Abstract Today the European airspace is facing multiple capacity constraints which are regulating demand during busy traffic periods of the day. These capacity limits cause inefficiencies in flight and airport ground handling. Current market forecasts predict an annual growth in passenger air traffic demand between 4.5 percent and 4.8 percent. This growth will be realized by an increasing number of aircraft movements reflected in an expected annual growth of jet airplanes by 3.3 percent with a negative impact on airspace capacity. To better manage the rare airspace capacity, the Single European Sky ATM Research (SESAR) and the Next Generation Air Transportation System (NextGen) program suggest free route airspaces, a Performance Based Navigation (PBN) and harmonized airspace structures as efficient concepts of improvement in air traffic efficiency. Beside today's minimum fuel and time objectives, a growing public awareness of the anthropogenic environmental impact necessitates further functions for flight planning and execution. Additionally, today's high safety standards must not be negatively influenced by the introduction of free route airspaces. In this paper, we present a trajectory calculation model capable of exploiting a 4D free route optimization potential while considering the divergent targets of safety, efficiency and environmental compatibility. In particular, the environmental effects of condensation trails depending on the time of the day are carefully considered. To further estimate the impact of free routes on airspace demand and on safety issues, the model is implemented in the simulation environment TOMATO, and the European flight intentions have been optimized for an entire day based on departure airports, arrival airports and original departure times July 2016. The resulting trajectories are evaluated against the number, location and duration of separation infringements. Despite constantly changing air speeds and cruising altitudes induced by the optimization target functions, the number and duration of separation infringements could be reduced by 30% due to optimized lateral and vertical trajectories. The results of this case study show a high potential for an increased airspace capacity under free routing conditions. Furthermore, fuel burn (20%) and airline direct operational costs (40%) could be significantly reduced.

Highlights • Optimized trajectories are more homogeneously distributed in Free Route Airspace. • The altitude range of optimized trajectories is extended in Free Route Airspace. • The number of conflicts can be reduced by optimized trajectories. • Fuel burn and operating costs can be reduced by optimized trajectories.