APU
Pronunciation: A-P-U (each letter)
Also written as: APU — Auxiliary Power Unit
Auxiliary Power Unit — a small onboard turbine engine that provides electrical power and bleed air to an aircraft while on the ground, independent of the main engines.
Full Definition
The APU is located in the tail section of most commercial aircraft and is operated when the aircraft is parked on stand and not connected to FEGP or a GPU. It supplies power for cabin systems, air conditioning, and engine start. In airside operations documentation, APU usage is often a topic in environmental and noise management policies, as APUs generate significant emissions and noise. Editors should always expand 'APU' on first use in documents intended for non-aviation audiences. APU start and shutdown procedures are part of the turnaround timeline and are referenced in handling manuals.
Usage
Usage note: Always expand on first use. In sustainability documents, APU usage is a measured emission source — take care to distinguish APU from GPU and FEGP in context.
In Context
- "The airline's turnaround procedures require APU shutdown within five minutes of FEGP connection." — Airline ground operations manual
- "APU noise restrictions apply between 23:00 and 06:00 at all stands within 300 metres of the terminal." — Airport noise management policy