Aerial refueling

Aerial refuelling, also referred to as air refuelling, in-flight refuelling (IFR), air-to-air refuelling (AAR), and tanking, is the process of transferring aviation fuel from one aircraft (the tanker) to another (the receiver) while both aircraft are in flight. The two main refuelling systems are probe-and-drogue, which is simpler to adapt to existing aircraft and the flying boom, which offers faster fuel transfer, but requires a dedicated boom operator station.

The procedure allows the receiving aircraft to remain airborne longer, extending its range or loiter time. A series of air refuelling can give range limited only by crew's physiological needs (like fatigue) and engineering factors such as engine oil consumption. Because the receiver aircraft is topped-off with extra fuel in the air, air refuelling can allow a takeoff with a greater payload which could be weapons, cargo, or personnel: the maximum takeoff weight is maintained by carrying less fuel and topping up once airborne. Aerial refuelling has also been considered as a means to reduce fuel consumption on long-distance flights greater than 3,000 nautical miles (5,600 km; 3,500 mi). Potential fuel savings in the range of 35–40 % have been estimated for long-haul flights (including the fuel used during the tanker missions).

Usually, the aircraft providing the fuel is specially designed for the task, although refuelling pods may be fitted to existing aircraft designs in the case of "probe-and-drogue" systems. The cost of the refuelling equipment on both tanker and receiver aircraft and the specialised aircraft handling of the aircraft to be refuelled (very close "line astern" formation flying) has resulted in the activity only being used in military operations; there are no regular civilian in-flight refuelling activities. Originally tried shortly before World War II on a limited scale to extend the range of British civilian transatlantic flying boats, and then employed after World War II on a large scale to extend the range of strategic bombers, aerial refuelling since the Vietnam War has been extensively used in large-scale military operations.