What restraint requirements exist for cargo stowed on or above the floor line behind passengers?

The correct answer is that cargo must be restrained to prevent movement under maximum accelerations. This is crucial for ensuring safety during flight, particularly because unrestrained cargo can become a projectile in the event of turbulence or sudden changes in speed or direction. When cargo is stowed above the floor line, it poses a greater risk of moving and causing injury to passengers or damage to the aircraft.

The requirement for restraint is designed to maintain the integrity of the cabin and ensure that all items remain securely stowed at all times, safeguarding both the passengers and crew during all phases of flight. Properly securing cargo also helps in complying with aviation regulations, which mandate that all items carried in the cabin must be adequately restrained, especially those situated in areas accessible to passengers.

Other options suggest either a lack of requirements or that only certain items need to be restrained, which does not account for the comprehensive safety protocols in place in aviation. It is important to adhere to the highest safety standards, making the restraint of all cargo that could potentially shift during flight not just advisable but mandatory.