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The throughput of the nation's busiest airports could be improved by more precisely spacing aircraft on final approach. More accurate final approach spacing ensures that the aircraft are safely separated, but that no avoidable gaps exist in the traffic flow. Ames Research Center and the Federal Aviation Administration (FAA) are continuing to design, develop, and plan deployment of a software-based decision support tool (DST), called the Final Approach Spacing Tool (FAST), to increase airport throughput. An early version of this DST, known as Passive FAST (pFAST) provides runway assignments and relative landing orders and is being deployed as part of the FAA Free Flight Phase 1 Program. Current research is focused on developing a future version of this DST, known as Active FAST (aFAST) that will allow air traffic controllers to achieve more accurate final approach spacing by providing heading, speed, and altitude commands.
Because of the extremely dynamic nature of air traffic situations, providing advisories to air traffic controllers requires a system whose decisions are reliable yet flexible. As a result, the aFAST system incorporates elements of fuzzy reasoning and rule-based decision making. Using these technologies, the basic implementation of a concurrent scheduling algorithm and a knowledge-based conflict-detection and resolution algorithm have been completed. These algorithms form the foundation of the aFAST system. They determine safe and efficient trajectories for arrival traffic by simultaneously sequencing aircraft along flightpath segments and by resolving all predicted conflicts among those aircraft. A patent application for these algorithms is being pursued in order to investigate their suitability for private and international ATC environments.
In order to evaluate the performance of the aFAST system, an innovative approach for its simulation was developed. Previous DSTs have focused, almost exclusively, on human-in-the-loop simulations to track the progress of their development, since no other reliable method of executing the advisories was available. The aFAST system will use a three-tiered testing process consisting of trajectory tracking, advisory tracking, and human-in-the-loop simulation. During trajectory tracking, aFAST uses its own solution trajectories to simulate radar tracks. The aircraft's initial positions that are used to determine an initial solution trajectory are specified in order to represent a complex traffic flow. Subsequently, each solution trajectory is used to simulate the next aircraft position, which is used to determine the next solution trajectory. This scenario allows the stability and performance of the aFAST system to be analyzed in an environment free of both prediction and flight technical errors. During advisory tracking, aFAST electroni-cally issues its advisories to an independent Pseudo Aircraft Simulation (PAS). PAS automatically executes these maneuvers using its own independent set of aircraft and atmospheric models. This scenario is suitable for investigating the effects of prediction errors. Finally, during human-in-the-loop simulations, air traffic controllers issue advisories to human pseudo-pilots that respond using PAS. This most realistic scenario can be used to study the effects of both prediction and flight technical errors, as well as to explore the usability and suitability of active advisories for achieving more accurate final approach spacing.
The aFAST system has used trajectory tracking to control several hours of flights to an airport with a single arrival runway. During these intentionally busy traffic scenarios, the aFAST system achieved safe and precise separation of the aircraft. In the near term, work will focus on the trajectory tracking and advisory tracking methods of testing. These techniques will be used to (1) quantify the aFAST system's sensitivity to prediction and flight technical errors and (2) assess the benefits of active advisories. Finally, preparation for more complex multi-runway scenarios will begin.
Point of Contact: John Robinson
(650) 604-0873
jerobinson@mail.arc.nasa.gov
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