IE-1 escapac ejection seat

IE-1 escapac

ejection seat

 

The lE-1 ESCAPAC ejection seat is a rocket assisted ejection system that provides a quick and safe means of escape from an aircraft. The ESCAPAC seat provides escape capability from ground level at zero-knots airspeed to all altitudes and airspeeds within the operational limits of the aircraft. The ESCAPAC seat has several variations between models. Seat modifications have been incorporated to give the occupant an improved escape and recovery system that assures directional stability during ejection and positive seat-man separation. A manual backup is provided to allow over-the-side bailout as well as emergency egress from the aircraft. In this section we will discuss the ESCAPAC 1E-1 ejection seat used in the S-3 aircraft. 

SYSTEM DESCRIPTION 

Following ejection initiation, the lE-1 ESCAPAC system is fully automatic through rocket thrust and burnout, seat-man separation, and parachute opening. 

The 1E-1 ejection seat is a very reliable seat system that is initiated by pulling either the primary (face curtain) or secondary (lower) ejection control handle (fig. 6-1). Two cables attached to the primary ejection control handle, or a single cable attached to the secondary ejection control handle, cause the firing control disconnect assembly to pivot for-ward. Two attached arms move two firing rods aft to actuate the actuating mechanism, which fires the M99 initiator(s) located between the guide rails. Through the aircraft-attached sequencing system, the power inertia reel hauls back the shoulder harness and stows the tactical air coordinator (TACCO) and sensor operator (SENSO) INCOS trays. Simultaneously, hot gas pressure from the M99 initiators(s) activates an aircraft attached 0.3-second delay initiator, which fires the rocket catapult. on the forward two seats, an additional 0.5-second delay MK 11 MOD 0 initiator is in series with the 0.3-second delay initiator to delay forward seat ejection sequencing by 0.5 second after the rear seats eject. The eject mode selector handles on the pilot's and co-pilot’s seat provide pilot or co-pilot control of individual or group ejection of crew members.

The first-phase propulsion of the rocket catapult starts the seat up in the guide rails. When the seat has moved approximately two-thirds the length of the guide rails, the second (or sustainer) phase of the rocket catapult ignites to provide boost for the additional height required during ejection. At sustainer separation, gas pressure from rocket ignition is used to ignite the seat stabilization control system, the yaw thruster, and the seat-attached 0.3-second delay initiator for harness release. Before the seat clears the guide rails, the following five functions occur: crew member services to the aircraft is disconnected; the parachute arming lanyard is pulled, which arms the parachute release actuator; the lanyard connected to the aircraft structure actuates the emergency oxygen bottle in the survival kit to supply the crew member with emergency

Figure 6-1.- Ejection seat system sequencing schematic.

bailout oxygen; the yaw vane is deployed, and the quick-disconnect coupling on the right side of the seat separates. Following burnout of the yaw thruster rocket and sustainer rocket, and upon the completion of the pitch stabilization control function, the seat-attached 0.3-second delay initiator fires. Gas pressure from the initiator enters the harness release actuator, which drives the piston upward to rotate the bell crank mounted below the actuator to retract two survival kit retaining pins and shoulder harness pin from two inertia reel straps. Retraction of retaining pins frees the crew member and his survival equipment from the seat. The base of the clevis on the lower end of the actuator piston strikes the firing control disconnect actuating arm. Movement of the arm retracts a spring-loaded retaining pin from the firing control disconnect assembly, and releases the ejection control handle cables from the assembly.

A crew member, who may still be holding one of the ejection control handles, is now freed from any restraints that would prevent the final separation from the seat. As the harness release actuator piston completes the stroke, the pressure within the actuator is ported to the man/ seat separator rocket, causing the rocket to ignite.

The thrust of the man/ seat separator rocket simultaneously rotates and propels the seat away from the crew member with a differential velocity of up to 25 to 30 feet per second. The probability of collision between the seat and a crew member or the parachute after separation is minimized, be-cause no attempt is made to decelerate the seat as the seat travels along a divergent trajectory. As the seat and crew member move into divergent paths, the parachute actuator is armed and the external pilot chute is deployed. After a 0.55-second delay, the main parachute is aerodynamically deployed. Just before the parachute shroud lines stretch, the ballistic spreading gun is fired to forcefully initiate parachute inflation.

If a crew member is above an altitude of 14,000 (± 500) feet, a preset aneroid in the parachute actuator delays parachute deployment until the crew member has descended to the correct altitude. The parachute actuator delay cartridge then fires, causing parachute deployment. The crew member can select parachute deployment at any altitude by pulling the manual ripcord on the parachute.

If the automatic ejection system malfunctions, the crew member can pull the internal jettison handle/ initiator(s) in the crew compartment to cut the window/ hatches away. Over-the-side bailout is initiated by pulling the harness release mechanism, which disconnects the rigid survival kit and the parachute from the seat structure. The crew member can then stand up and exit the crew compartment. When clear of the aircraft, the crew member pulls the parachute manual ripcord located on the left riser strap immediately above the parachute canopy release fitting. The parachute flaps are thereby released, and the parachute deploys.

COMPONENTS 

Figure 6-2 shows the front and rear views of the ESCAPAC 1E-1 ejection seat assembly and its various components. The ejection seat is the basic structure that supports the equipment and mechanisms necessary for crew member comfort and safety while in flight or during the ejection sequence. The seat and associated components are constructed almost entirely of aluminium. The seat is equipped with fixed window/ hatch breakers at each top forward corner to permit seat ejection through a 1/ 4-inch stretched acrylic window or hatch. At the upper centre of the seat are headrest cushions that provide cushioning for the safety and comfort of the crew member. on each side of the seat are three seat rollers, which allow for vertical height adjustment during normal conditions and upward travel during ejection. Extended seat bucket sides protect the crew member's knees and legs from flailing during seat ejection. The seat structure supports the parachute assembly and survival kit.

PRIMARY EJECTION CONTROL HANDLE.- The primary ejection control handle (face curtain) gives each crew member the means to manually initiate automatic seat ejection. The primary handle, which is an integral part of the nylon screen assembly, is connected through cables to the firing control disconnect assembly. The pivoted firing control disconnect provides a mechanical interlock between the primary and secondary ejection control handles.

SECONDARY EJECTION CONTROL HANDLE.- The secondary ejection control handle is located on the front frame of the seat structure. A cable connects the handle to a disconnect pulley assembly under the seat bucket. A second cable connects the disconnect pulley assembly to the firing control disconnect assembly at the top of the seat.

EJECTION CONTROL SAFETY HANDLE.- To prevent accidental seat ejection, a safety handle (head knocker), when placed in the down-and-locked position, prevents inadvertent actuation of all component parts of the firing control mechanism. The safety handle is identified by a yellow and black decal that reads

PULL OUT TO SAFETY EJECTION CONTROLS. A safety lock, incorporated in the safety handle, automatically locks the handle in the full-out position; the lock must be manually depressed before the safety handle can be moved to the up (recessed) position.

POWER INERTIA REEL INITIATOR.- The inertia reel initiator is located on the rear left side of the seat, below and to the left of the inertia reel. The inertia reel initiator powers the inertia reel for automatic power retraction of the shoulder harness during the seat ejection sequence. The initiator gases discharge into a tubing segment that is filled with high-vacuum grease, and then into the inertia reel.

POWER INERTIA REEL.- The inertia reel is centrally located in the upper part of the seat behind the headrest cushions. In the seat ejection sequence, the inertia reel provides automatic power retraction of the shoulder harness in preparation for seat ejection. The inertia reel facilitates voluntary forward movement of the crew member, and functions as a self-compensating restraint against involuntary forward movement resulting from excessive g-forces or other aircraft stresses. An inertia reel control handle on the left arm of the seat can be manually unlocked or locked to allow or prevent extension of shoulder harness straps. Two prestretched Dacron straps are part of the inertia reel. A flexible inertia reel cable couples the inertia reel to the inertia reel control handle.

GYRO SPIN-UP GAS GENERATOR CARTRIDGE.- The gas generator is attached to the pitch stabilization control (STAPAC), which is located under the seat bucket. The gas generator powers the gyro spin-up actuator, and subsequently powers the sear cam piston. The gas generator is a percussion-ignited device that is fired by ballistic gas pressure ported from the rocket catapult when the rocket portion fires.

VERNIER ROCKET.- The vernier rocket is a mechanically fired rocket motor located across and under the seat bucket; the vernier rocket is part of the pitch stabilization control unit. The gas generator powers the sear cam piston to fire the vernier rocket, whose rotation is controlled by the pitch rate gyro.

PITCH STABILIZATION CONTROL (STAPAC).- A unique but simple STAPAC stabilizes the seat during conditions of large centre of gravity (cg) main rocket thrust misalignment, and high aerodynamically induced pitch torque. The STAPAC, located under the seat bucket, operates from the time the seat leaves the guide rails until after rocket sustainer burnout. The STAPAC consists of a mechanically fired vernier rocket around the pitch axis, which changes the thrust/cg relationship and applies a correcting moment.

 

Figure 6-2.- Ejection seat assembly.

YAW THRUSTER.- To achieve safe separation of multi-crew seat trajectories, a yaw thruster is used on each seat to provide a controlled, lateral-angle dispersion from the aircraft's direction of flight. Two types of yaw thrusters are used on the forward and aft seats, with location always on the inboard side of each seat. A low yaw thruster, producing approximately a 10.4 pound-second impulse for 0.1 second, is installed on each forward seat, and a high yaw thruster, producing approximately a 21.0 pound-second impulse for 0.1 second, is installed on each aft seat. The yaw thruster is ignited by high-pressure gas ported from the top of the rocket catapult. To provide proper yaw rotational impulse for each seat installation, the yaw thruster is mounted to provide a predetermined moment arm about the centre of gravity of the seat/crew member system. The mounting bracket for each thruster incorporates a boss that, when combined with a fixed stop permanently mounted on each guide rail, will prevent incorrect installation. The right and left seats are yawed to produce changes in the trajectory paths. Each of the four crew member seats will be separated from the others at parachute full-open condition under nominal lateral centre-of-gravity conditions.

YAW VANE.- To assist in providing the proper yaw rotation at higher airspeeds, an aerodynamic yaw vane is installed on the out-board, lower aft side of each seat. The yaw vane deploys just as the seat leaves the guide rails and presents a drag area of 1/2 square foot to yaw the seat approximately 20 degrees. At this position, the vane is blanked by the man/seat structure, and becomes ineffective in creating any further increase in the degree of rotation.

Harness Release and Seat Separation

The harness release system provides automatic release of the shoulder harness and lap belts during the ejection sequence. The survival kit and shoulder harness are locked in the seat by three retaining pins, two through the survival kit lugs and one through the shoulder harness inertia reel strap lugs. Automatic release from the seat during the ejection sequence is accomplished by the harness release actuator, using a pressure-actuated 0.3-second delay initiator. Gas pressure, which exits from the outlet port of the harness release actuator, is used to actuate the man/seat separator rocket in the seat separation subsystem.

PRESSURE-ACTUATED 0.3-SECOND DELAY INITIATOR.- The 0.3-second initiator is located on the rear right side of the seat above the harness release actuator. The 0.3-second initiator is a pressure-actuated device with a conventional firing piston secured in the cocked position by a shear pin. Gas pressure from the rocket catapult actuates the initiator, which fires into the inlet port of the harness release actuator.

HARNESS RELEASE ACTUATOR.- The actuator is mounted on the rear right side of the seat. The actuator contains a piston and rod that are actuated by a 0.3-second delay initiator firing into the inlet port. Gas pressure exits from the outlet port to actuate the man/seat separator rocket. The piston rod, which extends below the actuator, is connected to the harness release bell crank. The bell crank initiates simultaneous automatic actuation of each component of the harness release system to cause man/seat separation during seat ejection. If the lap belts and shoulder harness assemblies fail to release automatically, the crew member can actuate the harness release handle to release the assemblies. The handle is also useful for routine removal and installation of the parachute and survival kit. The following components are connected to the multiple arm bellcrank: harness release actuator piston rod, survival kit retaining pins, inertia reel straps retaining pin cable, harness release handle cable, and bell crank return spring. The actuator also actuates the firing control disconnect actuating arm.

MAN/SEAT SEPARATOR ROCKET.- The separator rocket is mounted on the aft inboard side of the headrest area of each seat. The separator rocket is used to separate the crew member from the seat and drive the seat into a divergent trajectory. Pressure from the harness release actuator outlet port is used to initiate the separator rocket. The separator rocket nozzle is oriented to direct the exhaust plume forward, up, and away from the crew member.

 

Aircraft-Attached Ejection Seat Components

The following ejection seat related components are located on the aircraft structure and remain in the aircraft when the seat is removed for maintenance.

GUIDE RAILS.- Two guide rails are located on each canted bulkhead behind each crew member. Each set of guide rails is machined from aluminium extrusions. Each outboard rail has a machined cam at the top to release the aero-dynamic yaw vane as the seat travels up the guide rails. Two holes in each inboard guide rail allow installation of two seat servicing pins to support each seat at the 42-inch alternate maintenance position.

SEAT CONTROL SYSTEM.- The seat control system permits vertical height adjustment of each crew member's seat before and during' nor-mal flight. Phase reversal of two phases of a three-phase power source permits raising or lowering each seat according to the selected UP or DOWN position of the switch on the SEAT panel on the side console at each crew member station (fig. 6-3). The seat control system consists of a seat switch and a seat adjustment actuator and motor. Seat adjustment is provided by a twin barrel electromechanical actuator (fig. 6-4), which is driven by a 115/ 200-volt, 400-Hz, three-phase, four-pole induction motor. The motor is geared to a reduction gear train, which drives two screw barrels that are attached to mating flanges on the base of the rocket catapult. The rocket catapult is bolted to the top of the seat structure, which allows a 5.5-inch up and down adjustment of the seat parallel to the guide rails. Six rollers on the seat allow the seat to move up or down the guide rails.

 

Figure 6-3.- Seat control panel and seat switch.

Figure 6-4.- Seat adjustment actuator and motor assembly.

ROCKET CATAPULT.- The rocket catapult provides the necessary propulsion to eject the seat and crew member from the aircraft during the ejection sequence.

The performance capability of the rocket catapult at zero altitude and zero airspeed reduces the effects of high sink rate and nose down attitudes encountered during critical approach and landing operations. The rocket catapult is secured at the top centre of the seat back, and is supported at the base by twin barrels of the seat adjustment actuator. Two attachments on the actuator secure the actuator to the aircraft bulkhead.

M99 INITIATORS.- Two M99 initiators are installed on the M99 initiator actuating mechanism (fig. 6-5) near the top of each canted bulkhead behind the pilot's and co-pilot's seats, and one M99 initiator is installed at each tactical air coordinator (TACCO) and sensor operator (SENSO) seat location. The M99 initiator is a mechanically fired, pressure-developing source. Each M99 initiator, consisting of a constant-volume cylinder with a tube connection at one end, contains a mechanically fired mechanism and cartridge. The M99 initiator firing mechanism can be secured in a safe position by a safety pin that passes through the cap and a groove on the side of the M99 initiator pin. Pulling either the primary or secondary ejection control handle initiates the ejection sequence, which, in turn, rotates the firing control disconnect, moves two firing rods aft to rotate the actuating mechanism bell crank( s) that fires the initiator( s).

 

Figure 6-5.- M99 initiator location.

M99 INITIATOR ACTUATING MECHANISM.- The actuating mechanism is located between the guide rails, and is attached to the upper section of each canted bulkhead, behind each crew member's seat. The actuating mechanism for the forward seats have dual bell cranks (striker plates) and clevises to actuate the two M99 initiators installed on each side of the actuating mechanism. Since each aft seat requires one M99 initiator for the ejection sequence, the actuating mechanism is a single bell crank and clevis arrangement. During the seat ejection sequence, the seat-mounted firing rods are moved aft to rotate the actuating mechanism bell crank(s) and clevis(es) to fire the M99 initiator( s). Refer to figure 6-6 while reading the following text

M53 INITIATOR.- There are thirteen M53 initiators installed in aircraft-attached ejection seat plumbing. Eleven of the M53 initiators are installed between the guide rails, and two initiators are installed at flight station (FS) 263 (one each at the INCOS tray thruster location). Each pilot and co-pilot location has four M53 initiators; the TACCO location has one; and the SENSO station has two. The M53 initiator is a cartridge-actuated, gas-producing device triggered by gas pressure from a remote source. The M53 initiator consists of a constant-volume cylinder with a tube connection at one end and a gas-operated firing mechanism and cartridge. In the ejection seat sequence, gas pressure from the M99 initiator( s) actuates the M53 initiators. M53 initiators characteristically serve as line-boosters in the ejection seat system to counteract rapid pressure decay caused by tubing length.

PRESSURE-ACTUATED 0.3-SECOND DELAY INITIATOR.- Seven 0.3-second delay initiators are installed between the guide rails. Two 0.3-second delay initiators are installed at the pilot's, the co-pilot's, and the SENSO station; and one is installed at the TACCO station. At the pilot's and co-pilot's stations, an Mk 11 MOD 0 initiator is installed on the 0.3-second delay initiator. The 0.3-second delay initiator is a pressure-actuated device with a conventional firing piston secured in the cocked position by a shear pin. In the ejection sequence, the 0.3-second delay initiators are used as time delays in the inertia reel shoulder harness retraction, in the INCOS trays retraction, and in the group or solo ejection sequencing of crew members in the firing of the rocket catapult(s).

MK 11 MOD 0 INITIATOR.- A MK 11 MOD 0 initiator is installed below the floor line directly under the rocket catapult at the pilot and co-pilot seat locations. Each MK 11 MOD 0 initiator is installed on the 0.3-second delay initiator, and both fire into the rocket catapult. The MK 11 MOD 0 initiator is a cartridge-actuated device triggered by gas pressure from a remote source. In the ejection sequence, the MK 11 MOD 0 initiators are used as time delays in the group-ejection (all seats) mode to allow the two aft seats to eject 0.5 second before the front seats to permit proper spacing of personnel for safe parachute deployment and landing.

PLUMBING AND CHECK VALVES.- Most plumbing for the aircraft-attached ejection seat components is flexible hose-type plumbing located between the guide rails. There are a minimum of lines between the forward and aft seats and the INCOS tray thrusters. There are twenty check valves installed in aircraft-attached ejection seat components; all are located between the guide rails. In the ejection sequence, the check valves allow the correct group or solo-ejection selection to occur.

INCOS TRAY THRUSTER.- At both the TACCO and SENSO locations, a thruster is installed to retract the respective INCOS trays during the seat ejection sequence. The thruster is a pressure/ percussion device that employs sear pins, firing pins, and primers to ignite the main charge. In the ejection sequence, the INCOS tray is retracted at the same time that the inertia reel shoulder harness retraction occurs.

EJECT MODE SELECTOR VALVE.- A selector valve is installed on each inboard guide rail in the flight station. The selector valve consists of a beam assembly with a switch and handle and the valve body. The selector valve routes high-pressure gas from the M99 initiators to the aircraft sequencing system, depending on the selected position (GROUP EJECT or SELF EJECT) of the selector valve. When the pilot's or co-pilot's selector valve handle is in the down or GROUP EJECT position, an electrical ground is completed, which causes the GROUP EJECT indicators to come on at the SENSO and TACCO instrument panels. When either selector valve handle is in the up or SELF EJECT position and the aircraft altitude is less than 15,000 feet, the altitude sensor switch cause the indicator on the enunciators panel (located on the centre instrument panel) to come on.

 

Figure 6-6. Aircraft mounted CAD's.

ALTITUDE SENSOR SWITCH.- An altitude sensor switch is located on the forward bulkhead of the camera compartment. The sensor switch monitors the aircraft altitude. When the eject mode selector valve handle is in the up or SELF-EJECT position and the aircraft altitude is less than 15,000 feet, the sensor switch causes the seat select indicator on the enunciator panel (located on the centre instrument panel) to come on. When the aircraft altitude reaches or exceeds 15,000 feet, the seat select indicator goes off.

GROUP EJECT INDICATORS.- A group eject indicator is installed on the SENSO and TACCO instrument panels. When the pilot's or co-pilot's selector valve handle is in the down or GROUP EJECT position, a switch in the selector valve completes an electrical ground, and causes both group eject indicators to come on. When both selector valve handles are in the up or SELF EJECT position, the group eject indicators go off.

EJECTION WARNING SYSTEM.- The ejection warning system is used to warn the TACCO and SENSO that an emergency is occurring, and that seat ejection is about to be initiated. The system uses an eject switch on the eyebrow panel, an emergency power unit, a flasher, and eject indicators on the TACCO and SENSO instrument panels. The pilot or co-pilot sets the eject switch to EJECT, which turns on flashing eject indicators on the TACCO and SENSO instrument panels.

Figure 6-7.- Emergency egress system components and plumbing.

Window/ Hatch Severance System 

The emergency egress system provides a means of escape from the aircraft for crew members after ditching or after a wheels-up landing by initiation of explosive charges to blow out windows and hatches. The S-3 emergency egress system is distinguished from hot gas and actuator systems by its use of shielded mild-detonating cord (SMDC) instead of hot gas and explosive charges instead of actuators. The S-3 system is much less susceptible to inadvertent actuation than hot gas systems, and more convenient and safer for maintenance personnel. The S-3 emergency egress system (fig. 6-7) consists of two window-hatch external jettison handle/ initiators, three window/ hatch internal jettison handle/ initiators, window and hatch-severance explosive charges, fillet-severance and fillet-support severance explosive-shaped charges, SMDC's, and SMDC manifolds or one-way transfers.

FUNCTIONAL DESCRIPTION.- The S-3 emergency egress system is initiated from any one of five positions- two on the outside of the flight station, and three located in the crew compartment at the eyebrow panel and at the TACCO and SENSO instrument panels. All windows and hatches are cut and blown outward by the actuation of either exterior window/ hatch external jettison handle/ initiator, and by the pilot's,/ copilot's interior window/ hatch internal jettison handle/ initiator. The TACCO and SENSO window/ hatch internal jettison handle/ initiators cut only the respective panel next to the crew member, The system is used primarily for ground and water rescues. The handle/ initiators have a trigger action. once the system is actuated, the system will respond to completion without further action by crew members. The functional sequence is from the handle/ initiator (any one) to the SMDC, to the explosive charge, which is the actual cutting tool for the window or hatch glass. If either or both the TACCO and SENSO hatches are to be blown, the respective fillet and fillet support will be cut to allow complete egress of the hatch. When either the TACCO or SENSO crew member actuates the handle/ initator, the opposite hatch and the two flight station windows will not be cut, since an SMDC manifold (check tee) or one-way transfer restricts transfer of pyrotechnic energy flow to one direction. The emergency egress system is entirely self-sufficient and completely independent. The system does not depend on any other aircraft system, nor does the system aid, assist, or sequence with another system. The SMDC system is more reliable and much faster than a comparable hot gas system. The system is safer from the stand-point of inadvertent actuation due to the extremely high initiating velocities and pressures. The high operating velocity is much too fast to permit system initiation by ordinary sawing, filing, drilling, or hammering. With quick-release safety pins properly installed, the system is virtually inert.

COMPONENTS.- The following items are components of the window/ hatch severance system.

Window/ Hatch External Jettison Handle/ Initiator.- Two external jettison initiators are installed inside access doors on each exterior side of the aircraft just below and forward of the wind-shield aft posts, The external cartridge-activated initiator (fig. 6-8) is a mechanically fired device, with the firing pin relaxed (not pre-cocked) before handle actuation. The sear mechanism is a conventional ball-and-node type, which disengages completely after 3/ 4-inch of travel. During travel, the firing pin withdraws, but the handle does not disengage. The primer fires into a lead azide charge, which fires the output charge.

Figure 6-8.- External cartridge-actuated initiator.

Figure 6-9.- Internal canopy/ hatch severance initiator.

Figure6-10.- Pilot/ NFO window-severance linear shaped charge.

The external jettison initiators have no safety pins, but use a 10-foot lanyard to protect against inadvertent initiation. Either external initiator will cause all windows, hatches, fillets, and fillet supports to blow away from the aircraft.

Window/ Hatch Internal Jettison Handle/ Initiator.- Three window/ hatch internal jettison handle/ initiators (internal jettison initiators) are located in the crew compartment: one at the eyebrow panel and one each at the TACCO and SENSO instrument panels. The internal canopy/ hatch severance initiators (fig. 6-9) are the squeeze-to-pull type, which have a quick-release safety pin in the squeeze segment of the operation for safetying. The pilot's/ co-pilot's handle will blow all windows and hatches, whereas the TACCO and SENSO handles will blow only the hatch above the crew member. The basic internal jettison handle initiators are similar to the external jettison handle initiators except for the handle and the absence of the lanyard feature.

Pilot/ NFO Window Severance Linear Shaped Charge.- A window severance explosive charge (fig. 6-10) is attached to the inside periphery of the pilot's and co-pilot's windows. An SMDC connects to a transfer block at the lower front corner of the explosive charge. The window explosive charge is actuated by the pilot's/ co-pilot's internal jettison handle/ initiator or by either external jettison handle/ initiators through the SMDC segments. The explosive charge acts as the cutting device for the window glass.

Hatch Severance Explosive Charge.- The hatch severance explosive charge is similar to the window severance explosive charge. The explosive charges of the hatches can be actuated by the external jettison handle/ initiators or by the pilot's/ co-pilot's handle/ initiator. The TACCO or SENSO hatch explosive charge can be actuated individually by the respective TACCO or SENSO handle/ initiator.

Fillet and Fillet Support Explosive Shaped Charge.- Each right and left upper wing-to-fuselage fillet has a fillet-severance, explosive shaped charge attached near the outer and rear fillet attachments (fig. 6-11). The shape charge cuts the attached fillet from the aircraft to allow complete egress of the respective hatch. A fillet support is cut by a second shaped charge attached at the bottom.

Figure 6-11.- Fillet and fillet support explosive shaped charge.

 

Fillet Support Severance Explosive Shaped Charge.- A shaped charge is attached at the bottom of the internal fillet support to cut the support to allow the-fillet to separate from the aircraft during the emergency egress system operation (fig. 6-11).

Shielded Mild Detonating Cord (SMDC).- The 31 SMDC segments (fig. 6-12) act as the plumbing for the emergency egress system. The SMDC connects all external and internal jettison handle/ initiators; all connectors, tees, and manifolds or one-way transfers; all explosive charges; and all explosive shaped charges. Each SMDC segment is loaded with 1 to 2 grains per foot of hexanitrostilben I (HNS I). When initiated, the extremely high velocity and pressure of the cord is focused onto the end of the next adjacent SMDC segment, which acts as an acceptor charge.

Shielded Mild Detonating Cord (SMDC) Manifold.- Two SMDC manifolds are located on the pilot's and copilot's bulkhead. The SMDC manifold acts as a check tee or one-way detonating transfer device. The SMDC manifold is a self-contained unit housing a sealed receptacle for dual-shaped charges. Any detonation entering the side ports from either direction will transfer to the aft port. Any detonation originating from the aft port (TACCO or SENSO) segment of the SMDC manifold will not transfer back into the side portions. This would occur when either the TACCO or SENSO elects to cut the respective hatch; the remaining two windows and the opposite hatch would not be affected.

MAINTENANCE REQUIREMENTS Maintenance on ejection seats is primarily performed during aircraft inspections. The ejection system could be called a dormant system, as it is only operated in an emergency situation. A true functional test of the complete system can-not be performed because of the destructive functions of some of the components. For this reason it is of the utmost importance that you thoroughly know all aspects of the ejection system that you perform maintenance on and follow all the steps for testing components as outlined in the maintenance instructions manual (MIM).

Figure 6-12.- Shielded mild detonating cord tip (typical).

WARNING Do not perform maintenance on equipment with installed cartridges except in the presence of personnel capable of rendering aid if necessary.

Seat Removal and Installation 

Before entering the cockpit, ensure that all seat and canopy safety pins and devices are properly installed. Check that the ejection control safety handle (fig. 6-13) (head knocker) is in the down and locked position. Ensure that the pilot's and co-pilot's eject mode selector handles are set to the SELF EJECT position. Remove the parachute and survival kit by disconnecting the oxygen and communications quick-disconnect. Disconnect the emergency oxygen and emergency radio beacon quick-release lanyard attached to the aircraft's structure. Squeeze the harness release handle and disengage from holder. Remove the parachute actuator arming cable from the handle, and pull upward on the handle until the harness release actuator locks in the MANUAL DETENT position. Reseat the handle into the holder. Withdraw the inertia reel straps from the chute roller fittings. Rotate the aft end of the survival kit up and forward to release the forward mounting hooks from the seat mounting brackets. Remove the parachute and survival kit from the aircraft and deliver to the aviators equipment work centre. If the seat is not in the full down position, apply electrical power and lower the seat to the full down position. Do not hold the seat adjust switch in the UP or DOWN position for more than 15 seconds to prevent damage to the seat height actuator.

Remove the M99 initiator actuating cover and install safety pins in the initiators (fig. 6-5). The pilot and co-pilot seats require two safety pins, and the TACCO and SENSO seats require one safety pin. Remove, as required, overhead window or hatch assembly. Remove cover from top of the rocket catapult (fig. 6-14). Disconnect the inertia reel ballistic hose quick disconnect using the special key and flag assembly.

Figure 6-13.- Ejection control safety handle.

Attach the hoisting sling to the seat and overhead hoist. Using the hoist, apply upward pressure on the seat to prevent damage to the seat/ rocket during removal of the trunnion bolt. Remove the trunnion bolt and ensure that all seat connections have been disconnected. Raise the seat with the hoist. As the seat reaches the top of the guide rails, prevent the yaw vane from deploying. Caution must be taken to prevent injury to maintenance personnel as the yaw vane is deployed by a 40-pound spring force. Continue raising the seat until the lower rollers on the seat clear the guide rails. After the yaw vane trip lever has passed the cam on the outboard guide rail, reset the yaw vane latch. Lower the seat and secure it to the ejection seat cradle. 

CAUTION Do not rest the seat on the STAPAC cover on the bottom of the seat.

The seat installation is essentiality a reversal of the removal procedures