Police helicopter crashes onto Glasgow pub
Join Date: Dec 2008
Location: N/A
Posts: 845
Likes: 0
Received 0 Likes
on
0 Posts
PA - If a fuel systen had only an 'on' valve, a pump switch and a reserve tank selector valve - it's operation would be deemed very simple - but it's still more complicated than a fuel tank that is always on, allways selected with a pump which comes on with the ignition key (Like a car). An opportunity to screw up is not just a pilot error - it's a system error (perhaps a design error)
You miss the point about 'complexity' - it doesn't mean it's difficult to understand but just that each 'complication' (as in a watch) is an opportunity for a screwup. ANOTHER ONE of which is that : "there is a design eye reference point for seeing the panel. If you can't meet it, you need to be aware" but if you are not and if there are 1000 items of that degree of triviality it is most unlikely that some combination of errors won't be made. (it's not really pilot error - and it is part of the downside of 2 engines)
In aeroplanes you can see the suitability of 2 engines varys with scale, for small scale, probably up to the PC12 - it is clear that a single engined solution is probably better, for 737 maybe 2 engines. In HELICOPTERS the justification of 2 engines is less strong (single drive mechanism, and ability to autorotate) and only works when the hazard is great and at a bigger scale. So, to carry 25 people over 200ft jungle canopy only - multi engine justified (2 crew also - to help with the complexity). To carry 1 observer over a few small trees sometimes - obviously SHOULD NOT be done by twin.
That's the problem, no logic out there any more: PA AGREE: "too many regulators and consultants are incapable of looking at objectively.
"
(and an industry that thinks it is clever to con the customer into thinking bigger and more complex is better)
PG - it is not surprising that the basics of lowering a lever (with appropriate attitude change) are lost especially amongst (confident) pilots of twins, feeling imune from reality, protected by sytems.
(not suggesting this happened here - but it wouldn't be surprising at all)
You miss the point about 'complexity' - it doesn't mean it's difficult to understand but just that each 'complication' (as in a watch) is an opportunity for a screwup. ANOTHER ONE of which is that : "there is a design eye reference point for seeing the panel. If you can't meet it, you need to be aware" but if you are not and if there are 1000 items of that degree of triviality it is most unlikely that some combination of errors won't be made. (it's not really pilot error - and it is part of the downside of 2 engines)
In aeroplanes you can see the suitability of 2 engines varys with scale, for small scale, probably up to the PC12 - it is clear that a single engined solution is probably better, for 737 maybe 2 engines. In HELICOPTERS the justification of 2 engines is less strong (single drive mechanism, and ability to autorotate) and only works when the hazard is great and at a bigger scale. So, to carry 25 people over 200ft jungle canopy only - multi engine justified (2 crew also - to help with the complexity). To carry 1 observer over a few small trees sometimes - obviously SHOULD NOT be done by twin.
That's the problem, no logic out there any more: PA AGREE: "too many regulators and consultants are incapable of looking at objectively.
"(and an industry that thinks it is clever to con the customer into thinking bigger and more complex is better)
PG - it is not surprising that the basics of lowering a lever (with appropriate attitude change) are lost especially amongst (confident) pilots of twins, feeling imune from reality, protected by sytems.
(not suggesting this happened here - but it wouldn't be surprising at all)
Join Date: Nov 2005
Location: UK
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
I’m sure that the engineers at Airbus Helicopters are reviewing every post and trying their best to understand how Dave might have misread the gauges and/or warning lights and run out of fuel.
At least one poster mentioned that the training for engine failures in twin-engine helicopters is based on only one engine failing, not both in succession or simultaneously. An interesting thought. Could it be that because simultaneous engine failures supposedly cannot happen, that pilots are not trained for that possibility?
The continuous stream of bull**** on this thread continues to astound me...
Bladecrack, when it comes to BS, you can bet your bottom dollar you'll get it in bucketfulls where PG is involved.......
PG: that thread you posted..stating the Bleeding Obvious - what on earth are you rabbitting on about?
PG: that thread you posted..stating the Bleeding Obvious - what on earth are you rabbitting on about?
Bladecrack, thanks for the insight on training.
Pete: the question of how the aircraft ended up with the rotors not turning before it made contact with pub roof was raised early in this discussion -- pages and pages ago. It was triggered by initial info from AAIB.
That factor eventually evolved into the split to that stand alone autorotation thread during which you introduced yourself to the membership at PPRuNe.
We need not ressurrect that, it's already in the thread.
A provisional conclusion that the pilot (RIP, Dave) was surprised by both engines failing is probably valid. With the extensive explanation of EC-135 fuel system features provided by some folks here, it seems that one would expect fuel starvation to hit one engine before the other: failure in serial, not on parallel.
If in this case that didn't happen, and both dropped off at the same time, the surprise factor / startle factor seems almost certain.
Pete: the question of how the aircraft ended up with the rotors not turning before it made contact with pub roof was raised early in this discussion -- pages and pages ago. It was triggered by initial info from AAIB.
That factor eventually evolved into the split to that stand alone autorotation thread during which you introduced yourself to the membership at PPRuNe.
We need not ressurrect that, it's already in the thread.
A provisional conclusion that the pilot (RIP, Dave) was surprised by both engines failing is probably valid. With the extensive explanation of EC-135 fuel system features provided by some folks here, it seems that one would expect fuel starvation to hit one engine before the other: failure in serial, not on parallel.
If in this case that didn't happen, and both dropped off at the same time, the surprise factor / startle factor seems almost certain.
Join Date: Nov 2005
Location: UK
Posts: 281
Likes: 0
Received 0 Likes
on
0 Posts
A provisional conclusion that the pilot (RIP, Dave) was surprised by both engines failing is probably valid. With the extensive explanation of EC-135 fuel system features provided by some folks here, it seems that one would expect fuel starvation to hit one engine before the other: failure in serial, not on parallel.
If in this case that didn't happen, and both dropped off at the same time, the surprise factor / startle factor seems almost certain.
If in this case that didn't happen, and both dropped off at the same time, the surprise factor / startle factor seems almost certain.
BC
AAIB doesn't have that luxury, so they have their work cut out for them.
Join Date: Jul 2000
Location: Nova
Posts: 1,242
Likes: 0
Received 0 Likes
on
0 Posts
Lonewolf - that is one possibility, but I wouldn't rule out the possibility that the engines were intentionally shut down, but if so the reasons why remain a mystery.
ALERT Speculation obviously!!! ALERT
TR:
I remember some of the "single up to save gas" advocates. I'd be surprised if that is a common meme in commercial twin operations, as it probably would not pass the smell test for an SOP or Chief Pilot review. I always figured "if I've got two, I want two running!"
Digression.
Sea Story.
Avoid if not interested.
There was a tragic crash that got a change to our Squadron SOP when a bird on the other coast did just that ... ending in tears. This was over 30 years ago.
H-2 on a flight in California, from San Diego to points North (IIRC Alameda, but memory does not serve). Crew had chosen to single up (fly with one T-58 engine secured) once they got to altitude to extend range and fuel reserve. Long story short, trouble with the engine they were using got their attention, unable to restart enigne, the engine running didn't get beter, and it all didn't end well.
In discussions after that accident in our squadron (other coast) some interesting "lore" cropped up that had apparenlty been passed down by word of mouth from some of the old hands. This came down from as far back as when the H-2 (A/B) was a single engined helicopter. (The C/D and F were twins).
Turns out that a lot of the old salts had, particularly whilst deployed at sea, not infrequently singled up to save fuel on some long missions to extend their fuel margin. (I'd been taught that this was only done in an emergency if you ended up at rendezvous when the ship wasn't there. )
"Works fine on one engine at both max range and max conserve airspeed." True, it did. But ... te mishap investigation brought to light a tendency for (memory shady) oil to pool in the engine not running in such a case, due to windmilling and various bits inside the engine turning as a result. The investigaiton attributed that to most likely fouling igniter plugs/ingnition sequence when trying to restart.) But the killer was the one guy whose senior HAC, on a prevoius tour, had singled up (he never trusted the ship drivers to be where they said they'd be) on most missions. Per his recounting, they had done two separate single engine landings back on the ship when they'd not gotten a restart!
But they kept that story at sea ...
... so as to avoid trouble "back home." 
Our CO decided that "the taxpayers bought you guys two engines, you will use them unless and until they quit" and clearly stated that in the revised SOP.
He was a bit perturbed that he'd had to spell it out in writing, as he figured it was common sense. In this case, I guess he had to legislate common sense.
I remember some of the "single up to save gas" advocates. I'd be surprised if that is a common meme in commercial twin operations, as it probably would not pass the smell test for an SOP or Chief Pilot review. I always figured "if I've got two, I want two running!"
Digression.
Sea Story.
Avoid if not interested.
There was a tragic crash that got a change to our Squadron SOP when a bird on the other coast did just that ... ending in tears. This was over 30 years ago.
H-2 on a flight in California, from San Diego to points North (IIRC Alameda, but memory does not serve). Crew had chosen to single up (fly with one T-58 engine secured) once they got to altitude to extend range and fuel reserve. Long story short, trouble with the engine they were using got their attention, unable to restart enigne, the engine running didn't get beter, and it all didn't end well.
In discussions after that accident in our squadron (other coast) some interesting "lore" cropped up that had apparenlty been passed down by word of mouth from some of the old hands. This came down from as far back as when the H-2 (A/B) was a single engined helicopter. (The C/D and F were twins).
Turns out that a lot of the old salts had, particularly whilst deployed at sea, not infrequently singled up to save fuel on some long missions to extend their fuel margin. (I'd been taught that this was only done in an emergency if you ended up at rendezvous when the ship wasn't there. )
"Works fine on one engine at both max range and max conserve airspeed." True, it did. But ... te mishap investigation brought to light a tendency for (memory shady) oil to pool in the engine not running in such a case, due to windmilling and various bits inside the engine turning as a result. The investigaiton attributed that to most likely fouling igniter plugs/ingnition sequence when trying to restart.) But the killer was the one guy whose senior HAC, on a prevoius tour, had singled up (he never trusted the ship drivers to be where they said they'd be) on most missions. Per his recounting, they had done two separate single engine landings back on the ship when they'd not gotten a restart!
But they kept that story at sea ...
... so as to avoid trouble "back home." Our CO decided that "the taxpayers bought you guys two engines, you will use them unless and until they quit" and clearly stated that in the revised SOP.
He was a bit perturbed that he'd had to spell it out in writing, as he figured it was common sense. In this case, I guess he had to legislate common sense.
Avoid imitations
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,573
Received 419 Likes
on
221 Posts
With regard to a possible reason for the engines not providing power, other than the fuel issue. The preliminary report didn't say whether the evidence showed if the fenestron was working or not. There still has been no solution of the eye witness report that the aircraft was "tumbling".
Join Date: Dec 2007
Location: Pasadena
Posts: 633
Likes: 0
Received 0 Likes
on
0 Posts
Tumbling?
If the rotors were stopped early on in the sequence of events, then there's nothing much to stop the helicopter tumbling in response to the last manoeuvre and aerodynamic forces, as the constraints on its motion from the reservoir of rotor angular momentum has been removed. Helicopters tend to have lower moments of inertia than fixed wing aircraft, so could more easily tumble. If it was in fact tumbling, rather than just being seen spiraling in projection, then it argues for a rapid, high loss of rotor speed.
Join Date: Feb 2001
Location: Europe
Posts: 535
Likes: 0
Received 0 Likes
on
0 Posts
Does anyone actually know of any double engine failures - within say 30 seconds of each other - in twin engined helicopters? Perhaps in early C30 S76 days, pre-containment mods? And if so, was autorotation established successfully? Just wondering how likely it was for an experienced pilot like Dave not to dump the lever - should this have occurred. Another point; on modern IFR twins, with so many warning and cautions, visual and audio, could a delay identifying exactly what the alarms meant have cost critical time before lack of power to the rotors was identified and the lever dumped? Don't fly EC135s, but is the NR displayed digitally or graphically? Have to say a needle on a dial is much easier to read crudely than a digital number display.
Avoid imitations
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,573
Received 419 Likes
on
221 Posts
Awblain, Yes, but the aircraft still has a tail fin and horizontal stabiliser, which I would imagine would tend to oppose the tumbling motion the witness described, if the engines were already shut down at altitude. However, I'm certain no-one has done any research on this, for obvious reasons... so who knows?
IF the fenestron suddenly stopped doing it's job at low forward speed (and I'm certainly not saying it did but the fenestron duct seemed to have a lot of damage in the photos shown in the media), the effect would be sudden, rapid and increasing yaw rate.
The recognised "generic" method of dealing with this is to reduce torque and fly away so the fin can have more of an aerodynamic effect (dosen't work so well on some types). If this for some reason has insufficient effect, the only way to regain control is to attempt to get into autorotation. In extremis, the engines might have to be shut down completely.
If a very rapid yaw rate occurs, the result might well be divergences in roll and pitch too. Centripetal forces might mean that even with fuel in the tanks it may no longer reach the pickup pipes and the engines might flame out of their own accord.
But all this is supposition because detailed reports are yet to come. Hopefully remaining evidence in the wreckage will provide more answers.
IF the fenestron suddenly stopped doing it's job at low forward speed (and I'm certainly not saying it did but the fenestron duct seemed to have a lot of damage in the photos shown in the media), the effect would be sudden, rapid and increasing yaw rate.
The recognised "generic" method of dealing with this is to reduce torque and fly away so the fin can have more of an aerodynamic effect (dosen't work so well on some types). If this for some reason has insufficient effect, the only way to regain control is to attempt to get into autorotation. In extremis, the engines might have to be shut down completely.
If a very rapid yaw rate occurs, the result might well be divergences in roll and pitch too. Centripetal forces might mean that even with fuel in the tanks it may no longer reach the pickup pipes and the engines might flame out of their own accord.
But all this is supposition because detailed reports are yet to come. Hopefully remaining evidence in the wreckage will provide more answers.
The recognised "generic" method of dealing with this is to reduce torque and fly away so the fin can have more of an aerodynamic effect (dosen't work so well on some types). If this for some reason has insufficient effect, the only way to regain control is to attempt to get into autorotation. In extremis, the engines might have to be shut down completely.
Join Date: Dec 2007
Location: Pasadena
Posts: 633
Likes: 0
Received 0 Likes
on
0 Posts
Tail fin vs stopped blades
It does have a tail fin... but without any rotor speed, it also has four equally-long, flexible, stationary, carbon fibre projections on top, that will probably starkly modify its aerodynamics, especially since soon it probably wasn't going very quickly or at a conventional attitude.
The intermediate moment-of-inertia axis is probably pitch (with roll less, and yaw more), which would be naturally associated with "tumbling" to start if the accident process began with a pitching motion.
The eyewitness effect is also to be considered - is a "tumble" actually a corkscrew, or rotation in yaw? If the rotors were moving, then yaw is the only axis in which rapid motion is possible, and the large angular momentum vector should make it resistant to exciting motion in the other axes.
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".
If there was a data recorder or any video, then the speculation could be set aside, but it seems that no photographers have come forward. Even data from an accelerometer or magnetometer on a phone onboard might perhaps be useful.
The intermediate moment-of-inertia axis is probably pitch (with roll less, and yaw more), which would be naturally associated with "tumbling" to start if the accident process began with a pitching motion.
The eyewitness effect is also to be considered - is a "tumble" actually a corkscrew, or rotation in yaw? If the rotors were moving, then yaw is the only axis in which rapid motion is possible, and the large angular momentum vector should make it resistant to exciting motion in the other axes.
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".
If there was a data recorder or any video, then the speculation could be set aside, but it seems that no photographers have come forward. Even data from an accelerometer or magnetometer on a phone onboard might perhaps be useful.
Avoid imitations
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,573
Received 419 Likes
on
221 Posts
Lonewolf50,
Yes, it's obviously type specific to some extent, I was just trying to explain the general principle for those unfamiliar. In one type I flew, with not so many tail feathers, the only guaranteed "recovery" was enter autorotation asap and chop the engines, there was no real chance of flying away in powered flight.
Perhaps "generic" was the wrong term to use.
Yes, it's obviously type specific to some extent, I was just trying to explain the general principle for those unfamiliar. In one type I flew, with not so many tail feathers, the only guaranteed "recovery" was enter autorotation asap and chop the engines, there was no real chance of flying away in powered flight.
Perhaps "generic" was the wrong term to use.
Yes, it's obviously type specific to some extent, I was just trying to explain the general principle for those unfamiliar. In one type I flew, with not so many tail feathers, the only guaranteed "recovery" was enter autorotation asap and chop the engines, there was no real chance of flying away in powered flight.
Avoid imitations
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,573
Received 419 Likes
on
221 Posts
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".
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).
Join Date: Dec 2007
Location: Pasadena
Posts: 633
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Jul 2000
Location: Nova
Posts: 1,242
Likes: 0
Received 0 Likes
on
0 Posts
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!
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.
Avoid imitations
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,573
Received 419 Likes
on
221 Posts
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.
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.