Final answer:
Passengers and crew members must wear seatbelts in an aircraft during takeoff, landing, and turbulence to ensure safety and prevent injuries.
Step-by-step explanation:
In an aircraft, both passengers and crew members must wear seatbelts during takeoff, landing, and during any turbulence. This is to ensure the safety of everyone on board in case of sudden movements or accidents. For example, during takeoff and landing, when the plane is at a low altitude and experiencing maximum acceleration or deceleration, wearing seatbelts prevents passengers and crew members from being thrown around the cabin and getting injured. Additionally, seatbelts should be worn during turbulence because they can occur unexpectedly and cause the plane to jolt or shake. Seatbelts keep individuals safely secured in their seats during these situations, reducing the risk of injuries.