WHITE PAPER - Amtech-usa.org

WHITE PAPER
Sense-and-Avoid Requirement for
Remotely Operated Aircraft (ROA)
25 June 2004
OPR: HQ ACC/DR-UAV SMO
Major Derek Ebdon / Mr. John Regan
DSN 574-7230
Comm (757) 764-7230
derek.ebdon@langley.af.mil
john.regan@langley.af.mil

TABLE OF CONTENTS:
1. Scope
2. Purpose
3. Background
• FAA Order, 7610.4 Special Military Operations
• Equivalent Level of Safety
• ROA vs. RPV and UAV Terminology
• Pilot vs. Operator
• Operational Restrictions
• Due Regard
• ROA as “Aircraft”
4. Regulatory and Scientific Guidance for See-and-Avoid Requirements
• Minimum Separation Distance
• Participating and Non-participating Traffic
• Search Volume
• Detection Range
5. Proposed See-and-Avoid Requirement
a. General
b. Aircrew Warning and Collision Avoidance
c. Autonomous Maneuvering
d. Field of Regard
e. Lost Link Procedures
f. Emergency Situations
g. Integrity Management
6. Summary
7. List of Acronyms/Abbreviations
Annex 1: Required Detection Distance
2

1. Scope. This paper expands upon and supplements Air Combat Command’s formal
Capabilities Development Document (CDD) requirement for a “sense-and-avoid” system on
current and future Remotely Operated Aircraft (ROA). A ROA, for the purposes of this
document, is an unmanned aircraft that requires access to civil airspace without a Federal
Aviation Administration (FAA) Certificate of Authorization (COA). Currently, ACC operates
three ROA: the MQ-1, the MQ-9, and the RQ-4. Unmanned aircraft developed under the J-
UCAS program will also require this capability.
2. Purpose.
The objective is for current and future ROA to operate in all classes of airspace—both
domestically and internationally—with the same degree of access as aircraft with a pilot onboard
(i.e., file and fly). Normalized flight capability will allow ROA pilots/operators to file a flight
plan, obtain an ATC clearance, and fly in domestic and international airspace without the need to
obtain additional specific FAA or foreign civil aviation authority approval. In addition, for the
Air Force to operate a ROA in international airspace (over the high seas) under due regard, 1 a
sense-and-avoid (SAA) system will assist the user in meeting the safety intent contained in the
international aviation community agreement (Convention on International Aviation, Chicago
Convention, 1944). Such a system would also possess an inherent military utility that would
both enhance and simplify the integration of military ROA into the Air Order of Battle (AOB).
Before the FAA and foreign States’ civil aviation authorities will consider approval of
normalized flight operations for ROA, these systems must comply with applicable regulatory
requirements for airspace access. Foremost among these requirements is a “see-and-avoid”
capability onboard the aircraft. This document establishes the requirements for a ROA senseand-avoid
system that fulfills the intent of collision avoidance contained in the United States’
Federal Aviation Regulations (FAR) 2 and the Convention on International Aviation Rules of the
Air.
3. Background.
Without the capability to sense and avoid other aircraft, ROA are restricted to flight operations
within restricted and warning areas unless the military proponent obtains a Certificate of
Authorization (COA) from the FAA. To fly in the National Airspace System (NAS) without full
regulatory compliance requires a COA outlined by FAA Order 7610.4 and a waiver to AFI 11-
202V3, General Flight Rules. The COA process is also ponderous and has no applicability to
ROA flight in the domestic airspace of a foreign State or within international airspace that is
under the air traffic control (ATC) jurisdiction of another State. Approval to fly in the domestic
airspace of another State requires approval from the civil aviation authority of that State
(Convention on International Civil Aviation, Article 8).
Before ROA will be allowed to perform normalized flight operations in airspace other than
restricted areas and warning areas, the intent of the Federal Aviation Regulations’ “see-andavoid”
requirement must be met. ROA must be capable of performing the see-and-avoid
1 Convention on International Civil Aviation, Article 3.
2 One specific reference is found in 14 CFR 91.113.
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function and thereby achieving an “equivalent level of safety” (ELOS), comparable to an
aircraft with a pilot onboard. In addition, ROA must be equipped to meet the same airspacespecific
operating requirements as manned aircraft. ROA that do not possess this equipment
may be restricted to certain routes, confined to specified airspace, and restricted to altitudes that
do not provide maximum operational flexibility. Furthermore, the Air Force must develop
standards and procedures for ROA to assure both airworthiness and reliable operating
capabilities.
The following topics are mentioned for informative purposes and provide insight into the
interaction of the military (DoD) ROA community with the Air Force Flight Standards Agency
(AFFSA) and the FAA:
FAA Order 7610.4, Special Military Operations
In the late 1970s, the FAA and Department of Defense (DoD) reached agreement on the
operation of unmanned aircraft in the NAS, outside of restricted and warning areas. At
that time, these systems were labeled remotely piloted vehicles (RPV). The criteria for
the operation of DoD RPV in the NAS were written into FAA Order 7610.4, Special
Military Operations. Subsequently, some military organizations began using the term
“unmanned aerial vehicle (UAV)” for these systems, and that term became more
prevalent over time. Yet, this terminology was never included in FAA Order 7610.4.
The advent of the MQ-1 and the RQ-4 extended the operational capabilities of unmanned
aircraft significantly. As a result, the FAA and DoD determined additional guidelines
were needed to ensure safety could be maintained when ROA were operated in the NAS
outside restricted and warning areas. Therefore, in May 1999, the FAA, with DoD
concurrence, issued an FAA Notice that changed the criteria in FAA Order 7610.4 for
DoD RPV operations. This Notice implemented the COA process and changed the
designation of unmanned flight systems from RPV to ROA. Subsequently, the contents
of this Notice were incorporated into the next revision to FAA Order 7610.4. Since a
single document was developed jointly between the DoD and FAA, DoD publications
like AFI 11-202V3 refer to the FAA Order as an approved source.
Equivalent Level of Safety
In accordance with FAA Order 7610.4, Special Military Operations, Chapter 12,
Section 9: a ROA must achieve an “equivalent level of safety” (ELOS), comparable to a
manned aircraft. ELOS refers to a combination of systems and a concept of operations
that reduces the chance of a midair collision to an acceptable level. At this point in the
development process of a SAA system, we do not yet have all the information necessary
to establish a defensible and tangible value for ELOS (e.g., 10 -6 ). Historical midair
collision rates for manned aircraft will provide some indication of what this value should
be. However, further simulation, testing, and analyses will be required before we will be
able to define the requirement for “ELOS.”
ROA vs. RPV and UAV Terminology
During the coordination process leading to the creation of the FAA Notice that changed
the previous RPV criteria, the FAA and DoD reached agreement that these unmanned
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flight systems were aircraft based on the FAR definition of aircraft. 3 As such, DoD ROA
should comply with military certification standards that ensure an aircraft is airworthy
and that the aircraft’s equipment and operational capabilities are applicable to the class of
airspace within which the ROA is intended to operate. The term ROA is now
incorporated into AFI 11-202V3, General Flight Rules.
Pilot vs. Operator
The term "operator" was an accommodation within the DoD due to the Services’
differences in rank and military specialty of unmanned aircraft pilots/operators. The
pilot/operator fulfills the responsibilities of the “Pilot in Command” as defined in 14
CFR 1: “…responsible for the safe operation…” [AFI 11-202V2]. A term widely used
by senior leadership on the Air Staff is RPA -- Remotely Piloted Aircraft.
Operational Restrictions
FAA Order 7610.4 mandates that the military proponent for each proposed DoD ROA
operation in the NAS, outside of restricted or warning areas, submit an Application for
COA to the appropriate FAA regional office. The Application for COA should be
submitted at least 60 days prior to the intended operation and contain:
• Detailed description of the planned operation.
• Platform physical and operational characteristics.
• Coordination and communication procedures.
• Contingency procedures.
• Method that will be used to avoid other aircraft that provides an ELOS,
comparable to the see-and-avoid requirements for manned aircraft.
Due Regard
References: (1) Department of Defense Directive 4540.1, Use of Airspace by U.S.
Military Aircraft and Firings Over the High Seas and (2) FLIP General Planning Chap 7.
Normally, routine point-to-point and navigation flights follow ICAO flight procedures.
However, there are certain operational situations such as military contingencies, certain
classified missions, and politically sensitive missions that do not lend themselves to
ICAO flight procedures. Operations not conducted under ICAO flight procedures are
conducted under “due regard” or “operational” prerogative of military aircraft and are
subject to one or more of the following conditions:
• Aircraft shall be operated in VMC.
• Aircraft shall be operated within radar surveillance.
• Aircraft shall be equipped with airborne radar.
• Aircraft shall be operated outside controlled airspace.
These conditions provide for a level of safety equivalent to that normally given by ICAO
Air Traffic Control agencies and fulfill the USAF’s obligations under Article 3 of the
3 14 CFR 1, Definitions and Abbreviation – Aircraft means a device that is used or intended to be used for flight in
the air.
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Chicago Convention of 1944, which stipulates there must be “due regard for the safety of
navigation of civil aircraft” when flight is not being conducted under ICAO flight
procedures. Essentially, “due regard” obliges the military commander to be his own air
traffic control. Flight in VMC implies the existence of a see-and-avoid capability
onboard the aircraft. Operational necessity will require certain ROA to operate under the
provisions of “due regard” or “operational prerogative.”
ROA as “Aircraft”
Encompassing unmanned aircraft within established rules and regulations for manned
aircraft is in the best interest of the Air Force. Modifying existing regulations or drafting
new ones for another class of aerial vehicle (i.e., ROA) will further isolate these systems
as “exceptional.” To fly ROA in the NAS with the same operational flexibility as
manned aircraft (i.e., file and fly), these systems must be governed by the same
regulations as manned aircraft.
4. Regulatory and Scientific Guidance for See-and-Avoid Requirements.
The See and Avoid requirement derives from the FARs 4 and Convention on International Civil
Aviation Rules of the Air 5. . Detractors of ROA operations have always asked: “How will you
comply with ‘see-and-avoid’?” It is important to place the phrase in its complete context.
“Vigilance shall be maintained by each person operating an aircraft so as to see and avoid other
aircraft” represents the ultimate responsibility of the Pilot in Command 6 . Alternative translation:
4 14 CFR 91.113 Right of way rules: Except Water Operations
(a) Inapplicability. This section does not apply to the operation of aircraft on water.
(b) General. When weather conditions permit, regardless of whether an operation is conducted under instrument
flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft so as to see and
avoid other aircraft. When a rule of this section gives the right-of-way, the pilot shall give way to that aircraft and
may not pass over, under, or ahead of it unless well clear.
5 Annex 2, Section 3.2, Avoidance of collision - It is important that vigilance for the purpose of detecting potential
collisions be not relaxed on board an aircraft in flight, regardless of the type of flight or class of airspace in which
the aircraft is operating, and while operating on the movement area of an aerodrome.
6 91.113 Right-of-way rules: Except water operations.
(a) Inapplicability. This section does not apply to the operation of an aircraft on water.
(b) General. When weather conditions permit, regardless of whether an operation is conducted under instrument
flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft so as to see
and avoid other aircraft. When a rule of this section gives another aircraft the right-of-way, the pilot shall give
way to that aircraft and may not pass over, under, or ahead of it unless well clear.
(c) In distress. An aircraft in distress has the right-of-way over all other air traffic.
(d) Converging. When aircraft of the same category are converging at approximately the same altitude (except
head-on, or nearly so), the aircraft to the other's right has the right-of-way. If the aircraft are of different
categories --
(1) A balloon has the right-of-way over any other category of aircraft;
(2) A glider has the right-of-way over an airship, airplane, or rotorcraft; and
(3) An airship has the right-of-way over an airplane or rotorcraft.
However, an aircraft towing or refueling other aircraft has the right-of-way over all other engine-driven aircraft.
(e) Approaching head-on. When aircraft are approaching each other head-on, or nearly so, each pilot of each
(f)
aircraft shall alter course to the right.
Overtaking. Each aircraft that is being overtaken has the right-of-way and each pilot of an overtaking aircraft
shall alter course to the right to pass well clear.
(g) Landing. Aircraft, while on final approach to land or while landing, have the right-of-way over other aircraft in
flight or operating on the surface, except that they shall not take advantage of this rule to force an aircraft off
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the operator cannot rely solely on ATC if the weather is good enough to look outside. These
simple facts allow one to make another simple, yet accurate, statement: “Manned aircraft have a
‘see-and-avoid’ capability.” However, this capability is not reliant solely on human vision. To
quote FAA P-8740-51 How to Avoid a Midair Collision:
Collision avoidance involves much more than proper eyeball techniques. You
can be the most conscientious scanner in the world and still have an in-flight
collision if you neglect other important factors in the overall see-and-avoid
picture.
Hence, the complete “see-and-avoid” system exists only when proper scanning technique is
combined with these other important factors: crew, sensors, aircraft beacons, and the air traffic
control infrastructure.
With regard to a ROA, because there is no human sight capability, we refer to an onboard
detection system as a “sense-and-avoid (SAA)” system. SAA systems must be able to detect
conflicting traffic in sufficient time to perform an avoidance maneuver, and then either notify the
pilot of a potential conflict and propose a course of action, or maneuver autonomously so as not
to create a collision. Hopefully, the system will allow the aircraft to pass “well clear” according
to the rules in Part 91.113 and/or Part 91.111(a). 7 Thus, the goal of any sense-and-avoid system
is to perform those collision avoidance functions normally provided by a pilot in a manned
aircraft. Depending on the level of autonomy inherent in the ROA, these functions could fall
into a wide range from simple conflict detection and cueing to full autonomous conflict detection
and avoidance.
Minimum Separation Distance
The ROA SAA system must detect and predict traffic conflicts. A conflict is defined as
another aircraft that will pass less than 500 feet, horizontally or vertically, from the ROA.
When the SAA system detects a conflict, an operator initiated or autonomous
deconfliction maneuver will be performed in sufficient time so the ROA and other
aircraft miss each other, preferably by at least 500 feet. 8
Participating and Non-participating Traffic
The system will need to detect traffic conflicts created by both participating and nonparticipating
aircraft—both VFR and IFR. Participating aircraft squawk a discrete
transponder code and maintain two-way radio communications with ATC. On the other
hand, non-participating aircraft are not required to communicate with ATC and may not
even be equipped with a transponder. Although the total collision avoidance capability
onboard the ROA may include equipment to query participating aircraft for position
information in order to enhance performance, this capability is not sufficient to fulfill the
the runway surface which has already landed and is attempting to make way for an aircraft on final approach.
When two or more aircraft are approaching an airport for the purpose of landing, the aircraft at the lower
altitude has the right-of-way, but it shall not take advantage of this rule to cut in front of another which is on
final approach to land or to overtake that aircraft.
7 91.111 Operating near other aircraft.
(a) No person may operate an aircraft so close to another aircraft as to create a collision hazard.
8 FAA Order 8700.1 Change 3 Chapter 169 Paragraph 5.A.
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see-and-avoid requirement in the FARs. Hence, a system that detects non-participating
traffic is required.
Search Volume
One critically important factor for any SAA system is the search volume defined by
azimuth and elevation. The Convention on International Civil Aviation, Rules of the Air,
establishes the regulatory criterion that differentiates between a converging or
overtaking 9 situation. The critical factor for a SAA system is that it provide surveillance
of all of the airspace that lies within the converging angle: ±110° with respect to the
longitudinal axis of the ROA, although a lesser field of regard may achieve the desired
level of safety. No regulatory guidance for search elevation exists. NASA and DoD
studies have shown that, in head-on scenarios, a search elevation of ±15° with respect to
the flight path provides adequate coverage to detect converging aircraft that are using
climb and descent angles as high as 20° (rare for civilian aircraft and also for military
aircraft operating outside special use airspace). Overtaking scenarios, which are highly
unlikely at controlled airports, may require greater vertical coverage from the onboard
sensors. Further analysis and a review of the ROA’s concept of operations may be
required in order to determine the appropriate sensor coverage required to provide an
ELOS.
Detection Range
The sense-and-avoid system must detect the traffic in time to process the sensor
information, determine if a conflict exists, and execute a maneuver according to the
right-of-way rules. If pilot interaction with the system is required, transmission and
decision time must also be included in the total time between initial detection and the
point of minimum separation. (see Annex 1)
5. Sense-and-Avoid Requirement
a. General. The probability of a ROA colliding with another aircraft must be
comparable to that for manned aircraft (i.e., equivalent level of safety). The measure of
overall system performance shall take into account onboard sensors, beacons,
transponders, air traffic control, concept of operations, and reliability. The SAA system
shall possess the capability to detect both participating and non-participating aircraft day
and night (weather permitting), notify the ROA pilot/operator of the contact, and
determine if a potential collision hazard exists (Threshold). Should the contact
represent a hazard to safe operations, the system shall either provide a suggested conflict
resolution for pilot action or maneuver autonomously to avoid the other aircraft
(Threshold). The SAA system must consider warnings/directions from other avoidance
systems such as traffic collision alert system (TCAS) (Objective). The system shall
provide information to the pilot/operator on the progress of the resolution/avoidance
maneuver, time and conditions permitting (Objective). After conflict resolution, the
system will provide a recommended return-to-course action (Objective).
9 Convention on International Civil Aviation, Annex 2, Rules of the Air, Section 3.2.2.4
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g. Integrity Management. The SAA system shall have a means of indicating to
the pilot/operator that the sensor, computer system, display, or autonomous avoidance
capability is not fully operational (Threshold).
6. Summary.
ACC’s goal is to normalize ROA operations within civil airspace. Along with aircraft
airworthiness certification, which now includes Communications, Navigation, Surveillance/Air
Traffic Management (CNS/ATM) compliance, a sense-and-avoid capability is key to this effort.
The Capabilities Development Documents (CDD) for current and future ROA establish the
baseline requirement for sense-and-avoid systems. This White Paper expands upon and
supplements the basic information contained in CDDs.
These requirements may change due to evolving operational, technological, and regulatory
realities. The SAA system must be able to stand up to scrutiny, but does not necessarily stand
alone. Moreover, specific platforms may have additional requirements, which will be included
in annexes to this document or wholly within their respective CDDs. The program offices must
now seek technical solutions to provide this capability in the near future and thereby allow ROA
to have normalized access to both domestic and foreign States’ civil airspace.
//SIGNED-llw//
LAWRENCE L. WELLS, Col, USAF
Deputy Director of Requirements
10

7. List of Acronyms/Abbreviations:
ACC
ACAS
AFFSA
ATC
ATM
CNS/ATM
CDD
CFR
COA
DoD
ELOS
ERAST
FAA
FOR
FOV
ICAO
IFR
IPT
MOA
NAS
NMAC
POC
ROA
SAA
SMO
SPO
SUA
TCAS
UAV
VFR
VMC
Air Combat Command
Aircraft Collision Avoidance System
Air Force Flight Standards Agency
Air Traffic Control
Air Traffic Management
Communications, Navigation, and Surveillance/Air Traffic Management
Capabilities Development Document
Code of Federal Regulations
Certificate of Authorization and Waiver
Department of Defense
Equivalent Level of Safety
Environmental Research Aircraft and Sensor Technology
Federal Aviation Administration
Field of Regard
Field of View
International Civil Aeronautics Organization
Instrument Flight Rules
Integrated Product Team
Military Operations Area
National Airspace System
Near Mid-Air Collision
Point of Contact
Remotely Operated Aircraft
Sense and Avoid or See and Avoid
Special Mission Office
System Program Office
Special Use Airspace
Traffic Collision Avoidance System
Unmanned Aerial Vehicle
Visual Flight Rules
Visual Meteorological Conditions
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ANNEX 1
Required Detection Range
The DOD has conducted research that confirms NASA’s independent findings that the time
needed to complete the avoidance maneuver depends primarily on the bank angle of the
maneuver. 10 However, this generalization quickly becomes unreliable for ROA with very slow
true airspeeds (i.e.,