General Authority of Civil Aviation (GACA) Aeronautical Information Publication (AIP) Practice Exam

What is the function of APU inlet door?

1. To control bleed air

2. To start the engines

3. To regulate electrical power distribution

4. To facilitate cabin pressurization

The correct answer is: To control bleed air

The function of the Auxiliary Power Unit (APU) inlet door is to control bleed air. When the APU is operating, the inlet door opens to allow air to enter the APU for combustion and to facilitate the generation of bleed air for various aircraft systems. This bleed air is essential for starting the main engines, providing pneumatic power for air conditioning, heating, and various other systems when the aircraft is on the ground. The precise control of this airflow is crucial for the efficient operation of the APU and the aircraft's environmental systems. While starting the engines, regulating electrical power distribution, and facilitating cabin pressurization are important functions in aircraft operations, they are not the direct purpose of the APU inlet door. Instead, these functions are supported by the bleed air that the APU produces, which is routed from the APU through various systems when the inlet door allows air to flow into the unit.