Which acronym expands to Auxiliary Power Unit?

• A. Auxiliary Power Unit
• B. Air Processing Unit
• C. Auxiliary Propulsion Unit
• D. Auto Power Utility

Answer: (A)

APU stands for Auxiliary Power Unit—the three words themselves describe a separate power source used to run aircraft systems when the main engines aren’t running. The acronym is built from the initial letters of those words, so the correct expansion is the exact phrase Auxiliary Power Unit. The other options point to different ideas (air processing, auxiliary propulsion, or a nonstandard term), which don’t match what APU represents. In real use, an APU provides electrical power and bleed air to start engines and operate systems on the ground or in flight when needed.