The types of explosive devices incorporated in egress systems are varied. The AME working with these devices must know how they function, their characteristics, how to identify them, their service-life limitations, and all safety precautions. The AME who understands the importance of all of these factors and who correctly uses the maintenance manuals is better equipped to super-vise and train others. Always refer to the manual, Cartridges and Cartridge-Activated Devices (NAVAIR 11-100-1). The manual contains cartridge information and safety precautions for handling explosives.

Initiators

As previously discussed, initiators, such as the M99, start an action. Initiators are explosive devices, and no maintenance is allowed on explosive devices. When installing explosive devices or during aircraft inspections, initiators will be verified for expiration, and if newly installed they will be marked with an approved marking medium with all the information required by the cartridge manual, NAVAIR 11-100-1. Delay initiators serve the same function as initiators, but they have a built-in delay charge to allow another function to be performed before they fire. An example would be a 0.5-second delay initiator installed in the line to the rocket motor of the forward seat in a two-place aircraft. This would allow the rear seat to clear the aircraft first by delaying the firing of the forward seat ejection rocket for 0.5 second.

Detonating Cord Detonating cord is installed between different components of an ejection system, taking the place of pneumatic gas lines. The detonating cord is a stainless steel tubing filled with an explosive, and is more reliable and much faster than comparable pneumatic gas systems. The system is also safer from the standpoint of inadvertent actuation due to the extremely high initiating velocities, and pressures, as previously discussed.

Rocket Catapult

The rocket catapult, MK 16 MOD 1, used in the S-3 aircraft is rated as a class B explosive. The MK 16 MOD 1 is a self-contained, gas-initiated, two-phase, solid-propellant booster and rocket. The rocket catapult consists of two gas-initiated firing mechanisms, a solid-propellant booster assembly, a rocket launching tube, a gas-initiated rocket igniter, a solid-propellant rocket motor, and an output cartridge for actuation of other gas initiated escape devices.

Each firing mechanism consists of one firing pin (shear pinned in place) mounted inside a special fitting that combines the inlet port and firing mechanism housing. Two inlet port/ firing mechanism housings are threaded into each base cartridge assembly.

The catapult tube assembly consists, primarily, of a cartridge assembly, lock, unlock sleeve, unlock piston, unlock spring, outer housing, motor lock disk, mounting bracket, and front body housing. The rocket motor assembly consists, primarily, of a steel motor tube with canted nozzle assembly and a tungsten insert, a solid-propellant grain, an ignition charge, an output cartridge assembly, and a seat mounting lug to facilitate attachment to the aircraft ejection seat.

FUNCTION.- When the aircrewman pulls the face-curtain ejection handle or the alternate ejection handle or when the sequential ejection system is actuated, an external initiator begins the catapult operation by forcing gas through the inlet fitting( s) into the cartridge assembly of the rocket catapult. This gas pressure provides the force necessary to shear the pins that hold the rocket catapult firing pins in place. The firing pins then develop the energy necessary to fire the percussion primers in the cartridge assembly. The percussion primer then fires the ignition material within the cartridge assembly, which, in turn, ignites the booster cartridge. The piston unlock ring then moves downward, compressing the unlock spring and releases the lower tangs of the lock assembly. After the lower tangs of the lock assembly have been released, movement of the rocket motor assembly begins. As gas from the main cartridge charge expands and drives the assembly up the catapult tube, the nozzle is kept sealed by the motor lock disk. Near the end of the catapult stroke, the motion of the unlock sleeve is stopped by interference with the front body housing, and the shear pins between the unlock sleeve and the rocket motor assembly are sheared. At this point, the rocket motor has achieved a velocity of approximately 50 feet. per second. When the rocket motor has traveled another 0.9 inch (approximately), the shoulder on the lock strikes the immobilized unlock sleeve and stops. This action releases the upper tangs of the lock and unseals the rocket motor nozzle by severing the nozzle plug and retaining the motor lock disk. The hot, pressurized gases from the cartridge then pass into the rocket motor assembly through the nozzle. These gases energize the rocket motor firing mechanism, which ignites the rocket igni-tion material. The rocket ignition material and/ or the hot gases from the booster cartridge ignite the rocket motor solid-propellant grain. The rocket motor then provides additional thrust to the air-crewman seat after separation of the booster and rocket sections.

The rocket motor internal pressure energizes two output cartridge firing mechanisms that fire the output cartridge. The output cartridge then actuates other escape devices, which are attached to the output fitting.