At what RPM percentage does the APU EC Unit inhibit starting when rotating in flight or on the ground?

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Multiple Choice

At what RPM percentage does the APU EC Unit inhibit starting when rotating in flight or on the ground?

Explanation:
The key idea is that the APU electronic control unit uses a start-inhibit speed to prevent a new start when the APU is already turning. If the APU is windmilling or rotating on the ground or in flight and the rotor speed is above 15% of the rated RPM, the ECU inhibits a start command. This protects the APU from unnecessary starts, fighting against rotation, and potential mechanical or control issues. When the RPM drops below 15%, a start can be attempted again, ensuring the start sequence only engages from a safe, non-spinning or nearly-stopped state.

The key idea is that the APU electronic control unit uses a start-inhibit speed to prevent a new start when the APU is already turning. If the APU is windmilling or rotating on the ground or in flight and the rotor speed is above 15% of the rated RPM, the ECU inhibits a start command. This protects the APU from unnecessary starts, fighting against rotation, and potential mechanical or control issues. When the RPM drops below 15%, a start can be attempted again, ensuring the start sequence only engages from a safe, non-spinning or nearly-stopped state.

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