Direct Route Optimization for Air Traffic Management Improvement

Aircraft are able to connect any pair of points on earth by using direct routing thanks to the flight management system (FMS) which is the on-board system in charge of the navigation. From an air traffic control point of view, such direct routing is only possible in low density areas. When demand is high, aircraft have to stay on a route network for which crossing points are well located and do not change with time. This location stability, helps controllers to manage efficiently the traffic and ensure a higher capacity compared with management of the same traffic with direct routes for which crossing points always change in space and in time dimensions. This instability reduces the overall capacity of sectors. During the night, when traffic demand decreases, air traffic controllers often deliver direct routes to aircraft because they know that such aircraft will not interfere with other traffic. During the day, such direct route assignments are not proposed anymore and the controller keeps the aircraft on the route network in order to structure the traffic and to reduce the associated complexity. In this research we propose an intermediate milestone for which direct routes could be proposed to aircraft during the day when it is possible and this in order to reduce also the congestion at some points in the airspace. We then consider a real crossing in the French airspace where aircraft have to merge at the same point and exit toward different directions. An optimization algorithm has been developed for this crossing in order to minimize the workload of the controller in charge of this airspace. Three decision variables are then assigned to each aircraft: speed regulation, flight level setting and direct route setting. The associated objectives of this problem are the minimization of the conflict between aircraft (has to reach zero), the maximization of the number of aircraft having a direct route (avoiding the crossing) and the minimization of the flight deviation (speed and FL). When a direct is given to an aircraft, we must ensure that such aircraft is separated from other aircraft by one when they share the same spatial location; this ensure that the controller in charge of such aircraft has few monitoring workload for this aircraft (because it has no interaction with other traffic). This optimization must satisfy some constraints: speed and FL have to stay in a given range. This algorithm has been applied successfully to a test case quite similar to one located in the west of France ACC (Brest) for which the capacity of the crossing point has been strongly increased thanks to many direct routes that have been given.