When is it inappropriate to operate the APU in flight or on the ground?

When is it inappropriate to operate the APU in flight or on the ground?

• A. On the ground, when external power is available or when APU operation is restricted by maintenance or noise/weight considerations; in flight, when not required or when flight ops guidelines prohibit APU use.
• B. In flight when required.
• C. On the ground only during maintenance.
• D. In all conditions.

Answer: (A)

The APU is there to provide electrical power (and sometimes bleed air) when the main power sources aren’t available, so it should be run only when needed. On the ground, if external power is available, or if maintenance holds off APU use or there are noise or weight concerns, it’s not appropriate to run the APU. You’ll rely on the external power source in those cases and bring the APU online only when it’s really required. In flight, the APU isn’t used routinely; it’s kept off unless there’s a specific need or if flight operations guidelines permit it. In short, use the APU only when it’s required for power or operations and avoid it when other power is available or when rules restrict its use.

The APU is there to provide electrical power (and sometimes bleed air) when the main power sources aren’t available, so it should be run only when needed. On the ground, if external power is available, or if maintenance holds off APU use or there are noise or weight concerns, it’s not appropriate to run the APU. You’ll rely on the external power source in those cases and bring the APU online only when it’s really required. In flight, the APU isn’t used routinely; it’s kept off unless there’s a specific need or if flight operations guidelines permit it. In short, use the APU only when it’s required for power or operations and avoid it when other power is available or when rules restrict its use.