Flt. Lt. Sean Cunningham inquest
Because of the design/layout of the Hawk cockpit - if one checks the front seat pan pin from directly overhead - if the handle is out of its detent but remains upright - it would be difficult to spot...one needs to move ones head forward and down to check properly !
The rear seat is much easier to check because it is being viewed from the front !
The rear seat is much easier to check because it is being viewed from the front !
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Deliverance
There is good reason to treat the seat firing and the shackle as entirely separate issues, and with respect, I don't think you've grasped it.
If Flt Lt Cunningham had been in the Line Hut, (after the penultimate flight) signing in the aircraft (certifying by his signature that among other things, the seat was safe) and a Red Arrows Engineer, maybe doing the Friday night refuel and tow to the hangar - the seat fires! The shackle has no bearing on the engineers death as he was not strapped in. It is certainly something to be investigated, but it is irrelevant to the engineers death.
War story - In the early 80's, a Canberra electrician got muddled up and fired the canopy detonators in the hangar. This was the focus of the Unit Inquiry. The fact that 50% of the canopy dets didn't fire was very alarming and the subject of a separate investigation altogether.
I don't think it matters how the seat was activated. The fact is that once the sequence was initiated the system did not work as it should have. It would be the same as not fitting parachutes, useless.
As for the handle being in an unsafe state on 19 occasions, that's another issue entirely IMHO.
As for the handle being in an unsafe state on 19 occasions, that's another issue entirely IMHO.
If Flt Lt Cunningham had been in the Line Hut, (after the penultimate flight) signing in the aircraft (certifying by his signature that among other things, the seat was safe) and a Red Arrows Engineer, maybe doing the Friday night refuel and tow to the hangar - the seat fires! The shackle has no bearing on the engineers death as he was not strapped in. It is certainly something to be investigated, but it is irrelevant to the engineers death.
War story - In the early 80's, a Canberra electrician got muddled up and fired the canopy detonators in the hangar. This was the focus of the Unit Inquiry. The fact that 50% of the canopy dets didn't fire was very alarming and the subject of a separate investigation altogether.
I don't think it matters how the seat was activated. The fact is that once the sequence was initiated the system did not work as it should have. It would be the same as not fitting parachutes, useless.
As for the handle being in an unsafe state on 19 occasions, that's another issue entirely IMHO.
As for the handle being in an unsafe state on 19 occasions, that's another issue entirely IMHO.
Imagine what would have happened had the man on brakes been ejected from this A/C ?
(I am assuming that the seats would not have been made Seat Serv to save time for example)
Would it have mattered how the seat had been initiated ? I think it might.
Would ANYONE have believed that the poor sod hadn't been playing with the seat when it went off? RAFAT sky gods are infallible after all.
Would it have received more than 2 lines in the national press.
The pinched bolt is very much the secondary point. In almost any other scenario involving normal velocity it would probably have worked and NO-ONE would ever have been the wiser until holes in the cheese lined up again. It just wasn't his day.
Did most of you sleep through your seat lectures? Were you not interested enough to look at how it worked. Some of the comments on here make it seem that way.
It is a bomb that will do it's very best to kill you. Treat it with respect at all times.
I also repeat the question. Were ANY OTHER BOLTS FOUND PINCHING THE SHACKLE during the fleet checks or was this one the only example ?
If the MB web site statement is correct and this is a UNIQUE failure in use then it is hardly a bad design is it?
Now everyone is aware of the cause would not every Pilot, Instructor, Student, Armourer and Liney from here to eternity be checking very carefully for free movement and the correct number of threads? So is not the point about MB not having told the RAF about it not now redundant. They surely will add them to the distribution list from now on. I think the point about the former flight safety structure and culture in the RAF having been dismantled explains convincingly how that happened.
Oh! and trying to blame MB for a design flaw from the 70's or before! Grow up. It was a very sad accident which I am very glad I didn't see or have any involvement in. Let us really learn from it and never repeat it so he did not die in vain.
Don't assume check.
Rant mode off ......... And Relax.
Sir Peter
A strange post if I might say so. A few days ago you praised the same guys for giving you the strength to pursue a successful claim against MOD. Well done by the way. As far as I can see, they repeat facts because MoD keeps making the same mistakes. So far, all the facts we've heard about this accident scream airworthiness failings. If history tells us anything it is MoD has kept a lid on even worse.
The usual suspects are limbering up for an Airworthiness debate, something that should command the respect of many PPRuNers, although they are a bit like a stuck record sometimes.
As far as I can see, they repeat facts because MoD keeps making the same mistakes. So far, all the facts we've heard about this accident scream airworthiness failings. If history tells us anything it is MoD has kept a lid on even worse.
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Good post Mr Mungus.
Yes I am quite surprised at the number of people who were/are dependent upon these seats just did not appear to know that much about them.
I have just reread my post that made reference to the original design. It went on to refer to the checks and balances that were in place commending the post that someone had made on another forum (AARSE) The hundreds of people in various formations who would have had an input to ensuring continued airworthiness. Some have disappeared altogether or watered down over the years. The design was just one slice of cheese.
I agree with others that there were two separate mechanisms (the seat pin and the shackle bolt) that came together leading to the tragedy. So far we [the public] don't know much about the pin. perhaps we might next week when the SI is made public. Reading between the lines it looks like MB/MoD have introduced a modification to address the deficiencies in both areas. They could have done one without the other. Could have done neither if they could have demonstrated ALARP.
Yes I am quite surprised at the number of people who were/are dependent upon these seats just did not appear to know that much about them.
I have just reread my post that made reference to the original design. It went on to refer to the checks and balances that were in place commending the post that someone had made on another forum (AARSE) The hundreds of people in various formations who would have had an input to ensuring continued airworthiness. Some have disappeared altogether or watered down over the years. The design was just one slice of cheese.
I agree with others that there were two separate mechanisms (the seat pin and the shackle bolt) that came together leading to the tragedy. So far we [the public] don't know much about the pin. perhaps we might next week when the SI is made public. Reading between the lines it looks like MB/MoD have introduced a modification to address the deficiencies in both areas. They could have done one without the other. Could have done neither if they could have demonstrated ALARP.
Mrmungus
Possibly the most perceptive post on this thread.
I feel you probably understand the equipment quite well, I wonder if you are another of St. Barbaras brethren?
Possibly the most perceptive post on this thread.
I feel you probably understand the equipment quite well, I wonder if you are another of St. Barbaras brethren?
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Then my engineer scenario passed you by. I'll make it surreal for you:-
Flt Lt Cunningham is showing Konnie Huq, the Blue Peter presenter around a Red Arrow, she is in the seat for a photo op. Flt Lt Cunningham has checked the seat for safety. It goes off. The seat and Konnie land on Princess Diana's head, and Nelson Mandela, standing next to her has a heart attack
Please tell me what the relevance of the shackle is.
Flt Lt Cunningham is showing Konnie Huq, the Blue Peter presenter around a Red Arrow, she is in the seat for a photo op. Flt Lt Cunningham has checked the seat for safety. It goes off. The seat and Konnie land on Princess Diana's head, and Nelson Mandela, standing next to her has a heart attack
Please tell me what the relevance of the shackle is.
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Firing details unimportant, Deliverance, Mrmungus?
There's an uninterrupted chain of events from the last time the seat was secure and inert to it being accidentally fired and then failing to operate as expected.
I'd say that all the steps are relevant, especially if 19 other instances were recorded. The procedures are presumably designed to prevent any cases of accidental firing, and so any errors are notable.
I agree with Deliverance that the parachute failure was particularly serious, since it was unexpected. If that element of the seat had worked properly, then there probably would have been an injury not a death. While it might not have been a problem at speed, the seat is billed to protect at zero speed, and so its failure to do so is notable. In an uncontained engine failure and fire at the beginning of take off would it have required that performance?
The opportunity to mistighten the bolt does seem to be flaw in the design; however, if there was a shoulder to the bolt to ensure its position, it seems possible that it could contact the frame without the correct tension being set, and what would be the consequences of that? If a bolt needs to have play, then it seems particularly dangerous to lose sight of that over the years, as the natural tendency would be to tighten loose bolts. Fancy German bicycle components usually have a torque setting (with units) anodized next to the bolt hole (granted because it's easy to chew up the alloy); maybe a similar practice could have helped here
"Don't assume check?". The biggest problem seems to be a lack of appreciation somewhere in the chain from manufacture 30 years ago to accident in 2011 that the tension on the bolt is a crucial think to check. Are there other aspects of the design that could be sensitive to mis-setting and drifting to being less safe with time?
I'd say that all the steps are relevant, especially if 19 other instances were recorded. The procedures are presumably designed to prevent any cases of accidental firing, and so any errors are notable.
I agree with Deliverance that the parachute failure was particularly serious, since it was unexpected. If that element of the seat had worked properly, then there probably would have been an injury not a death. While it might not have been a problem at speed, the seat is billed to protect at zero speed, and so its failure to do so is notable. In an uncontained engine failure and fire at the beginning of take off would it have required that performance?
The opportunity to mistighten the bolt does seem to be flaw in the design; however, if there was a shoulder to the bolt to ensure its position, it seems possible that it could contact the frame without the correct tension being set, and what would be the consequences of that? If a bolt needs to have play, then it seems particularly dangerous to lose sight of that over the years, as the natural tendency would be to tighten loose bolts. Fancy German bicycle components usually have a torque setting (with units) anodized next to the bolt hole (granted because it's easy to chew up the alloy); maybe a similar practice could have helped here
"Don't assume check?". The biggest problem seems to be a lack of appreciation somewhere in the chain from manufacture 30 years ago to accident in 2011 that the tension on the bolt is a crucial think to check. Are there other aspects of the design that could be sensitive to mis-setting and drifting to being less safe with time?
Last edited by awblain; 2nd Feb 2014 at 19:48. Reason: typo
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Deliverance
(sorry I edited previous post as you posted)
It will come down to definitions of the pedantic extreme. The Coroner was specifically investigating a death. The SI is to be published next week. If it is "Circumstances leading to...etc" then we already have the difference between the two.
(sorry I edited previous post as you posted)
It will come down to definitions of the pedantic extreme. The Coroner was specifically investigating a death. The SI is to be published next week. If it is "Circumstances leading to...etc" then we already have the difference between the two.
Zulu 10: You also seem to be suggesting that every design should be right first time. You’re a creationist I assume?
In the case of ejection seats with 60 years of development I will firmly put my hand up and say YES.
In my mind every ejection seat that makes it into production aircraft MUST be right first time. Creationist? maybe. I'm also someone who worked on and around ejection seats for many years.
In the case of ejection seats with 60 years of development I will firmly put my hand up and say YES.
In my mind every ejection seat that makes it into production aircraft MUST be right first time. Creationist? maybe. I'm also someone who worked on and around ejection seats for many years.
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Nuts' bolts. I was not an armourer, so can only talk in the most general terms.
Some have been talking about bolt tensions etc, so for those who may not be unfamiliar with nuts' bolts...
A mechanism like a fork end on flying control cables, which is supposed to have movement, would normally have a shoulder bolt to prevent pinching. Often with a slotted nut & split pin, which would be just pinched against the shoulder of the bolt to prevent vibration, then split pinned.
A slotted nut has the slots cut into the body of the nut, not designed to take tension, a slotted nut is used on bolts designed to take shear loads.
A castellated nut has scalloped extensions to the main body of the nut & is used on bolts designed to take tension (& often shear loads as well)
Just from general airframe experience, I would say that the torque loading of a non shoulder bolt onto a moving mechanism, would be unreliable, due to possible differences in the 'Stiffness' of a stiff nut.
When a piece of equipment needs to be free, so that one can easily move it by hand, 'Torque loading becomes irrelevant in my view.
I seem to remember pilots moving the shackle by hand before getting into the seat, but that was a long time ago now & I could be mistaken.
As to whether the seat would have operated as speed, that would depend upon the exact geometry of the mechanism.
Simple nut' bolts for sure, but some may not be familiar with them.
Some have been talking about bolt tensions etc, so for those who may not be unfamiliar with nuts' bolts...
A mechanism like a fork end on flying control cables, which is supposed to have movement, would normally have a shoulder bolt to prevent pinching. Often with a slotted nut & split pin, which would be just pinched against the shoulder of the bolt to prevent vibration, then split pinned.
A slotted nut has the slots cut into the body of the nut, not designed to take tension, a slotted nut is used on bolts designed to take shear loads.
A castellated nut has scalloped extensions to the main body of the nut & is used on bolts designed to take tension (& often shear loads as well)
Just from general airframe experience, I would say that the torque loading of a non shoulder bolt onto a moving mechanism, would be unreliable, due to possible differences in the 'Stiffness' of a stiff nut.
When a piece of equipment needs to be free, so that one can easily move it by hand, 'Torque loading becomes irrelevant in my view.
I seem to remember pilots moving the shackle by hand before getting into the seat, but that was a long time ago now & I could be mistaken.
As to whether the seat would have operated as speed, that would depend upon the exact geometry of the mechanism.
Simple nut' bolts for sure, but some may not be familiar with them.
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Zulu 10: You also seem to be suggesting that every design should be right first time. You’re a creationist I assume?
In the case of ejection seats with 60 years of development I will firmly put my hand up and say YES.
In my mind every ejection seat that makes it into production aircraft MUST be right first time. Creationist? maybe. I'm also someone who worked on and around ejection seats for many years.
In the case of ejection seats with 60 years of development I will firmly put my hand up and say YES.
In my mind every ejection seat that makes it into production aircraft MUST be right first time. Creationist? maybe. I'm also someone who worked on and around ejection seats for many years.
I also think that you're confusing design standards with production standards - though I'm unsure if that's deliberate.
BTW: If you replace the '1' with a '0' at the end of the URL, then press refresh on your browser, you'll be able to quote others.
I too have experience, I just don't feel the need to state it publicly.
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Just from general airframe experience, I would say that the torque loading of a non shoulder bolt onto a moving mechanism, would be unreliable, due to possible differences in the 'Stiffness' of a stiff nut.
In my mind every ejection seat that makes it into production aircraft MUST be right first time.
Spot on. Pedantic to argue terminology. I know what he means and so does my 5 year old grandson and 90 year old mother.
SPHLC/Nutloose
The handle operates a mechanical linkage that pulls a sear out of the firing unit. There will be a small amount of free play or backlash in the system. The majority of the the handle travel upwards, pulls the sear, which is a wedge shaped plate through the bottom of the firing pin. As the sear is withdrawn it gradually moves the firing pin away from the cartridge, compressing the spring on the firing pin. When the sear is fully withdrawn the firing pin is no longer restrained by the sear and under the force from the spring, hits the cartridge, starting the ejection sequence. I guess if the handle is partially pulled and then released, the sear will reseat under the forces from the firing pin spring. It might be possible to reach a situation where the sear is resting on the crest of the ramp and is then in a metastable condition and could go either way with the slightest force, one way back to safe, the other way to fire the seat. This is just an engineering guess, I have never tried to reproduce this situation, but I bet a lot of others have over the last couple of years.
As a follow on, the T Mk 2 and later Hawks has a 'PINS' caption on the CWP. If I remember rightly it illuminates if the pins are left in with the canopy closed. It was introduced to try and prevent one of the other hazards associated with seats, leaving the safety pins fitted during flight. The pin operates a microswitch behind the fitting into which the handle seats. If the pin were fitted when the handle is partially pulled, it would not give a PINS warning at the appropriate time. I guess when the crew reach the end of the sortie they probably shut down the electrics before fitting the seat pins so it would not show up at that point. On the next sortie though, after closing the canopy the crew would expect to get a PINS caption but would not if the handle were not in the correct position. It's not how the system is intended to work and its not a very robust means of warning the handle is not safe, even though the pin is fitted. However it is progress in some senses.
Walbut
The handle operates a mechanical linkage that pulls a sear out of the firing unit. There will be a small amount of free play or backlash in the system. The majority of the the handle travel upwards, pulls the sear, which is a wedge shaped plate through the bottom of the firing pin. As the sear is withdrawn it gradually moves the firing pin away from the cartridge, compressing the spring on the firing pin. When the sear is fully withdrawn the firing pin is no longer restrained by the sear and under the force from the spring, hits the cartridge, starting the ejection sequence. I guess if the handle is partially pulled and then released, the sear will reseat under the forces from the firing pin spring. It might be possible to reach a situation where the sear is resting on the crest of the ramp and is then in a metastable condition and could go either way with the slightest force, one way back to safe, the other way to fire the seat. This is just an engineering guess, I have never tried to reproduce this situation, but I bet a lot of others have over the last couple of years.
As a follow on, the T Mk 2 and later Hawks has a 'PINS' caption on the CWP. If I remember rightly it illuminates if the pins are left in with the canopy closed. It was introduced to try and prevent one of the other hazards associated with seats, leaving the safety pins fitted during flight. The pin operates a microswitch behind the fitting into which the handle seats. If the pin were fitted when the handle is partially pulled, it would not give a PINS warning at the appropriate time. I guess when the crew reach the end of the sortie they probably shut down the electrics before fitting the seat pins so it would not show up at that point. On the next sortie though, after closing the canopy the crew would expect to get a PINS caption but would not if the handle were not in the correct position. It's not how the system is intended to work and its not a very robust means of warning the handle is not safe, even though the pin is fitted. However it is progress in some senses.
Walbut
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Thanks Walbut for clarifying the operation, I remember a famous picture from years past of some aerobatic team doing a manoeuvre, the safety on that seat was a lever and you could plainly see in the shot that on one of the seats, the lever is still in the safe position. I have looked for it, but alas cannot find it.
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In the case of ejection seats with 60 years of development I will firmly put my hand up and say YES.
In my mind every ejection seat that makes it into production aircraft MUST be right first time. Creationist? maybe. I'm also someone who worked on and around ejection seats for many years.
In my mind every ejection seat that makes it into production aircraft MUST be right first time. Creationist? maybe. I'm also someone who worked on and around ejection seats for many years.
Everything can be improved, subject to experience and technology. The requirement will always be there, of course.
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While we're waiting, some definitions from the
"Service Inquiry report into the accident involving Royal Air Force Aerobatic Team (RAFAT) Hawk T Mk1 XX179, near Bournemouth on 20 August 2011."
Cause: An event that led directly to the accident
Contributory Factor: A factor which made the accident more likely
Aggravating Factor: A factor which made the outcome worse
Other Factor: A factor which was none of the above, but was noteworthy in that it may cause or contribute to future accidents
Observations: An issue that was not relevant to the accident but worthy of consideration to promote better working practices
Military Aviation Authority | MAA Service Inquiries
"Service Inquiry report into the accident involving Royal Air Force Aerobatic Team (RAFAT) Hawk T Mk1 XX179, near Bournemouth on 20 August 2011."
Cause: An event that led directly to the accident
Contributory Factor: A factor which made the accident more likely
Aggravating Factor: A factor which made the outcome worse
Other Factor: A factor which was none of the above, but was noteworthy in that it may cause or contribute to future accidents
Observations: An issue that was not relevant to the accident but worthy of consideration to promote better working practices
Military Aviation Authority | MAA Service Inquiries