Fuel in an aircraft fuselage fuel tank is cooled by means of cold air flowing from the exterior of the aircraft to a cooling region inside the aircraft. The cooling region may be (a) located to the exterior of the fuel tank, (b) in thermal communication with the fuel tank and (c) in fluid communication with a region downstream of, and remote from, said cooling region, for example, an exhaust port on the outside of the aircraft. The flow of air may be caused by air entering a ram air intake, into which air passes as a result of the motion of the airborne aircraft relative to the surrounding air.