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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 17th Mar 2017, 18:05
  #561 (permalink)  
 
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Lomcevak,
Most accidents of this nature are traced back to a series of unfortunate coincidences; the holes in the cheese.
The point you make is the right one though, and one I made earlier. Everyone seems to agree that rpm and hence thrust were reduced during the climb: either the pilot commanded it, or he didnt.
For my part, it seems inconceivable that he would have commanded it, hence I am thinking about whether it was another in a string of instances of an Avon 122 uncommanded thrust reduction.
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Old 17th Mar 2017, 19:23
  #562 (permalink)  
 
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Unfortunately, the 100 series Avon has a history of power output incidents that Rolls-Royce were unable to fully explain, even when they were fully responsible for the engine in Service use. The AAIB report quotes this fact. Additionally, the Avon fuel control system includes several subsystems, other than the bleed-air system, that interact and effect engine performance. I suspect that no-one today can prove exactly if that engine was performing correctly on the day of the accident, apart from the stated parameters in the report. However, there does appear to be some conjecture bias against the pilots actions, rather than the machine.
As always, I try to limit my comments to facts.
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Old 17th Mar 2017, 19:29
  #563 (permalink)  
 
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Originally Posted by falcon900 View Post
Everyone seems to agree that rpm and hence thrust were reduced during the climb: either the pilot commanded it, or he didn't.

For my part, it seems inconceivable that he would have commanded it, hence I am thinking about whether it was another in a string of instances of an Avon 122 uncommanded thrust reduction.
The AAIB, on the other hand, have not ruled out either possibility:

"It was not possible to determine if thrust was modulated by the pilot during the climb because the throttle was not visible in the cockpit image recording during this part of the accident manoeuvre. However, of the two loops recorded during previous displays, where the cockpit action camera captured throttle position, one showed variation of the throttle position during the upward part of the vertical manoeuvre. In that case movement of the throttle correlated with engine speed changes. Throttle position changes can only be made by the pilot, indicating that he had deviated from his stated throttle technique on that occasion. Therefore, whilst mechanical issues cannot be ruled out, it is possible that the variation in thrust during the accident manoeuvre was commanded by the pilot."
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Old 17th Mar 2017, 20:16
  #564 (permalink)  
 
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If you're flying a relatively small flying machine with just the one engine then you'll definitely be aware of any noteable thrust and/or rpm variations without having to look at any gauges; even more so if you've not physically commanded them by moving the throttle!

That said, even in the event of a total loss of thrust at any stage of the display sequence, if the correct/appropriate actions were taken then no one would have died.
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Old 17th Mar 2017, 20:33
  #565 (permalink)  
 
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Looks like it's time for a reminder that the complete report is available to download (and read) from the AAIB website:

https://assets.publishing.service.go...017_G-BXFI.pdf

"The [test pilot] explained the difficulty in detecting reduced thrust during the ‘up vertical’ part of the manoeuvre, and given the pilot’s focus on external cues, if it was not selected by him he was probably unaware of it."
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Old 17th Mar 2017, 22:00
  #566 (permalink)  
 
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The manoeuvre was entered at 310 kts instead of 350 kts. What would the g forces be at the pull up at both speeds. Would it be an expectation of a pilot of the required level of experience, skill and training to recognise and guard against both extremities; excessive or insufficient energy. This particular aircraft, built for the job as a gun platform had plenty against excess, more than 9 g. So that did not present a problem. But why not accept this generosity where and when it was necessary.
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Old 17th Mar 2017, 22:01
  #567 (permalink)  
 
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Originally Posted by H Peacock View Post
If you're flying a relatively small flying machine with just the one engine then you'll definitely be aware of any noteable thrust and/or rpm variations without having to look at any gauges; even more so if you've not physically commanded them by moving the throttle!

That said, even in the event of a total loss of thrust at any stage of the display sequence, if the correct/appropriate actions were taken then no one would have died.
I could not agree more HP. Ultimately IMHO this tragedy has to come down to either pilot error or pilot incapacity of the mental of physical kind. However proving either would now seem to be impossible so we are left with nothing more than pure conjecture.
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Old 17th Mar 2017, 23:29
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HPeacock

That said, even in the event of a total loss of thrust at any stage of the display sequence, if the correct/appropriate actions were taken then no one would have died.[/QUOTE]

Ridiculous conclusion, if for example there been a total loss of thrust there would have been no control over where and perhaps on whom the aircraft impacted.
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Old 18th Mar 2017, 00:00
  #569 (permalink)  
 
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Ridiculous conclusion, if for example there been a total loss of thrust there would have been no control over where and perhaps on whom the aircraft impacted.
Sorry Cessnapete, but a fast jet in flight will have plenty of kinetic energy. Provided you can still steer the thing after a total loss of thrust, then you can invariably park it in an open space.

Do you think they'd allow a single engine Hawk through the middle of the TVAA (London) at 1300ft if there was 'no control over where and perhaps on whom the aircraft impacted'?

We'll have to agree to disagree!
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Old 18th Mar 2017, 08:58
  #570 (permalink)  
 
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Originally Posted by cessnapete View Post
Ridiculous conclusion, if for example there been a total loss of thrust there would have been no control over where and perhaps on whom the aircraft impacted.
Why don't you guys get together and rewrite the AAIB report with your own conclusions?

In the meantime, for the rest of us, there's an extensive discussion in the report on the pilot's options following a partial or complete loss of thrust at various stages of the manoeuvre - none of them involving loss of control.

I'll leave finding it to the interested reader, of whom there seem to be disappointingly few on here ...
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Old 18th Mar 2017, 10:18
  #571 (permalink)  
 
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Hopefully you might allow me to join you in your interested reader camp Dave, if only to stop you becoming lonely!
For my part, I am not trying to rewrite or dispute the AAIB report, but simply trying to come up with some sort of rational explanation for what transpired, not because I think it will exculpate the pilot, but because I think it might serve to put his actions into their proper context.
It seems to me that there is a world of difference between someone recklessly flying around wilfully disregarding normal safety protocols, and someone who fails to spot an uncommanded reduction of thrust in time to avail themselves of a 4 second long opportunity to escape safely.
Whilst I am not at the latter end of that spectrum just yet, the more I read, and the more this discussion goes on, the closer I am edging towards it.
Why does it matter? Well, because if it was in truth a technical issue which put the pilot unknowingly into the fateful position, and under pressure he made the wrong call without fully appreciating what had happened, it is hardly a unique scenario. Like everyone else, Pilots are not infallible, and under duress can get it wrong and it is reasonably foreseeable that they might. The tragedy which unfolded has as much to do with the decision to have a display of that type in that place, as it does with what did or didn't happen during the fateful 4 seconds.
In fairness, the AAIB report acknowledges this; it is just the subsequent flow of debate which doesn't seem to. In other words, it is important to understand the context of the pilots actions to set them properly in the overall context.
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Old 18th Mar 2017, 11:14
  #572 (permalink)  
 
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falcon900 -- Excellent post and agree. There are several reasons to continue picking over the bones.

a) The relatives deserve an explanation, for closure
b) There will be insurances in place. While money cannot restore the human loss it could help the relatives of the innocent.
c) If there are safety issues (human and mechanical) that can be addressed it might prevent future tragedies
d) The pilot will have to live with this for the rest of his life - and so will his family. Likewise all those responsible for the display and the airworthiness of the a/c
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Old 18th Mar 2017, 11:27
  #573 (permalink)  
 
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In the report, Appendix H, para 15.c.(3) states: "These tests indicated that the height loss from apex during the accident manoeuvre was not affected significantly by power setting". Therefore, whatever the thrust was past the apex the outcome of the pull through would not have been significantly affected. Similarly, the thrust at the apex would not have affected the pilot's ability to perform an escape manoeuvre. However, the low thrust on the pull up was significant in that it was a contributory factor to the low apex height and low apex airspeed achieved.
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Old 18th Mar 2017, 11:41
  #574 (permalink)  
 
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In the meantime, for the rest of us, there's an extensive discussion in the report on the pilot's options following a partial or complete loss of thrust at various stages of the manoeuvre - none of them involving loss of control.
Why does it matter? Well, because if it was in truth a technical issue which put the pilot unknowingly into the fateful position, and under pressure he made the wrong call without fully appreciating what had happened, it is hardly a unique scenario. Like everyone else, Pilots are not infallible, and under duress can get it wrong and it is reasonably foreseeable that they might. The tragedy which unfolded has as much to do with the decision to have a display of that type in that place, as it does with what did or didn't happen during the fateful 4 seconds.
Guys, I accept there was less thrust than required during the first half of the loop - be that an engine abnormality or pilot action. However, apart from the secondary consideration of line feature/rollout track and perhaps the required exit speed, the primary concern before reaching the apex is gate parameters. The whole reason behind having a gate is to stop you trying to finish the loop without enough sky below you. As mentioned before, the apex gate is not a snapshot, you can clearly see it coming well before the apex if you are 1000ft low. To continue after being say 100ft low is naughty, and going to be a late call, but you miss it by 1000ft! Furthermore, 4 sec is ample time to recognise any gate error and then stop the loop. You are already expecting to make the appropriate decision. Again, mentioned in detail before, unload and roll out. If too slow, keep a bit of pull on, nose below horizon, IAS rapidly building, unload then rollout.

If we are going to conclude that 4sec might not be enough time to assess, and then action a recovery then that will be the end of any looping at air shows. AH wasn't the first and won't be the last - but he crashed because he continued his loop despite having failed to achieve his gate. Had he not failed to achieve his gate the accident would not have occurred, but as to why he failed to achieve it, that's simply an observation.

Gate parameters - it's really that simple!
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Old 18th Mar 2017, 12:11
  #575 (permalink)  
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Early pull up

Interesting pic from another forum showing actual vs 'planned' (according to AAIB video) pull up..



A very early pull, inapropriate throttle and aileron inputs, no escape attempt until a late pull very strongly suggest a transient cognitive impairment..

Last edited by hum; 18th Mar 2017 at 12:28.
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Old 18th Mar 2017, 12:32
  #576 (permalink)  
 
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H P,
Agree entirely about gates, and indeed to a degree about 4 secs being enough time to check at the apex.
However, the second hole in the cheese in my hypothesis is that not having sensed the loss of thrust, he glanced at the altimeter at the apex, and took the partially obscured figure to be 3700, more or less what he might have expected, rather than the actual and problematic 2700. I don't think his 4 seconds was used searching for solutions, as I suspect he didnt' realise he had a problem.
Absolute conjecture, I admit, but would explain the continuation of the manoeuvre, with no apparent attempt to escape from it.
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Old 18th Mar 2017, 12:42
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One aspect to consider regarding the obscuration of altimeter digits by the needle is that the needle is only stationary at the instant at which the aircraft is at the apex. The rate of needle movement is low near the apex but needs to be considered with respect to the arc of movement over which any potential confusion between the 2 and 3 in the 'thousands' digit position exists.
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Old 18th Mar 2017, 13:03
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One aspect to consider regarding the obscuration of altimeter digits by the needle is that the needle is only stationary at the instant at which the aircraft is at the apex. The rate of needle movement is low near the apex but needs to be considered with respect to the arc of movement over which any potential confusion between the 2 and 3 in the 'thousands' digit position exists.
Not quite Lomcevak, there will always be a finite lag in a dynamic manoeuvre such as a loop. Moreover, he probably had it in Sby so there would have been an even more noticeable lag, ie, alt still slowly increasing as his RoC hits zero. Partly why you take a couple of peeps of the alt during the 2nd quarter of the loop; 'how's it looking!'. Taking a single snapshot of the alt at apex and then making a call is not the way to do it. It's a little like an approach DH. You don't hit it then make the call unprepared, but you need to be ready for the GA so you can have auctioned it at DH. He doesn't need to initiate his flyaway at the apex, but he must have made the 'yes/no' call. If you are guilty of trying to just take a snapshot without any prior awareness of 'how's it going?' Then there's a good chance you'll get it wrong!
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Old 18th Mar 2017, 13:16
  #579 (permalink)  
 
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HP,

Agreed that there will be a lag but that is, by definition, a phase difference so the needle will still be moving; it is just that the reversal in needle direction will be slightly after the actual apex. Actually, the greater problem in standby is that the needle sticks and then jumps. Therefore, as you say, the need is to introduce the altimeter into a scan pattern prior to the apex rather than just take a snapshot.
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Old 18th Mar 2017, 13:17
  #580 (permalink)  
 
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Originally Posted by hum View Post

A very early pull, inapropriate throttle and aileron inputs, no escape attempt until a late pull very strongly suggest a transient cognitive impairment..

Or inadequate currency...
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