At what altitude is the autopilot minimum engagement for standard ILS approaches with an operational radio altimeter?

For standard ILS (Instrument Landing System) approaches with an operational radio altimeter, the minimum altitude for autopilot engagement is typically 50 feet. This is significant because it allows the autopilot system to automatically manage the descent and landing phase of flight with a high degree of precision.

50 feet is a commonly accepted minimum engagement altitude because it enables the autopilot to effectively assist the pilot just above the decision height of the approach. This height is crucial for ensuring safe operations during low visibility or adverse conditions typically associated with ILS approaches. Since the autopilot can maintain control of the aircraft at this critical phase, it ensures a smoother transition from autopilot control to manual flying, if necessary, just before touchdown.

The options indicating 150, 200, and 100 feet do not align with standard practices, as these altitudes would generally not allow the autopilot to efficiently manage the final stages of the approach and landing, which are critical for maintaining safety and accuracy in these operations.