AAIB investigation to Hawker Hunter T7 G-BXFI 22 August 2015
Please be assured that I have no "agenda" regarding the takeoff or any other
part of the flight, beyond grasping for some rational explanation of what transpired. From the outset, Pilot error has been something of the bookies favourite, and the AAIB report more or less concludes the matter. There are however, at least in my mind, some loose ends.
I am happy to be guided by you Sika regarding how the Hunter should be handled, but if it was all so normal, why did the AAIB make the point that rotation was at a slower speed than "usual"?
Pulling up at a slower speed than usual into the "loop" plays a big part in this, and it does not seem without significance that some 25 minutes earlier, in his first interaction with airspeed during the flight, he dropped below his "usual" datum, and indeed towards the low end of (and arguably below) the viable range of speeds.
As I mentioned in an earlier post, figure 15 shows the rpm reducing materially during the climb phase of the "loop" and then increasing significantly after the apex. Why could this not indicate a mechanical issue followed by an attempted recovery? Pilot error seems rather a loose fit for the reduced rpm, and if I recall correctly, did the Hunter not have some form when it came to uncommanded transient thrust reduction?
part of the flight, beyond grasping for some rational explanation of what transpired. From the outset, Pilot error has been something of the bookies favourite, and the AAIB report more or less concludes the matter. There are however, at least in my mind, some loose ends.
I am happy to be guided by you Sika regarding how the Hunter should be handled, but if it was all so normal, why did the AAIB make the point that rotation was at a slower speed than "usual"?
Pulling up at a slower speed than usual into the "loop" plays a big part in this, and it does not seem without significance that some 25 minutes earlier, in his first interaction with airspeed during the flight, he dropped below his "usual" datum, and indeed towards the low end of (and arguably below) the viable range of speeds.
As I mentioned in an earlier post, figure 15 shows the rpm reducing materially during the climb phase of the "loop" and then increasing significantly after the apex. Why could this not indicate a mechanical issue followed by an attempted recovery? Pilot error seems rather a loose fit for the reduced rpm, and if I recall correctly, did the Hunter not have some form when it came to uncommanded transient thrust reduction?
The report states that Rolls Royce were happy that there were no JPT or thrust anomalies on take-off for the accident sortie. There are clear statements of the JPT reading on take-off and during the accident manoeuvre, showing that the JPT on take-off was significantly greater than during the accident manoeuvre and within the normal range (580 - 690 C).
The Pilot's Notes state "Ideally, ease the nosewheel off the ground between 115 and 135 knots depending on configuration" and "Depending upon weight and attitude, the aircraft unsticks between130 knots and about 155 knots". On airtests, the take-off is performed initially with full back stick to check the minimum nosewheel lift-off speed; for this configuration it is usually about 105 KIAS.
Falcon900,
If the ground roll was greater than expected and the end of the runway was getting closer, even if below the normal nosewheel raise speed I think that some pilots may try to take-off at a slightly lower speed than normal.
The Pilot's Notes state "Ideally, ease the nosewheel off the ground between 115 and 135 knots depending on configuration" and "Depending upon weight and attitude, the aircraft unsticks between130 knots and about 155 knots". On airtests, the take-off is performed initially with full back stick to check the minimum nosewheel lift-off speed; for this configuration it is usually about 105 KIAS.
Falcon900,
If the ground roll was greater than expected and the end of the runway was getting closer, even if below the normal nosewheel raise speed I think that some pilots may try to take-off at a slightly lower speed than normal.
Thanks Lomcevak.
Whichever way you look at it though, the takeoff seems to have been harder work than you might have thought necessary.
Turning to the accident manoeuvre itself, I continue to be puzzled by the reduction in JPT and rpm after the pullup. it seems inconceivable that the pilot would have commanded a reduction on thrust during this phase, and in marked contrast to previous flights and best practice.
For me at least, the thought of an uncommanded reduction in thrust in the climb starts to put a different complexion on things...
Whichever way you look at it though, the takeoff seems to have been harder work than you might have thought necessary.
Turning to the accident manoeuvre itself, I continue to be puzzled by the reduction in JPT and rpm after the pullup. it seems inconceivable that the pilot would have commanded a reduction on thrust during this phase, and in marked contrast to previous flights and best practice.
For me at least, the thought of an uncommanded reduction in thrust in the climb starts to put a different complexion on things...
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Whichever way you look at it though, the takeoff seems to have been harder work than you might have thought necessary.
The AAIB comment on the take-off but have no issues with it.
North Weald jet operators say a downwind take-off is not unusual.
An experienced Hunter pilot (sika humulta) says that the take-off was normal for a Hunter.
Which bit of the above is "harder work" exactly?
In response to the question, the reference to harder work relates to Lomcevaks suggestion that everything was normal, but that the premature arrival of the end of the runway precipitated the lower than usual rotation speed.
I do not wish to flog a seemingly dead horse, and so am happy to move on from the takeoff, simply noting that nothing that has been said would contradict the possibility of the engine developing less thrust than the pilot was expecting for the given throttle setting. A question which is central to the accident sequence of events
I do not wish to flog a seemingly dead horse, and so am happy to move on from the takeoff, simply noting that nothing that has been said would contradict the possibility of the engine developing less thrust than the pilot was expecting for the given throttle setting. A question which is central to the accident sequence of events
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It isn't , because he missed all, his gates, had a track record of low flying and failed to abort when his manoeuvre went catastrophically wrong .
The un-proven (despite extensive investigation by some of the worlds best investigators and the engine manufacturers) issues with engine thrust are irrelevant and a monstrous red herring .
The un-proven (despite extensive investigation by some of the worlds best investigators and the engine manufacturers) issues with engine thrust are irrelevant and a monstrous red herring .
The plain fact of the matter is that the aeroplane was both lower and slower than it should have been (both by massive margins) at what should have been an obvious energy check point. That the manoeuver or even the display was not aborted at that point is a matter of the pilot's responsibility - the cause of the energy loss is only a minor contributory factor. The pilot appears to have been drilling additional holes in the cheese. To suggest otherwise would be to suggest that a car crash was due to the light rain at a tight corner, rather than the driver's choice to enter that corner at 140mph.
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Perhaps, just perhaps, the pilot was avoiding selecting absolute maximum power because of an awareness of the overspeed incidents with this engine? A bit like not mashing the throttle into the carpet in a classic car. You want to help maximise the life of components and keep the vehicle running.
I have to hand Pilot's Notes for the Hunter F4. There are probably considerable differences from the T7 but still probably quite relevant.
The very short section (87) on aerobatics reads:-
(a) Until experience is gained, the following speeds, in knots, are recommended:-
Roll 350 Loop 425 Roll Off 450 Vertical Roll 500.
(b) It is recommended that until experience is gained, loops are started in the height band 10,000ft to 15,000ft.
No , I have not inadvertently added a zero to the last two figures.
I'm not sure I would consider myself experienced on type with 43 hours over 4 years.
11 practices in 4 years is not experienced. I would do at least that many in a month and after 3 seasons displaying JP3 and JP4 still worked to a 500ft base and I still very nearly killed myself once. I did watch an experienced but under-practiced colleague do a Shoreham except he impacted in an empty field. I can recall the whole scene in slow motion. We nearly dropped the coffin there was such a weight of sand in it.
With his experience, I find it surprising that the pilot was happy to display at a small airfield surrounded by housing. Even more surprising, and much more worrying, that anyone would authorise such a display. It seems pure luck that the death toll was not massively greater.
Please can we forget all the irrelevant stuff about the takeoff, altimeter settings, blah blah blah. A pilot, inexperienced on type, lacking in practice, may well have made an error in a display which should not have been happening.
The very short section (87) on aerobatics reads:-
(a) Until experience is gained, the following speeds, in knots, are recommended:-
Roll 350 Loop 425 Roll Off 450 Vertical Roll 500.
(b) It is recommended that until experience is gained, loops are started in the height band 10,000ft to 15,000ft.
No , I have not inadvertently added a zero to the last two figures.
I'm not sure I would consider myself experienced on type with 43 hours over 4 years.
11 practices in 4 years is not experienced. I would do at least that many in a month and after 3 seasons displaying JP3 and JP4 still worked to a 500ft base and I still very nearly killed myself once. I did watch an experienced but under-practiced colleague do a Shoreham except he impacted in an empty field. I can recall the whole scene in slow motion. We nearly dropped the coffin there was such a weight of sand in it.
With his experience, I find it surprising that the pilot was happy to display at a small airfield surrounded by housing. Even more surprising, and much more worrying, that anyone would authorise such a display. It seems pure luck that the death toll was not massively greater.
Please can we forget all the irrelevant stuff about the takeoff, altimeter settings, blah blah blah. A pilot, inexperienced on type, lacking in practice, may well have made an error in a display which should not have been happening.
.............. surrounded by housing .......?
Not relevant really, and most certainly not true.
Not relevant really, and most certainly not true.
Gentlemen,
I think we are in truth agreeing about most things here, and to be clear, I am not trying to exculpate the pilot or anyone else, just trying to string together, if only in my own mind, a coherent and credible sequence of events.
My current hypothesis goes along the following lines;
He sets the throttle levers for the start of the "bent loop", and accelerates towards the first gate, anticipating achieving the target entry speed as he has before.
He misses it, interestingly by roughly the same % margin as missed his target rotation speed on takeoff....
He begins the climbing phase of the "loop", and either a) he selects a materially REDUCED level of thrust or b) there is an uncommanded reduction of thrust.
He doesnt "feel" the reduced thrust, and arrives at the apex of the loop.
Glances at altimeter, and with pointer covering the numbers, reads it as 3700 rather than 2700.
Feels aircraft close to stall, but believes himself to have sufficient height to complete the manoeuvre, and applies power to address airspeed.
The rest, sadly, we know for sure.
I am not suggesting that this doesnt amount to pilot error, but at least to me, if the reduction in thrust was uncommanded , it all seems more understandable, if no less tragic.
The alternative would seem to require that we accept that the power was intentionally reduced during the climb.
I think we are in truth agreeing about most things here, and to be clear, I am not trying to exculpate the pilot or anyone else, just trying to string together, if only in my own mind, a coherent and credible sequence of events.
My current hypothesis goes along the following lines;
He sets the throttle levers for the start of the "bent loop", and accelerates towards the first gate, anticipating achieving the target entry speed as he has before.
He misses it, interestingly by roughly the same % margin as missed his target rotation speed on takeoff....
He begins the climbing phase of the "loop", and either a) he selects a materially REDUCED level of thrust or b) there is an uncommanded reduction of thrust.
He doesnt "feel" the reduced thrust, and arrives at the apex of the loop.
Glances at altimeter, and with pointer covering the numbers, reads it as 3700 rather than 2700.
Feels aircraft close to stall, but believes himself to have sufficient height to complete the manoeuvre, and applies power to address airspeed.
The rest, sadly, we know for sure.
I am not suggesting that this doesnt amount to pilot error, but at least to me, if the reduction in thrust was uncommanded , it all seems more understandable, if no less tragic.
The alternative would seem to require that we accept that the power was intentionally reduced during the climb.
Last edited by falcon900; 14th Mar 2017 at 15:14. Reason: typo
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Falcon900, we are singing from the same hymn sheet. That the accident happened because of pilot error is not in dispute. But why?
To my mind, there was little wrong for the first part of the flight, Knowing the aircraft and runway I can even rationalise the downwind take off which no pilot would countenance lightly. Yes, we can say this happened 2 kts early or late, but that really is Monday Morning quarterbacking. I can easily and do make such errors every flight, every day. It falls within what I call " normal".
However from just before the pull up there are suddenly gaping discrepances, from a previously "normal" flight, and I agree with others that the report seems to be thin on the human factors and medical side. It certainly stands greater scrutiny.
My agenda is to understand what actually happened to try to prevent it happening again. The Why.
Saying "It was pilot error" is stating the obvious and achieves little more than pointing a the finger of blame, which may be sufficient for those who lost loved ones, but not for me. Especially if the blame is subsequently mitigated by circumstances found to be outside the control of the pilot.
Something happens just prior to pull up which is not explained. The pattern of control and flight suddenly changes from "normal" to abnormal. Why?
To my mind, there was little wrong for the first part of the flight, Knowing the aircraft and runway I can even rationalise the downwind take off which no pilot would countenance lightly. Yes, we can say this happened 2 kts early or late, but that really is Monday Morning quarterbacking. I can easily and do make such errors every flight, every day. It falls within what I call " normal".
However from just before the pull up there are suddenly gaping discrepances, from a previously "normal" flight, and I agree with others that the report seems to be thin on the human factors and medical side. It certainly stands greater scrutiny.
My agenda is to understand what actually happened to try to prevent it happening again. The Why.
Saying "It was pilot error" is stating the obvious and achieves little more than pointing a the finger of blame, which may be sufficient for those who lost loved ones, but not for me. Especially if the blame is subsequently mitigated by circumstances found to be outside the control of the pilot.
Something happens just prior to pull up which is not explained. The pattern of control and flight suddenly changes from "normal" to abnormal. Why?
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The report is very exhaustive and does offer an answer to the 'why', albeit not to the satisfaction of most armchair investigators' curiosity: 'We can't know with a high degree of certainty'.
Through comprehensive examination of all the available evidence, several plausible contributing factors have been determined and explored in detail, leading to several safety recommendations in an effort to learn from the errors made and prevent reccurance, but there is no smoking gun and nor are we likely to ever find one.
IMHO
Through comprehensive examination of all the available evidence, several plausible contributing factors have been determined and explored in detail, leading to several safety recommendations in an effort to learn from the errors made and prevent reccurance, but there is no smoking gun and nor are we likely to ever find one.
IMHO
May I invite anyone interested to view this clip at the 04 seconds after the start point?
The heavy trail is backlit and seems to come from the Fuselage. I do not believe this trail is commented upon in the report, only another that is described as "from the wing tank area", or words to that effect.
The heavy trail is backlit and seems to come from the Fuselage. I do not believe this trail is commented upon in the report, only another that is described as "from the wing tank area", or words to that effect.
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Regarding the AAIB not reporting on things we think significant, I will paraphrase a qote from a retired AAIB inspector who was presenting at a course I was on. "AAIB reports report the findings and analysis relating to an accident or incident, they do not provide a comprehensive description of every line of enquiry That was considered and dismissed during the course of the investigation". I imagine if they did that this report would be considerably larger.