Final answer:
Part 91 requires passengers to fasten their safety belts or shoulder harnesses during takeoff, landing, taxi, and whenever the seatbelt sign is illuminated.
Step-by-step explanation:
Part 91 requires that all passengers be briefed on how to fasten and unfasten their safety belts or shoulder harnesses. Additionally, Part 91 requires that each person on board should fasten their safety belt or harness during takeoff, landing, taxi, and whenever the seatbelt sign is illuminated.