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Police helicopter crashes onto Glasgow pub

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Police helicopter crashes onto Glasgow pub

Old 9th Dec 2013, 19:08
  #921 (permalink)  
 
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I'm wondering whether the situation served up was so full of conflicts as to give no clear indication of appropriate response. Is this terminal - dump, AR? Is this transient - heave, think and hope? Just a very few seconds of the latter response could have cut off the retreat to the former.
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Old 9th Dec 2013, 19:10
  #922 (permalink)  
 
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Whirly
Even if the pilot had been incapacitated, the rotors wouldn't stop. It's pretty hard to think of ANY scenario in which the rotors would stop turning in that short a time, even if you wanted them to
I could think of one scenario, if the ac had auto pilot activated and ran out of usable fuel whilst the pilot was in capacitated, what would happen?

engines stop, AP keeps pitch on until rotors stop...
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Old 9th Dec 2013, 19:17
  #923 (permalink)  
 
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Ppruners are usually very ready to castigate the general media and their commentators for misleading and inaccurate reporting, but what about the professional media:

Glasgow helicopter crash not due to engine failure, AAIB reveals - News - Shephard

“Glasgow helicopter crash not due to engine failure, AAIB reveals”

The AAIB reveals no such thing. It says there was “... no evidence of major mechanical disruption to either engine...”. That explicitly does not rule out engine failure, say by flame-out for a fuel-supply or FADEC reason, I think the most common causes for engine failures.

Can we please now have some of the bile usually reserved for the BBC and the daily papers?
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Old 9th Dec 2013, 19:19
  #924 (permalink)  
 
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Even if the fuel supply stopped, this does not explain the aggressive decay in rrpm - unless the response to a double engine failure was to pull maximum pitch!

Stunning that there are some who believe that "Even a fully stalled rotor should still have some rotation as long as the lever was down." As henra has said, there is a "point of no return" for every helicopter in terms of rrpm afterwhich recovery is no longer possible. You should know the minimum rrpm for the type you fly or, if you can't remember, simply do not allow your rrpm to decay beyond the bottom of the green.

In my mind I was speculating that we might have read about a catastrophic main gearbox failure but now I have no idea as to what may have happened. So many details (on the surface) don't seem to add up.
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Old 9th Dec 2013, 19:20
  #925 (permalink)  

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Google maps, just across from the pub is the 2Canvas shop. In addition to a couple of cameras around the junction, on top of the lampost facing The Victoria, is that a CCTV camera?
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Old 9th Dec 2013, 19:35
  #926 (permalink)  
 
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Grenville

I think what we are fishing for is that in most (all?) serviceable and reasonably modern multi-engine helicopters, there is nothing you can do with the controls that will significantly droop the Nr unless the engines are set so as to permit Nr droop.

In the Sea King, the highest matched torque I ever saw in flight in the real aircraft (we did appalling things to the sim) was 135%, which is 12% over the gearbox transient limit. The Nr and both engines were perfectly happy (it was dark, in the mountains, going down rather fast, before NVG and I was the co-pilot staring rather hard at the engine gauges - the captain was a bit busy Aviating). I find it difficult to believe that a 35-yr-younger design wouldn't do better. And personal experience tells me that the rotor brake has no chance against the engines. So I'm assuming that, regardless of how the controls were handled, if the transmission was serviceable and the engines were running at governed Nf/Nr, the rotor would have been turning. Ergo, as the rotors were stopped at impact the engines must have been below governed Nf/Nr, and quite likely stopped, whether because wound back, shut down or for some other reason.
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Old 9th Dec 2013, 19:37
  #927 (permalink)  
 
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Does it rule out that the engines were shut down deliberately(as in drills for tail rotor drive failure). Main gear box and mechanical failure of engines ruled out. Makes no mention of tail rotor/fenestron though...??
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Old 9th Dec 2013, 19:41
  #928 (permalink)  
 
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Originally Posted by Sven Sixtoo View Post

I think what we are fishing for is that in most (all?) serviceable and reasonalby modern multi-engine helicopters, there is nothing you can do with the controls that will significantly droop the Nr unless the engines are set so as to permit Nr droop.
So is there such a setting on the EC135 which will configure the engines in such a manner so as to permit a catasprophic droop in Nr?
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Old 9th Dec 2013, 19:42
  #929 (permalink)  
 
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Sorry, you will need one of the type professionals to answer that.
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Old 9th Dec 2013, 19:43
  #930 (permalink)  
 
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"In my mind I was speculating that we might have read about a catastrophic main gearbox failure"

I was fully expecting the same.

The AAIB report specifically states the main rotor and tail rotor were not rotating at impact. Witness reports indicate "misfiring" sounds.....presumably engine surges. So presumably the engines were running very shortly before the accident.

How do you go from engines running to rotor stopped in such a short time frame.......you'd need both engines to stop more or less at the same time (pretty unlikely) and for the pilot to grossly mishandle the collective (even more unlikely). It beats me.

I really hope we don't end up with a final report where the cause "could not positively be determined".
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Old 9th Dec 2013, 19:47
  #931 (permalink)  
 
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High Spirits

AAIB say "No evidence of mechanical failure".

Now I am quite aware that absence of evidence does not equal evidence of absence. But AAIB are the most conservative of bodies in their statements. I may be wrong, but given that they say that they can't find anything broken, I would bet a lot of money that they can prove that the fenestron would have been going round if the main rotor had been going round.

Further to that, a quick check of the report shows that they have explicitly said so:

providing drive from the
No 2 engine power turbine to the main rotor and to the
fenestron drive shaft.

And that, of course, only says that the fenestron drive shaft could have been going round, not the fenestron itself. However, given the "no mechanical failure" statement, we can be confident that the fenestron would have been turning if drive had been provided.

Last edited by Jetdriver; 10th Dec 2013 at 22:20.
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Old 9th Dec 2013, 19:49
  #932 (permalink)  
 
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It's a pity there is no mention of the position of the engine control switches and/or throttles.
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Old 9th Dec 2013, 19:52
  #933 (permalink)  
 
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Indeed, which may either be significant to other matters or may be that they are mangled beyond recognition.
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Old 9th Dec 2013, 19:53
  #934 (permalink)  
 
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How do we know for sure that one engine was not already out and the pilot was expediting the trip home, perhaps on AP and then when the second engine quit the AP just tried to continue the flight?
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Old 9th Dec 2013, 19:54
  #935 (permalink)  
 
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One of the smallest spaces on any aircraft is the one between the pilots ears. We've spent decades reducing the capacity of that space to be the root of disaster, but what we can do little to do is to increase the capacity of that space to respond to chaos.

The one man we would wish we could consult is no longer available to us.

I think we are all glad not to have been where he was.

But I wish I could have observed what he saw, in a sim.
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Old 9th Dec 2013, 19:57
  #936 (permalink)  
 
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Grenville, I think you misinterpreted my comments. I did not suggest that a stalled rotor should be recoverable. I said that I believe a stalled rotor with the collective fully down may still have some small rotation. The AAIB have stated that there was zero rotation, so even if there had been a double engine failure and a completely mishandled entry into autorotation (which I would not expect from this pilot) this doesn't quite add up. No rotation suggests to me a mechanical failure in the transmission. As the AAIB are indicating against that, I am quite puzzled by this accident.
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Old 9th Dec 2013, 20:01
  #937 (permalink)  
 
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rotor accelration

henra said
and stop the rotor in a frighteningly short time.
In support of that I noticed the following.

Regarding a different EC135 incident[1] the NTSB report said:

1741:48, the main rotor RPM had decreased to 73 percent.
...
a rapid increase in main rotor rpm, to about 125 percent, which occurred at 1741:53
...
At 1741:56, the pilot transmitted, "mayday mayday, our engines are out, we're going down."

125% is 3 times the Knietic Energy of 73% (square law)

It seems that aerodynamic forces can change the rotor speed very rapidly (at least upwards).

With the same input force (or is it power, or are they the same thing?) it would go from 0% to 73% (or the reverse) in about a second and a half.

[1] NTSB Report Untitled Page
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Old 9th Dec 2013, 20:02
  #938 (permalink)  
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Yes, I'm most surprised that the engine control positions haven't been mentioned yet. I'm of the understanding that this information is of primary importance in incidents where there's no obvious, gross mechanical failure, even more so in the case where there's no flight data recorder, and one - if not the - first thing to be noted when the investigators get access.

Also, I'd appreciate some informed info on the basic physics. If the rotors had stopped by the time the helicopter impacted, then what had happened to their rotational energy such that the helicopter itself wasn't rotating? Is there anything other than a managed reduction in speed that could do this?
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Old 9th Dec 2013, 20:05
  #939 (permalink)  
 
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Try this
The pilot used ALT ACQUIRE on the auto pilot at a fairly low level, he was close to the helipad I think.
He was distracted and did not apply power (only 3 axis autopilot).
Helo slowed and then decended and entered vortex ring. Pilot (brain scrambled)
applied full collective. Over pitch etc etc.
Can you stall the blades with both engines working?
He might have shut down the engines before impact. Feds did not say if 'speed select levers' shut off.
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Old 9th Dec 2013, 20:07
  #940 (permalink)  
 
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It's a pity there is no mention of the position of the engine control switches and/or throttles
I think the fact the AAIB have not stated the position of the throttles and fuel switches will prove to be quite telling.
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