Global Time-Based Conflict Solution: Towards the Overall Optimum

Kurzfassung

The goal of future Air Traffic Management (ATM) is simple: every airborne vehicle shall fly as efficient as possible. 4D-Trajectory-Based Operations promise improved efficiency, safety benefits, and high predictability in advance. Highly accurate 4D-trajectories allow early conflict detection and efficient conflict resolution. Independently predicted 4D-trajectories ensuring highest efficiency for everyone create conflicts already with low traffic densities. These conflicts are usually solved by lateral, vertical, or time-based avoidance. However, time-based conflict solution is avoided nowadays because increase/decrease of speed needs to be done well in advance in order to reach the initial conflict point at another, conflict-free time. Besides worsening passengers’ comfort, this procedure also changes estimated time of arrival and thus possibly affects the already planned arrival sequence. The idea under investigation in this paper is to perform time-based conflict avoidance by shifting whole flights from departure to arrival in time. Since this procedure preserves original route, altitude and speed profile, it does not decrease operational efficiency of flights. A time shift of a trajectory is performed only when the overall number of conflicts in the scenario decreases with implementation of that time shift. The algorithm does not distinguish between departure, en-route, and arrival conflicts. Therefore, en-route and airport related conflicts are solved at the same time. Conflicts are solved in chronological order. The results can be used for high accuracy flow management. By solving all conflicts of a scenario it can be proven that the traffic amount can be handled on an aircraft-by-aircraft base when implementing calculated advance and delay times. In a more advanced ATM environment where predicted trajectories can be followed with high accuracy, results can be used directly as reference input for real traffic. Since the only operation done on trajectories is moving them in time by few minutes, the initial nominal trajectories only need to be calculated once per flight. Thus, prediction of trajectories could be done outside the optimization tool in a flexible way by airline operation centers or very precisely aboard of aircraft. The scenario used for de-confliction trials is based on one real day of European traffic containing 33 thousand flights. All flights are assumed to fly as direct as possible while respecting some local waypoints for departure and arrival procedures. The corresponding 4D-trajectories produce 28 thousand conflicts based on the underlying conflict metrics. The big majority of these conflicts can be solved by shifting whole flights in time by five minutes at maximum. The paper presents details about the implemented algorithm and results from above described traffic sample. Analysis is done with different maximum time shifts, results are discussed for different phases of flight. Limitations of the procedure are described, and solutions are proposed to solve remaining conflicts.