ment motor fires to deploy the personnel parachute and
start switch signal, the sequencer will simply continue
the harness release system operates to free the occupant
in the wait mode. This mode is a safety feature designed
from the seat. The occupant is momentarily held in the
to ensure that the drogue and parachute can only be
seat bucket by the sticker straps.
deployed after the seat has physically separated from
the aircraft.
MODES 2, 3 and 4: MEDIUM and HIGH
The ignition of the underseat rocket motor is timed
S P E E D S / L O W A LT I T U D E a n d A L L
to occur just as the seat separates from the ejection
SPEEDS/MEDIUM ALTITUDE.--The drogue
catapult, at about 200 milliseconds, so as to maintain a
bridle is released, the parachute deployment rocket fires
uniform vertical acceleration profile on the seat and
to deploy the parachute, the drogue bridle is released,
occupant. The motor has a burn time of 250
and the harness release system operates to free the
milliseconds. Once the sequencer is switched into the
occupant from the seat. The occupant is momentarily
ejection mode, its first action is to electrically fire the
held in the seat bucket by the sticker straps.
drogue deployment canister, which occurs at precisely
MODE 5: ALL SPEEDS/HIGH ALTITUDE.--
40 milliseconds after the start switch (approximately
The drogue bridle remains connected until the seat has
220 milliseconds from seat initiation), while the seat
descended to 18,000 feet. This arrangement prevents
rocket motor is burning. This happens regardless of the
prolonged exposure to low temperature and un-
speed and altitude conditions.
substantial air. This enables the occupant to ride down
The sequencer then enters its most crucial period,
in the seat supplied with emergency oxygen to a more
when it will sense the seat airspeed and altitude and
tolerable altitude. When the seat has descended to
choose the appropriate timings from a set of five
18,000 feet, the parachute deployment rocket motor
available sequences. This occurs during a 60
fires to deploy the personnel parachute, the drogue
millisecond environmental sensing time window that
bridle is released and the harness release system
starts just after the drogue canister is fired, and is
operates to free the occupant from the seat. The
completed before the drogue is fully deployed and
occupant is momentarily held in the seat bucket by the
pulling on the back of the seat. The sequencer measures
sticker straps.
the speed and altitude from the information it receives
ALL MODES.--The personnel parachute, when
from three types of sensor: pitot pressure, base pres-
developed, lifts the occupant and survival kit from the
sure, and accelerometer.
seat, pulling the sticker straps from their clips. This
Several samples of each parameter are taken during
arrangement ensures that there is no possibility of
the environmental window. These are used to determine
collision between the seat and occupant after
the ejection conditions. The sequencer then selects the
separation.
appropriate times for the remaining events, known
Q2-6. For all configurations, if the seat is command
as mode selection, and completes the sequence
ejected, gas from the command sequencing
accordingly.
system enters through what initiating system?
ALL MODES.--The start switches close after
Q2-7. During ejection, what distance does the seat
approximately 32 inches of the seat travel, and after
have to travel before the drogue chute
0.04 seconds the drogue deploys onto the bridle to
deploys?
stabilize and decelerate the seat.
Q2-8. MODE 1 occurs at what speed and altitude?
MODE 1: LOW SPEED LOW ALTITUDE.--
The drogue bridle is released, the parachute deploy-
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