Выписка из британского Jump Pilot's Manual от 2008-го года по поводу использования сидений парашютистами
3.8. Seat / seat belt removal
It is quite common for all or some of the passenger seats and seat belts in jump aircraft to be removed prior to parachuting use. Seat belts are usually either attached to the seats themselves or to the cabin floor. When removing seat belts from a cabin floor attention must be paid to the remaining floor fittings which may need to be covered in order to protect them from snagging on parachutists’ equipment.
3.9. Restraints
In smaller aircraft it is common for parachutists to be unrestrained because the presence of belts/restraints on the floor would be hazardous to parachutists when exiting the aircraft because of their potential to snag parachute equipment or cause hang ups.
In larger aircraft, or where the Flight Manual requires it, it is common for alternative (usually single point) restraints to be provided where seats have been removed. These are usually attached prior to take off and disconnected prior to jumping. It would normally be the responsibility of the jumpmaster to ensure that restraints were utilised correctly, but ultimately it would be the responsibility of the pilot to be satisfied that there were an adequate number of restraints for the parachutists on board.
Where parachutists are utilising aircraft seating it would be usual for them to use whatever restraint belts came with the seats.
объясняется это тем, что эксплуатант не может отвечать за доставку подобного груза в конкретную точку.
но для доставки парашютиста самолеты должен иметь оборудованные пассажирские места для обеспечения безопасного взлета и посадки парашютистов внутри воздушного судна.
только вот не знаю где найти документ описывающий характеристики указанных пассажирских мест.
Allows skydivers to use the floor of an aircraft as a seat, provided that there is
a seat belt for each skydiver to use
https://www.faasafety.gov/file ...