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AAIB investigation to Hawker Hunter T7 G-BXFI 22 August 2015

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AAIB investigation to Hawker Hunter T7 G-BXFI 22 August 2015

Old 7th Mar 2017, 07:42
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...but the pilot appears to have no backup plan in mind for an escape manoeuvre when the aircraft did not achieve the expected loop apex height and speed.
I'd be extremely surprised if a display pilot of AH's experience didn't have a backup plan. Specifically, the report details AH's own discussion of gates and what he would do if he failed to achieve them. The fact that there were gates in place means by implication that there was a plan should they not be achieved. Why have a gate at all if you're planning to blithely fly the manoeuvre regardless?

Therefore that indicates to me that he was either unaware that he had missed his gate or unable to react appropriately.
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Old 7th Mar 2017, 07:57
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Well said Wiggy. It seems some people, who perhaps haven't flown this type of machine, are unaware of the gross inconsistencies that seem to be present.

These are not small errors, the sum of which add up to something awful, but major deviations from the planned profile and indeed norm. and the differences must have been sensed by AH at the time (acceleration rates, stick force per G, rate of pitch, buffet levels, engine noise, thrust lever position, to name a few) as well as the obvious of just looking at the instruments and the outside picture.

I really cannot believe that any pilot would deliberately continue a manoeuvre knowing he had got so badly out of shape or if he knew he had an engine or systems problem. It just beggars belief. Therefore the only conclusion can be that he didn't know he was so much out of shape or was hugely distracted.

This isn't a case of being blasÚ, gash or trying to "wing it". It is much much more. Something happened, and we don't know what. Or most importantly, Why.
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Old 7th Mar 2017, 08:17
  #303 (permalink)  
 
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Having only been inverted in a light aircraft myself, is the reason AH came out of the loop 'aligned with the A27' (rather than intended heading) a symptom of 'getting it wrong' at the apex and/or entry?

Last edited by Parson; 7th Mar 2017 at 08:27.
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Old 7th Mar 2017, 08:18
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Originally Posted by DaveReidUK
That is also addressed in the report:

"Estimated errors associated with reading partially obscured ASI:
0-250 KIAS: 2KIAS
250-275 KIAS: 5 KIAS
275-410 KIAS: 15 KIAS"
DaveReid -- Yup, I did see that, and thank you, but as I said in my earlier post I am wondering about the pitot-static.
1.12.3.4 Pitot-static system
It was not possible to test or check the integrity of the aircraft’s pitot and static
systems due to the extensive structural disruption resulting from the accident,
but the altimeters and ASIs were removed from the cockpit and bench tested.
It's alleged or implied that this highly experienced pilot entered a manoeuvre at the wrong speed and wrong altitude. Both readings are affected by the static. But due to the accident damage they couldn't check the static; only the instruments were tested. The instruments are useless if the static isn't OK. I was an instrumentation and control engineer in an allied field so my comment isn't a wild guess or stab in the dark.

Perhaps one of the fast jet pilots could comment on whether that might have been a problem?

Edit: note that while the quote above from the report refers to pitot-static systems (i.e. plural) elsewhere it states that there is only one pitot-static on this type.

Last edited by Lemain; 7th Mar 2017 at 08:29. Reason: Afterthought, added as "Edit"
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Old 7th Mar 2017, 08:33
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It's alleged or implied that this highly experienced pilot entered a manoeuvre at the wrong speed and wrong altitude. Both readings are affected by the static. But due to the accident damage they couldn't check the static; only the instruments were tested. The instruments are useless if the static isn't OK. I was an instrumentation and control engineer in an allied field so my comment isn't a wild guess or stab in the dark.
Whilst a blocked static would freeze the altimeter, the ASI would continue to function 'normally' apart from a tiny error associated with any changes in height from the equivalent frozen static pressure. If the static source had failed at ground level (it clearly hadn't) then the ASI would slightly under-read at 3000ft.
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Old 7th Mar 2017, 08:43
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The manoevre has been called a loop, and for that we can calculate a safety gate. The final manoevre was more akin to a barrel roll (p10-as the aircraft approached the vertical it began a LH roll). Maybe because the speed was lower that needed for a full loop, but no surprise that only 2700ft was achieved. The aircraft exited the manoevre 60deg off hdg, so perhaps AH accepted the lower altitude as he knew it was not a complete loop and intended to continue rolling, as he did and ended up rolling out off his planned track. Safety gates for barrel rolls are somewhat more fluid than loops.

Last edited by Capt Scribble; 7th Mar 2017 at 09:07. Reason: Sp
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Old 7th Mar 2017, 08:51
  #307 (permalink)  
 
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H Peacock, thank you. I would suggest that "frozen" is not a good adjective. "Blocked" or "severed" are also considerations. This a/c didn't fly every day. Statics are pipes that bugs can go down, moisture can collect, corrode, evaporate... So one might consider the consequences of the static being severed or leaky. Suppose there was a leak from the static pipe, inside the port wing, what would the pressure have been at the static inlets to the ASI and Altimeter? That's probably a rhetorical question as it would depend on true airspeed and perhaps angle of attack. I would doubt anyone has modelled that because one hopes to ensure the integrity of the static.
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Old 7th Mar 2017, 09:11
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Cockpits

I would just like to follow up the discussion about the possibility of confusion between two different aircraft.
Even to my eye, the T7 and the T5 look so different in many ways, even including the throttle/variable noise levers and control grips.

These images are in the public domain and no copyright is claimed.


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T5 Cockpit.jpg (253.6 KB, 110 views)
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Old 7th Mar 2017, 09:26
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The manoevre has been called a loop, and for that we can calculate a safety gate. The final manoevre was more akin to a barel roll (p10-as the aircraft approached the vertical it began a LH roll). Maybe because the speed was lower that needed for a full loop, but no surprise that only 2700ft was achieved. The aircraft exited the manoevre 60deg off hdg, so perhaps AH accepted the lower altitude as he knew it was not a complete loop and intended to continue rolling, as he did and ended up rolling out off his planned track. Safety gates for barrel rolls are somewhat more fluid than loops.
He was flying a 'bent' loop with the change of axis on the way up. Now it doesn't really matter how he got there, but from wings level and inverted he had several options. Yes he could fly the second half of a barrel roll, but that would have kept him pointing away from the display line (effectively behind him). It would have avoided the accident, but was never going to work from a display point of view which is all he appeared to be trying to focus on. I agree that a BR has a very different kind of gate parameters, but last thing you'd ever want to do from an inverted but 'low' height is to pull through. The second half of a loop is always going to use up more sky than any other course of action.

Think of it another way, if your barrel roll goes awry, the last thing you'd want to do is try to half-loop out of it!

Last edited by H Peacock; 7th Mar 2017 at 10:25.
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Old 7th Mar 2017, 10:29
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Camera recordings of previous flights indicate that the pilot did not fly the display sequences as accurately as might be desired. There appears to have been a tendency to fly manoeuvers a bit lower than the ideal. So something of a habitual pushing of the limits? Makes for more exciting viewing from the ground, but no room for error if things go wrong, as they did at Shoreham.
If that statement is correct (IF) then the 'something happened to the pilot' scenario looks less likely.

It may be suggested that any pilot involved in a display carrying out manoeuvres outside of the safety criteria - even if he gets away with it - should be banned from further display. At any display there will be enough experienced pilots around to be aware when safety measures are stretched.
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Old 7th Mar 2017, 10:41
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Observation on pitot static checks on the Hunter , during my time maintaining them on ETPS when doing the inverted spinning etc the leak checks were done every pre-flight due to the nature of the flying.
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Old 7th Mar 2017, 11:21
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Its very interesting all these theories regarding the pilot and potential incapacitation. I thought that there had been a comprehensive look at this within the report by the aviation medics and this had been debunked somewhat?

If the pilot had suffered incapacitation during the accident manoeuver (something like a TIA - a 'mini stroke'), I would expect that there would be a biochemical marker in the blood to indicate this?

I am more expert in this field than I am in flying fast jets as well.

This is surely a minor possibility compared to the facts of the case which of course have been well established and much discussed on here and as the evidence stands then its a very remote possibility. I would put much more credence on possible engine issues (for example) as being a contributory factor in this accident.
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Old 7th Mar 2017, 13:21
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Originally Posted by Parson
Having only been inverted in a light aircraft myself, is the reason AH came out of the loop 'aligned with the A27' (rather than intended heading) a symptom of 'getting it wrong' at the apex and/or entry?
It looked to me from one of the videos that the roll intended to change the axis of the loop was accomplished before the airplane was vertical. That would have displaced him farther along his run-in axis than if he had planned to roll in the vertical, resulting in him being beyond the line he wanted to be on at the bottom of the loop (and therefore lined up with the road rather than offset east from the runway) and also reduced the height he expected to achieve at its apex. I've wondered if him seeing that he was on the wrong line as he was coming down the backside of the loop was momentarily distracting and caused him to briefly pause the steady increase in pull necessary to minimize the loss of altitude as his speed increased. Being a bit too low on the run-in, a little slow on the run-in, not having full thrust available, rolling before being vertical, and not pulling enough initially on the downside of the loop: no one of those would have done more than than reduce the margin he expected to have at the bottom of the maneuver but together could have slightly more than eliminated it.
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Old 7th Mar 2017, 13:34
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Originally Posted by bvcu
Observation on pitot static checks on the Hunter , during my time maintaining them on ETPS when doing the inverted spinning etc the leak checks were done every pre-flight due to the nature of the flying.
Hi bvcu, Did you see the section on that, in the report? 2.3.1.1 Pitot-static instruments I guess you've got the report in pdf? If you do a 'find' on 'pitot' 'static' and 'pitot-static' you'll find several refs. My interpretation is that the static was not checked after one servo-altimeter was exchanged some time before. The record keeping was poor and the Report says the serial No of the Alt was "transcribed" incorrectly. Would be interesting if you could cast your educated eye over that issue.

Just seems to me that if an experienced pilot was at the wrong altitude and speed the static is a very obvious common factor and is pretty much buried in the report. Not to mention the vulnerability of the combined pitot-static head with bods rushing around in the excitement of an air show.
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Old 7th Mar 2017, 14:03
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Originally Posted by Tailspin Turtle
It looked to me from one of the videos that the roll intended to change the axis of the loop was accomplished before the airplane was vertical.
I suppose it depends on how you interpret the AAIB's finding that

"as it approached the vertical, the pilot initiated a roll to the left"

There is no suggestion in the report that the roll was started earlier than planned.

That would have displaced him farther along his run-in axis than if he had planned to roll in the vertical, resulting in him being beyond the line he wanted to be on at the bottom of the loop (and therefore lined up with the road rather than offset east from the runway)
Another, simpler, explanation (and the one offered by the AAIB) was that the 60░ roll was more than intended, thereby offsetting the loop axis by a correspondingly greater amount away from the display line.
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Old 7th Mar 2017, 14:26
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After re-reading the report, I still have the opinion that the performance of the engine has not been sufficiently examined. My thoughts are based on information published in the report and other evidence. The other evidence is that similar Avon engines have suffered from power loss that was subsequently unexplained. Also, the video evidence of a considerable, possibly fluid, trail from the Fuselage of the accident aircraft seconds before the final manoeuvre is not mentioned at all.
Lastly, the report states:

"The engine manufacturer’s analysis of JPT and engine speed, derived from
the cockpit action camera recordings, revealed no anomalies during takeoff
and transit steady state conditions. There was insufficient data to verify engine performance during the dynamic manoeuvres".

This is wishy-washy. The Avon engine performance can be precisely calculated from the RPM and JPT values that the report states are recorded.
IMO, the following analysis should be possible: A precise assessment of the engine acceleration and thrust output on the take-off, compared to design performance. An accurate assessment and comparison of the percentage thrust achieved during the pull-up where 100% would be normally used.
My impression from the published illustration of varying engine performance parameters in the final manoeuvre is that, they might reflect the "throttle-pumping" actions of a pilot trying to get a full engine response. Of course, if the engine was only selected to partial throttle settings the achieved performance would be reduced but, it is possible that problems in fuel supply or engine control systems would simply prevent the achievement of full power.
The detailed component strip report lists some deficiencies in the engine fuel system, what I fail to read is some correlation between the deficiencies and the possibility that the engine could have underperformed in thrust levels or, perhaps more importantly, reliable throttle response?
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Old 7th Mar 2017, 15:44
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Originally Posted by Treble one
If the pilot had suffered incapacitation during the accident manoeuver (something like a TIA - a 'mini stroke'), I would expect that there would be a biochemical marker in the blood to indicate this?
There are apparent biomarkers for ischemic stroke, but I believe they are still at the research stage and not yet used in hospitals (there are myocardial infarction markers used as standard now). Standard approach to TIA/stroke is (I believe) CT scan to rule out haemorrhagic, followed by MRI for better view of infarcts. Depending on other injuries and treatment the pilot may have had cranial CT/MRI, but he may well not have done. If he did and they showed anything I would expect it to be reported on and some sort of action to follow - after all, any diagnosis of a TIA/stroke is an instant 1 month medical driving ban, I can't see why flying would be treated more leniently.

However, not all TIAs show up even on MRI, so unless the patient can remember and report them they remain completely unknown (for "mini-stroke" depends on the definition - some definitions are along the lines of "mini-stroke = a TIA that shows up on MRI").

Source: my own experience and knowledge of the experience of other people with the same rare blood clotting disorder it turns out I have...
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Old 7th Mar 2017, 16:26
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Thanks if789, consider this..if he was placed in induced coma, quite a serious decision, it is posssible CT may have shown diffuse one sided swelling which may have been attributed to head injury, particularly if there had been localising signs, ie pupil size. This may have been residual evidence of a dense transient stroke. Reading from the fj boys, the throttle is not advanced sufficiently at the start of the manoevre, if it is on the left this suggests left sided weaknesss, which may also suggest the left roll as with only a right side functioning the chap would feel lopsided and nudge the stick to the left, if right handed, and possibly a left visual field defect as well. I can't complete the analysis as with all the upside down and roll even my left/right is confused.
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Old 7th Mar 2017, 19:03
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JPT and engine RPM do not correspond to thrust on 100 series Avon . It does if no faults. However any problem with the bleed valve system with correct indications but lack of thrust .The report states BVCU was ok on strip but any leak on a connection will cause problems which couldn't be checked. Anyone remember the problems in the early 80's when we were doing bleed valve checks on a run at the end of every days flying due to a problem with diaphram material in the BVCU until they were all modded ? On the 200 series engine the thrust was checked on an airtest if i recall by checking that the brakes wouldn't hold at full power. Not enough power on 100 series for this. Many times spent extended times in the run bay setting up the BVCU . How much of that experience is around now as the manuals of that era don't have the detail ?
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Old 7th Mar 2017, 19:13
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Read that Lemain , quite scary as couldn't imagine signing that out as airworthy as it should have a duplicate inspection {independent} but that would cost two licenced engineers . So if done correctly shouldn't have been a serial number error . I'm guessing that a static leak at that altitude would have some effect but not as much as at altitude .
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