FAA Aircraft Dispatcher Practice Exam

Which of the following best describes an APU?

1. An auxiliary power unit providing power during ground operations

2. A system that converts hydraulic pressure to mechanical power

3. Only used for emergency landings

4. A device that improves fuel efficiency

The correct answer is: An auxiliary power unit providing power during ground operations

An auxiliary power unit (APU) primarily serves to provide power to an aircraft while it is on the ground, particularly when the main engines are not running. This includes supplying electrical power for lighting, avionics, and other systems essential for pre-flight checks and ground operations, as well as providing pneumatic power for starting the main engines and for environmental control systems. This functionality is critical, especially in situations where the aircraft is parked away from terminal gates or during longer boarding processes where external power sources are not available. The APU helps enhance efficiency and reduces the reliance on ground power units or other external energy sources, positioning it as an invaluable component in modern aviation operations. In contrast, other options describe different systems and functionalities that do not align with the core purpose of an APU, clarifying why they are not suitable descriptions.