1 Abstract The regulation of European air traffic, as currently done by the CFMU and the regional ATFCM cells, essentially consists in delaying on the ground all flights that may encounter congestion at some stage of their trip. This preventive strategy is based on the assumption that avoiding en-route traffic overload contributes to safety and that ground delays should, in theory, be cheaper
... [Show full abstract] than their en-route equivalent from the airspace users' viewpoint. This study aims at performing a comparative environmental analysis of ground and en-route delays, along with assessing the corresponding costs.