What is the purpose of the APU (Auxiliary Power Unit)?

The purpose of the APU (Auxiliary Power Unit) is to provide both electrical power and bleed air while the aircraft is on the ground. This is significant because it allows the aircraft to operate systems such as lighting and air conditioning without relying on the main engines or ground power units. The APU generates the necessary electricity and can supply bleed air for engine start or environmental control systems, ensuring that the aircraft can maintain vital functions while it is on the ground or during pre-flight checks. This capability enhances efficiency and convenience for both ground crews and passengers before takeoff.

In contrast, the functions related to navigation, aircraft propulsion during takeoff, and in-flight entertainment are managed by other systems within the aircraft and do not align with the primary functions of the APU.