Some aircraft have seltbelts that attach to the seat which is free to slide for adjustment fore and aft by means of rails with detents for the latching mechanism.
The Army added armor to the seat and pilots added weight to the seat load by the wearing of body armor and other equipment.
Alas, when the aircraft crashed with any significant forward momentum....the seat with a tightly secured human crash dummy launched itself against or through the forward end of the aircraft.
Several Chinook pilots found themselves outside the aircraft in a hostile environment with very serious injuries.
Attaching the belts to the floor of the aircraft then added a problem of using the pilot's innards as a cushion for a runaway armored seat.
