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In this paper, we briefly describe the Free Flight policy for air traffic control, review previous automation tools for conflict detection and resolution, analyze Free Flight conflict detection, and present a conflict resolution advisory solution. For analysis, tactical cases are governed by safety oriented collision avoidance algorithms and strategic cases by economics oriented algorithms. Our results, based on optimal control theory, establish a tactical alert zone that augments the protected airspace zone around an aircraft. Within the tactical alert zone an aircraft is no longer able to avoid penetrating the protected airspace zone of an intruder aircraft. Thus, our advisory system notifies a pilot or air traffic controller of the optimal control strategy prior to penetrating the tactical alert zone. Far before the tactical alert zone, an advisory for a strategic maneuver is given, based on an economical conflict resolution strategy that uses safety as a constraint.
Krozel et al. (Mon,) studied this question.