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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 22nd Mar 2017, 22:05
  #701 (permalink)  
 
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Roll off the top

MM and biscuit

My post #142 last section referred to this.

But that isn't the escape manoeuvre....it's accelerate whilst unloading....and roll level before you get to 45 degrees pitch. 1/2 Cuban or horizontal 8 depending on your upbringing....
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Old 22nd Mar 2017, 22:14
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Thanks mr angry, understood.
Either of the 'get outs' you mention - half roll off the top or unload & accelerate if far too slow etc., would work for me in my simple aeroplanes, and I have practiced them, being well used to my somewhat variable aerobatic ability! (In my case the unload and accelerate option would be more because a possible flick into an inverted spin would be more exciting than I'd like...)

It simply seemed unusual not to have practiced them in this came hence my speculation about mindset. I suppose cost or flying hours availability might be an issue, since the report seems to describe a very abbreviated conversion to type and to a Hunter aerobatic routine. If you don't think you need to trial any actual get out effort, this would not be a concern.
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Old 22nd Mar 2017, 22:30
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airpolice,

taking into account the situation at the apex, low, slow and out of energy... not a good time to roll the aircraft without being really sure of what's happening with the energy
People use 'energy' far too liberally; here you mean airspeed. And at the apex of the accident manoeuvre the aircraft was not 'out of energy'; it had 105 KIAS and the data in Appendix H shows that with 80 KIAS it was possible and straightforward to execute an escape manoeuvre. However, if someone has not been trained to fly this and has not practised it then I fully accept that they may be very circumspect about trying it!

With respect to departures and spinning, I have only had two departures in a T7 and both because the handling pilot (not me!) allowed the rudder to float. One was during a full flap stall, and a 1 turn erect spin resulted, and the other was during a -1g full lateral stick roll, during which a developed spin did not occur. In both cases centralising the rudder and stick effected a recovery. The only inadvertent inverted spins that I have heard about were as a result of a centralised recovery from a nose high, low speed unusual position recovery, and I suspect that the rudder may well have floated due to sideslip in both cases.

mrangry..

In a 1/2 horizontal/Cuban 8 (rolling on a down 45 line), elevator and rudder are used to maintain a straight flightpath. In an escape manoeuvre, even on a down 45 line, in order to prevent a potential departure the rudder needs to be restrained at neutral and the elevator used to maintain close to the zero lift angle of attack (in practise neutral elevator/trim position). It is important that this subtle difference in control strategy is understood by anyone flying minimum speed loops at low level.
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Old 22nd Mar 2017, 22:36
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biscuit74,

You are not alone in your opinion. On page 218 of the Shoreham report it states:

"Safety Recommendation 2017-002: It is recommended that the Civil Aviation Authority require pilots intending to conduct aerobatics at flying displays to be trained in performing relevant escape manoeuvres and require that their knowledge and ability to perform such manoeuvres should be assessed as part of the display authorisation process."

Hopefully, the next edition of CAP403 will include this.
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Old 22nd Mar 2017, 22:40
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Biscuit74,

A relevant question. Like AH I also have a military background and am presently employed in the airline business.

I also have wondered about this "escape manoeuvre" which he so say didn't practice.

I will give an example which many reading this may associate with. In the civilian world, every year (at least) we go into the simulator to practice an engine failure at V1 on takeoff, which is deemed a "worst case" by the regulatory authority. We get quite good at that over the years. However, as a simulator instructor conducting training as well as checking, I have also seen less predictable results if the engine failure occurs at a slightly different point. Say, 500ft IMC on departure. Every civilian pilot is proficient at V1 cuts, but I would also say at risk of significant error should the failure occur at a different point. Because it is rarely practiced.

The regulator can only dictate "worst case" proficiency. But is a failure at V1 actually "worst case" for checking? Should failures at different points be also mandatory? This is not a digression.

Similarly with the Shoreham accident. What is the escape manoeuvre he so say didn't practice? Is it at the top of the loop having not made the gates? (The V1 cut equivalent) Is it when pointing vertically downwards and realising all is not as anticipated? Is it at some other point? All equally relevant I suggest.

Putting my old military hat on as a low level pilot, there was always one thing and one thing only that was in the forefront of the mind. Dying of deceleration sickness. In those days, it was a not unusual occurrence. The ground is totally unforgiving, and no error is permitted when manoeuvring near the ground.

Not only could he have escaped from it easily at the top of the loop in several possible ways, without practicing some mythical "escape manoeuvre" to satisfy regulation, but he would have had that terrain awareness respect inbuilt which every low level fast jet pilot learns from the earliest of days. It becomes almost instinct to be extremely careful when pointing at the ground.

This is why I do not believe AH would have consciously flown the manoeuvre as it transpired. Something must have happened to explain WHY he continued.
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Old 22nd Mar 2017, 23:23
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Originally Posted by Mike Metcalf48
IIRC from my Hunter flying back in the day, coarse aileron input at slow speed would cause departure from controlled flight. The resulting spin was quite unstable and thus dangerous outside of the test environment. We ensured pilots were aware of this trap and, if anybody would care to post it, is detailed as a warning in the pilots' notes. So I am not surprised this pilot was neither taught nor had practised recovery from slow speed inverted at the top of a loop (nb this wasn't a loop or even a 'bent loop' BTW). It would have been quite a leap of faith to do so when training in the Hunter. Once this pilot had found himself significantly below his gate (assuming he even was alert to the situation), he had little option. It is possible he could have avoided the ground if he'd flown optimum AOA - light buffet - but with the ground rushing up to him, the natural human reaction would be to pull harder.

I read the AAIB Hunter test report. The evaluated type was a single seat Hunter with an Avon 200. Whilst similar, it is quite a different beast to the 2-seat Avon 100 trainer. It doesn't matter how much you fudge it, it is not going to be representative and cannot be compared. The very capable TP should have known this and ensured a Hunter T7, in the same fit, weight and balance, was used to evaluate. So, I am afraid it is like apples and pears. The fact that the TP safely flew an 'escape manoeuvre' is down to his experience, ability - lots of Hunter time spent spinning, I am told - and pre-flight spin prevention planning on this distinctly different variant.

Perhaps, given the technical findings (ejection seats etc) of the investigation, the TP couldn't find a civil reg T7 he was happy to operate.

Please correct me if Im wrong but I thought the thrust differences between the Avon 100 and the 200 Were compensated for by operating the 200 series engine rpm at 'reduced" rom based on RR data to simulate 100 series thrust during aeros

From my days at Boscombe flight test,when we had some T7s and F6's and FGA9s to play with, the wing, fin and horizontal stab/elevators Of the T7 and "big bore" single seaters were "aerodynamically" the same, there are differences in pylons etc. One of our F6's had one original wing and one "donated" from a T7 that had been reduced to spares.

The report states (can't remember where) that consideration was taken of the aerodynamic effect of the twin seat cockpit vs the single in the test aircraft.

While there may be performance differences i don't think it's anything like as severe as you suggest.
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Old 22nd Mar 2017, 23:46
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Originally Posted by n305fa
Perhaps, given the technical findings (ejection seats etc) of the investigation, the TP couldn't find a civil reg T7 he was happy to operate.
AFAIK, none of the other three T.7s on the UK register are currently flying.
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Old 23rd Mar 2017, 00:09
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OK, re the 'wrong type' mindset, I wasn't going to mention this because a) It's embarrassing and b) I have no idea if it's relevant - but:
Whilst current on a pretty powerful swept wing jet transport, I was doing a single engine piston renewal and, on the go-around, I started to increase the attitude inappropriately. Well, I don't know what kicked in first a) I was doing it wrong or b) the ASI was going the wrong way but I stuffed the nose down pretty quickly.
I can assure you that the controls/view/sounds/environment didn't look anything like a big jet - but (initially) I did it . . . .
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Old 23rd Mar 2017, 02:19
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My degree was in psychology, and from that perspective I feel few of the posited scenarios really allow for the vagaries of human cognition. The human mind takes the fewest shortcuts when deliberate undivided attention is being devoted to an unfamiliar task. This pilot was undertaking a somewhat familiar task, and thinking psychologically I'd speculate that something caused his attention to be distracted in a way which felt perfectly professional in the moment. Perhaps a thrust anomaly, perhaps a heading error. But immediately the new task is in the foreground. In such circumstances the 'routine' task can be done so 'automatically' that one may simply see what one expects to see, or not register something unexpected which is abnormal. Such 'misdirection' is the stock in trade of magicians, but is actually a fundamental weakness of human cognition.
My point is that nobody is immune to this: one can make it more or less likely, but it's always a potential occurrence. A lot of the debate about 'could a pilot overlook this or attempt that' misses the point: he was probably cognitively misdirected by something that was in itself relatively benign or even an objective or conjectured false alarm. A final tragic factor in such cases can be exacerbated confusion upon spotting the approaching danger: that anomaly may at least momentarily be attributed to the in-fact-trivial but unusual problem rather than the real one of being behind the overall situation.
The Invisible Gorilla: And Other Ways Our Intuitions Deceive Us
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Old 23rd Mar 2017, 12:33
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Rolling out of a manoeuvre that has gone wrong hardly needs practicing. It is second nature to anyone who has flown aerobatics and those who have done a military QFI tour and taught UPs (unusual positions). The accident was caused because the pilot did not respect the gate parameters (for reasons unknown), or misjudged his ability to complete the manoeuvre.
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Old 23rd Mar 2017, 13:21
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robdean,

Thank you for your post and that all sounds very familiar! The way you have written it appears to be related to a single distraction/misdirection followed by a single cognitive error. If you have a sequence of errors over a period of, say, 15 seconds (in this case incorrect pull-up airspeed, incorrect power setting, excessive roll angle change, continuing the manoeuvre when a decision criteria, the gate height, has been failed), is it still possible that all of these can be caused by a single distraction/misdirection before commencing a manoeuvre or is there a potential mechanism whereby each error constitutes the distraction that triggers the next error in the chain?
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Old 23rd Mar 2017, 14:37
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LOMCEVAK Misdirection may not be an ideal term, depending on how it is interpreted, in that an illusionist will actively misdirect, and the onlooker will be misdirected. Here there is no deliberate third-party misdirection, but the consequences can be the same.

People crash cars when texting not because they are deliberately not looking at the road: they think they are still monitoring the road. And to some extent they are, enough to usually have no consequences and thus leave the impression that their monitoring was unimpaired. Statistics prove this very wrong.

Texting is irresponsible, but problem solving in a cockpit can be essential. Yet if you focus on the wrong problem at the wrong moment, you may metaphorically be 'texting' whilst something catastrophic is developing. For instance, if in mid-manoeuvre you find yourself, say, surprised to be drifting compass bearing, or seeing a minor thrust anomaly, that need not be imminently dangerous. But the cognitive danger is: you fly a manoeuvre 50 times no problem. 51st time there's a trivial issue. You split attention to the very noticeable, unusual issue which you always otherwise devote in full to 'routine' monitoring which though routine and 'never' far from nominal is in fact safety critical. Then comes confusion and exponentiating attention-narrowing anxiety: you are behind the aircraft and something ugly is unfolding very fast. Probably because at some point you glanced and saw what you expected to see rather than what was really there.

This is perhaps an unrecognised area in that it is as much 'human limitation' as 'pilot error' - we must all constantly perform 'cognitive triage', devoting attention where is is most needed, but it is the nature of the human mind that it cannot get this right instantly on every occasion, especially as it takes some attention to even a trivial issue in order to simply establish that it is indeed trivial

A related danger lies in fixating upon an element of the anomaly which blinds you to the bigger problem, even to the extent of missing the obvious: I'd not be surprised for there to have been CFIT incidents involving crews busily trying to figure out why the stupid 'terrain' enunciation wouldn't shut up.

There is a psychological tenet which I could quote here outside its usual application: 'we are free to construe but bound by our constructions'. You can jump to any number of conclusions, but once you jump to one your mind is no longer open.

Last edited by robdean; 23rd Mar 2017 at 15:02.
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Old 23rd Mar 2017, 15:32
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Originally Posted by DaveReidUK
AFAIK, none of the other three T.7s on the UK register are currently flying.

I believe there are two other T7's which were flying, until the ban - one of which did have an in date permit to fly certificate (expired May2016). Not sure on the 3rd as this is with a company that deals with military contracts and their aircraft are on the military register. However, it maybe because of the CAA grounding civilian hunters that those 2 couldn't be used. Has this been lifted does anyone know or is it still in place?


After all there is no real reason provided that all the maintenance is carried out correctly and the new guidelines meet etc that permit applications couldn't be considered - after all it would appear to be no heredity fault with the airframe itself. Aerobatics manoeuvres are still restricted for vintage jets and the Jet provosts have been displaying since without incident.
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Old 23rd Mar 2017, 20:19
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Let me speculate on the mindset, and the escape manoeuvre; and also on the day to day mind set and emergency practices.

Firstly, the commercial sim is used every 6 months to practice and check well known non-normal and emergency situations. Generally they are discussed, briefed and practiced; or they have been seen before and are a regular standards check. There are too many WTF moments.
There is speculation about the escape manoeuvre required during a loop and being low/slow at apex, and the knowledge & currency of that. If you were performing a straight forward simple loop along your line I would suspect you would be mindful of what to do in a coupe of 'what if' moments. The manoeuvre is a simple lop.
Now throw in the bent loop while making a line adjustment: where is the focus? I suggest it is on the line adjustment and not on the monitoring of the manoeuvre and the escape routes.
The low energy entry, both speed & height, and perhaps even too low a G pull-up. To be aware of all those and monitor the apex is quite a work load. Add in to that the line adjustment concentration and perhaps the monitoring of the 'gate' was lacking as the line adjustment took priority.
The root causes then become low energy at entry; wrong alignment at entry; wrong pull up point at entry. The last 2 could take over the prime concentration at apex as the required line for the descent becomes visible. Rolling away from that 'magnet' would be difficult human nature, and when, in the downward vertical, the realisation of the inevitable becomes apparent it is too late.
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Old 23rd Mar 2017, 21:27
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Originally Posted by Hebog
I believe there are two other T7's which were flying, until the ban - one of which did have an in date permit to fly certificate (expired May2016). Not sure on the 3rd as this is with a company that deals with military contracts and their aircraft are on the military register. However, it maybe because of the CAA grounding civilian hunters that those 2 couldn't be used. Has this been lifted does anyone know or is it still in place?


After all there is no real reason provided that all the maintenance is carried out correctly and the new guidelines meet etc that permit applications couldn't be considered - after all it would appear to be no heredity fault with the airframe itself. Aerobatics manoeuvres are still restricted for vintage jets and the Jet provosts have been displaying since without incident.
Not sure if the Hunter grounding has been removed but there may be issues in compliance with MPD2016-01 http://publicapps.caa.co.uk/modalapplication.aspx?catid=1&pagetype=65&appid=11&mode=deta il&id=7760
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Old 24th Mar 2017, 03:39
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Whilst looking at the RPM plots in the AAIB Report, I find it strange that the RPM decreases so abruptly (twice) in the climb. If you extrapolate from 7000 to zero RPM, this would have taken about 6 seconds, whereas the extrapolated 'spool-ups' where in the normal region of 20+ seconds.


Maybe the graphs are not precisely drawn, but the rate of decrease of RPMs seems to indicate some sort of mechanical abnormality.
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Old 24th Mar 2017, 04:22
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scifi

The engine speeds discussed and displayed around page 51 of the report were derived from audio recordings. The graphics show only a small portion of the vertical axis.

Elsewhere in the report it is claimed that a pilot would not be able to sense or hear any variation in the thrust level.

The data was arrived at through minute analysis of the audio recordings in an effort to explain why the aircraft did not achieve the target (gate) apex height and speed.

Historically there have been unexplained losses of thrust from similar engines while in military service but Rolls Royce, the manufacturer, have never been able to establish a definitive cause.

The engine was not spooling down towards zero, just a fall off of a few hundred rpm or so. This is enough to indicate that the thrust was not at maximum throughout the climb, or at any point in the climb. There appears to have been a reduction in thrust at two points in the climb. Rolls Royce have been unable to find any fault with the engine that may have resulted in less than full thrust being developed, nor for an intermittant reduction in thrust.

The alternative explanation offered is that the pilot did not initially select full thrust when commencing the climb and adjusted the throttle during the climb. There is no visual evidence from on board cameras to support this view and it would go against normal practice when performing this manoeuvre.
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Old 24th Mar 2017, 09:21
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Originally Posted by RAT 5
The root causes then become low energy at entry; wrong alignment at entry; wrong pull up point at entry. The last 2 could take over the prime concentration at apex as the required line for the descent becomes visible.
Interesting take on this, but it seems to me that the first two, low energy and wrong alignment at entry, would not be factors since surely these initiating parameters would be the most easily met, and they weren't.
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Old 24th Mar 2017, 09:40
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Originally Posted by RAT 5
The root causes then become low energy at entry; wrong alignment at entry; wrong pull up point at entry.
Given that impact with the ground resulted from divergence from the planned vertical profile of the manoeuvre, how does the aircraft's horizontal position or track become a "root cause" ?
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Old 24th Mar 2017, 09:43
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Chuck: Indeed, they do not seem to have been met, as planned. Why? is a good question, as yet unanswered. I was considering the 'Why was the obvious escape manoeuvre not executed?' If the wrong alignment at pull up was realised on the run-in, and then the pull up point was changed to try and give more space; and then the plan to bend the loop was made on the way up (i.e. the manoeuvre was made 'on the fly' as it was being performed) and then the proper line was searched for going over the top. That is where the concentration would be and not on the gate parameters.
That's my thinking of a possible Why did he not roll out of the back side of the apex.
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