Police helicopter crashes onto Glasgow pub
TC, makes sense, given the higher operating rpm. Thanks. (But if you unload the tail (by going flat pitch as can be) while the main is at higher pitch ... you still run in to V^2 and its inverse, I suppose.
TC, the other time the head/rotor blades can stall is at high speed, retreating blade stall, but the fix for that is usually a reduction in pitch and speed if one remains in control ... and so really doesn't fit this event.
As to VRS, that is usualy a power on condition, which again seems not to fit this event.
Question we may never be able to answer: what was the helo and the crew doing in the sixty seconds before it all began to go wrong?
TC, the other time the head/rotor blades can stall is at high speed, retreating blade stall, but the fix for that is usually a reduction in pitch and speed if one remains in control ... and so really doesn't fit this event.
As to VRS, that is usualy a power on condition, which again seems not to fit this event.
Question we may never be able to answer: what was the helo and the crew doing in the sixty seconds before it all began to go wrong?
A 5% reduction in main rotor thrust will cause about a 20% reduction in TR thrust.
it doesnt have the same inertia as the head
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Having spent some time hovering over large built up areas at night I do not believe that surface definition is that difficult from the air. There is usually sufficient environmental lighting for the buildings to stand out and ground features easily recognised. This building had lighting all around and would have been easily identified from the air.
The AAIB report states the aircraft struck the building with the blades not rotating. It cannot therefore have arrived "in flight". In addition, loss of hydraulic power at the bottom of the NR range would have simply compounded the pilots attempts at controlled flight.
This was a "crash" in the traditional sense. Arriving at an undetermined point with no control at all. Sadly!!
The AAIB report, as I read, infers the Fenestron was still able to be turned by the No 2 engine FPT accepting however that the Fenestron detached during the crash sequence. I think this rules out Fenestron related theories!!
DB
The AAIB report states the aircraft struck the building with the blades not rotating. It cannot therefore have arrived "in flight". In addition, loss of hydraulic power at the bottom of the NR range would have simply compounded the pilots attempts at controlled flight.
This was a "crash" in the traditional sense. Arriving at an undetermined point with no control at all. Sadly!!
The AAIB report, as I read, infers the Fenestron was still able to be turned by the No 2 engine FPT accepting however that the Fenestron detached during the crash sequence. I think this rules out Fenestron related theories!!
DB
On a different line of enquiry, perhaps someone might confirm the a/c heading was roughly north at impact?
The AAIB says they'd come in from the direction of Bargeddie, i.e., on a track of roughly 280, which would pass close to the accident site en-route GCH. I presume that's one of the standard routings inbound?
If the impact heading reflects any forward movement during the final descent, that would represent a considerable right turn at some point. If it was an autorotation descent on a northerly track, the south-west corner of the much taller building on their right would have been in very close proximity. Could that have affected the Rad-Alt, as someone was speculating earlier? The RA must have some cone of search, which is likely to be fixed in relation to the a/c structure. It would be relevant to know how wide that cone is, and if it is biassed forwards.
The sudden appearance of that massive roof on the right-hand side might in itself have cued a premature (with 20/20 hindsight) flare from an autorotation.
The AAIB states:
Preliminary examination showed that all main rotor blades were attached at the time of the impact but that neither the main rotor nor the fenestron tail rotor were rotating
As far as I can remember, any suggestion that the main rotor was stationary during the descent originated only from witness(es). I infer no hard evidence that the a/c fell from (say) 500 ft with a stationary main-rotor (stalled or otherwise), unless and until the investigators' assessment of VS at impact indicates it. If that should prove to be the case, however, I accept that the heading at impact would be random.
PS
Lonewolf_50,
I think the less this accident has in common with AF447 the better, particularly any HF aspects...
The AAIB says they'd come in from the direction of Bargeddie, i.e., on a track of roughly 280, which would pass close to the accident site en-route GCH. I presume that's one of the standard routings inbound?
If the impact heading reflects any forward movement during the final descent, that would represent a considerable right turn at some point. If it was an autorotation descent on a northerly track, the south-west corner of the much taller building on their right would have been in very close proximity. Could that have affected the Rad-Alt, as someone was speculating earlier? The RA must have some cone of search, which is likely to be fixed in relation to the a/c structure. It would be relevant to know how wide that cone is, and if it is biassed forwards.
The sudden appearance of that massive roof on the right-hand side might in itself have cued a premature (with 20/20 hindsight) flare from an autorotation.
The AAIB states:
Preliminary examination showed that all main rotor blades were attached at the time of the impact but that neither the main rotor nor the fenestron tail rotor were rotating
As far as I can remember, any suggestion that the main rotor was stationary during the descent originated only from witness(es). I infer no hard evidence that the a/c fell from (say) 500 ft with a stationary main-rotor (stalled or otherwise), unless and until the investigators' assessment of VS at impact indicates it. If that should prove to be the case, however, I accept that the heading at impact would be random.
PS
Lonewolf_50,
I think the less this accident has in common with AF447 the better, particularly any HF aspects...
Last edited by Chris Scott; 11th Dec 2013 at 17:47. Reason: PS added.
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Arriving flying & rotor/fenestron speeds?
Re Double Bogey: the helicopter arrived on the pub roof without any rotor speed, according to the AAIB. I don't think that necessarily implies that it arrived 20 feet above the pub roof without any rotor speed. The violence of the impact will surely eventually be measured securely from analyzing the deformation to the wreckage, the radar trace and any CCTV/sound recordings that might surface.
Re 212man: My understanding is that the speeds of the rotor and fenestron are locked together, but that they have fully independent pitch controls and approximately orthogonal incident airflow. As such, I would expect that one, neither or both could be stalled (or thrusting) provided that they are turning at a reasonable speed. I'm not sure that anything about the mechanical state of the wreckage is currently valuable apart from the statement that everything appears to have been found intact and moveable.
Re 212man: My understanding is that the speeds of the rotor and fenestron are locked together, but that they have fully independent pitch controls and approximately orthogonal incident airflow. As such, I would expect that one, neither or both could be stalled (or thrusting) provided that they are turning at a reasonable speed. I'm not sure that anything about the mechanical state of the wreckage is currently valuable apart from the statement that everything appears to have been found intact and moveable.
Purveyor of Egg Liqueur to Lucifer
Dab
The AAIB report, as I read, infers the Fenestron was still able to be turned by the No 2 engine FPT accepting however that the Fenestron detached during the crash sequence. I think this rules out Fenestron related theories!!
The AAIB report, as I read, infers the Fenestron was still able to be turned by the No 2 engine FPT accepting however that the Fenestron detached during the crash sequence. I think this rules out Fenestron related theories!!
You may have read it that way, but what the report says is;
"Initial assessment provided no evidence of major mechanical disruption of either engine and indicated that the main rotor gearbox was capable of providing drive from the No 2 engine power turbine to the main rotor and to the fenestron drive shaft."
Which means that drive was capable as far as the trds. Therefore everything rearward of and including the flexi coupling connecting the TRDS to the MRGB is still in play as possibly contributing to the incident.
Purveyor of Egg Liqueur to Lucifer
There is of course one obvious reason why the blades may have been stationary while airborne.
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Direction of travel
Chris,
Yes basically the aircraft was heading west following the clyde, clyde heliport is on the banks west of the crash site. It would need to clear the Kingston bridge (m8 motorway) further west, it has 18metres clearance for shipping and on top, 12 metre lighting columns, to give an idea of how high the machine should have been (I assume you fliers have minimum vertical clearances)The Kingston bridge is about 1 mile west of the crash site, with roughly another mile further to the heliport
When it crashed it was facing directly North, so it somehow turned right during the incident.
And as the following keeps coming up, may I impart local knowledge:
1) you can't ditch in the clyde at this point, there are 4 bridges in close proximity, Presenting very small landing areas between, especially for the descriptions of the auto rotation glides (I'm not an aviator)
2) there is no way this was selected as a landing site, the whole area is very well lit, and this roof is below the lanterns, so its illuminated, also there is a huge wall north and east, again, floodlit, you wouldn't choose to glide in here.
3) they had just flown over glasgow green, a huge flat park with big open spaces, about 200 yards east of the crash site, 100 yards north was an empty, illuminated huge car park, I'm pretty sure this roof was not an intended landing site. So as I see it, the accident happened within about 200 yards of forward travel, if some thing serious had occurred 200 yards prior, it would have landed on the green
Any geography or local construction questions I am happy to answer.
Yes basically the aircraft was heading west following the clyde, clyde heliport is on the banks west of the crash site. It would need to clear the Kingston bridge (m8 motorway) further west, it has 18metres clearance for shipping and on top, 12 metre lighting columns, to give an idea of how high the machine should have been (I assume you fliers have minimum vertical clearances)The Kingston bridge is about 1 mile west of the crash site, with roughly another mile further to the heliport
When it crashed it was facing directly North, so it somehow turned right during the incident.
And as the following keeps coming up, may I impart local knowledge:
1) you can't ditch in the clyde at this point, there are 4 bridges in close proximity, Presenting very small landing areas between, especially for the descriptions of the auto rotation glides (I'm not an aviator)
2) there is no way this was selected as a landing site, the whole area is very well lit, and this roof is below the lanterns, so its illuminated, also there is a huge wall north and east, again, floodlit, you wouldn't choose to glide in here.
3) they had just flown over glasgow green, a huge flat park with big open spaces, about 200 yards east of the crash site, 100 yards north was an empty, illuminated huge car park, I'm pretty sure this roof was not an intended landing site. So as I see it, the accident happened within about 200 yards of forward travel, if some thing serious had occurred 200 yards prior, it would have landed on the green
Any geography or local construction questions I am happy to answer.
Last edited by CJ Romeo; 11th Dec 2013 at 18:23. Reason: Typos!
Edit: After re-reading I'm afraid I misunderstood your point. The T/R itself follows a square rule but not any different than the main rotor. I misinterpreted this as that behaviour between main and tail followed a square rule. So you can ignore my comment/question
/Edit
It is driven with a fixed gear ratio (something along 1/8) against the main rotor.
Main rotor operating at 80% so will be the T/R. Both will then only create 64% of the respective Lift at 100% if nothing else changes.
@Thomas Coupling: I'm really curious as to why a 5% drop in M/R RPM leads to 20% loss at the back?
Did you get any explanation from the AW guys?
Lift normally follows (Rho/2)*Cl*A*v^2.
Since nothing else changes between front and rear this would require a change of Cl by Factor 4 (e.g. from 1.2 which would be rather high and occur at an AoA 8-10° to 0.3 which would occur at an AoA of ~2-3°). I don't want to say that is impossible but it is at least a bit strange.
The blocking effects of the Fenestron shrouding should rather decrease with reduced volume flow which also contributes to my surprise about these values.
CJ Romeo,
Thanks for all that local info. The sequence of events seems to have been complex, as well as rapid, and the lack of flight data all the more unfortunate. Hope the FADECs will have retained some snippet of evidence - whether positive or negative - despite the impact. And then there's the local CCTV...
Thanks for all that local info. The sequence of events seems to have been complex, as well as rapid, and the lack of flight data all the more unfortunate. Hope the FADECs will have retained some snippet of evidence - whether positive or negative - despite the impact. And then there's the local CCTV...
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Thank you electric john.
I know Glasgow very poorly but the car park to the east does look a lot larger. The lack of a mayday call is instructive in itself as the pilot probably had so much workload that he could not send a message. The posts indicating that police helicopters are single piloted is very interesting indeed. Its hypothetical what difference a co-pilot would have made to the situation.
I know Glasgow very poorly but the car park to the east does look a lot larger. The lack of a mayday call is instructive in itself as the pilot probably had so much workload that he could not send a message. The posts indicating that police helicopters are single piloted is very interesting indeed. Its hypothetical what difference a co-pilot would have made to the situation.
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I may have got the wrong end of the stick.
When the fuel is low, say 95l as drained, does the pilot have to manage the filling of the supply tanks by switching between the forward and aft transfer pumps in the main tank manually (depending on attitude)? Thanks.
When the fuel is low, say 95l as drained, does the pilot have to manage the filling of the supply tanks by switching between the forward and aft transfer pumps in the main tank manually (depending on attitude)? Thanks.
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@RVDT
This is what we´ve talked about ... although we have 92 kg supply tanks capacity (S/N late 600), indication is always 44kg and 40kg...
I found this note in Training manual:
*4 kg can not be displayed, bacause for crash safety the fuel sensors must not contact the fuel cell ceiling
Or this, in RFM, about Supply tanks I and II:
*values depending on the type of fuel tank
JR
Last edited by Jet Ranger; 11th Dec 2013 at 19:35.
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Normally when within and transitting the Glasgow Zone GLA ATC give you a Squawk (26**) Mode 'C', I'm assuming that the GLA radar situated on the airport would have the track/altitude until it went below the line of sight for that radar?
P.S. An SBS user in Paisley adjacent the airport last noted the helicopter at 725ft.
P.S. An SBS user in Paisley adjacent the airport last noted the helicopter at 725ft.
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Another fenestron question
Sorry to harp on about the fenestron, but so far it hasn't been eliminated as a cause. Does anyone know which version of fenestron is fitted? Is it like in the older Bundeswehr EC135 with a hydraulic assist located within the fenestron hub, or is it the more clever lighter low-force version described in USP5542818, please?
The difference would affect any analysis of failure modes.
Many thanks,
henry_crun
The difference would affect any analysis of failure modes.
Many thanks,
henry_crun
Don't know the EC-135, so I'll ask.
At what rotor rpm, or at what % rotor rpm, would you expect to get a "low rotor rpm" caution or warning light while in flight?
At what rotor rpm, or at what % rotor rpm, would you expect to get a "low rotor rpm" caution or warning light while in flight?