During what conditions must the autofeather system be armed?

The autofeather system must be armed during takeoff, climb, approach, and landing conditions to ensure optimal engine performance and safety in the event of an engine failure. The system is designed to automatically feather the propeller of the failed engine, which reduces drag and allows for better control and performance of the aircraft.

By arming the autofeather system during these critical phases of flight, pilots are better prepared to respond to an engine failure. During takeoff, if an engine fails, feathering the propeller allows for the best rate of climb or aircraft performance with the remaining operating engine. In the approach and landing phases, it is equally crucial because any engine failure can lead to increased drag, which may compromise the ability to maintain glide slope and control of the aircraft.

In contrast, the other choices do not encompass the full range of operational conditions where the autofeather system provides vital assistance. Only arming the system during takeoff and landing would not account for potential engine issues during climb, where maintaining performance is also important. Limiting the system to descent would disregard its critical function in ensuring safe operations during takeoff and approach phases.