What Is an APU (Auxiliary Power Unit)?
The little jet engine in the tail of every airliner that keeps the lights on at the gate. The 2026 explainer.
FlightyFlow Team·· 4 min read
The 30-second answer
An APU (Auxiliary Power Unit) is a small jet engine, usually in the tail of an airliner, that produces electricity and pressurized air without running the main engines. It's how the aircraft stays cool at the gate, runs its lights, and starts its main engines.
Why it matters to passengers
- Cabin temperature at the gate depends on the APU running (or external ground air).
- APU outages cause delays — the aircraft can't start its main engines on its own.
- APU restrictions at some airports (noise/emissions) require ground power instead.
See APU-related delays in FlightyFlow
#APU#ground power#aviation
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