APU
A small turbine engine, usually in the tail, that supplies electrical power and bleed air on the ground.
Also written
auxiliary power unit
The APU runs the air conditioning and electrics while the main engines are shut down, and provides the bleed air to start them. Its exhaust is the small round port at the very back of the fuselage, and its distinct whine is what you hear over a stand before startup. Many airports restrict APU running to limit noise and fuel burn, using ground power and preconditioned air instead.
Nearby in Aviation
- airside — The part of an airport beyond security, where aircraft operate.
- apron — The paved area where aircraft park, load, refuel and are serviced.
- ATIS — A looped broadcast of an airport's current weather, runway in use and other essential information.
- callsign — The name a flight uses on the radio, usually an airline telephony name plus a flight number.