Hybrid metaheuristics to aid runway scheduling under uncertainty at London Heathrow airport

London Heathrow Airport is a very popular and busy airport. Indeed it is one of the busiest airports in the world. In order to control noise for residents on flight paths, only one of Heathrow’s two parallel runways can be used for departures at any given time. We aim to increase the throughput of the departure system, and in particular the runway, which is a bottleneck for the whole system. Minimum time separations must be imposed between departing aircraft in order to control congestion and ensure safety, both at take-off and in the air. Reordering the aircraft can often reduce the total required separations and therefore increase the throughput of the runway. The problem of finding the best order for take-off is often called the Departure Problem. When aircraft are ready to depart they are directed from their stand, around the taxiways, to holding points at the end of the runway. The small physical size of Heathrow airport, combined with the congestion at busy times, means that it is most practical to perform the take-off scheduling within the holding points, rather than earlier. This reordering task is currently performed manually by the runway controller. There are various constraints to consider when reordering the aircraft. Some aircraft have a target take-off time which imposes a fifteen minute window upon the aircraft. These must be adhered to and the valid take-off orders are constrained accordingly. A reordering to reduce total delay in the system would naturally tend to delay aircraft that are associated with larger separations so this needs to be controlled. The physical structure of the holding points where the reordering must take place imposes complex constraints upon what reordering can take place and how much effort it takes. The required separations between aircraft depend upon the size, speed and departure routes of the aircraft. Ensuring that separations are maintained between all adjacent aircraft is not sufficient to ensure that required separations are maintained between other aircraft.