emergency oxygen system is automatically
activated during ejection by a lanyard connected
to the cockpit floor. An oxygen/communications
hose is connected to unions on the LH rear top
of the lid assembly, and provides connections
between the seat occupant and the aircraft and
survival kit systems.
RADIO LOCATOR BEACON. A URT-
33A radio locator beacon is located in a cutout
in the left thigh support. The beacon is actuated
during ejection by a lanyard connected to a
common anchorage point with the emergency
RUCKSACK ASSEMBLY. The rucksack
assembly is attached to the underside of the lid
assembly by five fabric straps and a double cone
and pin release system. The rucksack contains a
life raft and the survival aids. Yellow manual
deployment handles mounted on the kit enable
the occupant to deploy the rucksack and contents
onto a lowering line after seat/man separation.
The LRU-23/P life raft inflates automatically on
rucksack assembly deployment.
The operation of each component and
subsystem is discussed in the following
paragraphs. The operation of the system as a
whole is discussed later in the chapter.
Explosive charges are contained in an ejection
gun initiator, JAU-56/A (figs. 5-3 and 5-4), and
a secondary cartridge. Gas pressure from the seat
firing system or the aircraft command sequencing
system operates twin firing pins in the ejection gun
initiator to fire the explosive charge.
Gas enters the manifold valve through one or
both of the inlet ports, depresses the check valves,
and passes down through the vertical bore into
the initiator. Gas pressure acts upon the twin
firing pins in the initiator, shearing the shear pins
and forcing the firing pins down to strike the
percussion caps and ignite the explosive filling.
The gas pressure generated within the catapult
1. Passes to the ballistic latches to operate the
pistons, which retain the multipurpose initiator
2. Propels the catapult piston upwards.
The initial movement of the piston forces the
spring-loaded top latch plunger out of the breech
groove back into the barrel latch (fig. 5-4). The
piston continues to rise, thrusting against the top
crossbeam of the seat, the upward movement
causing the shaped end of the top latch plunger
to ride out of, and disengage from, the barrel
latch. Further upward movement of the piston
uncovers the secondary cartridge, which is fired
by the pressure and heat of the initiator gas. After
approximately 38 inches (965mm) of travel, the
piston head strikes the guide bushing and shears
the three dowel screws. After a further 4 inches
(101mm) of travel, the piston separates from the
barrel and moves away with the ejected seat.
Main Beams Assembly
The main beams assembly supports the major
components of the ejection seat. The operation
of the components supported by the main beams
assembly is discussed in the following paragraphs.
SHOULDER HARNESS CONTROL SYS-
TEM. When the ejection control handle is
pulled, gas from the RH seat initiation system is
piped into the breech to operate the cartridge. The
gas also passes to the operating piston in the
governor housing, forcing it upwards to operate
the trip lever and bring the locking pawl into
contact with the ratchet wheel.
The gas from the impulse cartridge in the
breech impinges on the end of the piston forcing
it along the cylinder. Horizontal movement of the
piston is transmitted via the threaded drive screw
to rotate the splined shaft, spool assemblies, and
ratchet wheel, which winds in the webbing straps
to pull back and restrain the occupants shoulders.
The engaged locking pawl locks the spools in the
Withdrawal of the webbing straps at excessive
speed causes the two governor pawls to rotate
outwards under centrifugal force and engage the
teeth on the housing, preventing rotation of the
splined shaft and spool assemblies and further
withdrawal of the straps. This system prevents the
occupant from being thrown forward on crash
landing or sudden deceleration if the shoulder
harness control lever is in the disengaged position.
Easing of tension on the webbing straps allows
the pawl springs to reassert themselves and
disengage the pawls from the teeth, permitting free
withdrawal of the straps again.
PARACHUTE DEPLOYMENT ROCKET
MOTOR. Upon seat ejection, gas pressure from