Final Approach Spacing Tool (fast) Velocity Accuracy Performance Analysis

The NASA passive Final Approach Spacing Tool (FAST) provides advisory information to the terminal air traffic controller for sequencing and merging of landing aircraft. It consists of the Trajectory Synthesizer (TS) and the Scheduling Logic (SL). FAST has undergone extensive field testing and performance evaluations of the FAST TS algorithms have been conducted. However, no analytical performance evaluations of the FAST SL logic have been performed to date. This paper evaluates the sensitivity of the FAST SL algorithms to velocity errors which are introduced by the radar tracking software. A linear error covariance analysis was performed of the terminal area radar and its alpha-beta tracking filter software. For comparison, an alternate Kalman tracking filter was also evaluated. Using these radar tracking velocity estimation error histories for a typical aircraft flight profile, the FAST TS estimated time of arrival (ETA) statistics history was obtained. To determine the impact of the velocity and ETA errors on FAST SL, figures of merit were defined which predict the probability that FAST SL will reach an incorrect aircraft sequencing decision. These figures of merit were then evaluated, based on the velocity and ETA statistics histories. Copyright ã 1998 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved Introduction Passive FAST is a decision aid to the air traffic controller which consists of two key modules. The first is the Trajectory Synthesizer (TS) which is used to predict the aircraft trajectory history to the runway threshold based on the current time, position, and speed. The second module is the Scheduling Logic (SL) which determines the air traffic controller preferred sequencing of aircraft within a flight segment or merging of aircraft onto a common flight segment. This is accomplished by examining the trajectory variables from two aircraft at a time, for all aircraft in the Terminal Radar Approach Control (TRACON) and by evaluating a set of fuzzy logic propositions to determine the preferred choice. Figure 1 illustrates the data flow surrounding and through FAST. The aircraft horizontal position and velocity estimates are obtained from the ARTS radar and its tracking software. This data is combined by the FAST TS with altitude information, provided by the aircraft barometric altimeter, to obtain predicted aircraft flight path histories. FAST uses these predicted trajectories to determine the preferred sequencing or merging of aircraft in the TRACON. The logic flow of the error analysis is illustrated in Figure 2. The analysis approach consists of deriving the velocity estimation error model, based on an estimation error analysis of the ARTS radar and its tracking software.