A conflict resolution algorithm that can provide automated separation assurance for the next-generation air traffic control system has been developed. The algorithm generates resolution trajectories that can be sent to the aircraft from a ground-based system via a data link. With suitable reconfiguration, the algorithm can also be installed onboard aircraft to support airborne separation assurance. It handles the complete spectrum of conflict types encountered in en-route airspace, including ascents to cruise altitude and descents to arrival fixes. The resolution trajectories are patterned after changes to flight plans (route changes), altitude clearances, and speed profiles that controllers customarily issue to pilots in resolving conflicts.

The algorithm generates 4D resolution trajectories by evaluating successive alternative trial resolution maneuvers. Each conflict is first assigned a type category that determines a set of acceptable trial resolution maneuvers and the preferred maneuver aircraft. Then, a trajectory engine generates a 4D trajectory for each trial maneuver, and an associated conflict detector checks it to ensure it is conflict-free. If it is not, the algorithm examines an alternative maneuver. This iterative process continues until a successful resolution is found. The resolution algorithm has been evaluated in both non-real-time simulation as well as in controller and pilot interactive simulations. It is implemented in software as a JAVA applet. Results from both types of simulations indicate that the algorithm has the potential to resolve conflicts efficiently at significantly higher than current traffic levels.

The algorithm resolves conflicts over the range of operational conditions that a controller resolves by manual procedures in the current system. The algorithm has the ability to resolve conflicts that are predicted to occur as long as 20 minutes and as short as 2 minutes from the time aircraft would lose separation. It handles conflict scenarios ranging from pairs of aircraft in cruise to multiple descending and decelerating aircraft converging onto an arrival fix. Candidate resolution trajectories are accepted only if they resolve both the primary conflict and avoid introducing new conflicts as an unintended byproduct of the resolution. Furthermore, when provided with the positions, altitudes, and flight plans of all traffic in neighboring airspace, the resolutions are constructed to be conflict-free for a specified time interval that can be specified by the user.

A significant improvement in the performance and functionality of the resolution algorithm, referred to as the Multi Resolver, was conceived and implemented in software in 2007. This improvement in the algorithm is identified as Version 2. The Multiple Resolver extends the capability of the original algorithm by attempting to generate up to three types of resolutions for each aircraft of a conflict pair. The three types consist of a horizontal, a vertical, and a speed maneuver.

After attempting to generate as many of the six possible resolutions (three types for each aircraft), the Multi Resolver selects the resolution and corresponding aircraft that results in the least delay; however, the least-delay resolution may be overridden by rules that give preference to one or the other aircraft or to a particular resolution. As a result of these rules, a non-minimum delay resolution may be offered as the preferred choice. All available resolutions are saved and are available to the user. Fast time simulation evaluation of the Multi Resolver option has shown a substantial delay reduction compared to the standard original algorithm.

This work was done by Heinz Erzberger of Ames Research Center. This software is available for use. To request a copy, please visit here .


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This article first appeared in the January, 2019 issue of Tech Briefs Magazine.

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