When can the autofeather switch be armed?

The autofeather switch can be armed when both power levers are above 90% N1. This condition indicates that the engines are producing sufficient power, which is crucial for the autofeather system to function effectively.

The purpose of the autofeather system is to automatically feather a propeller in the event of an engine failure, reducing drag and allowing the aircraft to maintain better performance with the remaining operational engine. If either power lever is below the 90% N1 threshold, it suggests a reduced power state that would not typically warrant arming the autofeather, as it could lead to unnecessary or incorrect feathering of the propeller.

Thus, arming the autofeather switch is primarily intended for a situation where the engines are operating within a normal and powerful range, confirming that the aircraft is ready to respond effectively to an engine failure scenario. This understanding helps ensure the safety and performance of the aircraft during critical phases of flight.