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-   -   Police helicopter crashes onto Glasgow pub (https://www.pprune.org/rotorheads/528850-police-helicopter-crashes-onto-glasgow-pub.html)

HLCPTR 1st Dec 2013 19:15

Fortyodd2
 

Re: the link you directed me to - 2nd post.
"2. There is
no strict relevance to operations in PC1 or to Cat A standards, as the
procedures developed for such operations specifically avoid the HV curve and are
detailed in a separate FLM supplement".

All UK Police Operations are conducted according to PC1/CAT A standards.
As factual as that statement may be, it only applies to take-off and landing procedures and has little bearing on an aircraft in flight which experiences an engine failure while within the HV curve (as defined by Press Alt, OAT, air(wind) speed and aircraft weight).

Stu B 1st Dec 2013 19:15

It is hard to understand how an onlooker could see clearly enough in the dark to discern stationary rotor blades, but discerning motion of the whole helicopter is much more plausible. But in the dark what would have been seen most clearly would have been its lights, and they could very easily have given a misleading appreciation of its gyrations. A "tumbling end over end" motion as I understand the journalist believed he saw is hard to explain. But imagine fro a moment a helicopter exhibiting a very high yaw rate, and at a significant bank angle in the dark. In aircraft axes, the helicopter is yawing, but in earth axes that yawing will appear as a "cartwheeling" motion and could easily be described as tumbling end over end, especially in the dark with the observer not realising he was seeing the aircraft in somewhat of a "plan view".
How would a helicopter get in such a condition - well the loss of drive to the fenestron could generate a high yaw (depending on airspeed (yaw stability and yaw damping) and rotor torque (as the engines try to spin the cabin in opposition to the torque applied to the rotor). And the bank angle - various mechanisms - aerodynamic rolling moment form the fuselage at very high sideslip; immediate lateral stick input in response to sudden yaw rate; even perhaps lateral stick input due to the inertia of the stick and hand on it in a very aggressive yaw acceleration. Although entry to autorotation after power loss can be and is trained and practised, the loss of yaw control and resultant sudden yaw rate when the reaction to engine/rotor torque is no longer restrained by a tail rotor or fenestron cannot be, and would be very disorienting, especially in the dark. I have a faint recollection of once seeing video of a helicopter loosing its tail rotor drive and the gyrations were sickening to see. Nevertheless, if the aircraft can be got into autorotation so there is no engine torque being applied to the rotor, there will then be no torque reaction back onto the fuselage and the yaw rate will damp down and - with enough height and a measure of good luck - enough control regained in pitch and roll (though not of course yaw) to have some chance of a survivable arrival. But add in the hazards of darkness and a very obstruction-littered urban environment, and the challenge facing the pilot would be enormous.

Incidentally, an early observer of the fairly-recent San Francisco 777 crash described that aircraft as "having cartwheeled", but all the pundits on PPRuNe immediately dismissed that as impossible and inconsistent with the condition and layout of the wreckage. Some time later video emerged and was posted. It clearly showed the aircraft *yawing* through ~360 degrees but while at a roll attitude of of perhaps 30-40 degrees. The observer's description of "cartwheeling" was not at all an unreasonable description of what the video showed (allowing for the fact he only saw it once, in real time, and was not "primed" for what he was about to witness), but his account was simply interpreted too literally by the pundits and rejected as "impossible". We should not too lightly dismiss eye-witness reports that do not fit our own preconceptions. They may need some careful interpretation (and they may be wrong in some respects - forensic recollection of sudden, rapidly-evolving events is not something humans are good at), but we would be well advised to strive to see if there might be significant insights concealed within them.

The accident at Glasgow was a truly horrific event both for the crew and for those in the bar. God rest the souls of all who perished.

Thomas coupling 1st Dec 2013 19:25

Standard overhaul you are quite right, it does seem a little tense - this thread.
Please ask away and those who know will surely help?

Dead Man's Curve:
Twin's do have a very small DMC but it is very very small. Take-offs and landings stay out of them. Cruise obviously stays out of it.
Police helo's hover a LOT and "x" % of the time they are well clear of the DMC. Occasionally in the heat of a chase etc they can inadvertently drift into the zone but it is rare.
In this particular case - indications (eye witness/pictures/noises) suggest the main and tail rotor blades were stationary or close to that. For that to be the case as a consequence of being in the DMC it would suggest he lost both engines and didn't lower the collective at all prior to hitting the deck.

STANDTO 1st Dec 2013 19:29

Latest eye witness stuff from the scene in this article. Suggestion of MGB letting go.

Do they really just give up like that? In my limited time in choppers, I thought the MGB chips sensors would pick up the early signs of failure in plenty of time.

Police killed in Glasgow helicopter crash had won bravery commendations | UK news | The Guardian

DIBO 1st Dec 2013 19:40


It is hard to understand how an onlooker could see clearly enough in the dark to discern stationary rotor blades
amen

Originally Posted by /published by Dailymail
...band Esperanza assumed the collapsing ceiling was a minor problem.
Audience member .... said: ‘Above the music, I heard a loud whoosh and a wooden panel fell down near the stage.
One of the musicians joked, “Looks like we’re bringing the roof down.”’

And then, only then, hell broke loose. Is not what one expects when a 2tons object freefalls from a height thru the roof.

Lon More 1st Dec 2013 20:14

Re an attempt to land on the roof in darkness. The pub walls were white with illuminated pub signs on them. Also it's a well known location, I wonder how many times he'd flown past it?

Pilot DAR 1st Dec 2013 20:15

I have read most but not all of this, and some of it pains me. (and I'm only a novice heli pilot) I know no more about this sad event, than what I have read here. The theme of stopped rotors keeps reappearing. I have a question for the truly knowledgeable posters here:

If a pilot were to conduct a reasonably successful autorotation, unfortunately onto a roof, which was unable to support the weight of the helicopter, and following the touchdown, the rotor RPM decayed for any number of reasons, would that not give the band time to make a remark about bringing the roof down, before the helicopter with a now stopped rotor dropped through the roof ('cause following the auto, the stopped rotor no longer carried any of the weight of the helicopter)? (sorry for the run on sentence). If a helicopter sat atop a roof, which could not support it, and it was creating no lift itself, it might drop through with a stopped rotor, which could then have apparently undamaged blades? A fuselage dropping nose down through a roof with beam structure could be sheared as it passed between beams, causing cabin damage, and crew injury?

My training did not ever include full on autos, but I can imagine wanting the rotor to be stopped once you were down, letting alone any influences already stopping it.

FSXPilot 1st Dec 2013 20:22

Could he have been incapacitated? As single pilot operation that would be game over. I guess we will have to wait about a year for the AAIB to report. RIP all. :-(

Stu B 1st Dec 2013 20:29

While I was composing my post and saying

It is hard to understand how an onlooker could see clearly enough in the dark to discern stationary rotor blades
, someone else posted the suggestion that this could have been an optical illusion from the aircraft's strobe lights. Perhaps another example where something a witness says can be understood - in this case the witness may have formed a wrong impression, but perhaps there may have been a mechanism through the strobes for him thinking he saw what he claimed he saw. (My scepticism about the chap seeing the blades was primarily because of the darkness, but of course the light from the strobes neatly solves that aspect.)

In Post 47 I raised the issue of a reported period between the first sign to occupants of the bar that something had happened, then the catastrophic building collapse some period later, enough for the "joke" about the band bringing the ceiling down between the two stages of the event. And soon after, in post #62, HeliComparator (a very well-respected name around here) suggested exactly the two-stage scenario that DIBO has proposed above.

awblain 1st Dec 2013 20:37

I believe Stu B has it right
 
"Tumbling end over end" equals "primarily spinning around the rotor axis"

I can go for that.

Add a powerful strobe interrupting the view, and I think we can see how that description of a plausible loss of yaw control might be described by an eyewitness as a loss of pitch control.

Mechta 1st Dec 2013 20:40

DIBO wrote:

We're talking here about helmet wearing crew, properly strapped in a 4 point harness on an crash resistant seat (at least 15G spikes vertically), mounted in an energy absorbing fuselage. Not what HSE is talking about...
There is always the possibility that, having made the firm landing after an autorotation, the crew got out, or were getting out, of the helicopter as quickly as they could. Then, as the roof collapsed, they were crushed between the helicopter and the roof structure as it fell through.

jugofpropwash 1st Dec 2013 20:53

Pilot DAR's scenario seems reasonable, and would account for the time lapse reported by those inside the bar between the initial ceiling damage and the total collapse.

I am not a pilot, but used to be attached to an avionics unit of the National Guard, so I spent a fair amount of time around helicopters and pay more attention to those going over than most do. That said - I've never seen an auto rotation, and as such would be unable to identify the difference between a controlled or semi controlled auto rotation and some other catastrophic failure that resulted in total loss of control - especially in the dark and from a distance. I suspect that most of the witnesses are no better qualified than I am in that respect.

AvNews 1st Dec 2013 20:55

Eurocopter EC135 T2: history of the Glasgow crash helicopter | World news | The Observer

mary meagher 1st Dec 2013 20:56

Clearly whatever caused the catastrophe was abrupt, not enough time nor height to glide (autorotate) down, nor to choose the place of arrival. I recall from the London accident discussion that single engine helicopters must track along the river, and that twin engine helicopters probably also follow the river route if availble. While the North Sea transport helis have floats attached, useful if they manage to arrive right side up, I wonder if these smaller choppers have something similar, and if not would a river ditching have been any use to the crew as well as serving to avoid those on the ground....

Not enough time to radio of any problem, pilot trying to do his best. Any clues of popping noises or lack of engine noise could be distorted by wind conditions, or echos from nearby buildings.

Whichever fuel is used in this type, and whatever system was in place to inhibit a post inmpact fire, credit to those designers for saving many many more lives. Likely that the exits from the pub must have met regulations as well.

I once sat in on a practice autorotation in a news helicopter; it really was a non-event. But in daylight. Don't remember if the seats had any special foam to prevent spinal injury in a heavy landing.

jumpseater 1st Dec 2013 21:00

Re falling like a stone vs an auto rotation. I see autorotations on occasion from the office window. They are noticeably faster and steeper than an 'ordinary' approach. I'd be surprised to hear someone describe it as a falling stone. I'd also expect an eyewitness to hear rotor or airframe noise unless they were in a very noisy or insulated environment.

Assuming there were others on the street I'd expect others to have commented on some sounds of the descent if the aircraft was in autorotation close to the ground. Even when in London I'm aware of helicopter noise if one is operating, that may just be me being in the trade and interested in helo's though.

Evelyn Higginbottom 1st Dec 2013 21:02


While the North Sea transport helis have floats attached, useful if they manage to arrive right side up, I wonder if these smaller choppers have something similar, and if not would a river ditching have been any use to the crew as well as serving to avoid those on the ground....
G-SPAO was fitted with an emergency flotation system.

A river landing, at night, is not desirable but, it is unlikely that this was even a factor for as you said yourself:


Clearly whatever caused the catastrophe was abrupt, not enough time nor height to glide (autorotate) down, nor to choose the place of arrival.

jugofpropwash 1st Dec 2013 21:10

Just a thought, but if they landed/auto rotated successfully on the roof - perhaps only then realizing that they were on a roof and not on the roadway/parking lot - then they might have attempted to quickly unbelt and exit the helicopter so they could warn the occupants of the building. Being unbelted/helmets off/doors open would have made them more susceptible to injury when the roof gave way and they dropped.

mickjoebill 1st Dec 2013 21:15

Engines apparently silent?
 
How much of the sound of a jet engine is made by turbine spinning and how much by ignition, perhaps 50%?

I can't find a report from survivors referring to the distinctive noise made by a jet engine when heard from close proximity (even when shutting down)

Does a seizure of a MGB simultaneously seize the engines?

chopjock 1st Dec 2013 21:18


Does a seizure of a MGB simultaneously seize the engines?
No
engines are two stage and not connected to MGB.

RedhillPhil 1st Dec 2013 21:33


Originally Posted by Sir Niall Dementia (Post 8182706)
RedHillPhill;


A brilliant bit of fishermans' tall tales! The 135 has two engines driving one set of rotors through free power turbines into a combiner box then the main gear box, (at least the one I spent 3 hours 40 min in today does)


There are no clutches, pulling up the collective too early in an auto can slow the blades dramatically (enough to totally screw your day) pulling back on the stick tends to "g load" the rotor disc and increase the rotor rpm.


:mad: me! I thought the BBC was bad, maybe they're getting their info from angling sites now.


Doubtless others will criticise my description, but I'm trying to keep it simple for the care in the community cases who have come out of the woodwork again.



Many thanks. I know about fishing and I am more than aut fait with railways but of helicopters I know little.


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