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Police helicopter crashes onto Glasgow pub

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Police helicopter crashes onto Glasgow pub

Old 14th Jan 2014, 22:23
  #1721 (permalink)  

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The dynamics of a helicopter with no rotor speed can probably be investigated accurately with a small-scale model that has an accurate weight distribution, certainly to the point of the onset of a "tumble".
Yes, I'm sure you're right. But as already said, no-one has bothered to do it (and why would anyone.....?) so we don't know for sure; although we could argue one way or the other all night long. I'm not going to do so because it's pointless.

However, the failed fenestron theory does also fit in with the evidence of the witness, at least to some extent. A rotating aircraft could be described as "tumbling" whichever way it was rotating through the air. But it's all supposition, hence me mentioning it because two stopped engines wouldn't normally result in stopped rotors (despite the suppositions of some who have obviously never flown a twin engined helicopter in their life and are talking through their backside).
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Old 14th Jan 2014, 22:46
  #1722 (permalink)  
 
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I fully agree that it's all speculation, and won't help to understand the causes.

However, I do find it interesting that the two seemingly remarkable eyewitness reports from the night of the accident: that the aircraft was "tumbling" and that the "rotors were not moving" could be consistent with each other.

If confirmed, then it strikes me as one of the most remarkable and unexpected accidents, and a rare case where eyewitness accounts might have been crucial in unravelling the process of the crash.

I suggest that no-one's tried to model a tumbling, crashing helicopter because no-one considered a helicopter would crash without its rotors turning, unless there was some sort of complete gearbox failure.
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Old 15th Jan 2014, 07:20
  #1723 (permalink)  
 
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Firstly, if the aircraft really was tumbling, don't you think it's remarkable that it struck the roof of The Clutha in a perfectly upright, wings level attitude?

Secondly, if the aircraft was, as it's last radio transmission suggested, simply transiting back to base, I don't really think the fenestron drive failure would result in an instant forced landing into a very 'hostile' area. Nor can I imagine any plausible fenestron control failure in forward flight that would trigger an immediate auto into the City centre.

Is there any suggestion the aircraft was at low speed/hover immediately prior to the accident?

Having said all that, I don't fly the 135, but I presume the tail fin has an aerofoil profile for a reason?

Not too sure I really buy the fuel starvation theory either? Though it's difficult to rule out contamination.

There are more prosaic reasons for rapid/unexpected total power loss.

All IMVHO obviously!

Last edited by Tandemrotor; 15th Jan 2014 at 07:33.
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Old 15th Jan 2014, 08:13
  #1724 (permalink)  

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If a pilot had completely lost control of a rapidly yawing / rolling / pitching aircraft, which had gone below its critical Nr, it's more than likely he would become disorientated. It's possible in this state that his last action might be to secure both engines in an attempt to recover things. It might not be possible to recover at all.

I mentioned critical Nr. It's worth bearing in mind that an aircraft yawing, from an uncontrolled torque reaction, has also lost effective rotor rpm, to perhaps a surprising and critical degree. One rotation in yaw per second = 60 main rotor RPM.
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Old 15th Jan 2014, 08:59
  #1725 (permalink)  

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impressive quoting skills SS !
SS has deleted his original post that I answered, then changed the quotes around to suit.
Sorry, I had to change that because the original looked as if I was quoting AnFI as saying the bit about the switches, which he of course he wasn't, he was quoting from another source.

The thing about AnFI's reference is that the person in the tale got into the habit of leaving the transfer pumps on in order to not fall into the same trap of the tall fellow in the tale, that left them switched off. (Presumably, tall chap forgot, on this one occasion, to switch them on during the start up/pre take off phase as per the 105 FLM?)

The quoted person, therefore never did a shutdown or start up as per the FLM in all his time on the 105, and when the time came to complete a proper start up, with all the switches correctly in the off position, because of the non conformal procedure that had become his habit, the transfer pumps problem arose. (Not being a 105 man, I presume there is no transfer pump warning light that would say they were switched off?)

If the man in the tale had adopted the habit described on a 135 there would be a few indicators the pumps were off, not necessarily to prevent actual flight with the transfer pumps off, but at least they would tell the pilot that they were.

For example.
Switchology - Prime and transfer pump switches are next to each other. Post engines start, prime pumps are switched off, transfer pumps are switched on.
Visual indicators - When the prime pumps are on the CAD indicates this. When the Transfer pumps are off, the CAD also indicates this. Monitoring of fuel levels.
Procedures - Pre flight systems checks, Pre start checks, Pre take off checks, Take off checks, 'CAD indications'.

If the habit adopted by the chap in the tale quoted by AnFI was to 'follow the instructions in the FLM' instead of adopting his different set of start up/shut down procedures, then the problem he found himself in wouldn't have happened. Nothing to do with a complexity or simplicity of any particular system, simply a human failing from not following the correct procedures.


I'm often asked, why do you switch off the inverter?
My answer, because that's what is says to do in the FLM when closing down.

Here's a 135 question, how many engines are running when you do the Hyd checks?
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Old 15th Jan 2014, 10:32
  #1726 (permalink)  
 
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Sid, with regard to your last post....I fully agree..

Here's a 135 question, how many engines are running when you do the Hyd checks?
One, with N2 appr 73-74%, don't do it in the powertrain accelleration phase.....so here"s a follow up question: Is it allowed to do it with both engines idle?
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Old 15th Jan 2014, 10:41
  #1727 (permalink)  
 
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ElectricJohn
It didn't - it was nose-down.
You sure? That isn't what the AAIB said.

The aircraft's final resting position depends only upon what is supporting it, and where!

There are scenarios which fit all that you have described. Tumbling seems very unlikely to me.
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Old 15th Jan 2014, 11:06
  #1728 (permalink)  

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.....so here"s a follow up question: Is it allowed to do it with both engines idle?
Yes, during the 'quick start up'.
(Flight idle)

Last edited by SilsoeSid; 15th Jan 2014 at 14:43. Reason: Engines at flight idle not ground
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Old 15th Jan 2014, 11:33
  #1729 (permalink)  

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Is there any suggestion the aircraft was at low speed/hover immediately prior to the accident?
En-route back to base, one minute out, slow(ing) to below 80 kts in order to raise downlink and/or arm flotation gear?
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Old 15th Jan 2014, 12:48
  #1730 (permalink)  
 
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ElectricJohn
It does appear to have been angled downwards at impact though, from the pictures.
Please don't think I'm being obtuse, but I don't think it's possible to draw that conclusion? All the photographs I have seen speak only to the final resting position of the aircraft, not the moment of impact.
I'm actually more curious as to why there doesn't seem to have been much discussion about why it might have been flying very low and making odd noises some time before whatever caused the final crash sequence.
There is a reasonably straightforward theory which 'fits', but not one I am prepared to put forward, as it would be totally speculative.

The only people with any factual idea are in Farnborough. We will hear from them when they consider it appropriate and accurate.
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Old 15th Jan 2014, 14:26
  #1731 (permalink)  
 
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Re 'nose down' resting angle. Helicopter, in more or less level attitude, pancakes onto flat roof, with fuselage (bulk of weight) in middle of roof, tail close to edge. Roof is strongest nearest edge (walls), but subjected to greatest force at weakest point, nearest (unsupported) middle. Nose penetrates further into building than tail. Thus apparent nose down angle - little or nothing to infer in terms of how/why the helicopter crashed onto it.
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Old 15th Jan 2014, 16:46
  #1732 (permalink)  

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The horizontal stabiliser would still have an aerodynamic effect during a high rate of descent, rotors turning or not.
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Old 15th Jan 2014, 16:48
  #1733 (permalink)  

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Going back over a thousand posts, http://www.pprune.org/8194594-post783.html
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Old 15th Jan 2014, 17:21
  #1734 (permalink)  
 
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SS

You seem to imply in that post that both engines were 'closed down'? That would require both intent and action. I don't think there is evidence yet to support that? Though I do agree with you in some other aspects.

Any tail rotor/fenestron failure I can imagine, would likely have been flyable down to very low speeds. (perhaps our EC135 pilots could help?) Apart from when virtually in the hover, I would imagine massively out of balance powered flight (indeed anything) would be preferable to autorotation into a city centre?

Unless at very low speed, tail rotor failure might not fit the little known information???
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Old 15th Jan 2014, 18:57
  #1735 (permalink)  

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Tr, you're quite right, you can control a tail rotor problem on a 135 quite well, even down to a run on, as long as she doesn't break away below 40 kts. Wind from the left is a good thing, which it was on the night.

Tr drive/control failure drills look for an airspeed of at least 70kts, once you've got out of the initial situation then you can see if you can achieve the 40 kts on approach or not. However what if there's the tail problem on reducing through 80kts, power pulled to try and get airspeed on, and it starts to go wrong? If you're spinning (eye witnesses), how long do you try and get airspeed over the fin? At some point, the twist grips have to be a consideration, and then you deal with the cards dealt, ie your going where your right foot is!

All of this didn't happen near to the pub, that's just where it all finished.

Until we have the gps info such as speed & height and switch positions, we have very little to go on. However, it still leaves us with the question of how the blades were not rotating on impact.

All the above is well and good if the ac is complete, but are there any thoughts on whether the tail might have partially separated pre impact?
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Old 15th Jan 2014, 19:42
  #1736 (permalink)  
 
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However what if there's the tail problem on reducing through 80kts
Would that be on approach to base? As you also said:
En-route back to base, one minute out, slow(ing) to below 80 kts in order to raise downlink and/or arm flotation gear?
In which case you would probably be at (and likely to keep?) a low power/low torque setting. Unlikely to increase power to any great extent until the bottom of the approach? (I would guess one minute out would be about one mile, and therefore about 3-400'?)

Ergo, very little torque demanded? Very little tail rotor authority required, a bit like your 40kts example.

The only way I can see tail rotor failure requiring immediate autorotation into a city centre is if the failure happened in OGI hover? Is that fair, and do we think it was hovering immediately prior to the accident? (That's not what they are reported to have told ATC?)

All idle speculation of course.
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Old 15th Jan 2014, 19:50
  #1737 (permalink)  

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All the above is well and good if the ac is complete, but are there any thoughts on whether the tail might have partially separated pre impact?
Those were my thoughts too, especially after I read about the fenstrom/tailboom frame attachment cracking issues already known about on the type. However, the fenestron was with the main wreckage.

I wonder how far the frame can partly separate and distort and "lean back" before the rear driveshaft disengages?
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Old 15th Jan 2014, 20:00
  #1738 (permalink)  

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No 135 pilot, or I'd hazard a guess any helicopter pilot with a tail rotor problem, would continue straight into any base, let alone one such as Glasgow.

They asked air traffic for clearance into the zone to return to base, they wouldn't have needed to tell them they were doing anything on the way in, unless perhaps it caused a delay. They could well have slowed over the city to 'have a look at something', at which point something possibly happened, again the GPS info should tell us.
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Old 15th Jan 2014, 20:02
  #1739 (permalink)  
 
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Shy.

Reminds me of an accident to a B206 G-WLLY.

Sid
No 135 pilot, or I'd hazard a guess any helicopter pilot with a tail rotor problem, would continue straight into any base, let alone one such as Glasgow.
I don't think I ever said that's what he was intending? I just said pretty much any form of continued flight offered a better chance of survival than autorotation into a city centre.

Tail rotor failure in OGI hover is the only regime I can imagine that would require such extreme action, (take a look at YouTube for some examples) and I haven't heard any witness statements say he was hovering?

That is all.

Last edited by Tandemrotor; 15th Jan 2014 at 20:14.
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Old 15th Jan 2014, 20:35
  #1740 (permalink)  
 
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S'Torque
The horizontal stabiliser would still have an aerodynamic effect during a high rate of descent, rotors turning or not.
It would - to shuttlecock the nose down, as would the moment of the drag from the boom, given that the rotor lift was surely sharply reduced just before that point... in the same circumstances, the hypothetical slow/stopped rotors would tend to shuttlecock it belly down.

If the circumstances were right for a sharp pitch down, then it could even establish a "tumble".
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