MARTIN-BAKER SJU-5/A EJECTION SEAT

The SJU-5/ A ejection seat is a ballistic catapult and rocket system that gives the pilot a quick and safe means of escape from an aircraft. The seat system includes an initiation system that jettisons the canopy, positions the pilot for ejection, and fires the seat catapult. Canopy breakers on the top of the seat allow the seat capability to eject through the canopy should it fail to jettison. As the seat ejects from the aircraft, a rocket motor on the bottom of the seat is fired. Then a drogue gun is fired to deploy two drogue parachutes. These parachutes either remain attached to the top of the seat or they are released to deploy the main parachute, depending upon the altitude and the number of g's applied to the seat. An automatic time-release opens the main parachute container and releases the drogue parachutes that deploy the main parachute.

SYSTEM OPERATION

Before flight, the ejection seat safe/ arm handle is kept in the SAFE position. In this position, the visible portion of the handle is coloured white and placarded as SAFE. When the aircraft is ready for flight, the pilot sets the safe and arm handle to the ARMED position. In this position, the visible portion of the handle is coloured with yellow and black markings and placarded as ARMED. The ejection sequence (fig. 6-19) starts when the pilot pulls the ejection control handle. The up-ward movement of the handle removes two sears from the seat initiator and fires two cartridges with the seat initiator.

Firing Sequence

Ballistic gas generated by the right cartridge within the seat initiator actuates the pin puller. The gas also activates the shielded mild detonating cord (SMDC) initiator. The SMDC then activates the aircraft identification friend or foe unit (IFF) and the canopy jettison system. Additionally, it activates the inertia reel cartridge and the 0.3-second delay initiator. Ballistic gas generated by the left cartridge within the seat initiator starts the 0.3-second delay initiator. Ballistic gas pressure from either 0.3-second delay initiators ignites the primary cartridge within the catapult.

Catapult Firing and Initial Seat Movement 

Ballistic gas pressure developed by the catapult primary cartridge causes the inner and intermediate barrels within the catapult to rise and release the top latch mechanism. The secondary cartridges within the catapult fire progressively as the rising barrels are exposed to the heat and pressure of the primary cartridge gas. Progressive firing of the catapult secondary cartridges provides a relatively even gas pressure during catapult extension. This eliminates excessive g-forces during ejection. As the seat moves upward, the emergency oxygen system is activated. A trip rod withdraws the firing link from the drogue gun and starts a 0.5-second internal timer. Another trip rod withdraws the firing link from the time-release mechanism. Aircraft electrical power and personal services (oxygen and communication) between the seat and the aircraft are disconnected. At this point in the sequence, the leg restraint lines are drawn through the snubbing units to restrain the pilot's legs to the seat bucket. When the leg restraint lines become taut, the upper portion of the leg restraint line shears from the lower portion, which is attached to the floor bracket. Forward movement of the lines is prevented by the snubbing units.

After 72 inches of catapult extension, the rocket motor initiator is fired by a cable that is attached to the drogue gun trip rod. Ballistic gas pressure generated by the cartridge within the rocket motor initiator is routed to a pressure actuated firing mechanism located on the rocket motor. Flame and pressure ignite the rocket motor propellant grain. The thrust of the motor is approximately 4,500 pounds and lasts for 0.25 second.

Aircraft and Seat Separation

Separation of the seat from the aircraft occurs at approximately 76 inches of catapult extension. At this point, the inner barrel separates from the intermediate barrel. The seat is now clear of the aircraft. The drogue gun primary cartridge fires after a 0.5-second delay to propel the piston from the drogue gun barrel. The inertia of the piston extracts the parachute flap closure pin and deploys the 22-inch controller drogue. The controller drogue, in turn, deploys the 60-inch stabilization and retardation drogue. The 0.5-second time delay allows the seat to reach its maximum altitude before the drogues are fully developed. The seat will stabilize and decelerate because of the drogues, which are held to the seat by the scissor mechanism.

If the drogue gun primary cartridge fails to fire, ballistic gas pressure will pass to the drogue gun when the time-release mechanism (TRM) fires. This gas shears the firing pin retaining pin. The firing pin then strikes the secondary drogue gun cartridge, which results in drogue deployment. Should both the drogue gun primary and time-release mechanism cartridges fail to fire, operation of the manual override handle will fire the manual override initiator cartridge. This duplicates the function of the TRM and fires the drogue gun secondary cartridge. The drogue gun then deploys the drogue parachutes and personnel parachute concurrently. The TRM altitude-sensing barostatic time release prevents the 1.5-second timer from starting at altitudes above 11,500 feet. The barostatic time release ensures that the pilot descends rapidly through the upper atmosphere to a more survivable altitude. At altitudes between 7,500 and 11,500 feet, the time delay for deployment of the personnel parachute is con-trolled by an internal g-limiter, which interrupts the timing sequence until the deceleration force is less than 1.5 g's. This results in lower parachute opening loads. At altitudes below 7,500 feet, the 1.5- second timer starts without interruption. After the 1.5-second timer delay, the TRM cartridge fires. This releases the upper restraint mechanism, lower restraint mechanism, parachute mechanical lock, and drogue shackle. When the drogue is free from the scissor mechanism, it deploys the personnel parachute. The personnel parachute lifts the pilot and the survival kit from the seat and pulls the sticker-clip strap lugs from their clips. This is necessary to ensure that collision between the seat and the pilot is avoided. The radio beacon activates when pilot and seat separation occurs. Then a normal parachute descent begins. While descending in the parachute, the pilot can pull the survival kit handle to separate the kit halves. This allows deployment and automatic inflation of the life raft. The life raft and survival kit items are connected by a lanyard to the survival kit lid, which is attached to the pilot.

 

Figure 6-19.- Ejection seat sequencing schematic.

 

SYSTEM COMPONENTS 

The SJU-5/ A ejection seat system (fig. 6-20) provides support for the pilot during normal flight conditions and a method of escape from the air-craft during emergency conditions. Selected seat system components are discussed in the following paragraphs and keyed to figure 6-20.

Catapult

The catapult (3) is a cartridge-actuated device that provides the initial force required to eject the seat from the aircraft. The catapult is located within the main beam assembly (6) and is attached to the bulkhead of the cockpit by two mounting lugs. The ejection seat is installed on the catapult with three pairs of slippers located on the inboard side of the main beam assembly. The main beam assembly fits into catapult guide rails located on the outboard sides of the catapult's outer barrel. The ejection seat is locked to the catapult by the top latch mechanism. The catapult consists of three major parts: the inner barrel, the intermediate barrel, and the outer barrel.

INNER BARREL.- A neck-shaped piston head, fitted with a set of expander and piston rings, is attached to the lower end of the inner barrel to provide a gas seal with the intermediate barrel. A breech is located at the upper end of the inner barrel for the primary firing mechanism and cartridge. The breech has a groove on the out-side edge into which the plunger of the top latch mechanism of the ejection seat is engaged.

INTERMEDIATE BARREL.- The inter-mediate barrel is located between the inner barrel and the outer barrel. The intermediate barrel increases the length of catapult extension. It also restrains bending loads incurred during ejection. A piston head fitted with two sets of six expander and piston rings is attached to the lower end. The piston head serves as a gas seal between the intermediate barrel and the outer barrel. A guide bushing is riveted to the upper end of the intermediate barrel to keep the inner barrel steady during extension. The guide bushing rivets are sheared by the neck-shaped piston head of the inner barrel during ejection. This allows separation of the inner and intermediate barrels. Twelve pressure rings are installed on the intermediate barrel to absorb the inertia forces encountered during barrel separation.

OUTER BARREL.- The outer barrel houses the intermediate and inner barrel assemblies. Two breeches are located on the aft side to accept the auxiliary cartridges. Two guide rails are bolted on the outboard sides of the outer barrel. The lower end is used to attach the catapult to the aircraft. The upper end has a square aperture to engage the plunger of the top latch mechanism. The upper fitting is threaded for the guide bushing that retains the intermediate barrel. The guide bushing is locked in place by a dowel screw.

TOP LATCH MECHANISM.- The main beam assembly is secured to the catapult by the top latch mechanism, which is located on the upper end of the left beam. The mechanism consists of a housing with a spring-loaded plunger. The inboard end of the plunger is shaped to engage the catapult inner barrel. The outboard end is threaded to accept the top latch hand wheel. When the hand wheel is installed, it permits removal of the ejection seat from the catapult.

 

Figure 6-20.- Martin-Baker SJU-5/ A ejection seat.

Manifold Check Valve

The manifold check valve (24) (figs. 6-20 and 6-21) provides an interface between the ejection seat and the catapult. The manifold check valve is mounted to the top of the catapult. The valve is held against the primary firing mechanism by a spring-loaded plunger and a retaining pin. The valve contains two inlet ports, which connect the hoses from the 0.30-and 0.30/ 0.75-second delay initiators. Internal check valves ensure that 400 to 600 psi gas pressure is maintained at the catapult primary firing mechanism.

Main Beam Assembly 

The main beam assembly (6) (fig. 6-20) is the main structure of the ejection seat. The main beam assembly consists of left and right vertical beams bridged by three cross members. The assembly supports the major components of the ejection seat. Three slippers are bolted to the in-board side of each beam to engage the guide rails on the catapult outer barrel. The upper cross member is used to hold and correctly position the top of the catapult. This member withstands the full thrust of the catapult during the ejection sequence. The bolts that attach the upper cross member to the main beam assembly also attach the top latch mechanism to the left beam. The inertia reel (12) and the upper attachment for the seat height actuator are mounted to the centre cross member. Two tabular tubes are secured to the centre and lower cross members. The tubes have two sliding runners that attach to the seat bucket. The seat height actuator rod is attached upper cross member.

Figure 6-21.- Scissor mechanism and manifold check valve

SCISSOR MECHANISM.- The scissor mechanism (25) (fig. 6-20) (also shown in fig. 6-21) is located on top of the main beam assembly upper body of the time-release mechanism. The scissor mechanism has a moveable jaw, which is held in the main the closed position by the shackle plunger.

TIME-RELEASE MECHANISM.- The time-release mechanism (TRM) (23) (fig. 6-20) (also shown in fig. 6-22) is mounted on the out-board side of the right beam. The TRM automatically releases the drogue parachutes, deploys the personnel parachute, and releases the pilot from the ejection seat at the proper time in the ejection sequence. The TRM consists of a time-delay mechanism, barostat assembly, barostatic g-controller, spring-loaded firing mechanism, connecting rod, cartridge, and a shackle plunger assembly. The shackle plunger is secured in the scissor shackle plunger housing to lock the scissor mechanism in the closed position, as shown in figure 6-21.

Figure 6-22.- Time-release mechanism.

In this position, the drogue shackle is secured to the ejection seat. Gas lines connect the TRM to the manual override initiator and to the secondary cartridge of the drogue gun. A piston located on top of the upper body engages the parachute mechanical lock to secure the personnel parachute.

The TRM 1.5-second time-delay mechanism delays seat/ man separation and deployment of the personnel parachute until the drogue parachutes stabilize and decelerate the ejection seat. The barostat assembly delays the deployment of the personnel parachute until the pilot and the ejection seat descend to 14,500 feet. This delay prevents prolonged descent in the upper atmosphere. When ejection occurs above 7,500 feet, a barostat g-controller delays the deployment of the personnel parachute until deceleration loads are less than 3 g's.

DROGUE GUN.- The drogue gun (1) (fig. 6-20) (also shown in fig. 6-26) is mounted on the outboard side of the left beam. The drogue gun deploys the drogue parachutes during the ejection sequence. The drogue gun incorporates a 0.5-second delay to ensure that the ejection seat has cleared the cockpit prior to deploying the drogue parachutes. The gun consists of a body and a barrel assembly. The drogue gun body contains a time-delay mechanism, a spring-loaded firing pin, and two cartridges (primary and secondary). The barrel assembly contains a piston that is held in place by a shear pin. The barrel holds the primary cartridge and water seal. The primary cartridge is mechanically fired by a trip rod attached to the cockpit bulkhead. A chamber connected by a gas passage to the barrel holds the secondary cartridge and a gas-operated firing mechanism. This chamber ensures that actuation of either cartridge will fire the piston from the barrel.

INERTIA REEL ASSEMBLY.- The inertia reel (12) (fig. 6-20) is mounted on the center cross member of the main beam assembly. During normal operation in the UNLOCK position, the inertia reel is free to extend or retract as required by the pilot's movements, but an automatic lock feature will prevent rapid forward movement. When the rapid movement ceases, the inertia reel returns to normal operation. When the inertia reel is in the LOCKED position, it will retract the straps but will not allow them to extend. When the ejection sequence is initiated, a pyrotechnic cartridge is used to activate the inertia reel. This retracts and locks the pilot into the correct position for ejection.

ROCKET MOTOR INITIATOR.- The rocket motor initiator (4) (fig. 6-20) is mounted on the outboard side of the left beam. The rocket motor initiator consists of a cartridge chamber, a firing mechanism, and a coiled static line. The chamber is attached to the trombone fittings (9) by an outlet connector. The static line is coiled into a plastic container. The upper end of the line is attached to the quadrant lever and the lower. end is attached to the drogue gun trip rod.

SEAT HEIGHT ACTUATOR.- The seat height actuator is mounted in the main beam assembly forward of the catapult gun. The actuator permits adjustment of the seat bucket within a vertical travel of approximately 5 inches. The seat height actuator consists of an electric motor and housing, gearbox, bearing housing, and jackscrew assembly.

AIRCRAFT SEAT PARACHUTE.- The aircraft seat parachute container (13) (fig. 6-20) is located near the top of the main beam assembly. The parachute consists of a 22-inch controller drogue, a 5-foot stabilizing main drogue, and a 17-foot personnel parachute. The controller drogue deploys the stabilizing drogue that decelerates and stabilizes the ejection seat during the initial phase of the ejection sequence. The personnel parachute provides the pilot with a safe means of descent. The parachute container provides support for the pilot's head during for-ward acceleration or wind blast. The personnel parachute is packed in the container first. It is secured by flaps and a closure pin that is attached to the personnel parachute withdrawal line. The withdrawal line attaches the main drogue to the apex of the personnel parachute. Then the main and controller drogues are packed. They are secured by four flaps and a closure pin, which is attached to the drogue withdrawal line. The drogue shackle secures the parachute withdrawal line and extender strap. Then the drogue shackle is secured in the scissor mechanism.

Seat Bucket The seat bucket (14) (fig. 6-20) is mounted on the lower forward side of the main beam assembly. It is attached to studs on the seat bucket runners. The components described in the following paragraphs are related to the seat bucket.

EJECTION CONTROL HANDLE.- The ejection control handle (16) is located on the front of the seat pan. It is the only means by which ejection can be initiated. The handle is moulded in the shape of a loop and is connected to the sears of the ejection seat initiators. The seat initiators have two rigid lines that connect to the trombone fittings. An upward pull of the loop removes both sears from the dual initiators to initiate ejection. Either initiator can fire the seat. After ejection, the handle remains attached to the seat. The ejection control handle is made safe by using the ejection seat safe/ arm handle and safety pin.

EJECTION SEAT SAFE/ ARM HANDLE.- To prevent inadvertent seat ejection, an ejection seat safe/ arm handle (18) 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 coloured yellow and black with the word ARMED showing. In the SAFE position, the visible portion of the handle is coloured white with the word SAFE showing. By placing the handle to the SAFE position, it causes a pinto be inserted into the ejection firing mechanism. This prevents withdrawal of the sears from the dual seat initiators.

SHOULDER HARNESS CONTROL HANDLE.- The shoulder harness control handle (11) and seat height adjustment switch (10) are mounted on the left side of the seat bucket. The shoulder harness control handle is connected to the inertia reel. The seat height adjustment switch controls electrical power to the seat height actuator motor.

MANUAL OVERRIDE HANDLE.- The manual override handle (17) is located on the right side of the seat bucket. The handle is connected to the lower restraint mechanism. It is also connected to the manual override initiator.

MANUAL OVERRIDE INITIATOR.- The manual override initiator (19) is mounted in a covered compartment in the lower aft right side of the seat bucket. A linkage connects the sear to the manual override handle. Pulling the handle releases the lower restraints. Full upward movement of the handle is prevented by the pin puller. However, during ejection, the pin puller is automatically retracted. This allows the manual override handle to pull the sear from the manual override initiator, which will override the automatic sequencing. This is accomplished by routing gas pressure to the time-release mechanism and the secondary cartridge of the drogue gun.

PIN PULLER.- The pin puller (20) (fig. 6-20) (also shown in fig. 6-23) is located on the aft right side of the seat bucket. Full aft rotation of the manual override handle is prevented by the pin puller. A pin extended from the pin puller engages a slot in the manual override linkage. During the ejection sequence, gas pressure from the right seat initiator cartridge retracts the pin.

ROCKET MOTOR.- The rocket motor (8) is attached to the bottom of the seat bucket. A rigid line from the rocket motor firing mechanism is connected to the inboard trombone fitting on the aft left side of the seat bucket. The trombone fitting interfaces with the rocket motor initiator, which is located on the main beam assembly. The rocket motor consists of a firing mechanism, igniter cartridge., manifold, four nozzles, and 17 propellant tubes. Gas pressure from the rocket motor initiator forces the firing mechanism into the igniter cartridge. The rocket motor ignites as the catapult nears the end of its extension and raises the ejection seat to a height sufficient for a safe ejection, even if the aircraft has zero speed and zero altitude. The rocket motor produces approximately 4,500 pounds of thrust for 0.25 second. The nozzles on the seat are positioned forward and outward. This positioning allows the thrust to pass close to the centre of gravity of the ejection seat and pilot.

SEAT SURVIVAL KIT.- The SKU-3/ A seat survival kit (fig. 6-24) consists of a two-piece bonded fibre glass container and a seat cushion. The kit is located in the seat bucket and functions as a seating platform for the pilot. The survival kit contains the torso harness attachments, locking system, retaining lanyard, survival equipment, radio beacon, and emergency oxygen. A bracket for insertion of the negative-g strap is mounted on the forward lower half of the survival kit. The emergency oxygen system, located in the lid of the survival kit, consists of an emergency oxygen cylinder, reducer assembly, actuation assembly, and manifold assembly. A lanyard and quick-disconnect fitting provide automatic actuation of the emergency oxygen system during ejection. If the aircraft oxygen system fails, emergency oxygen is available by actuating the emergency oxygen manual release. The release is a green ring located on the forward left side of the survival kit. A mounting is provided for the radio locator beacon and lanyard. The lanyard actuates the beacon upon ejection.

 

Figure 6-23.- Manual override system

Figure 6-24.- SKU-3/ A survival kit

LEG RESTRAINTS.- Two leg restraint line snubbing units and lines are mounted to the for-ward structure of the seat bucket. The leg restraint lines are secured in locks located on the inboard sides of the seat bucket. The leg restraints secure the pilot's legs to the seat during ejection. They consist of two adjustable leg garters, a restraint line, and a snubber unit for each leg. One garter is worn on the thigh and one on the lower leg. The restraint lines are routed through the garter rings and the snubber unit. One end of each restraint line is secured to the cockpit floor and the other is secured to the seat by a releasable pin. During ejection, the slack in each line is taken up and the leg lines separate at the tension rings. When the pilot and seat separate, the pins are normally released by the time-release mechanism. They may also be released by pulling the manual override handle. Both the lower garter and thigh garter contain a quick-release buckle. The leg restraint line runs through a ring that is disconnected by the buckle. This permits the pilot to exit the air-craft while wearing both the upper and lower garters. The lower restraint mechanism locks are located in the lower aft portion of the seat bucket. These locks are connected by a cross shaft and linkage to the leg restraint line locks and the negative-g strap lock.

COMPONENT OPERATION

The operation of SJU-5/ A system components and subsystems is discussed in the following paragraphs.

Catapult

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 hand wheel 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 hand wheel 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 cartridges 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.

INERTIA REEL ASSEMBLY.- During the ejection sequence, gas pressure is used to fire the inertia reel cartridge. The gas pressure forces the head of the piston along the cylinder. The horizontal movement of the piston is transmitted by a threaded drive screw to rotate the ratchet wheel. The rotation of the ratchet wheel retracts the inertia reel straps and restrains the pilot in the seat. Then the locking pawl locks the spools in the retracted position. Extension of the inertia reel straps at excessive speed causes the governor pawls to rotate outward because of centrifugal force. They engage the rack on the housing, which prevents any additional extension of the straps. When the shoulder harness control handle is in the rear position, the system restrains the pilot from moving forward. With no tension applied to the inertia reel straps, the pawl will reset itself and disengage from the rack. This will allow free extension of the straps.

ROCKET MOTOR INITIATOR.- During the ejection sequence, the static line connected to the drogue gun trip rod and to the rocket motor initiator is withdrawn from the aft initiator housing. When the static line is extended to approximately 72 inches, a spring-loaded plunger is unlocked. The plunger rotates the quadrant lever and removes the sear from the firing mechanism. Removal of the sear fires the cartridge in the breech. The gas produced is routed to the rocket motor firing mechanism, which ignites the rocket motor.

AIRCRAFT SEAT PARACHUTE.- The drogue shackle, which contains the parachute withdrawal line and extender strap, allows the drogues to be deployed without extraction of the personnel parachute. A mechanical lock secures the parachute withdrawal line to prevent premature deployment until pilot and seat separation has occurred. The lock is released by a piston in the upper body of the time-release, mechanism. The parachute risers are routed down the forward side of the parachute container. Quick-release fittings are located on the end of the risers and connect to the pilot's torso harness. The inertia reel straps are routed from the inertia reel, through the parachute riser roller fittings, and are secured in the inertia reel locks.

SEAT BUCKET SUPPORTED COMPONENTS

The seat bucket supports several components on the lower portion of the ejection seat. The operation of these components is discussed in the following paragraphs.

Ejection Seat Initiator

With the safe and arm handle in the down or ARMED position, an upward pull on the ejection control handle removes the two sears from the firing mechanisms and causes the two cartridges within the initiator to fire. Gas pressure from either cartridge will initiate seat ejection.

Manual Override Initiator

Aft rotation of the manual override handle positions the safe and arm handle up to the SAFE position and releases the lower restraint. In this position, the pin puller engages a slot in the manual override handle linkage and prevents actuation of the manual override initiator. During the ejection sequence, the pin puller is retracted inboard. This allows the manual over-ride initiator to be actuated and override the automatic sequencing. Gas pressure from the manual override initiator is piped to the time-release mechanism and the secondary cartridge in the drogue gun.

Pin Puller 

During the ejection sequence, gas pressure from the right seat initiator cartridge enters the pin puller and operates a spring-loaded ball lock. This allows the -pressure to retract the pin and disengage it from the manual override linkage.

Seat Survival Kit The seat survival kit is opened by operating the release handle located on the right forward side of the kit. During the ejection sequence, the oxygen hose and communication lead disconnect from the aircraft. The emergency oxygen and radio beacon are automatically actuated. During parachute descent, the pilot may operate the release handle to open the survival kit. This allows deployment and inflation of the life raft. The life raft and survival equipment are connected by a lanyard to the survival kit lid, which is attached to the pilot.

Manual Override System

Operation of the manual override handle will rotate the cross shaft of the lower harness locks, leg restraint line locks, and the negative-g strap lock. This is necessary for emergency ground egress from the aircraft. Full aft rotation of the handle is prevented by engagement of the pin puller piston in a slot of the manual override handle linkage. This prevents firing of the manual override initiator.

During the ejection sequence, gas pressure from the right seat initiator cartridge operates the pin puller to withdraw the pin puller piston from the slot in the manual override handle linkage. In the event of a time-release mechanism failure or drogue gun failure above barostatic altitude, aft rotation of the manual override handle will fire the manual override initiator. Gas pressure from the manual override initiator cartridge operates the lower harness release system. It will also pass up the trombone fitting and fire the time-release mechanism cartridge. This cartridge operates the upper harness release mechanism, scissor mechanism release plunger, and parachute lock. Additionally, the gas pressure passes to the drogue gun and fires the secondary cartridge.

Leg Restraint System

As the seat travels up the guide rails during the ejection sequence, the leg restraint lines are drawn through the snubbing units. This action pulls the pilot's legs aft against the seat bucket. As the seat continues to rise, the leg restraint lines become taut. When the force on the bottom fittings reaches approximately 900 pounds, the shear ring will shear. The shearing releases the lower portion of the leg restraint lines.

Automatic Harness Release System

Firing of the time-release mechanism cartridge moves the piston and connecting rod down and rotates the cross shaft. Rotation of the cross shaft releases the inertia reel locking plungers and releases the inertia reel straps. Simultaneously, gas pressure is routed down the trombone fitting to fire the cartridge in the manual override initiator. Gas pressure from the manual override initiator cartridge presses against the head of the piston. Movement of the piston rotates the bell crank lever and releases the spring-loaded locking plungers of the lower harness locks. This releases the lap belt lugs and rotates the cross shaft. Rotation of the cross shaft releases the looking plungers in the leg restraint line and negative-g strap locks.

 

COMPONENT TEST AND TEST EQUIPMENT 

Ejection seats and associated components are carefully designated, manufactured, and tested to ensure dependable operation. Such equipment must function perfectly the first time it is used. Malfunction or failure to operate usually results in severe injury or death to crew members. You must use the utmost care in maintaining escape system equipment. Proper handling and strict compliance with the maintenance procedures presented in the maintenance instructions manuals (MIMs) and the maintenance requirements cards (MRCs) are mandatory and cannot be overemphasized.

NOTE: The information presented in this chapter must not be used in place of information provided in the MIM. The SJU-5/ A ejection seat undergoes a variety of functional checks during the 364-day special inspection. In-depth testing of the firing unit mechanisms, catapult gun, time-release mechanism, drogue gun, and a complete mechanical operational check is required. The time-release mechanism and drogue gun checks are discussed in the following paragraphs.

Drogue Gun Check-out

The drogue gun must be removed from the ejection seat to accomplish the check-out. You should make sure the drogue gun is disarmed before performing any maintenance on it. Then, you should remove the drogue gun barrel and piston and inspect them for damage and corrosion. The three tests used in the check-out are the time-delay test, the firing pin protrusion test, and the firing pin cocking test. These tests must be done with the barrel and piston removed. These tests are discussed in the following paragraphs.

TIME-DELAY TEST.- To complete the time-delay test, you should perform the following steps in sequence. 1. Install the drogue gun adapter on the time-delay test base. Connect the adapter electrical cables to the time-delay test set timer. Then connect the test set to a 110-volt ac 60-Hz power supply. An air source regulated to 80 psi is also required. Figure 6-25 reflects the correct mounting of the drogue gun to the test set. 2. Extend the ram connecting plunger by pressing the reset button on the test set. The reset

Figure 6-25.- Drogue gun time-delay check-out

button also sets the timer to zero. Remove the lock wire from the drogue gun firing link and remove the hex head plug from the base of the drogue gun. Ensure the drogue gun is secured to the test set with the clamp. Next, attach the drogue gun firing link to the test set connecting ram plunger with the connecting link and connecting pins. Install the light interrupter into the base of the drogue gun.

NOTE: Before proceeding any further with the test, ensure quality assurance (QA) personnel are present to witness the results. 3. Press the time-delay test set actuate button and record the time required to pull the firing link from the drogue gun. The elapsed time should not exceed 0.5 0.1 second. If the testis unsuccessful, the drogue gun must be replaced. 4. Remove the light interrupter and drogue gun from the test set and secure the equipment.

FIRING PIN PROTRUSION TEST.- To complete the firing pin protrusion test, you should perform the following steps in sequence.

1. Place the protrusion gauge over the firing pin.

2. Check the position of the inner centre shaft of the gauge. It must be flush or slightly above the gauge outer case, as shown in figure 6-26.

3. If the firing pin fails this test, the drogue gun must be replaced.

FIRING PIN COCKING TEST.- To complete the firing pin cocking test, you should perform the following steps in sequence.

1. Place the drogue gun clamp into a vice and position the drogue gun on the clamp. Screw the cocking handle into the base of the drogue gun.

2. Pull the handle until the firing mechanism is fully extended. With the mechanism fully extended, install the firing link into the drogue gun.

3. Release the tension on the cocking handle. If the mechanism is cocked, the firing link will be held firmly in place.

4. Remove the handle and install the hex head plug and washer.

5. Lock wire the firing link to the drogue gun housing by inserting the lock wire through the housing and roll pin, which is attached to the firing link.

NOTE: At this point in the procedure, request QA to inspect the engagement and lock wiring of the sear.

Figure 6-26.- Drogue gun firing pin protrusion check-out

Time-Release Mechanism Check-out 

The time-release mechanism must be re-moved from the ejection seat to perform this check-out. You should ensure the TRM is disarmed before performing maintenance on it. Then, remove the firing body from the time-delay g-sensing release mechanism. Re-move the lock wire from the firing link and remove the hex head plug and washer from the base of the unit. Inspect the TRM for damage and/ or corrosion. If damaged or corroded, check the MIM for corrective action to be taken.

Time Delay Check-Out

To complete the time delay check-out, you should perform the following steps in sequence.

1. Remove the light interrupter from the test set and screw it into the base of the time-delay g-sensing release mechanism, as shown in figure 6-27. Install the TRM adapter on the time-delay test set base. Connect the adapter

Figure 6-27.- Time-release mechanism time delay check-out

electrical cables to the time-delay set timer. Then connect the test set to a 110-volt ac 60-Hz power supply. Again, you will need an air source regulated to 80 psi.

2. Extend the ram connecting plunger on the test set by pressing the reset button. Position the TRM on the test set and secure it with a test set clamp. Attach the time-delay g-sensing release mechanism firing link to the test set ram connecting plunger, connecting link, and connecting pins. NOTE: At this point, you should ensure QA personnel are present to witness the elapsed time function.

3. Press the time-delay test set actuate button and record the time required to pull the firing link from the time-release g-sensing release mechanism. The elapsed time should not exceed 1.5 0.1 seconds. If the time is greater than 1.5 0.1 seconds, the unit must be replaced.

FIRING PIN PROTRUSION CHECK.- To complete the firing pin protrusion check, you should perform the following steps in sequence.

1. With the cartridge body removed from the TRM, place the TRM protrusion gauge over the firing pin.

2. Check the position of the inner center shaft of the gauge. It must be flush or slightly above the outer case of the gauge.

3. If the firing pin fails this test, it must be replaced.

FIRING MECHANISM COCKING TEST.- To complete the firing mechanism cocking test, you should perform the following steps in sequence.

1. Place the TRM clamp in a vice and position the TRM on the clamp. Screw the TRM cocking handle into the base of the TRM. Pull the cocking handle until the firing mechanism is fully extended.

2. In this position, install the test firing pin into the time-delay g-sensing release mechanism. The test firing pin is furnished as part of the TRM test set.

3. Release the tension on the cocking handle. Ensure the mechanism is cocked by pulling on the test firing pin. If the firing mechanism is cocked, it will be held firmly in place.

4. Remove the cocking handle from the TRM. Then remove the TRM from the clamp. The TRM is now cocked and ready for the barostat test check out.

Barostat Check-Out 

To complete the barostat check-out, you should perform the following steps in sequence.

1. Connect the TRM test box to a 110-volt ac 60-Hz power supply. Ensure all protective plugs and parts of the test set are installed in the test box holes labelled "cocking control and altitude."

2. Position the TRM in the test set and secure it with a clamp screw, as shown in figure 6-28.

3. Insert the operating handle through the hole in the test set labelled "firing control." Screw the handle into the test firing pin.

4. Set the test box altimeter to 1013 millibars. With this setting, the altimeter will show a reading, in feet, above sea level and the altitude test will be relative to sea level.

5. Ensure the test set cover and seal are clean before closing the cover. A light application of pressure might be required to seal the cover.

6. Turn the vacuum release valve clockwise to the CLOSED position. .

NOTE: Before you continue with the test, QA personnel should be present to witness the results.

7. Set the test set switch to the ON position. Make sure the vacuum pump starts and the red indicator light is illuminated.

8. While you monitor the test set altimeter, set the on/ off switch to OFF when the altimeter reaches 30,000 feet.

9. Pull the operating handle to remove the test set firing pin from the TRM. The TRM should not operate at this time.

10. Monitor the test set altimeter while you slowly open the vacuum release valve. Open it until the altimeter indicates a steady descent rate, but not exceeding 200 feet per second.

11. Record the reading on the altimeter at which the TRM actuates. The actuation must occur at 13,000 1,500 feet. If the TRM fails the test, it must be replaced.

12. After actuation, open the test set vacuum release valve. When the altimeter indicates zero, carefully open the test set cover.

13. Remove the clamp and disconnect the test firing pin from the TRM. Then remove the TRM from the test set.

Figure 6-28.- Time-release mechanism barostat check-out.

14. Secure the test set and re cock the TRM. the MRCs and MIMs. The steps requiring QA Lock wire the firing link to the TRM and install action are also very important the hex head plug and washer in the base of the TRM. All ejection seat parts and components received from supply must be checked or tested

NOTE: QA should inspect the sear installation before being put into service. It is also recommended that ejection seats reinstalled on their mated ejection catapult guns.

Other Tests

Cannibalisation of ejection system components must beheld to an absolute minimum.

Other tests are required for this ejection seat. The swapping of components increases the risk of error. These tests are performed in strict compliance with possibility of maintenance error. Minimizing cannibalisation should also decrease the possibility of logbook record error.


Many thanks to Mr J. Wendle Spanwick III of Knoxville, Alabama USA for donating the above article.