An aircraft comprising: a fuselage ; a mechanical failure sensor ; a plurality of seats in the fuselage ; and a modal restraint system including a plurality of seatbelt subsystems (38a-38e), each seatbelt subsystem (38a-38e) adapted to secure an occupant to one of the seats , each seatbelt subsystem (38a-e) comprising: a strap feeder unit ; and a strap selectively retractable into and extendable from the strap feeder unit , the strap positionable adjacent to the occupant so as to at least partially dispose the occupant between the strap and the seat ; wherein, the strap feeder unit is adapted to switch between a plurality of modes including an unfixed mode and a fixed mode, the strap extendable from and retractable into the strap feeder unit in the unfixed mode, the strap substantially unextendable from the strap feeder unit in the fixed mode; wherein, the strap feeder unit is in the unfixed mode by default; wherein, the strap feeder unit is operable to switch to the fixed mode in response to a precautionary event, thereby reducing freedom of movement of the occupant relative to the seat of the aircraft; and characterized in that the precautionary event further comprises the mechanical failure sensor detecting an aircraft mechanical failure. a fuselage ; a mechanical failure sensor ; a plurality of seats in the fuselage ; and a modal restraint system including a plurality of seatbelt subsystems (38a-38e), each seatbelt subsystem (38a-38e) adapted to secure an occupant to one of the seats , each seatbelt subsystem (38a-e) comprising: a strap feeder unit ; and a strap selectively retractable into and extendable from the strap feeder unit , the strap positionable adjacent to the occupant so as to at least partially dispose the occupant between the strap and the seat ; wherein, the strap feeder unit is adapted to switch between a plurality of modes including an unfixed mode and a fixed mode, the strap extendable from and retractable into the strap feeder unit in the unfixed mode, the strap substantially unextendable from the strap feeder unit in the fixed mode; wherein, the strap feeder unit is in the unfixed mode by default; wherein, the strap feeder unit is operable to switch to the fixed mode in response to a precautionary event, thereby reducing freedom of movement of the occupant relative to the seat of the aircraft; and characterized in that the precautionary event further comprises the mechanical failure sensor detecting an aircraft mechanical failure. a strap feeder unit ; and a strap selectively retractable into and extendable from the strap feeder unit , the strap positionable adjacent to the occupant so as to at least partially dispose the occupant between the strap and the seat ; wherein, the strap feeder unit is adapted to switch between a plurality of modes including an unfixed mode and a fixed mode, the strap extendable from and retractable into the strap feeder unit in the unfixed mode, the strap substantially unextendable from the strap feeder unit in the fixed mode; wherein, the strap feeder unit is in the unfixed mode by default; wherein, the strap feeder unit is operable to switch to the fixed mode in response to a precautionary event, thereby reducing freedom of movement of the occupant relative to the seat of the aircraft; and characterized in that the precautionary event further comprises the mechanical failure sensor detecting an aircraft mechanical failure. <EOS>