What is the primary function of an APU?

What is the primary function of an APU?

• A. An APU provides electric power and compressed air when the main engines are not operating.
• B. An APU powers the main propulsion engine.
• C. An APU controls the aircraft's hydraulics.
• D. An APU manages cabin pressurization.

Answer: (B)

The main job of an APU is to provide electrical power and pneumatic (compressed air) power for starting the main engines and for operating aircraft systems when the main engines aren’t running. On the ground, the APU can run the aircraft’s electrical systems and supply bleed air for engine starts and air conditioning, so you don’t need ground power or air. It does not power the main propulsion engine, and it doesn’t directly control hydraulics or cabin pressurization, though bleed air from the APU can feed systems that support those functions when available.

The main job of an APU is to provide electrical power and pneumatic (compressed air) power for starting the main engines and for operating aircraft systems when the main engines aren’t running. On the ground, the APU can run the aircraft’s electrical systems and supply bleed air for engine starts and air conditioning, so you don’t need ground power or air. It does not power the main propulsion engine, and it doesn’t directly control hydraulics or cabin pressurization, though bleed air from the APU can feed systems that support those functions when available.