What is the function of the APU while on the ground?

• A. Provide electrical power and air conditioning while the aircraft is on the ground.
• B. Only provide air conditioning when in flight.
• C. Power the engines during takeoff.
• D. Control cabin lighting in flight.

Answer: (A)

On the ground, the APU acts as a self-contained power source, supplying electrical power to the aircraft’s systems and providing conditioned air for the cabin while the engines are shut down. This lets the crew run equipment, lights, and environmental controls without needing external ground power or running the main engines. The APU can also supply bleed air to assist with air conditioning or engine starts, but its primary ground role is delivering power and comfortable cabin conditions. It does not power engines during takeoff, and cabin lighting in flight is managed by the aircraft’s electrical system rather than the APU alone.