Under which conditions must flight crewmembers keep their safety belts fastened?

The requirement for flight crewmembers to keep their safety belts fastened during specific phases of flight is rooted in safety regulations aimed at protecting personnel in the event of turbulence, accidents, or emergency situations. During takeoff and landing, which are critical phases of flight with the highest risk factors, it is essential that crew members are secured with their safety belts to minimize the risk of injury.

In addition, the use of shoulder harnesses during takeoff and landing further enhances safety by providing additional restraint that can prevent movement and potential injury from sudden movements or unexpected events. This dual layer of restraint—safety belts and shoulder harnesses—is mandated during these phases to ensure that crewmembers remain secure and focused on their duties, prepared to handle any situation that may arise.

The answer reflects the specific regulatory requirements that aim to maximize crewmember safety, emphasizing the importance of being properly restrained throughout these critical flight phases.