Current European Air Traffic Control (ATC) system is far exceeded by the demand and the resulting delays are a financial and psychological burden for airlines and passengers. One of their main sources is the hourly capacity constraints, defined on each en-route ATC sector, but poorly representing the workload of controllers. Whereas previous works were mainly focused on optimizing the ground delay slot allocation process performed by the Central Flow Management Unit (CFMU) to meet these constraints, we propose to directly solve all conflicts occurring above a given flight level by ground delaying, while minimizing the maximal delay. We present a Constraint Programming (CP) model of this large scale combinatorial optimization problem and the results obtained by its implementation with the FaCiLe constraint library.
