Police helicopter crashes onto Glasgow pub

[Fortyodd2]

Feathers,
No it does not. In fact, if you look at the previous Glasgow aircraft crash in 2002, (G-SPAU), the pilot had to go back into the wreckage to turn off the engines as they were still running. No fuel was spilt and no post crash fire either.

[Thomas coupling]

Safety Flight: I mentioned the ELT going off. (The ARCC received a signal)
I missed the post that said David was @ 700' in the cruise.


I sincerely wish NOT to upset readers with the following "theory of events":
Please do not read further if you think it may offend you.

IF and a massive IF he lost it at this height and weighing in at approx 2.5 tonnes he would have free fallen @ 10m/s squared. It meant 50% terminal velocity in 3s. 99% terminal velocity in 6 seconds. I estimate a minimum impact speed of around 90m/s(200mph).
You state the u/c can cope with a vertical landing of around 6mph??? Is that correct?
For those who are not familiar, the wreckage compression stopped about 1 foot below the gearbox platform. That means the rest of the cabin area (approx 4 feet without extended u/c skids(?) was crushed. This is consistent in my mind with wreckage I have seen from several aircraft crashes and road traffic accidents I attended, where high speeds and hard stops have been involved.
Thus - this accident started long before the end. IF he was @ 700 feet en route to his base, he went from this to the pub roof stationary AND vertical without his engines or his rotors.

My theory (and I only post this because this is what readers are here for: theories. Don't lambast me because you think "what does he know". I don't! That is why it is a theory).

The cab was 1 mile from base @ cruise height and maybe 70-80kts (due to the proximity of his decent into base). Evidence shows him to have been airborne for 1:37hrs [Up 2045, lost contact: 2222]. He had uploaded 400Kg fuel. Take away his MLA of 95Kg gives us 305Kg useable for normal ops. At 3.3Kg/min fuel usage this gives us: 1:32hrs to MLA. I therefore surmise that he may have had a fuel caption illuminated on one or both engines (amber or red - can't remember).
2 eye witnesses have independently stated that they heard "mis firings" and "back firings" from the engine. I surmise that while comfortably weighing up the fuel scenario, he was suddenly hit by stall or surge on one engine. In both situations Nr will drop (albeit by a small amount) as T4 and Tq argue with each other and the remaining engine compensates for the lack of power output from the duff engine. While he initiates the correct actions to deselct the duff engine (and switches the controls for that engine - off), either then, or shortly thereafter, the remaining healthy engine flames out due to a fuel irregularity caused by low fuel.
In the meantime he has slowed somewhat below min speed (65kts) thus demanding more power to retain Nr in the governed range and he has noticed that the Nr is decaying fast. By the time he has fully lowered the lever to slug the Nr he has slowed further to look for a landing spot close by, the Nr is now down around his knees.
[There is an element in me that thinks that here we have a pilot who has always (except for his very early days of training) flown twins. He subconsciously may have thought that this could not be happening to him and as a result, delayed the onset of hard down collective.]
I also happen to think Hydraulics disengage @ 65bar and he loses control of the a/c allowing it to flip backwards if he was pulling back at the time and tumble vertically. I wait to see if the engine switches show one engine properly shut down and the other starved of fuel but swtiches still in the ON position.

Please feel free to savage this theory?

[Feathers McGraw]

Fortyodd: Thanks for that, presumably it is the integrity of the fuel tankage that removes the need for such a crash switch.

TC: Very interesting, particularly with regard to the twin engined helicopter comments. I've seen it said here repeatedly that twins are never expected to suffer a double engine failure, that cannot but have an effect on the mindset of people that fly them I would have thought.

[jayteeto]

1:37 airborne uses approx 325kg, leaving 75kg on board. This should be around the time the amber caption illuminates, however it might not have quite got low enough to illuminate a warning. So although another possible theory is stated, we cannot say if a warning light came on for fuel (as you state of course).

[hoodie]

Originally Posted by Thomas coupling

For those who are not familiar, the wreckage compression stopped about 1 foot below the gearbox platform. That means the rest of the cabin area (approx 4 feet without extended u/c skids(?) was crushed.

Tc, where does this info come from? The pictures of the aircraft being recovered with cabin area under a tarpaulin may be unrepresentative for these purposes if the cabin area was partially cut away during the rescue effort, or damaged during the building collapse.

[flying friend]

Flying Friend

with some nervousness this is my first post on this great forum. I am not a pilot - I'm an architect. The hole in the pub roof is clearly punched through - if it was a 'secondary collapse' a wider area of the roof would be involved. My guess is the space between the roof joists would have been filled with rubble from the demolition of the upper floors of the building. I think the helicopter unfortunately went straight in at some speed, the secondary event described was several hundredweight of rubble sliding down creating noise and thick dust.

[Thomas coupling]

Flying friend (sounds like a menthol sweet!)

Welcome and your input is appreciated.

[Steve Stubbs]

Its been some 15 years since I stopped flying twins, but for Feathers Magraw in my 8500 odd twin hours I several times lost an engine, and I always immediately thought - now I am flying a single. In the many, many sim checks I did, in those engine fail or shutdown circumstances I always briefed the other pilot that we now fly NR as an absolute priority.

Those of us around then will remember the twin engine flameout on a Bristow AS332L just north of Aberdeen on the ILS. He got a restart done and landed safely. We all learned a strong lesson from that. Lets hope today's twin drivers are still thinking the same.

[nigelh]

TC . All quite possible but two things don't stack up .
If he fell , free fall , the whole way he would have lost his hydraulics much earlier ? Or ( excuse my ignorance ) is there a reservoir as in the 350 , which will give you two or 3 major cyclic movements with assistance ?
In a free fall the chances of landing correct way up must be small ?
Circa 200mph onto a roof surely would destroy the aircraft ??!!!!
Other than that .... Perfect theory

[Sven Sixtoo]

Might I suggest that if the rotor had stopped it would nevertheless have quite a bit of drag (the instant some airflow gets hold of it it starts turning which creates lift which creates drag which ...) and thus an aerodynamically induced rotor stop at a few hundred feet would result in a braked fall with a force vector that tended to keep the aircraft upright - sort of like a drogue. So damned bad luck could have pointed the aircraft at the pub with nothing to do but wait and turn stuff off for four or five terrible seconds.

None of which suggests any reason why the rotor stopped or why the whole sequence started.

Iain

[chopjock]

fuel tanks

Ok I have a technical question concerning the fuel system.
Let's assume for a moment no 1 engine had a problem (It was later found to be damaged) and either stopped or was shut down. At a similar time the low fuel amber warning light came on (or was already on). With no 1 inop, does that mean the usable fuel for no1 is stuck in no 1 supply tank ? Because now no 2 would use up it's supply tank fuel even quicker if it has to do all the work and for longer. So imagine you think you have enough fuel to reach your destination on two, then you have an engine failure, would you still get as far on only one?

[Tailspin Turtle]

TC: Please feel free to savage this theory?

I'll preface my augmentation of your theory by noting that in my opinion there is no necessity to shut down a failed engine if you are on approach in a helicopter (or in a light twin on short final for that matter) unless it is surging or actually on fire. An engine might surge while running out of fuel or when trying to digest a bad bit of fuel but it could also be caused by FOD (a bird strike?) or a compressor blade failure. If an engine did surge and the pilot responded by shutting down one, it's possible that he shut down the good one, inadvertently and tragically forging a necessary link in the chain of events.

[Adroight]

and the pilot responded by shutting down one, it's possible that he shut down the good one

A sensible theory at last and very relevant in a single pilot operation.

I have seen two pilots in the sim analyse an engine problem and then jointly agree to shut down the wrong engine and do so when they were under no particular stress. This happened in the 1988 BM 737 accident too.

[cattletruck]

I admit I'm a little out of my depth with this question, but unlike an airplane, both engines in a twin helicopter are coupled by the same load. So if one engine starts surging and generally misbehaving then what does the FADEC do to the other engine good engine that doesn't know about it's twin brother's indecisiveness at providing the necessary power to the MGB?

What would the engine indicators be showing in such a condition on the 135?

[skadi]

I admit I'm a little out of my depth with this question, but unlike an airplane, both engines in a twin helicopter are coupled by the same load. So if one engine starts surging and generally misbehaving then what does the FADEC do to the other engine good engine that doesn't know about it's twin brother's indecisiveness at providing the necessary power to the MGB?

What would the engine indicators be showing in such a condition on the 135?

The good engine will take over. F. e. if you fly with 2 x 55% TQ, when in OEI you will get ~110% TQ on the good engine unless you lower the collective ( powerlever ) and get the approbiate indications on your engine instruments, split needles ( N2, TQ etc )

skadi

[Munnyspinner]

Cattle truck, that's a good question. Also, the anecdotal incidence of pilots shutting down perfectly serviceable engines is higher than the accidents stats would suggest. However, there are a number of high profile accidents where this occurred. The various reasons for this type of error are well documented. It would be interesting to know what the FADEC reaction is to one engine malfunctioning when twin engines operate through a common drive. Presumably, if one starts to go offline, the other spools up to compensate to maintain the required power setting? Given earlier comments about fuel feed and the potential for one engine to flame out due to fuel starvation 2 mins before the other what would happen if the 'critical' engine (I.e.first to go on a low fuel ) was operating normally when no 2 went off line?
Thanks Skadi!

[DOUBLE BOGEY]

I would suggest shutting down the wrong engine in a modern EC product is a little harder to do as all digital indications of failure are clearly indicated against the offending engine. Of course this would not rule out a cognitive failure to place the hand on the correct switch or lever.

Would current EC135 pilots agree or not?

[jayteeto]

Difficult to answer, however we are taught to select engine to idle, check correct, then shutdown. I am sure that the switch positions have been noted, that would make the enquiry easier, if they have actually been moved.

[Cows getting bigger]

Not an EC135 driver but I do have a few thousand hours in DA42s. For those not familiar with the aircraft it is a simple twin with ECU controlled engines managed by a single power lever for each engine. Additionally each engine has ECU AUTO/B switch which allows for the manual selection of ECU B. Fiddling with ECUs is not part of the immediate action drill on engine failure. Engine instrumentation comes via a Garmin G1000 display.



One 'advantage' of an engine failure in a twin aeroplane is that you get significant yaw in the direction of the failed engine. Indeed, first recognition of failure will probably come through the rudder pedals.

In about 800hrs of DA42 instructing, of which probably half that time has been spent in engine failure modes I have twice encountered pilots, one of whom was a qualified twin driver who was undergoing differences training, who have attempted to secure the wrong engine. On both occasions they correctly followed the identification and rectification drills right to the point they went to retard the 'correct' throttle.

It happens.

[cattletruck]

Originally Posted by skadi

The good engine will take over. F. e. if you fly with 2 x 55% TQ, when in OEI you will get ~110% TQ on the good engine ...

Thanks skadi, I understand that occurs when the bad engine stops completely, but what if it's surging, banging and up to all sorts of bad behaviour on it's way out, can anyone hazard a guess what the engine indicators would show as the FADEC of the good engine fights the FADEC of the bad engine until the bad engine finally stops turning?

The old hydro mechanical FCUs were relatively slow to react to transient demand - which depending on the circumstances could be a good thing. New electronic metering systems are quite capable of responding in milliseconds which under non-normal conditions could cause more problems than good.