Directs in European air traffic management: When and why are they actually granted?

Directs, i.e. instances in which an aircraft skips one or more waypoints to head straight to the next one in the flight plan, are essential instruments in the toolbox of air traffic controllers. They can be used both to reduce the flown distance and to avoid conflicts, thus directly affecting the efficiency and safety of the system. In spite of their importance, few studies have analysed how directs are used in real operational contexts. We here present an analysis of how and when directs were granted in the European airspace in 2015 and 2019. While effective at reducing delays, results indicate that directs are mostly associated with low traffic situations, hence weakly affecting delayed flights. We further estimate the real and potential savings they entail for the system, in terms of CO2 emissions, showing how they are minor with respect to the global environmental impact of aviation.