Ok, I’ll stick my oar in

The Hawk Mk10B seat has a single Pip pin safety in the seat pan firing handle

A Spanish Typhoon Mk16 seat initiated all by itself a few years back, this was a assembly failure of the main gun firing unit and is unique to the Mk16.

I assume its the MAA who will carry out the investigation along with the RAF Police and Civ Pol.

On a Mk10 when the drogue gun fires, the drogue withdrawl line pulls out the 22″ drogue chute followed by the 5′ drogue chute (This remains attached to the seat until separation). If you eject above 10’000 feet, you will stay in the seat until it decends to 10’000 (Oxygen). Then the barostatic time release unit will release the occupant by the unlocking the upper and lower harness locks and the Neg G and V. At the same time the BTRU will allow the scissor shackle or new gas shackle to release the drogue chute which pulls out the main chute. The sudden jolt of the main chute causes the sticker straps to snap out giving you clean separation from the seat. The seat falls away to the ground while you hang on the chute.

The BTRU also has a ‘G’ controller and the idea is that above 7’500 feet, the ‘G’ Controller can prevent you from leaving the seat until it’s safe to do so. Below 7’500 feet, there isn’t time so the ‘G’ controller is ignored and the seat will allow you to release despite the higher risk, after all it’s better to have some chance than no chance.

Every way I look at this accident, there appears to be 2 separate problems, the seat initiated and the seat failed to separate. A possibility of initiating the seat could come from motoring the seat pan down onto an obstruction under the seat, this in turn in a million to one chance, push the sear out of the seat pan firing handle firing unit and initiating an ejection. This would result in the normal ejection sequence.

If the BTTDFU or BTDFU (Breech type time delayed firing unit) initiated, then the main gun would extend and the trip rods for the Drogue gun and BTRU would trip and the drogue and BTRU would work, as would the static line for the Remote Rocket Initiator. What wouldn’t work in this scenario is the Harness Power Retraction Unit (HPRU) which means the occupant would be free to be thrown around. Not good!

The second failure is odd, I’m assuming the drogue gun has fired, this would allow the drogue to deploy .5 sec after being tripped. 1 second later the BTRU (1.5 secs after being tripped) would fire and as it was a Zero Zero ejection, the BTRU would release the harness locks AND release the scissor shackle allowing the drogue chute to pull the main chute out of the headbox and pilot parachutes to the ground.

If on contact with the ground the Pilot was fully harnessed to the seat but the main chute had deployed, this would be a failure of the locks to release. If the main scissor shackle failed to unlock leaving the drogue only, and the harness locks released, the Pilot would still be attached to the seat by the scissor shackle (via the drogue line) and likely the sticker straps. If the BTRU or BTRU cartridge failed, the Pilot would be attached to the seat by both the harness locks and the scissor shackle (drogue line).

A post on the PPRUNE site mentioned that Martin Baker had stated that prelim investigation revealed no tech faults so I don’t know if that includes cartridges or not. I’m going to hazard a guess, and this is based on no evidence, that for some reason the drogue chute could not extract the main parachute or that the scissor shackle did not release for other reasons. I’m basing this on Martin Bakers alleged statement stating there were no technical faults.

Post 9 !!

More haste less speed

AFAIK there’s only one safety pin that secure the ejection handle.

Scene 1 (Aircrew)
Could you imagine, a rapid dash to the flight line, into the cockpit to strap up. Pin removed stowed. No thanks I will do my own harness up, neg g strap/QRF through lower firing handle, harness secured. Checks completed harness pulled tight, lower handle pulled far enough to fire seat!!

Scene 2 (Ground crew)

New boy in the seat bay, not done much yet but he is OK. Para pack/harness repacked ready to go onto the seat, packed by another newish boy, was the scissors shackle u bolt torqued up OK?? Too tight the shackle will not release, drogue cant be withdrawn, parachute not deployed seat/man are not seperated.

This is all supposition as I do not know anyone involved. BUT when cuts are made the economies have consequences!!!!!!!!