Q: While listening to the flight deck communications, I’ve heard the pilot use the term “APU.” What is this?
A: “APU” is the acronym for “Auxiliary Power Unit.” The APU is actually a small jet engine that is usually in the tail of the aircraft. (On many aircraft, you can see its exhaust coming from the tail.) It provides for functions other than propulsion: We primarily use it to start the engines, but it also enables us to operate certain aircraft systems for preflight checks. The APU provides electrical power and pressurized air for heating or air-conditioning on the ground when the aircraft engines are not running. The APU can also be used airborne as a backup source for the same purposes.
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