When a departure alternate is required for a three-engine air carrier flight, what is the maximum distance allowed?

The requirement for a departure alternate when operating a three-engine air carrier flight is based on the need to ensure safety in the event of an engine failure shortly after takeoff. The correct answer specifies a maximum allowable distance of two hours from the departure airport at normal cruising speed in still air with one engine not functioning. This is relevant because a three-engine aircraft can maintain safe flight and reach an alternate airport even with one engine inoperative.

The regulation is designed to enhance safety, ensuring that an aircraft can reach an alternate airport in the case an emergency arises soon after takeoff. The two-hour distance is also practical, providing sufficient options in various situations and allowing dispatchers and crew to manage contingencies effectively.

This contrasts with other options that either limit the distance or do not account for the aircraft's performance with a failed engine. Understanding these parameters is crucial for flight planning and ensuring compliance with operational safety standards.