The pilot and passenger seat belt and shoulder harness requirements are referenced in FAR 91.107 and FAR 91.105. During takeoff and landing, crew members must wear both seat belts and shoulder harnesses (if equipped), unless the shoulder harness would interfere with their duties. In-flight, crew members must keep their seat belts fastened while at their station (pilot seat). The use of a shoulder harnesses in flight is not required, but it is encouraged when feasible.