Engines Auxiliary Power Unit (APU) Practice Exam

During APU start, what condition is assessed by permissives before the start command is issued?

The weather forecast for the flight. The fuel tank level for the APU. Power available, doors closed, and no faults. The pilot's mood.

Correct Answer:

Power available, doors closed, and no faults.

Explanation:

Permissives are the prestart checks that must be true before the APU start command is allowed, to ensure a safe and reliable start. The essential conditions are that electrical power is available to drive the start motor and control circuitry, the APU bay doors are closed so there’s no risk of debris ingress and proper enclosure/airflow, and there are no faults detected in the system that would indicate a problem. When these three are satisfied, the system can initiate the start sequence without risking damage or unsafe operation. Weather information or fuel level for the APU isn’t part of this specific gating logic, and the pilot’s mood has no bearing on the start process.

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