Aerial refueling, also called air refueling, in-flight refueling (IFR), air-to-air refueling (AAR) or tanking, is the process of transferring fuel from one aircraft (the tanker) to another (the receiver) during flight.
The procedure allows the receiving aircraft to remain airborne longer, extending its range or loiter time on station. A series of air refuelings can give range limited only by crew fatigue and engineering factors such as engine oil consumption. Because the receiver aircraft can be topped up with extra fuel in the air, air refueling can allow a take-off with a greater payload which could be weapons, cargo or personnel: the maximum take-off weight is maintained by carrying less fuel and topping up once airborne. Alternatively, a shorter take-off roll can be achieved because take-off can be at a lighter weight before refueling once airborne. Aerial refueling has also been considered as a means to reduce fuel consumption on long distance flights greater than 3000 nautical miles. Potential fuel savings in the range of 60% have been estimated for long haul flights.
The two main refueling systems are probe-and-drogue, which is simpler to adapt to existing aircraft, and the flying boom, which offers greater fuel transfer capacity, but requires a dedicated operator station.
Usually, the aircraft providing the fuel is specially designed for the task, although refueling pods can be fitted to existing aircraft designs if the “probe-and-drogue” system is to be used (see later). The cost of the refueling equipment on both tanker and receiver aircraft and the specialized aircraft handling of the aircraft to be refueled (very close “line astern” formation flying) has resulted in the activity only being used in military operations. There is no known regular civilian in-flight refueling activity. Originally employed shortly before World War Two on a very limited scale to extend the range of British civilian trans-Atlantic flying boats, and then after World War Two on a large scale to extend the range of strategic bombers, aerial refueling since the Vietnam War has been extensively used in large-scale military operations for many different military aircraft operations. For instance, in the Gulf War and the Iraqi invasion of Kuwait and the Iraq War, all coalition air sorties were air-refueled except for a few short-range ground attack sorties in the Kuwait area.