APUs are typically powered by a small gas turbine engine, which drives a generator to produce electrical power. The compressed air produced by the APU can be used to start the main engines, provide air conditioning and pressurization for the aircraft cabin, and operate other systems such as the hydraulics and fuel pumps.
APUs are an important safety feature on aircraft, as they provide a backup source of power in the event of a main engine failure. They also allow aircraft to operate independently of ground support equipment, such as electrical power units and air compressors.
APUs are typically mounted in a pod or compartment on the fuselage of the aircraft, and are often located near the tail of the aircraft. The APU exhaust is typically directed through a nozzle to reduce noise and heat.
APUs are a vital part of modern aircraft operations, and provide a number of important safety and operational benefits.
