Image Number 4 for United States Patent #7500639.
An aircraft ejection seat includes a frame and a headrest. The vertical position of the seat is adjusted by a pair of motor driven lead screws that cooperate with threaded barrel nuts attached to the seat frame. The upper end of one of these motor driven lead screws drives a slip coupling driving a splined shaft. The splined shaft then drives a gearbox mounted to the seat frame. The gearbox in turn drives an upper lead screw, which acts on an upper barrel nut to move the headrest up and down relative to the seat frame. The upper lead screw is driven in the opposite direction from the lower lead screws. Consequently, as the seat moves up to accommodate a shorter pilot, the headrest moves down to accommodate the shorter torso of the shorter pilot.