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Author Topic: Mk10 ejection seat aircraft grounded  (Read 5992 times)
NewsMan
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« on: 14 November 2011, 00:00:03 »
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Mk10 ejection seat aircraft grounded

Royal Air Force aircraft fitted with the Mk10 ejection seat found on Hawk T1s have been temporarily grounded following the death of a Red Arrows pilot on [...]

Read more: Mk10 ejection seat aircraft grounded

From Pilots & Planes Military Aviation (MAV)
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« Reply #1 on: 14 November 2011, 19:31:44 »
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are there details known on HOW exactly the pilot died?
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Rattler
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« Reply #2 on: 14 November 2011, 20:45:02 »
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are there details known on HOW exactly the pilot died?


You are a morbid one, ey?  hahahihi

Anyway, while there are no official comments (and not to be expected until the preliminary findings report - published usually 6 month into the investigation) I have heard through the grapevine that he died from polytrauma from a fall of around 50 mtrs after he involuntarily got ejected and one/the/all seats parachute(s) failed to open.

Flight Lieutenant Sean Cunningham, the pilot involved in the fatal mishap:



Disclaimer: The following is wild speculation.

If I had to speculate I would investigate whether the cause for the unplanned ejection (if it was one) was the same as in the case of the partially ejected pilot of an A6 (Lt. Keith Gallagher, survived this bizarre mishap), the "Top Latch Mechanism":

The mechanism consists of a spring-loaded plunger, which extends from the seat between the two main structural beams of the seat. The plunger, when locked, extends through a "window" in a tab at the top of the ejection gun. The ejection gun is mounted to the cockpit structure. As a result of the design, the top latch plunger is the sole item that retains the seat in the aircraft. Normally locked by spring pressure, the firing of the ejection gun presses the plunger from the window, allowing the seat to depart the aircraft.



In the case of the MB (Mk7, though) seat of Lt. Gallagher, this bolt broke, the cause has never been established with scientific certainty, but there is a reasonable probability that it cracked because of the negative gs when maneuvering trying to unblock unresponsive fuel transfer valves (the A6 in question was a tanker version).

Now, if you take into consideration that the aerobatic teams go through many cycles of positive and negative Gs and that the Hawk fleet had been grounded briefly in 2010 because of a "crack found in an ejection seat" it does not seem far fetched to assume that the investigation will focus on this aspect beneath others.

Three facts stand in the way of my nice theory:

After Lt. Gallaghers mishap all ejection seats got a heavily tightend up inspection cycle for the top latch bolt which in theory should prevent the same mishap to happen again, and: I have no clue whether the MK10 operates on the same principle as the MK7. Last, Lt. Gallaghers mishap did not involve the intitation of the ejection sequence, his seat was "lifted" by the negative Gs and only after having passed the "point of no return" in the cockpit rail was the rest of the ejection sequence triggered (opening of parachutes, seat separation, etc.), the rockets never fired.

This said, all flights of the Red Arrows are documented on video from ground, so the investigation should have enough clues to establish the "HOW" of the death of the pilot.

Rattler
« Last Edit: 14 November 2011, 20:52:59 by Rattler » Logged

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« Reply #3 on: 14 November 2011, 21:17:53 »
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so he was ejected without his intent?

isn't it so that even on groundlevel the ejection should be 100% survivable?
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Rattler
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« Reply #4 on: 14 November 2011, 22:05:53 »
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so he was ejected without his intent?

This is the basic assumption, there was no reason to eject voluntarily (Ejection initiation MK10: Handle on seat pan initiates gas operated seat firing system, sequenced by trip rods in the rails: Ejection gun and multi-tube rocket pack system as in all MartinBakers)

isn't it so that even on groundlevel the ejection should be 100% survivable?

*NO* ejection is 100% survivable, thats for starters, and there might be many reasons why the parachutes did not deploy.

Indeed the Martin Baker MK10 seat is a zero/zero seat (usage umbrella from zero height at zero velocity), but - especially when the ejection was not planned - things can go wrong, just a few ideas where the parachutes might fail, color insert by me in the normal MK10 operating sequence:

- Seat firing handle pulled causing seat initiation cartridge to fire

Lets assume for a moment this was not the case as the handle (see below) was not pulled. So we dont know whether the ejection was sequenced correctly (starting with the primary cartridge aka ejection gun) or whether maybe the rocket pack simply fired all by its own disrupting the mnormal sequence where this takes place much later

- Harness retraction unit operated, command firing initiated

As the MK 10 has no electronic sequencer we can not be sure this was executed (as we cannot be sure what triggered the primary cartrige firing or whether it was triggered at all): Probably first injuries?

- Primary cartridge fired causing inner and intermediate pistons to rise, releasing top latch

OK, here is the hint: MK10 is top latch operated, this would have had to be released for the seat to go, so inner and intermediate pistons of the ejection gun have actuated

- Seat rises up guide rails

Obviously. We dont know, though, whether it did in the scheduled way or arkwardly (with rockets firing), the video will probably help the investigation in this respect

- Miniature detonating cord trip initiates canopy fracturing system

The canopy appears to have been fractured as planned (the canopy is not jettisoned), another hint that this part of the sequence was triggered (trip rod in the rail) which seems to hint at the seat ejecting up the rails correctly:



- Secondary cartridges fire in turn as seat rises
- Electrical connections separate disconnecting seat actuator circuit, IFF
switch and oxygen regulator supply lead
- Aircraft portion of main oxygen generating system block separate
disconnecting main and back-up oxygen
- Personal equipment connector aircraft portion disconnects from seat portion
- Anti-g suit hose disconnects
- Leg restraint lines draw back and restrain aircrew’s legs
- Leg restraint lines become taut and rivets shear, freeing lines from floor brackets
- Trip rods withdraw sears from drogue gun and barostatic time-release units
- Emergency oxygen trips
- Remote rocket initiator operated by static line, cartridge fires to ignite rocket pack
- Rocket pack sustains upward thrust of ejection gun, diverging trajectories for front and rear seats

Up to here we can assume all this was executed as the pilot was reported through the grapevine to have been ejected to a height of roughly 200 ft

- After delay mechanism has operated, drogue gun piston fires

The delay mechanism is triggered by a trip rod and takes into account barometric pressure and registered TAS. Definitely a source where something could go fatally wrong (see below different characteristics for different situations), maybe the "inner" delay had not yet ended as the seat assumed to be high in the air at high speed?

- Ejected piston withdraws closure pin from closure flaps of drogue parachute pack and deploys drogues.

Again, only if the seat is understanding the situation correctly, else the drogue closure flaps dont open: No chute!

- Deployment of drogues stabilize and retard the seat and aircrew

see above and below

- Low altitude/High speed - (configuration, Rattler)
- Seat descends stabilised by drogues
- Barostatic time-release unit completes run and fire


- High speed/high altitude -
(configuration, Rattler)
- Barostatic capsule operates to prevent parachute deployment above pre-determined altitude

- Barostatic controlled g-switch delays parachute deployment above 7000 ft until speed and g-force are reduced

Bolded by me might go wrong in a zero/zewro situation where the seat believes to be in a high speed/high altitude config

- Barostatic time release unit operates below pre-determined altitude, completes run and fires

same

OTOH, the following should allow a conscious pilot to override the automatic sequence, but then he would have to

a) understand his problem
b) execute the override

and 200 ft is not much time to get it done if you need your separation and chute terminated at 100 ft latest: 3 seconds in total for all, or so?


- 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 straps, leg restraint lines and personal equipment connector man portion
- Drogues withdraw 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
- Normal parachute descent follows
- Aircrew releases either of two quick-release connectors to lower survival pack to end of line
- Survival pack opened manually when necessary


As you can see, nothing is fail safe, and Murphy is your friend (enemy) especially in critical situations (check out the ejection story "Survival Instinct" I posted a while ago as a reply to one of Chuck Andersons concept pix to see what stuff can go wrong and how sometimes just sheer luck helps you to survive)

Rattler


Martin Baker MK10 ejection seat:

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« Reply #5 on: 14 November 2011, 22:20:24 »
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do I understand correctly that:

the canopy was ejected away from the airplane?
that the seat with pilot was ejected correctly?
but that the parachutes didn't deploy?
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« Reply #6 on: 14 November 2011, 23:00:30 »
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do I understand correctly that:

the canopy was ejected away from the airplane?
that the seat with pilot was ejected correctly?
but that the parachutes didn't deploy?

The canopy was not jettisoned (not the plan in the Hawk), it was fragmented by an explosive cord, correctly so.

The seat with the pilot was ejected, whether correctly or not we dont know (but assume something went wrong in the process)

The parachute did not deploy (or not in time).

The investigation will show, we can only speculate and that does not leadd very far.

Rattler
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