parachute is deployed, to allow the velocity of the seat to reduce. The stabilizer drogue provides maximum deceleration while maintaining the seat in the optimum attitude for the occupant. The sequence timings of modes 2, 3, and 4 progressively extend the drogue phase with increasing speed and altitude so as to ensure that the parachute extractor is fired only when the seat velocity has reduced to a suitable level. The drogue bridle is jettisoned shortly after the parachute starts to deploy, both to avoid an entanglement and to allow the seat to fall clear of the occupant. Mode 5 is the high-altitude ejection sequence, in which deployment of the main parachute is delayed until the drogue-stabilized seat falls through the 18,000-feet altitude boundary. This allows the occupant to be brought down to a safer atmospheric condition in the shortest possible time. Once the parachute deployment sequence is initiated, the seat performs in an identical manner to that of modes 2, 3, and 4. BAROSTATIC RELEASE UNIT (BRU).— When the RH multipurpose initiator cartridge fires during ejection, gas pressure from the cartridge enters the piston housing and moves the piston upwards, rupturing the frangible disc and allowing the pawl to pivot clear of the rack assembly slotted end. When the altitude is such that the barostat is not restraining the mechanism, the rack assembly will rise under the action of its spring, the rate of ascent being governed by the delay mechanism. After the delay has elapsed, the rack disengages from the gear train and the firing pin rises rapidly to strike the cartridge. If the cartridge has not previously been fired electrically by the sequencer, the gas produced by the car- tridge passes out of the BRU to operate the upper- and lower-harness locks and the secondary cartridge in the parachute deployment rocket motor. DROGUE DEPLOYMENT CATAPULT.— During ejection, the drogue deployment catapult fires and ejects the drogue and canister. As the drogue deploys, the bridle breaks out of the frangible container and detaches from the channels on the main beams. The drogue stabilizes and decelerates the seat. In the high-altitude mode, the seat descends rapidly on the drogue to a predetermined altitude. The drogue bridle releases then operate, the personnel parachute deploys, and the occupant separates from the seat. In all other modes, the upper and lower drogue bridle releases operate after a short predetermined delay, as the personnel parachute deploys and seat/man separation occurs. The impulse cartridge is fired by an electrical signal from the sequencer. Gas from the cartridge propels the telescopic piston upwards, shearing the end cap rivets. Continued movement of the piston thrusts the canister upwards, shearing the rivets in the threaded ring and propelling the canister and drogue assembly away from the seat. The bridle is pulled from its frangible container and out of the channels on the seat’s main beams. As the bridle reaches full extension, inertia causes the canister to fly clear, and the drogue is extracted and deployed to stabilize and decelerate the seat. MULTIPURPOSE INITIATOR.— When ejection is initiated, the catapult ballistic latches operate to retain both multipurpose initiator lanyard spigots. As the seat moves up the guide rails, the static lanyard spigots break the shear pins and the lanyards pay out from the housings. When the lanyards become taut, the upper fittings withdraw the firing pins against spring pressure until the wedge-shaped disconnect devices separate. The firing pins move rapidly upward under spring pressure to fire the cartridges. The gas generated passes to the underside of the piston heads on the start switch plungers. The plungers move up, shearing the shear pins, until the gold- plated portions of the plungers complete an electrical connection in the switch assemblies. Sequencer timing then commences. Gas from the cartridges also passes out of the units to the barostatic release unit (RH side only), the pitot deployment mechanisms, and the underseat rocket motor. PITOT ASSEMBLY.— When the pitot assembly is installed on the seat beam, the inboard static pressure connector connects to a void in the seat beam. The sequencer is installed on the forward face of both pitot assemblies and connects to the dynamic and forward static pressure connectors. On ejection, gas pressure from the impulse cartridges in the multipurpose initiators enters the body and operates the lower piston. Movement of the lower piston pushes the pitot arm locking plunger out of engagement with the hole in the body, and at the same time, opens a gas passage to the upper piston. The upper piston moves outward to move the pitot arm to the deployed position. The pitot arm locking plunger engages with the second hole in the body and locks the pitot arm in the deployed position. 5-30