Which of the following describes the function of an Auxiliary Power Unit (APU)?

The function of an Auxiliary Power Unit (APU) is to supply power for ground operations and engine start. An APU is a small turbine engine located on the aircraft that provides the necessary electrical power and pneumatic pressure for systems while the aircraft is on the ground, rather than relying solely on the main engines, which is crucial during pre-flight checks and procedures.

When the main engines are not running, the APU allows power to be drawn for essential operations, such as powering lights, air conditioning, and other electronic systems, ensuring that the aircraft can operate independently before takeoff. Additionally, the APU generates the compressed air required to start the main engines, making it a vital component in the overall functionality of the aircraft on the ground.

The other choices, although related to aircraft operations, do not accurately describe the main role of an APU. While providing electrical power to the cockpit and controlling cabin temperature are important functions, they can also be managed by other systems on the aircraft. Enhancing aircraft navigation systems is outside the scope of the APU’s functions and typically involves various avionics systems.