On the ground, what is the expected end state when the APU is fully operational?

• A. It powers the main propulsion
• B. It requires main engines running
• C. It charges only the battery
• D. It provides bleed air and electrical power to aircraft systems

Answer: (D)

When the APU is fully operational on the ground, it provides both bleed air and electrical power to the aircraft systems. This means environmental control, cabin pressurization, and avionics can run, and the APU can even supply pneumatic air to start the main engines if needed. It does not power the main propulsion itself, and its job isn’t limited to charging the battery—its primary role is delivering usable electrical power and bleed air for the aircraft systems while the engines are off.