Tactical contracts re-planning in 4D air-traffic control

Continuous growth in the air traffic density, mainly over Europe and the U.S., introduces a need for new concepts in air-traffic control. One of such new concepts involves air-traffic management using four dimensional (4D) contracts. According to this approach, all the air traffic is pre-planned and optimized in advance in four dimensions: 3D location and time. Before take-off each aircraft is given a flyable conflict-free flight plan, called 4D contract, which it is responsible to comply with. Whether, for any reason, the aircraft can not respect its prescribed 4D contract, a new 4D contract should be re-computed for it in a matter of minutes. The paper introduces an algorithm for re-planning of the 4D contracts within the mentioned time limitations. The update task is treated as an optimization problem minimizing the influence of the contract change on the surrounding traffic. To increase the efficiency of the algorithm, only the neighboring traffic is considered during the re-planning process. The lists of neighbors for each aircraft are computed in advance and stored for efficient re-planning. Numerical examples are used to demonstrate the performance of the proposed algorithm.