A firing pin in the catapult firing mechanism is actuated by ballistic gas from the 0.3-second delay initiator. The firing pin then strikes the catapult primary cartridge. The ballistic gas from the primary cartridge starts the inner and intermediate barrels to extend upward. The upward movement of the inner barrel releases the spring-loaded top latch plunger from the retaining groove on the inner barrel. As the inner barrel continues to extend up-ward, the ports of the inner and intermediate barrels expose the secondary cartridges. The secondary cartridges are ignited by the pressure and heat of the primary cartridge. The secondary cartridges assist in propelling both barrels and seat upward. After approximately 37 inches of travel, the piston head on the intermediate barrel contacts the pressure rings. These rings absorb the inertia force. The inner barrel continues to extend until it contacts the inner guide bushing. The inner barrel shears the rivet connecting the inner guide bushing to the intermediate barrel. This shearing separates the inner and intermediate barrels. The intermediate and outer barrels remain with the aircraft. The inner barrel remains with the ejection seat.

Manifold Check Valve

Gas from the delay initiators enters the manifold check valve and causes two internal check valves to be depressed. Then gas pressure passes to the catapult primary firing mechanism and severs the shear pin holding the firing pin.

Main Beam Assembly

The main beam assembly supports the major components of the ejection seat. The operation of the components supported by the main beam assembly is discussed in the following paragraphs.

TOP LATCH MECHANISM.- When the ejection seat is installed on the catapult, the top latch handwheel is removed. The top latch mechanism plunger passes through a hole in the outer barrel of the catapult and engages the locking groove. A locked indication is given by the position of the plunger and the indicator within the top latch mechanism housing. When the locking indicator spring-loaded plunger and mechanism housing are flush with each other, the top latch mechanism is locked. To remove the seat, you must install the top latch handwheel on the top latch plunger. This releases the seat from the catapult gun.

DROGUE GUN.- As the ejection seat rises, the trip rod withdraws the firing link from the drogue gun firing mechanism. This releases the spring-loaded firing pin. Firing pin movement is slowed for 0.5 second by an escapement mechanism to allow the ejection seat to clear the aircraft. After a 0.5-second delay, the firing pin activates the primary cartridge. Heat and pressure from the primary cartridge cause the secondary cartridge to fire. The gas produced by both car-tridges shears the shear pin and expels the piston from the drogue gun barrel. The drogue withdrawal line is attached to the piston. When expelled, the piston withdraws the pin from the closure flaps of the parachute container and deploys the drogue parachutes. The secondary cartridge serves as a backup system to the mechanically fired primary system. The cartridges in the time-release mechanism and manual override initiator provide gas pressure to the gas-operated secondary firing mechanism of the drogue gun. If the drogue gun primary firing mechanism fails, the gas-operated secondary firing mechanism cartridge will be fired by the secondary cartridge and the combined gas pressure will expel the piston from the drogue gun barrel to deploy the drogue parachutes.

TIME-RELEASE MECHANISM.- As the ejection seat rises, the trip rod also withdraws the firing link from the TRM and releases a spring-loaded firing pin. Firing pin movement is prevented for 1.5 seconds by a barostat and g-controller. When the altitude of the seat is less than 14,500 feet and acceleration forces are less than 3 g's, the barostat and g-controller release the firing mechanism. After the 1.5-second delay, the firing pin activates the cartridge. The gas produced by the cartridge passes to the upper body chamber and forces the shackle plunger down. This allows the scissor mechanism to open. At the same time, the gas actuates the connecting rod in the lower body and opens the inertia reel locks. Gas pressure is also provided to operate the piston to release the personnel parachute, manual override initiator, and the drogue gun secondary cartridge.

SCISSOR MECHANISM.- When the TRM cartridge fires, the shackle plunger retracts into the upper body of the TRM. This action allows the movable jaw of the scissor mechanism to open and release the personnel parachute from the container.