Seat Bucket Assembly

The ejection seat is fitted with a seat bucket assembly. The operation of the components supported by the seat bucket assembly is discussed in the following paragraphs.

UNDERSEAT ROCKET MOTOR/LAT-ERAL THRUST MOTOR.- The underseat rocket motor Mk 123 Mod 0 (forward seat) or Mk 124 Mod 0 (aft seat) is secured under the seat bucket, and is ignited as the catapult nears the end of its stroke. The thrust is approximately 4,800 pounds for 0.25 second, and sustains the thrust of the catapult to carry the seat to a height sufficient for a safe ejection. The thrust also provides the zero-zero capabilities that ensure a safe ejection.

EJECTION SEAT SAFE/ARM HANDLE.- To prevent inadvertent seat ejection, an ejection seat safe/arm handle is installed. To safety the seat, you must rotate the handle up and forward.

To arm the seat, you rotate the handle down and aft. When in the ARMED position, the portion of the handle that is visible to the pilot is colored yellow and black, with the word ARMED showing. In the SAFE position, the visible portion of the handle is colored white, with the word SAFE showing. By placing the handle to the SAFE position, it causes a pin to be inserted into the ejection firing mechanism. This prevents withdrawal of the sears from the dual-seat initiators.

LEG RESTRAINT SNUBBERS.- As the seat travels up the guide rails during ejection, the leg restraint lines, which are fixed to a floor bracket, are drawn through the snubbers. Inertia draws the legs against the front of the seat bucket, and the legs are retained in this position by the leg restraint lines. When the lines become taut and a predetermined load is attained, the special break rings fail and release the lines, leaving only a short loose end protruding from the snubbers. The leg lines are restrained by the snubbers, and the legs secured until the taper plugs are released from their locks when harness release occurs.

EMERGENCY RESTRAINT RELEASE HANDLE.- Rotation of the emergency restraint release handle to permit emergency ground egress will rotate the cross shaft of the lower harness release mechanism to release the lower harness locks, leg restraint line locks, and negative-g strap

lock. Full rotation of the handle to withdraw the sear of the firing unit is prevented by the pin puller engaging the rear end of the slot in the emergency restraint release operating link.

SHOULDER HARNESS CONTROL LEVER.-

The shoulder harness control lever, mounted on the left side of the seat bucket, is connected to the inertia reel, and provides manual control for the shoulder straps. In the forward position, the shoulder straps will be locked, and in the aft position, the shoulder straps will be unlocked so the occupant will be free to turn and move about.

SEAT HEIGHT ACTUATOR SWITCH.-

The seat height actuator switch controls electrical power to raise and lower the seat bucket to suit the needs of the occupant.

PIN PULLER.- During ejection, gas from the RH seat initiator cartridge enters the pin puller plunger housing and lifts the plunger out of engagement with the groove in the piston.

Movement of the plunger allows gas to enter the cylinder and withdraw the piston out of engagement with the slot in the emergency restraint release operating link, the piston being held in the operated position by residual gas pressure. The operating link is then disengaged from the lower harness release cross shaft by the action of a spring-loaded plunger in the operating link guide bracket mounted on the seat bucket side.

LOWER HARNESS RELEASE MECHA-NISM.- When the sequencer fires the barostatic release unit cartridge, the piston in the RH ballistic manifold acts on the harness reel cross-shaft lever. It rotates the cross shaft to withdraw the plungers in the upper harness locks and release the shoulder harness reel straps. At the same time, gas passes via the RH ballistic manifold down the RH trombone tube assembly, entering the emergency restraint release piston housing and face-firing the cartridge. The combined gas pressure from the two cartridges operates the emergency restraint release piston, operating the linkages to release the lower harness locks, the leg restraint line locks, and the negative-g strap lock.