For a two-engine airplane, what is the maximum distance that a departure alternate airport may be from the departure airport?

The distance a departure alternate airport may be from the departure airport for a two-engine airplane should account for the time it would take to reach that airport under specific operational conditions. The correct choice indicates that the maximum distance is determined by the aircraft's ability to maintain flight on one engine, which is a critical factor for safety.

For a two-engine airplane, if an engine fails after departure, the pilot must ensure they can safely reach an alternate airport. The regulation states that this distance needs to be determined based on the aircraft's performance with one engine operating, particularly at normal cruise speed in still air. This requirement emphasizes the need for redundancy in engine power and ensures that, even in the case of an engine failure, the aircraft can reach safety within a reasonable timeframe, which is indicated as one hour in this context.

Choosing this option recognizes the inherent limitations of operating with one engine and reflects a conservative and safety-oriented approach to flight planning. In contrast, other options either overestimate the distance based on capabilities with both engines functioning or do not appropriately consider the need for emergency response when one engine is compromised. Thus, 1 hour at normal cruise speed in still air with one engine operating aligns correctly with safety regulations for two-engine aircraft, validating why this is the