What does the APU provide during ground operation and maintenance?

The APU, or Auxiliary Power Unit, serves as a crucial component during ground operations and maintenance by providing a self-contained source of pneumatic and electrical power. This capability allows the aircraft to operate various systems independently of the main engines, which is particularly important when the aircraft is on the ground. The APU can supply power for starting the main engines, powering onboard systems like lighting and avionics, and providing compressed air for engine starting or environmental control systems.

The ability of the APU to deliver both pneumatic and electrical power enables ground crews to conduct maintenance and operational checks without needing to run the aircraft engines, making it an essential part of ground support operations. The flexibility it offers in terms of power supply enhances both safety and efficiency during pre-flight preparations and servicing of the aircraft.