway
Utilization (with
today's
technology)
Associated
Initiatives
Target Date Source Cost Benefit
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
176

Enabler
Grouping
Number
Enabler
Enabler
Grouping
Capacity
Benefit
Mechanism
NAS5.8 Wake Vortex ATM Tools Improved Final
Approach /
Initial
Departure
Throughput
NAS5.9 Monitor (to
support
increased
reduction in
lateral
separation)
ATM Tools
NAS4.0 Datalink Communication
Enhancement
NAS4.0 Datalink Communication
Enhancement
NAS4.0 Datalink Communication
Enhancement
NAS4.1 A/G Datalink Communication
Enhancement
NAS9.0
NAS9.0
NAS9.0
Enhanced Flow
Management
Enhanced Flow
Management
Enhanced Flow
Management
Enhanced Flow
Management
Enhanced Flow
Management
Enhanced Flow
Management
Improved Final
Approach /
Initial
Departure
Throughput
Enroute and
TMA
Improved
Throughput
Surface
Improved
Throughput
Planning
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Surface
Improved
Throughput
Planning
Improved
Throughput
Planning
Improved
Throughput
Ref. Figure
Number
Table D-1
Transition Database
Capacity
Operational
Enhancement
6.8 IMC - Reduction
in lateral
separation to
2500 feet
6.8 IMC - Increased
reduction in
lateral separation
to 1000 feet
6.6 Reduced
Intervention Rate
Buffer
6.9 Good Visibility -
Improved
Surface
Sequencing,
Scheduling and
Routing
6.5 Local/Airport
Level Enhanced
Arrival Planning
6.7 Reduced
Separation
Buffer (A/C
guidance)
6.9 Good Visibility -
Reduce Schedule
Uncertainty
6.5 National Level
Colloborative
Traffic
Management
6.5 Local/Airport
Level Integrated
Airport Flow
Planning
Associated
Initiatives
Target Date Source Cost Benefit
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
177

Table D-1
Enabler
Grouping
Number
NAS9.1
NAS1.0
Enabler
Real Time
Information
Exchange
RNP 1 - RNP
0.3
Enabler
Grouping
Enhanced Flow
Management
Navigation
Enhancement
NAS1.1 RVSM Navigation
Enhancement
NAS1.2 RNP 0.2 Navigation
Enhancement
NAS1.3 RTA Navigation
Enhancement
NAS1.3 RTA Navigation
Enhancement
NAS1.4 RNP 0.1 Navigation
Enhancement
NAS1.5 Wake Vortex Navigation
Enhancement
NAS1.5 Wake Vortex Navigation
Enhancement
Capacity
Benefit
Mechanism
Planning
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Surface
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Improved Final
Approach /
Initial
Departure
Throughput
Improved Final
Approach /
Initial
Departure
Throughput
Ref. Figure
Number
Transition Database
Capacity
Operational
Enhancement
6.5 National Level
Improved TFM
6.6 Reduced Lateral
Spacings Along
Fixed Airways
6.6 Reduced Vertical
Separation
Standard
6.6 Reduced Vertical
Separation
Standard
6.7 Reduced
Separation
Buffer (A/C
Guidance)
6.9 Good Visibility -
Improved
Surface
Sequencing,
Scheduling, and
Routing
6.7 Reduced Vertical
Separation
Standard
6.8 Reduction in
lateral separation
6.8 Reduction in
longitudinal
separation
Associated
Initiatives
Target Date Source Cost Benefit
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
178

Table D-1
Enabler
Grouping
Number
Enabler
Enabler
Grouping
NAS1.6 DGPS Navigation
Enhancement
NAS1.7 Glideslopes Navigation
Enhancement
NAS1.8 HUD Navigation
Enhancement
NAS1.9 Map Display Navigation
Enhancement
NAS8.0
NAS2.0
Reduce
Turnaround
Time
RMP 1 - RMP
0.3
Not Modelled
Surveillance
Enhancement
NAS2.1 Radar Tracker Surveillance
Enhancement
NAS2.1 Radar Tracker Surveillance
Enhancement
NAS2.2 ADS-B (A/A) Surveillance
Enhancement
Capacity
Benefit
Mechanism
Improved Final
Approach /
Initial
Departure
Throughput
Improved Final
Approach /
Initial
Departure
Throughput
Surface
Improved
Throughput
Surface
Improved
Throughput
Surface
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Ref. Figure
Number
Transition Database
Capacity
Operational
Enhancement
6.8 Additional
Available
Runways
6.8 Additional
Available
Runways
6.9 Low Visibility -
Visual
throughput in
CAT IIIb
6.9 Low Visibility -
Visual
throughput in
CAT IIIb
6.9 Good Visibility -
Reduce Schedule
Uncertainty
6.6 Reduced Lateral
Spacings Along
Fixed Airways
6.6 Reduced
Intervention Rate
Buffer
6.7 Reduced
Separation
Buffer (Ground
Vectoring)
6.6 Reduced
Intervention Rate
Buffer
Associated
Initiatives
Target Date Source Cost Benefit
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
179

Table D-1
Enabler
Grouping
Number
Enabler
Enabler
Grouping
NAS2.3 ADS-B (A/G) Surveillance
Enhancement
NAS2.3 ADS-B (A/G) Surveillance
Enhancement
NAS2.4 RMP 0.2 Surveillance
Enhancement
NAS2.5 RMP 0.3 Surveillance
Enhancement
NAS2.6 RMP 0.1 Surveillance
Enhancement
NAS2.7 ADS Surveillance
Enhancement
NAS2.8 ASDE Surveillance
Enhancement
NAS2.8 ASDE Surveillance
Enhancement
Capacity
Benefit
Mechanism
Enroute and
TMA
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Arrival and
Departure
Transitions
Improved
Throughput
Improved Final
Approach /
Initial
Departure
Throughput
Surface
Improved
Throughput
Surface
Improved
Throughput
Ref. Figure
Number
Transition Database
Capacity
Operational
Enhancement
6.6 Reduced Vertical
Separation
Standard
6.7 Reduced Vertical
Separation
Standard
6.6 Reduced Vertical
Separation
Standard
6.7 Reduced Lateral
Spacings: More
Arr & Dep.
Transitions
6.7 Reduced Vertical
Separation
Standard
6.8 IMC - Increased
reduction in
lateral separation
to 1000 feet
6.9 Good Visibility -
Improved
Surface
Sequencing,
Scheduling and
Routing
6.9 Low Visibility -
Improved
Surface
Guidance and
Control
Associated
Initiatives
Target Date Source Cost Benefit
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
180

Table D-1
Enabler
Grouping
Number
Enabler
Enabler
Grouping
NAS2.9 AMASS Surveillance
Enhancement
NAS6.0
NAS6.1
NAS6.2
NAS6.3
NAS6.3
Wind Field
(aid to reduce
lateral/longitud
inal
intervention
rate buffer)
Wind &
temperature
gradients (aid
to Reduced
Intervention
Rate Buffer)
Aircraft
Weather
Reports
Convective
Weather
Forecast
Convective
Weather
Forecast
Weather Info
Enhancement
Weather Info
Enhancement
Weather Info
Enhancement
Weather Info
Enhancement
Weather Info
Enhancement
Capacity
Benefit
Mechanism
Surface
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Enroute and
TMA
Improved
Throughput
Planning
Improved
Throughput
Planning
Improved
Throughput
Planning
Improved
Throughput
Ref. Figure
Number
Transition Database
Capacity
Operational
Enhancement
6.9 Low Visibility -
Improved
Surface
Guidance and
Control
6.6 Reduced
Intervention Rate
Buffer
6.6 Reduced
Intervention Rate
Buffer
6.5 Local/Airport
Level Enhanced
Arrival Planning
6.5 Local/Airport
Level Integrated
Airport Flow
Planning
6.5 National Level
Colloborative
Traffic
Management
Associated
Initiatives
Target Date Source Cost Benefit
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
ATM Concept
Baseline
181

182

Appendix E. Constraints Model
Traffic Character
- Schedule
- Speed Mix/Envelope
- Altitude Mix
- Climb/Descent Performance
En Route Configuration
-SUA
- Topography
- Traffic Flow Patterns
- Route Complexity
En Route
Control Performance
- Decision Support
- Proficiency
Nav/Guidance Performance
- Accuracy
- Availability/Coverage
- Integrity
-GNE Rate
CONDITION:
LOCATION:
Comm Performance
- Availability/Coverage
- Integrity
- Message Delivery
Performance
Monitoring Performance
- Availability/Coverage
- Integrity
- Accuracy; Latency
Definition
Arrival is from the beginning
of the STAR to the end of the
STAR. Departure is from the
beginning of the SID to the
transition to en-route.
Terminal Area Configuration
and Flow
- Special Use Airspace
- Routes/Airways
- Severe Weather
-Terrain
TMA
Arrival/Departure
Control Performance
- Sequencing Efficiency
- Separation Precision
- Runway Load Balancing
Monitoring Performance
- Availability
-Integrity
- Accuracy; Latency
Airplane Performance
- Arrival: Speed Schedule, descent path
- Departure: Speed schedule, climb path,
engine out
CONDITION:
LOCATION:
Nav/Guidance Performance
- Accuracy
- Availability
-Integrity
Comm Performance
- Availability
-Integrity
- Message Delivery
Performance

Definition
From the end of the STAR
to the beginning of Final
Approach.
Runway Configuration and
Flow Pattern
-
Noise/Environment
- Quotas and Schedule
- Restrictions
Flight Path Constraints
- Obstacles
- Special Use Airspace
- Missed Approach Constraints
- Arrival Path Constraints
- Departure Path Constraints
CONDITION:
LOCATION:
Approach
Transition
Nav/Guidance Performance
-Accuracy
- Availability
- Integrity
Control Performance
- Sequencing Efficiency
- Separation Precision
- Flight Path Efficiency
- Runway Assignment
Efficiency
Monitoring Performance
- Availability
- Integrity
- Accuracy; Latency
Comm Performance
- Availability
- Integrity
- Message Delivery
Performance
Departure Path Length
(affects traffic compression)
- Obstacles
- Departure Path Constraints
- Noise / Environment
Wake Vortex
- Airplane Weight
Increased Time
Runway Operation
Dependencies
- Crossing Runway or
Flight Paths
Parallel/Diverging
Departures
Other (e.g. political)
Control Performance
- Separation Precision
Runway Occupancy Time
- Runway Access Time
- Accel Performance (ground)
- Flight Crew Procedures
T/O Checklist
Initial
Departure
Monitoring Performance
- Availability
- Integrity
- Accuracy; Latency
Airplane Performance
- Airborne Accel/Climb Perf.
- Speed Schedule
CONDITION:
LOCATION:
Nav/Guidance Performance
- Accuracy
- Availability
- Integrity
Comm Performance
- Departure/Takeoff
Clearance
- Availability
- Integrity
- Message Delivery
Performance

Approach Configuration
- Approach Path Length
-
Other Runway Dependencies
- Runway Occupancy Factors
Airplane Performance
- Approach Speed
- Weight Class
- Braking Performance
- Gate Assignment
CONDITION:
LOCATION:
Wake Vortex
- Visibility
Final
Approach
Nav/Guidance Performance
- Accuracy
- Availability
- Integrity
- Gross Navig. Error Rate
Control Performance
- Finall Approach
Sequence
- Spacing Precision
- Go-around decision
- Blunder Detection &
Alarm
Monitoring Performance
- Availability
-Integrity
- Accuracy; Latency
Comm Performance
- Availability/Coverage
- Integrity
- Message Delivery
Performance
Turnaround Time
- Maintenance
- Load/Unload
-Dispatch
- Deicing
Control Performance
- Departure/Flight Plan
Clearance
- Pushback Clearance
Pushback Availability
-Operator
-Power Cart
Gate
Docking Guidance
Number of Gates, by
Aircraft Size
Comm Performance
- Availability
-Integrity
- Message Delivery
Performance
CONDITION:
LOCATION:

Definition
End of taxiway to gate.
Airplane Performance
-Speed
- Maneuverability
Control Performance
- Tower Visibility/Awareness
- Cockpit Visibility/Awareness
- Decision Time and Integrity
Pushback Performance
Apron
Monitoring Performance
- Availability
- Integrity
- Accuracy; Latency
Terminal/Airport Configuration
- Terminal Building
- Apron/Gate Layout
- Apron/Taxiway Layout
CONDITION:
LOCATION:
Nav/Guidance Performance
- Accuracy
- Availability
- Integrity
Comm Performance
- Availability
- Integrity
- Message Delivery
Performance
Taxiway Configuration
- Taxiway/Runway Crossings
-Distance
- Load Limitations
Control Performance
- Tower Visibility/Awareness
- Cockpit Visibility/Awareness
- Decision Time and Integrity
Flow Patterns
Taxiway
Monitoring Performance
- Availability
-Integrity
- Accuracy; Latency
Airplane Performance
- Speed
- Maneuverability
CONDITION:
LOCATION:
Nav/Guidance Performance
- Accuracy
- Availability
-Integrity
Comm Performance
- Availability
-Integrity
- Message Delivery
Performance