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

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
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