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How an Auxiliary Power Unit Works

The APU is a small turbine engine installed near the rear of the fuselage. Honeywell
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Key Takeaways:

  • An Auxiliary Power Unit (APU) is a small turbine engine providing essential power on the ground for starting main engines, generating electricity for onboard systems, and powering environmental controls like heating and cooling.
  • It significantly enhances operational efficiency and passenger comfort by allowing the aircraft to be self-sufficient at the gate, thereby saving fuel and reducing wear on the main engines.
  • Primarily active before takeoff and after landing, APUs can also serve as an emergency electrical power source during flight, though their ground operation can be subject to noise restrictions at some airports.
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An aircraft auxiliary power unit serves as an additional energy source normally used to start one of the main engines on an airliner or business jet. The APU is equipped with an extra electrical generator to create enough power to operate onboard lighting, galley electrics and cockpit avionics, usually while the aircraft is parked at the gate. Drawing bleed air from its own compressor, an APU also drives the environmental packs used to heat and cool the aircraft.

Rob Mark

Rob Mark is an award-winning journalist, business jet pilot, flight instructor, and blogger.

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