Shoreham Air Show Plane Crash

[Boac]

om - the 'extra' footage they saw is from the Go Pro on the rear bulkhead - that would be very interesting and would, I think, enable an 'expert witness' to draw a conclusion.

[om15]

I see, this might be like an onion, each layer leading to another one, the AAIB report does, aside from the tragedy of the accident, demonstrate that these aging but powerful aircraft are not managed and maintained in a manner that meets current safety levels.

[Pontius Navigator]

Om15, I thought the prosecution said it was maintained to the highest standard, ergo you can't blame the aircraft.

[Ex-Ascot]

I thought that vertical descent was rather slower than perhaps one might expect. Again, maybe just camera angle and not being able to judge speed in the absence of any other markers in that shoot.

No expert in chucking aircraft around the sky, it would have broken the china, but obviously done my bit. He does seem to stay in a dive for sometime before pulling out of the loop. At the end of the day he dam nearly made it he pancaked in, or was it a waffle. What does Boac think? Could he have pulled a bit harder and made it. JUST. Not within his 500' display limit of course.

[Boac]

I prefer not to make too much comment while the case is in progress, but my view is that the 'slow' pitching on the way down was due to lack of speed, and, again, no - from pull-through it a one-way street. This based only on the AAIB report, and a bit of experience.

"The manoeuvre was continued into the downward half of a
loop although the apex height of approximately 2,700 ft was
significantly below the lowest value of 3,500 ft that the pilot
stated was required to complete the manoeuvre in order not
to descend below his 500 ft aerobatic minima."

"The combination of low entry speed and less than
maximum thrust meant that the apex height was below the
minimum gate height of 3,500 feet and the airspeed at the apex
was 105 +/- 2 KIAS. This was the lowest apex airspeed identified
by the pilot of G-BXFI and was less than his normally expected
airspeed of 150 KIAS. In these circumstances the correct action
would have been to perform an escape manoeuvre; rolling erect
and then pulling out of the resulting dive"

[Ex-Ascot]

....and a bit of experience.

[om15]

Om15, I thought the prosecution said it was maintained to the highest standard, ergo you can't blame the aircraft.

PN, there doesn't seem to be any evidence of aircraft malfunction or a defect that caused the crash, but I can't see how the prosecution can claim that the aircraft was maintained to the highest standard because based on the AAIB report an expert witness could demonstrate that it wasn't.

Information included in a previous AAIB report indicated that there had been several cases involving the type of engine fitted to this aircraft where an un-commanded reduction in engine speed had occurred and subsequent engineering investigation did not establish a clear cause. This investigation was unable to determine whether a reduction in engine speed recorded during the accident manoeuvre was commanded by the pilot.
The aircraft’s engine was subject to a Mandatory Permit Directive (MPD) which imposed a calendar life on the engine type, and provided an option to extend that life using an Alternative Means of Compliance (AMOC). Proposals for an engine life extension using an AMOC inspection programme had to be approved by the regulator. Related tasks were being conducted by the maintenance organisation, but the regulator had not approved the operator or its maintenance organisation to use an AMOC to this MPD.

The investigation found that defects and exceedences of the aircraft’s operational limits had not been reported to the maintenance organisation, and mandatory requirements of its Airworthiness Approval Note had not been met. During prolonged periods of inactivity the aircraft’s engine had not been preserved in accordance with the approved maintenance schedule. The investigation identified a degraded diaphragm in the engine fuel control system, which could no longer be considered airworthy. However, the engine manufacturer concluded it would not have affected the normal operation of the engine.
The aircraft had been issued with a Permit to Fly and its Certificate of Validity was in date, but the issues identified in this investigation indicated that the aircraft was no longer in compliance with the requirements of its Permit to Fly.

From the report the following was noted

Maintenance and airworthiness
64. The ejection seat manufacturer’s recommended installed cartridge
life was two years with a maximum total (shelf) life of six years. This
recommendation was included as a limitation in the aircraft’s AAN, which
formed the basis for its certification. The maintenance organisation
had adopted a six-year installation life for ejection seat cartridges. This
extension to the installed life had not been documented in accordance with
the maintenance organisation’s procedures, nor had it been approved by
the CAA.
65. At the time of the accident, the two-year installed cartridge life had been
exceeded by more than 4½ years and the six-year total life had been
exceeded by more than a year.
66. The CAA was not aware of the extension to the ejection seat cartridge
lives.
67. The CAA did not have a documented procedure for approving extensions
to ejection seat cartridge lives but stated that applications for extensions
would be considered on a case-by-case basis, and would only be
granted for a short period upon proof that new cartridges were on order.
68. The maintenance organisation had new cartridges available, which had
not been fitted to the ejection seats in the aircraft.
69. CAP 632 requires the pilot escape systems of swept-wing jet aircraft,
such as the Hawker Hunter, to be ‘fully serviceable’. The use of timeexpired
ejection seat cartridges meant that the ejection seats fitted to
G-BXFI did not meet this requirement.
70. The practice of using time-expired ejection seat cartridges in civil-operated
ex-military aircraft was not confined to G-BXFI or its maintenance
organisation.
71. The engine fitted to G-BXFI was not preserved during periods of inactivity
as required by the aircraft’s approved maintenance program.
72. Neither the operator nor the maintenance organisation had an approved
Alternative Means of Compliance with the Mandatory Permit Directive
related to engine life (MPD 2001-001).
73. The maintenance organisation did not have access to the previous
operator’s AMOC. It based scheduled maintenance tasks on entries in
the aircraft maintenance records associated with MPD 2001-001.
74. The maintenance organisation submitted a proposal for an AMOC to
MPD 2001-001 to the CAA which in turn requested this be resubmitted
to include additional tasks detailed in CAP 562 Leaflet 70-80. However,
no further application to the CAA was made by the maintenance
organisation.
75. The serial number of the right altimeter did not match that recorded in the
technical records.
76. Engine rpm exceedences occurring during a test flight in 2011 were not reported or investigated.
77. There was no formal or documented monitoring of engine performance,
either during engine ground runs or in flight, which would enable engine
performance deterioration to be identified.
78. Video evidence showed that the g-meter fitted to the aircraft was defective
during the accident flight and in September 2014. No related defects had
been reported or recorded, and the maintenance organisation stated that
it was not aware of any.
79. The AAN and Permit to Fly required the fatigue state of the aircraft to
be recorded after each day’s flight. The maintenance organisation read
and recorded the fatigue state once each year; between these readings,
monitoring of high fatigue inducing events relied on the pilots reporting
high loads seen on the g-meter.
80. The aircraft was being operated with the aileron trim position indicator
inoperative.
81. The aircraft had been operated with the flaps extended at speeds
exceeding the limit for doing so. This had not been reported in the aircraft
technical log.
82.The maintenance organisation issued a Certificate of Validity to the Permit
to Fly. At the time of the accident the aircraft did not meet airworthiness
requirements or the conditions of its Permit to Fly.
83. CAA oversight of the maintenance organisation and the operator did not
identify the deficiencies with the aircraft’s airworthiness.
84. The maintenance organisation did not have an established safety
management system and was not required to have one.
85. The diaphragm of the fuel pump governor had degraded due to the
combined effects of age and chemical attack. The engine manufacturer
concluded that it would not have prevented the engine from operating
normally but considered that it had exceeded its known predictable
functional capability and its continued integrity would be severely
affected.
86. MPD 2001-001 was published to mitigate the effects of ageing on the
Rolls-Royce Avon series of engines, including the engine fuel systems.
87. The AMOC approved for a previous operator of the aircraft did not
include routine inspections of the condition of engine fuel systems. This
inspection regime, continued by the current maintenance organisation,
did not identify the degradation of the fuel pump governor diaphragm.
88. The aircraft was fitted with underwing drop tanks made from phenolic
asbestos. This hazard had not been identified.

[Boac]

Perhaps a little explanation for those not familiar with aircraft manoeuvring and 'g' and the like.

I cannot recall the 'normal' stall speed of a Hunter, but would guess between 100 and 110kts.Thus at 105kts the aircraft has limited performance, and if 'erect' would require a stall recovery to be flown (power, nose down) hence the comment "and then pulling out of the resulting dive". However, while at the top of a loop, with less than 1g experienced, it will not 'stall' (while you can exceed the critical wing angle of attack you will not 'stall' in the classic sense at 0g for example, since the aeroplane effectively is 'weightless'). Now, whilst the tailplane/elevator still has 'authority' to move the nose in pitch, the wings cannot produce significant lift. Getting the ship going downwards will increase speed and allow the wings to generate enough lift to change the flight path. BUT if a 'bad' combination of speed and height exists, somewhere around or before the vertical is the point of 'coffin corner' - it is too late to do anything to avoid a crash, and is also probably outside ejection parameters too - even rolling upright and trying to pull out would probably not work. Trying to pull more g at too low an airspeed has two effects, 1 it produces lots of drag which limits further speed (and performance) increase and 2 it can produce the classic swept-wing manoeuvre stall with wing-rock - as in the external video.

This is why one uses performance 'gates' for aerobatics. Even in a Tiger Moth, you would not attempt a loop if you only had 60kts airspeed, for example! For a low-level loop there would be at least 2 'gates' - speed and height at entry and at the top, and some pilots may have other gates eg half-way up. An assessment of 'margin' at each decides the next manoeuvre with the option of the mentioned 'escape manoeuvre', which, of course, would re-write your display!

I have finished up more than once upside down and pointing at a ground which is quite large in my canopy in practice combat. There are no real 'gates' for those sort of manoeuvres which is why we used 5000ft as a minimum height for 'combat'. I recall losing a few friends who were flying Jaguars and I think it was said that more than 40 degrees nose down below 4000ft at low speed was potential 'bye bye' land, but I cannot remember the exact figures.

As I have said before, without seeing the 'in-cockpit' video it is difficult to work out exactly what happened at Shoreham.

[om15]

Thank you for the clear explanation Boac, I managed to follow that, one point that occurs to me is that the pilot will require instant and accurate throttle response when he requires to gain speed in these types of manoeuvres.
The point that the AAIB made regarding low utilisation aircraft engine preservation is pertinent for these display aircraft, aircraft or engines that are laid up for a period (typical period of 30 or 60 days) will either be ground run, up to take off power, regularly, or "inhibited", this process is the pumping of oil based inhibiting fluid through the fuel system to expel all traces of Jet A1, kerosene does have a water content and if just left in a system will corrode the working of the valves, controllers and flow units. A typical fuel control unit (FCU) or hydromechanical unit (HMU) contains many finely machined clearances and valves that are designed to control the flow and pressure of fuel supplied to the burners dependent on engine speed, throttle input, altitude, OAT, trim selection and so on, any small amounts of corrosion that reduces (or enlarges) these orifices will result in uncommanded fuel flow changes resulting in power loss or power surges.
Secondly, in the larger fan engines, the engine must be rotated regularly to prevent the bearings from being affected by the load of the shaft, usually the fan is rotated to turn the N1 and the N2 is rotated through an adaptor on the auxiliary gearbox, this is probably not quite so critical on the Avon, but still should have been taken into account.

Following maintenance on an A300 that had been laid up for a year or so (previous operator had gone bust and leasing company did not even consider maintenance requirements) we carried out an acceptance flight/ CAA airtest, the handling pilot being a CAA flight test pilot, throttling back after the climb the no 2 flamed out and shut down, couldn't be restarted, we headed for home on one engine, subsequent investigation showed the HMU was completely unserviceable due to corrosion, as was the HMU on the other engine when sent for shop inspection.

Most engine manufacturers now stipulate that any FCU that has not been inhibited properly must be removed and sent for overhaul. In the case of this aircraft a typical maintenance schedule should have called up power runs every 30 days or a system of inhibiting between operations.

A second point noted was that ground power assurance runs had not been carried out to record engine parameters, a typical run would require idle RPM, max RPM, ITT (or TGT) at idle, cruise, take off, oil pressures and temperatures, slam check times for acceleration, run down times, these plotted on graphs after correction for OAT, PA wind speeds, and then a proper assessment of engine health and performance could be established.

To not carry out any of the above on a single engine display aircraft indicates that the aircraft was not maintained to the "highest standard".

[Pontius Navigator]

BOAC, may I talk generally?

If there is a significant vertical velocity with an aircraft in a horizontal attitude and a low horizontal velocity, what manoeuvre will have the better affect in arresting a descent.

Is it to raise the nose and increase thrust or lower the nose to accelerate and increase lift?

[Boac]

om - in the sort of aeros we are looking at - ie low level, the throttle would normally be at full power throughout a loop, possibly being reduced if performance towards the bottom was satisfactory.

PN - your description fits a stalled condition. AF447 had most of those characteristics while deeply stalled (other than a 'horizontal attitude' - its nose was well up). The only recovery would be to lower the nose and accelerate. Raising it would further stall the wing - again, see AF447.

[Ex-Ascot]

What is going on? There do not seem to be any press reports about the progress of the case. Have they all gone off skiing?

[Boac]

Indeed - silence here.

[Ex-Ascot]

Still no reports. Obviously boring and no drama to write about.

[Ex-Ascot]

All of a sudden there is some reporting. Mainly pointless eye witness accounts.

[Pontius Navigator]

EA, aka impact statements, not really an appropriate word after an aircraft impact.

Looking at the second video clip, it looked like the proverbial "pulling like a bastard" which brought the nose up but did not arrest the sink rate.

It may be counter intuitive but had the nose been lowered could it have made a difference? Would it have been possible to change the flight line notwithstanding it would not have avoided the crash,?

[Boac]

it looked like the proverbial "pulling like a bastard"

- yes, and the drag thus created prevented any speed increase which would have enabled more manoeuvre capability, but lowering the nose............!?

Would it have been possible to change the flight line notwithstanding it would not have avoided the crash,?

- of course, unless totally out of control for whatever reason, you can choose where you crash. The keys are:

Knowing you are going to crash

Making the decision. At Shoreham, "pulling like a bastard" = hoping to pull out in time - and very much "oh sh!t" 'instinctive'. The best place to avoid the crash was at the top of the loop where the prosecution has alleged he was "1000ft too low".

In my accident (ejection, Harrier) I had the luxury of something over 40 seconds of knowing I was going to crash due to the speed at which the engine failed and thus had 'plenty of time' to select somewhere to 'park' the wreckage, with a large area of Germany spread out in front of me to choose from. Hill had, I guess, about 10-15 seconds (finally) with very limited options. I know the crash site well, and the line he was on (I think his chosen display pull-out line for that manoeuvre anyway) represented the least 'risky' in terms of buildings/factories or terrain clearance, but unfortunately 'busy'.

[k3k3]

Those few seconds of watching the underside of the aircraft with the nose high but still descending were filled with dreadful certainty of what was about to happen.

The odd thing was how my brain processed it, the aircraft seemed to fill my field of view even though I was halfway down the runway, and I heard nothing of the impact/explosions, I saw the flash of orange, then the fire followed by the black smoke, all in apparent silence.

The A27, where the first impact happened, is slightly higher than the airfield, could this have had a bearing on the outcome?

[Pontius Navigator]

"the least 'risky' in terms of buildings/factories or terrain clearance, but unfortunately 'busy'."

It was the classic crew room delima, hospital, school, old folks home. 10-15 seconds is not really enough time for chosing least bad option.

[Boac]

https://www.wscountytimes.co.uk/news/cr ... -1-8789113

"170kts" at the top of a loop!! Not without reheat, I fancy! I suspect Mr Watts is either confused or needs better glasses. The read-out from the actual accident reckoned about 105kts - which is a bit slow.