An aircraft comprising: a fuselage; a mechanical failure sensor; a plurality of seats (22, 24) 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 (22, 24), 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 (22, 24); 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 (22, 24) 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 (22, 24) 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 (22, 24), 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 (22, 24); 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 (22, 24) 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 (22, 24); 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 (22, 24) of the aircraft; and characterized in that the precautionary event further comprises the mechanical failure sensor detecting an aircraft mechanical failure.