The Vulcan XH558 & General Aviation Thread

[Renegadenemo]

There's hundreds of things on an aircraft that you could over / under tighten and bring about catastrophe that have been known about forever - leave the wheel nuts loose and see what happens, for instance. But the fix on that simple scissor shackle whatnot surely could have been offered as a school design project.
As I understand it, the drogue fires and pulls on the shackle that then tugs the main 'chute out of wherever it lives but this time it was too tight and the main 'chute remained resolutely packed away. The poor guy could only sit there waving his arms in a hopeless battle for balance as he was fired way up into the air then fell to earth again. I don't know what happened within the MoD but I know that civilian operators of the seat were sent to check the nuts and bolts after this accident.
Where's SBT - he'll know what's what.

[sbt]

Where's SBT - he'll know what's what.

I'm afraid I don't.

To say I'm shocked by this is a bit of an understatement. MB have a massive reputation for the utmost reliability, as does the RAFs safety equipment servicing. RAF pilots have been flying around sat on what is basically a bomb in large numbers for over half a century with, as far as I know, only one other seat related fatality to a pilot - and that was down to a loose object in the cockpit getting caught in the mechanism.

With regard to 'Lessons being learnt' and things being known for 20 years - it seems from the article that the MOD/RAF HAVEN'T known about this, due to MB basically informing everybody but them.

I'll have a look-see (probably over the weekend) to see if the Service Enquiry has been posted up yet. That may be instructive regarding where the RAF thinks things need to be changed, other than the physical changes that MB have made to the seat.

Safety equipment is often itself a safety risk. An example that may resonate with Bill etc. is the 2011 accident on HMS Tireless where Leading Operator Mechanic Paul McCann and Operator Maintainer (Weapons Submariner) 2 Anthony Huntrod were killed in a fire caused by damaged Emergency Oxygen Generator units.

This has personal relevance as 25 years ago I spent 2 hours strapped into a live Mk 10 seat bimbling around over Salisbury Plain.

[sbt]

Just read the Service Enquiry (its available via the MOD Website) over lunch yesterday.

Firstly it wasn't the Scissor Shackle that was overtightened, it was the ordinary shackle that was held in the jaws of the Scissor Shackle that was overtight. The amount it was overtight by was 0.009 inch. The fact that it was overtight was not obvious due to the problem being that it caught on a pair of lugs it only encountered once the Scissor Shackle had opened. In the unfired seat the shackle was free to move around by hand within the closed Scissor Shackle. Also if the aircraft had been travelling above 50 kts (which is below the aircrafts stall speed) when the seat fired the forces involved would have pulled the Drogue Shackle past the lugs

The Drogue Shackle was fitted in line with the instructions, with 1.5 threads showing above the nut. Unfortunately the bolt on the Shackle was manufactured shorter than specified.

Secondly, it was really really hard to get the Seat Firing Handle (SFH) into the position where it was fired. It required the Pilot to have strapped in incorrectly on his previous sortie, getting a Crotch Strap from his harness through the SFH, which would have led to it being in 'Position 2', where the Safety Pin was ineffective but the SFH would still have had to have been given a firm and deliberate upward pull to fire it. Then the Safety Pin would have had to have been withdrawn in a particular but unlikely manner to lever the SFH up into 'Position 3' where a 'tap' in the right direction would fire the seat. It was even then still likely that the SFH would drop back to Position 2 or could have been lowered to the safe 'Position 1' if noticed to be out of position.

The Pilot then did his 'Full and Free' check on the controls, which the out of position SFH obstructed slightly. So the Pilot tapped it out of the way...

The SI also concentrates heavily on the culture that had built up withing the Red Arrows that meant that it was less likely the issue with the Shackle would be noticed, the Pilot would have delayed takeoff to determine the situation WRT the SFH more carefully and also made it more likely that the Pilot would withdraw the pin hurriedly, with less opportunity to notice the out of position pin and SFH. There was a big issue with the safety and management culture and practise within the Red Arrows back in 2011 with most of the focus being on safety during the display manoeuvres and a less than effective system of external supervision that meant that things had drifted, over many years (decades) away from the way the rest of the RAF do things without the right checks and balances being in place.

This is not new, there were three SIs involving the Red Arrows in 2011 and they all said the same thing. Action to correct the situation was in train before this SI had been finalised.

[Renegadenemo]

Absolutely fascinating stuff. Thanks for taking the time to pass that on.

[Dangermouse]

A bit of a tangent, but does anyone know where the "frozen chicken in test cannon" legend began?

I've heard versions in which the users were NASA, British Rail, assorted aircraft manufacturers, various organisations that they borrowed the thing from, etc. About the only constant is the punchline "Thaw the chicken"!

[Renegadenemo]

A bit of a tangent, but does anyone know where the "frozen chicken in test cannon" legend began?

Something tells me that testing the windows of the high-speed trains is where it began and that there's some truth in that version.

[mtskull]

A bit of a tangent, but does anyone know where the "frozen chicken in test cannon" legend began?

Something tells me that testing the windows of the high-speed trains is where it began and that there's some truth in that version.

I was very interested to watch an episode of Mythbusters where they investigated this; their empirical findings were that, in terms of ability to cause damage, there is negligible difference between a frozen and a thawed chicken.

In the same vein, many years ago when I was in ground school for my BAe Jetstream 41 type rating, we were assured that the J41 had the only windscreen that was certified against a cat strike.
Apparently, during testing with the chicken gun, the testers took a break and left the gun loaded with a chicken. Enter the works cat, which scents a free feast, clambers into the gun barrel and gets the shock of its prematurely curtailed life when testing resumes....

[quicksilver-wsr]

I was very interested to watch an episode of Mythbusters where they investigated this; their empirical findings were that, in terms of ability to cause damage, there is negligible difference between a frozen and a thawed chicken.

I was going to post to similar effect.

The "frozen chicken" myth - like the "NASA spent twenty-five zillion dollars developing a zero-gravity pen, while the Russians used a pencil" myth - is something that just gained factual status through repeated use down the years, when in fact it has little basis in fact at all.

That said, ingesting a smaller bird is not the end of the world (except for the poor bird!).

Nigel

[Renegadenemo]

I was very interested to watch an episode of Mythbusters where they investigated this; their empirical findings were that, in terms of ability to cause damage, there is negligible difference between a frozen and a thawed chicken.

You'll find that Mythbusters got it wrong the first time and had to re-do the chicken gun experiment proving conclusively that a frozen bird is way more dangerous than a thawed one. It stands to reason - the stiffer material deforms more slowly so the pressure is that much greater because the point of contact is smaller for longer. Force x area...

[mtskull]

I was very interested to watch an episode of Mythbusters where they investigated this; their empirical findings were that, in terms of ability to cause damage, there is negligible difference between a frozen and a thawed chicken.

You'll find that Mythbusters got it wrong the first time and had to re-do the chicken gun experiment proving conclusively that a frozen bird is way more dangerous than a thawed one. It stands to reason - the stiffer material deforms more slowly so the pressure is that much greater because the point of contact is smaller for longer. Force x area...

That's interesting; must look out for that one. I must confess to having been surprised by their findings first time around.