Introduction of the rocket pack to the range of Mk. 4 and Mk. 5 seats created the basic Mk. 6 and Mk. 7 ranges respectively. However, many of the Mk. 7 range of seats were subsequently embodied with additional improvements in design such as Power Retraction Systems, Remote Fired Rocket Systems and Sequencing Systems as later described. Following development of the highly successful Mk 10 rocket assisted seat, a simplified, lightweight variant of this seat, designated the Mk 8, was introduced for primary trainer aircraft, such as the Embraer Tucano. The most significant design simplification was the removal of the rocket motor, to save weight. In most other respects the Mk 8 seat retains the excellent design features and functionality of the Mk 10 seat. The Mk 8 seat provides runway level escape at speeds down to 70 knots, and has a maximum escape speed capability of 425 knots.
Specifications
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Specifications
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Mk 8 (AU8LD)
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Operating ceiling
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50 000 ft (15,250 m)
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Minimum height/speed
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Zero/70 knots in near level attitude
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Crew boarding mass range
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78.2 to 116.2 kg
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Crew size range
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5th to 95th percentile
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Maximum Speed for ejection
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600 KIAS
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Parachute type
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GQ Type 1000 Mk 2
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Parachute deployment
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Drogue assisted
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Drogue parachute type
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5 ft
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Drogue deployment
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Drogue gun. Initiated by trip rod
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Harness type
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Combined
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Ejection seat operation type
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Ejection gun
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Ejection gun
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Single, two stage
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Gun stroke length
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Variant dependent
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Ejection initiation
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Handle on seat pan
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Electronic Sequencer
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No
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Barostatic time-release unit
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Yes + g-restrictor. Initiated by trip rod
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Automatic back-up unit
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No
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Manual override handle
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Yes
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Timers
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No
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Seat adjustment
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Up/down. Actuator operated 28 Vdc
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Arm restraints
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No
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Leg restraints
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Yes, two garters
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Oxygen supply
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Bottled emergency oxygen
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Onboard oxygen generating system connection
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Personal survival pack
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Yes
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Aircrew services
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Oxygen (main and emergency) and mic/tel
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Command ejection
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No
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Canopy jettison
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No
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Miniature detonating cord
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No
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Interseat sequencing system
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No
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How it works
Seat firing handle pulled causing seat initiation cartridge to fire
Harness retraction unit operated
Primary cartridge fired causing inner and intermediate pistons to rise, releasing top latch
Secondary cartridges fire in turn as seat rises
Electrical connections separate disconnecting seat actuator circuit
Leg restraint lines draw back and restrain aircrew’s legs
Leg restraint lines become taut and rivets shear, freeing lines from ejection gun cross beam
Trip rods withdraw sears from drogue gun and barostatic time-release units
Onboard oxygen and mic/tel disconnected
Emergency oxygen trips
After delay mechanism has operated, drogue gun piston fires
Deployment of drogue stabilises and retards the seat and aircrew
Low altitude/High speed –
- Seat descends stabilised by drogue
- Barostatic time-release unit completes run and fires
High speed/high altitude –
- Barostatic capsule operates to prevent parachute deployment above pre-determined altitude
- Barostatic controlled g-switch delays parachute deployment above 8000 ft until speed
and g-force are reduced
- Barostatic time release unit operates below pre-determined altitude, completes run and fires
Manual separation (override) used if automatic system fails
Gas from cartridge used to free drogue shackle link, release parachute mechanical lock,
operate upper harness locks and lower harness release mechanism to free lower harness
lugs, negative-g strap and leg restraint lines
Drogue withdraws parachute from container
Sticker straps momentarily hold aircrew in seat
Parachute develops, lifts aircrew and survival pack from seat and pulls sticker clips from
clips causing aircrew and seat to diverge
Aircrew operates survival pack release strap which lowers survival pack on drop line below aircrew
Normal parachute descent follows