Engines Auxiliary Power Unit (APU) Practice Exam

In soft alternate mode, which indicators are visible on the engine panel?

ON and ALTN Only ON Only ALTN Neither

Correct Answer:

ON and ALTN

Explanation:

In soft alternate mode, both indicators on the engine panel light up to show two linked pieces of information: the engine is on (ON) and the alternate path is active (ALTN). This dual indication helps the crew confirm that the engine is running while the system is using its backup/alternate configuration. If only the ON light were visible, you wouldn’t know that the alternate path is engaged; if only the ALTN light were visible, you’d know the alternate mode is selected but not that the engine is currently on. If neither light is on, there’s no clear status of either condition. So seeing both ON and ALTN together is the correct, informative state in soft alternate mode.

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