A ground holding model for aircraft deconfliction

In the SESAR traffic growth predictions, traffic complexity will become an issue that the current Air Traffic Management organization is not able to handle. The 4D trajectory concept offers new perspectives for deconflicting the traffic by ground-holding aircraft before they take-off. This paper studies the possible complexity reduction achievable by optimizing the aircraft take-off times. Therefore a simple model is introduced to detect pairwise 3D possible conflicts and define conflicting take-off time differences. Two resolution algorithms are tested on a real traffic data sample collected in the French airspace. The first one is based on a Constraint Programming model of the problem and ensures the optimality of the maximum delay required to solve every conflict. The second one uses an evolutionary computation algorithm to minimize the mean delay among the aircraft population. A sliding window model is introduced to reduce the size of the problem and to regularly update the current situation. Experimental results performed in the French airspace with fast time simulation show that with perfect 4D trajectory, every conflict over flight level 290 can be solved by delaying less than a quarter of the traffic within a range of delays varying from 1 to 90 minutes and a mean delay of 4 minutes. The Constraint Programming approach gives better results than the evolutionary computation approach. Adding uncertainty around 4D trajectories dramatically degrades the results.