What is a primary function of the Auxiliary Power Unit (APU)?

The Auxiliary Power Unit (APU) serves a crucial role in providing power to the aircraft, particularly when the main engines are not running. This small engine is typically located in the tail section and is responsible for generating electrical power for essential systems such as lighting, air conditioning, and avionics while on the ground. Additionally, the APU can provide bleed air for starting the main engines and for running pneumatic systems, enabling functions like cabin heating or cooling.

The ability of the APU to supply power becomes especially important during pre-flight preparations and post-landing when the engines are off but power is still required. Without the APU, the aircraft would not be able to operate many of its systems on the ground, leading to increased inefficiencies and possible operational delays.

This understanding underscores the vital contribution of the APU to aircraft operations in both pre-flight and post-flight scenarios, confirming its primary function.