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Hawker Hunter Crash at Shoreham Airshow

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Hawker Hunter Crash at Shoreham Airshow

Old 29th Aug 2015, 22:03
  #541 (permalink)  
 
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HIGH PRESSURE PUMP ISOLATION SWITCH (HPPIS). When the switch is set to ISOLATE, one HP pump is cut off from the servo system which continues to control only the other HP pump.

Extracts from an old AAIB report:

In May 1980 an RAF two seat Hunter T7 experienced a power reduction, and a hot relight was attempted. As this was being completed by one pilot, the other pilot had retarded the throttle slightly and operated the HPPIS as the first pilot ceased pressing the relight button. The engine speed increased to 6,000 RPM, but the EGT exceeded full scale deflection and the engine began to vibrate. The instructor took control and advanced the throttle slightly, whereupon there was a slight increase in engine speed, followed by a 'muffled bang' and the engine speed then decreased rapidly. Both pilots then ejected safely, but the aircraft was destroyed in the ground impact and post crash fire. The power reduction was attributed to an unidentified failure in the fuel system.

In December 1981, another RAF Hunter T7 experienced an engine malfunction while preparing to land. At about 1000 feet agl and after selecting flap, gear down and airbrake in, and as the airspeed decreased through 250 kt, the instructor advanced the throttle slightly. Both pilots then noticed a slight 'rumbling sound' and that the indicated engine speed was lower than expected for the throttle setting. The instructor moved the throttle further forward, but the engine did not respond. He then operated the HPPIS and the engine speed increased as expected before reducing to low RPM. At about that time, witnesses on the ground saw a plume of flame from the aircraft's jetpipe. Both pilots then ejected safely. Subsequent examination of the wreckage found that the engine turbines had experienced severe in-flight overheat damage. A fault was later found in the BVCU diaphragm which had caused the compressor to stall as the throttle was opened. It was subsequently established that the HPPIS had been operated while the throttle had been set to a position corresponding to about 7,000 RPM.

In addition to these accidents, records kept on a computerised database between 1980 and 1992 showed 22 cases involving the Avon Mk 122 engine where engine speed had dropped and subsequent engineering investigation had not established a clear cause. Anecdotal evidence indicated that Avon Mk 122 engines had suffered from unexplained power reductions from time to time during RAF service, but in most cases the aircraft had returned safely and the subsequent RAF engineering investigations, including related engine ground runs, had failed to identify associated causes or to reproduce the symptoms.
Doesn't sound right to me. If the pilot lost thrust going up or over the top then they would just roll out as others have said. If the power was lost going down then the throttle would be at idle anyway - again as others have said. Sounds like journo-bollo to me!
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Old 29th Aug 2015, 22:08
  #542 (permalink)  
 
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Just a thought and not aimed purely at AH but if you constantly fly a number of airframes can this cause a possible problem of handling issues etc. This is too aircrew as I have always been interested to find out regardless of this particular incident.
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Old 29th Aug 2015, 22:56
  #543 (permalink)  
 
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Bigbux

You may be thinking of the accident at RAF Wyton on 29 Jun 1966, when Victor SR2 XM716 was destroyed. IIRC the B of I found that the cause of the accident was pulling rolling G at speed outside the aircraft Release to Service limits.
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Old 30th Aug 2015, 08:38
  #544 (permalink)  
 
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Elevator PFC manual reversion?

PFC manual reversion has also been accountable for Hunter losses in service although aileron reversion is more tricky AIUI.
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Old 30th Aug 2015, 09:01
  #545 (permalink)  
 
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I've been following the thread but not closely enough so apologies if this has been mentioned. Didn't a US Aggressor company lose a couple of Hunters in quite quick succession recently - were the circumstances similar? I wonder if it won't be regulation that stoofs event flying; rather, the cost of indemnity.

Does anyone know how much it costs to insure a private flying operation, and what the scrutineering and underwriting criteria will now include?

That's not a rhetorical question, I don't know and would be interested to get an idea. I've managed to get some suitably qualified and experienced clients who do event flying at standard rates, it'll be interesting to see how more resilient underwriters become to shouty people who can argue a case with (generally) more insight.
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Old 30th Aug 2015, 09:30
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My copy of Hunter T7 pilot's notes, last amended 1972 states the following in the Emergency Procedures section.
"Sudden drop in engine speed....below 20,000 ft. If the engine fails to respond to normal throttle movements close the throttle fully and set the HP isolating switch to ISOLATE."
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Old 30th Aug 2015, 09:36
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Originally Posted by Al R
I've been following the thread but not closely enough so apologies if this has been mentioned. Didn't a US Aggressor company lose a couple of Hunters in quite quick succession recently - were the circumstances similar?
Yes, ATAC lost two Mk.58's, one in 2012 and another in late 2014. Pilots killed in both incidents. Pilot of the 2012 crash had reported fuel transfer problems just prior to the crash, and I've not seen any reports yet about the 2014 crash on approach to Point Mugu.
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Old 30th Aug 2015, 10:11
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On the question of whether indemnity/ insurance costs might have a greater impact than any regulation changes, I think that there is reason to think that this is unlikely.
Insurance underwriters are fairly dispassionate and analytical as a breed, and of necessity look through the human aspects of accidents to the financial. Courtesy of the 1700 or so deaths on UK roads each year, not to mention a much larger number of injuries, there is a substantial body of case law, not to mention custom and practice which enables underwriters to assess the likely financial impact of loss of life and serious injury resulting from an accident involving one of their insured. In arriving at their premium rates, insurers use sophisticated risk assessment and management techniques, and I believe that dramatic premium increases for all insured tend only to arise where something transpires which changes the risk landscape fundamentally.
In this case despite the horror of what has happened, I do not believe that the outcome has a significant impact in underwriting terms: the possibility of an insured aircraft having an accident and giving rise to third party claims will have been one of the risks understood when premium rates were established. Whilst the loss of so much human life has shocked us all, the eventual cost of the accident to the underwriters may well not fall outwith their estimates for a such an eventuality, bearing in mind they will have had to consider hypothetical scenarios such as a FJ crashing into, say, a shopping mall, etc etc.
In considering future underwriting rates, they will focus on whether the risks have gone up, down, or stayed the same. Even if there are no regulation changes (unlikely I think) all operators and pilots will, at least for a time, become more conservative, with the result that the prospects for a similar event reduce, and hence the risk insured goes down.
All rather dispassionate, and not intended to suggest that on a human level, underwriters would be any less shocked than the rest of us.
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Old 30th Aug 2015, 10:31
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Yes, ATAC lost two Mk.58's, one in 2012 and another in late 2014. Pilots killed in both incidents. Pilot of the 2012 crash had reported fuel transfer problems just prior to the crash, and I've not seen any reports yet about the 2014 crash on approach to Point Mugu.
My understanding is that in both ATAC cases the aircraft were fitted with small tanks and suffered from a fuel transfer failure from one tank. If they had either landed immediately or jettisoned their tanks they would have been OK. Unfortunately, in both cases the pilots continued to fly until the aircraft were in an out of trim situation that was NOT cleared for landing.

Both pilots lost control on approach and crashed!

I do not believe that this had any relevance to the Shoreham crash.

While I am writing I will express my disgust at the Daily Telegraph for an article published on Saturday.

They showed a picture of a Mig followed by an article about the Shoreham accident. The authors had clearly done a Google search and then just quoted a part of an Accident Report from an accident at Dunsfold. There would appear to be no connection or relevance to what was written. It appeared that the authors knew nothing about aviation, let alone display flying or jet aircraft.

IMHO the Editor should not have published the article and deserves grief from all interested. I have written to the Editor expressing my concerns.

I was also surprised to learn that many vintage jet aircraft fly without cartridges in either their ejection seats, or external drop tanks when carried. Apparently this is due to the cost of storage and servicing of explosive cartridges! Is this correct?
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Old 30th Aug 2015, 10:52
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falcon900. Sorry but I do not think your rosy view of insurance premium calculation ties in with the reality of the insurance market that I have experienced. Your simplistic description would see all insurance at fixed risk-cost, independent from claim history and specific risk. Please put me in touch with an insurer who operates in the way you describe.

OAP
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Old 30th Aug 2015, 11:07
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OAP,
If you read what I wrote again, you will note that I specifically referred to insurance rates "for all insured", i.e. the market. Individual insured do indeed see an impact on their premiums after a claim, but single events do not tend to drive up the market rate unless there is something truly exceptional in relation to ongoing risk.
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Old 30th Aug 2015, 11:37
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Loss history definitely plays a role in the cost of insurance, but the overall trend is unambiguously downward thanks to improving aviation safety. There are plenty of people willing to bet that this trend will continue over the long term, despite the odd outlier.

At the same time, ultra-low interest rates mean there's a lot of money in financial markets looking for a better return. Plenty of this has found its way into insurance and reinsurance markets, and that's also keeping premium costs down.
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Old 30th Aug 2015, 13:39
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This had NOTHING to do with HPPIS operation or BVCU failure.

The Dec 81 crash was on (Our) engine air test and we were waiting for it to land.

The flame from the rear was a good 40ft long. We thought they had gone in with it.

Even the guy in the tower (I met him in the Falklands) who hit the crash button didn't see a parachute.

Both seats both pilots the canopy AND the A/c were all in the same small field. It was very very close.

At Shoreham there was no flame, no unburned fuel (white smoke).
It sounded normal in all video i have heard Listen to the dash cam video). No pops or bangs. there was a nice shot from above showing hot efflux.

I am certain that engine was running normally.


The drop tanks. Yes it is acceptable to have no carts in the ERUs (In Civi use). I don't know if these were armed or not but I doubt it.

Indeed the Swiss disabled all their inboard tank jettison to make sure they would not drop off.

It's been 30 years but I'm sure the T7 had no rear tank, so even had it been a full fuel load or similar at take off the droppers would have fed first and been empty or had little left.

Seats are a different matter. That I believe is the operators choice.

MB have said they are no longer going to support old seats. Who can blame them when you think of the vitriol thrown their way after the Scampton failed ejection.

Australia have stopped flying their historic flight Sabre because of this issue.


Hope this helps
MM

Last edited by Mrmungus; 30th Aug 2015 at 14:27. Reason: Big fingers and small tablet.
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Old 31st Aug 2015, 01:47
  #554 (permalink)  
 
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Elevator PFC manual reversion?
I haven't waded through every post in this thread, so don't know if it has been mentioned before, but I believe Vulcanpilot's suggestion may have merit. I've flown the Hunter enough (including the accident aircraft ) to appreciate that manual reversion is not an impossible feat but if, for some reason, Andy found himself in 'manual' as he pulled out of the looping manoeuvre then obviously he'd be faced with an increasing stick load that he might just not have been able to cope with (pull hard enough) given the lack of sky beneath him. IF this occurred during the back side of the 'loop' then he'd have no choice in his actions, as rolling off the top etc clearly would not be an option.
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Old 31st Aug 2015, 05:47
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Not sure that is accurate Pontius. The speed involved off the top of the loop would be low enough to allow reasonable stick pressure. As I recall, it only became a real problem above about 360 knots. Would the hydraulic failure warning horn have given time to abandon the manoeuvre before the controls reverted to manual? Mind you it is some years since I was instructing on the Hunter! Maybe a Hunter QFI would like to remind us?
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Old 31st Aug 2015, 07:34
  #556 (permalink)  
 
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Elevator PFC manual reversion?
How does that explain the large, sudden increase in pitch rate shortly before the crash, which to me, looks like the point of recognition?

The fact that AH lost control on his very first manoeuvre of the display makes it easy to believe that partial incapacitation was a cause.
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Old 31st Aug 2015, 08:03
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what should the height / speed at the apex to complete the back 3/4 of e.g. a loop, and what is is the min height drop from apex to come out wings level (ignoring margins). and how much margin would be typically added?

out of interest how does this vary by type for e.g. a hawk / typhoon etc.?
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Old 31st Aug 2015, 08:59
  #558 (permalink)  
 
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I know what you mean, Newt and agree the forces would be easily manageable when low speed over the top. What I was considering was a hyd snag on the way down and control(s) reverting to manual, with the subsequent pull required to exit the 'loop' increasing as the speed increased. I could imagine Andy being more than capable of exerting the required back-stick pressure initially but, maybe, the required force to recover in the height available, as the speed increased, was just not available.

How does that explain the large, sudden increase in pitch rate shortly before the crash, which to me, looks like the point of recognition?
ZeBedie,

A suggestion might be that the hyds returned to life and the sudden 'snap' of pitch change that we see is the result of the stick being held back/pulled back in manual and then, suddenly, having the benefit of hydraulic power applied to flight controls. It obviously takes XXX seconds for that effect of the controls to materialise but, in the meantime, gravity continues to suck and the velocity vector stays in place.
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Old 31st Aug 2015, 09:00
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I do not wish to speculate on the accident. However, I have now seen an unusual detail on video posted at youtube. During the hard rolling break after the fast flypast, a definite trail is seen for two seconds and again, after the reversal, the trail can be seen faintly for approx three seconds. The video is jerky but, I consider the trail to be real and not an aberation.
The video can be seen on youtube under "Shoreham Hawker Hunter disaster (added material) - Tragic Hawker Hunter Plane crash". The detail I am commenting on occurs in the first fifteen seconds of the recording.

OAP
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Old 31st Aug 2015, 09:37
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Video from above.

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