Which flight crewmembers are allowed to leave their station during cruise?

The correct choice indicates that during cruise, the flight engineer and either pilot are permitted to leave their stations, but only one at a time. This is crucial for maintaining safety and operational efficiency during flight.

In a typical multi-crew operation, the flight engineer has specific responsibilities and must ensure that the aircraft's systems are functioning correctly while in cruise. Allowing one pilot to leave the cockpit for necessary tasks, such as attending to personal matters or performing checks, ensures that there is still a qualified person at the controls at all times.

This procedure is reinforced by aviation regulations which emphasize the need for at least one pilot to be present to monitor the flight, manage communications, and respond to any emergencies that may arise.

Other options suggest scenarios where either only one pilot can leave, which does not take the role of the flight engineer into account, or allow both pilots to leave simultaneously, which is not permitted due to the potential risk of leaving the aircraft without immediate pilot oversight. Overall, the selected answer reflects a balance between operational flexibility and safety.