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
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 seats 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
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
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.