What type of doors does an APU feature?

An Auxiliary Power Unit (APU) typically features an APU inlet door and an APU exhaust door as its primary functional components related to airflow. The APU inlet door allows ambient air to enter the unit to support combustion and cooling processes, while the APU exhaust door facilitates the expulsion of exhaust gases generated during operation. This design is crucial for the efficient functioning of the APU, ensuring that it can generate the necessary electrical power and bleed air for aircraft systems while maintaining safe operation by managing airflow and exhaust.

In contrast, other options such as flap doors and intake doors are not standard terminology associated specifically with APU design, nor are service and access doors primarily functional in the context of APU operation. Pressure relief and cooling doors, while potentially relevant to certain systems, do not directly represent the primary components of an APU. Thus, the identification of the inlet and exhaust doors as key elements underscores their importance in the operational integrity of the APU.