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

• A. To power the main engines
• B. To provide electrical power and bleed air for engine start and ground operations
• C. To enhance fuel efficiency
• D. To control cabin temperature

Answer: (B)

The main function of the Auxiliary Power Unit (APU) is to provide electrical power and bleed air for engine start and ground operations. APUs serve as a critical support system in aircraft, especially during ground operations when the main engines are not running.

During these times, the APU generates electricity to power onboard systems and provides bleed air necessary for starting the main engines and for environmental control systems. This capability allows aircraft to operate efficiently on the ground without needing to rely on the engines for power, which can save fuel and decrease wear on the main engines.

Additionally, by supplying bleed air, the APU ensures that essential air pressure is available for starting the engines and for various pneumatic systems that may be in operation. Hence, its role is crucial for the overall functionality and readiness of the aircraft when it is on the ground.