Police helicopter crashes onto Glasgow pub
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Witness A
AAIB said "Radar contact with the helicopter was lost at 2222 hrs.
Around this time, the helicopter was seen and heard
by a witness who described hearing a noise like a loud
“misfiring car”, followed by silence. He then saw the
helicopter descend rapidly."
This looks key. AAIB have had a week to interview numerous witnesses. They chose to quote only one in the entire report, perhaps because of the high confidence in that witness or because he was representative of the collective witness statements.
Sound: Notice the abrupt transition from "misfiring car" to "silence"
Visual: "He then saw the helicopter descend rapidly". He heard it before he saw it, in fact he may not even have seen it before the descent. How clearly could he see it in the dark at all, lit by just normal navigation lights? No one has mentioned a searchlight at anytime.
So what event creates a sound like a misfiring car, then silence then instant vertical descent with no auto-rotation and rotors arrested so quickly that there is no residual rotation just a few seconds later on impact? The answer lies therein.
Around this time, the helicopter was seen and heard
by a witness who described hearing a noise like a loud
“misfiring car”, followed by silence. He then saw the
helicopter descend rapidly."
This looks key. AAIB have had a week to interview numerous witnesses. They chose to quote only one in the entire report, perhaps because of the high confidence in that witness or because he was representative of the collective witness statements.
Sound: Notice the abrupt transition from "misfiring car" to "silence"
Visual: "He then saw the helicopter descend rapidly". He heard it before he saw it, in fact he may not even have seen it before the descent. How clearly could he see it in the dark at all, lit by just normal navigation lights? No one has mentioned a searchlight at anytime.
So what event creates a sound like a misfiring car, then silence then instant vertical descent with no auto-rotation and rotors arrested so quickly that there is no residual rotation just a few seconds later on impact? The answer lies therein.
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...at the time of the impact but that neither the main rotor nor the fenestron tail rotor were rotating.
....the helicopter struck the flat roof of the single story building with a high rate of
descent and low/negligible forward speed.
descent and low/negligible forward speed.
If the rotor is not rotating there is no gyroscopic stability. No/negligible (forward) velocity, the report says. Wind was a few knots. If still in the air, the a/c would topple. Now suppose that before impact the rotor was rotating very slowly. A slowly moving rotor blade would probably the first contact with a hard object which would bounce off, make a heck of a din, gather speed and the a/c could topple 'end over end' across hard objects making a tortured noise like a massive lawn scarifier over a stone path. I wonder if they need to widen the search a little for another point of first impact where a blade hit?
Avoid imitations
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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 wrote the word in italics for a reason. For example, the drive and fenestron may remain working, but control of the blade pitch might not.
A few questions for those suitably qualified on type: What form does the EC135's tail rotor pitch control mechanism take (as in from yaw pedal to the fenestron itself? Is it cable, more than one cable, a push/pull rod, hydraulic or a combination of one or more? Is maximum positive pitch runaway practiced in the EC135 simulator?
More is known about generic helicopter tail rotor drive shaft failures than is known about tail rotor control failures. In-flight diagnosis may be very difficult in the face of confusing and rapidly divergent aircraft behaviour. Simulators may not realistically replicate actual aircraft behaviour, btw, it's known as "off model", where the simulator response is a mere "best guess".
Purveyor of Egg Liqueur to Lucifer
yellowbird135
Sure, why not, must have been a wild guess....previous posters have been trying to explain how tedious and thorough the people from AAIB are....and then you come up with this???
Mind you, the report said that "approximately 95 litres of fuel were drained from the fuel tank", which doesn't necessarily mean that they drained it until it was empty, perhaps that's as much as their container could hold.
By the way, considering the 135 has 3 fuel tanks …. !
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Freewheel Disengagement?
Just one to throw into the ring for discussion as the idea of the rotors coming to a stop has me thinking more on the transmission. Loss of fuel, he could auto rotate although at the height he was at i believe it would not be achievable. I vaguely remember an incident on the Lynx freewheel actuator that caused loss of drive but if memory serves this would result in a twist on the intermediate drive shafts of which at first pass isn't shown on the pictures ? Thoughts…
Helicopter Crashes Caused by Freewheel Disengagements
Helicopter Crashes Caused by Freewheel Disengagements
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Some pages ago someone summed up different scenarios, and at the end added "Sabotage, or another cause starting with an S".
I didn't understand what that could stand for, but I certainly got a chill after reading the AAIB press release today...
I didn't understand what that could stand for, but I certainly got a chill after reading the AAIB press release today...
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Perhaps the pilot lost all cockpit indicators through some serious electrical fault and had assumed last known state or single engine ops and was initially unaware that he had actually lost both engines.
Funnily enough, this exact time last week my car battery literally exploded causing the instrument cluster to flicker into reset mode continually. It turned out to be the voltage regulator had failed on the alternator which pumped high voltage in the sealed battery causing the electrolyte to boil and divest its pent up pressure in a mater of minutes spraying acid all over nearby components.
Obviously helicopter's electrical systems with their extra complexity are built to significantly higher standards, but by being so close to returning to base after a few hours out perhaps made the occurrence of a double engine failure even harder to believe before it was too late.
I flew a JetBanger with a weak battery (started with external power) when the generator failed in flight. Lost radios, fuel pressure and even the enunciator (PTT did nothing). First indication was a slight twitch in the tail, also observed on the Tq dial (about 1%), which was caused by the two electric fuel pumps on their way out. Maneuvering limits were observed for a safe RTB.
Funnily enough, this exact time last week my car battery literally exploded causing the instrument cluster to flicker into reset mode continually. It turned out to be the voltage regulator had failed on the alternator which pumped high voltage in the sealed battery causing the electrolyte to boil and divest its pent up pressure in a mater of minutes spraying acid all over nearby components.
Obviously helicopter's electrical systems with their extra complexity are built to significantly higher standards, but by being so close to returning to base after a few hours out perhaps made the occurrence of a double engine failure even harder to believe before it was too late.
I flew a JetBanger with a weak battery (started with external power) when the generator failed in flight. Lost radios, fuel pressure and even the enunciator (PTT did nothing). First indication was a slight twitch in the tail, also observed on the Tq dial (about 1%), which was caused by the two electric fuel pumps on their way out. Maneuvering limits were observed for a safe RTB.
Last edited by cattletruck; 10th Dec 2013 at 04:57. Reason: tidy
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Still Possible Fuel Starvation
In reference to the fuel system diagram in post #1026.......
If BOTH transfer pumps failed would that not leave about 95 liters of Unusable fuel in the lower Main fuel Cell??
Therfore... NO Fuel in the two aft SUPPLY fuel cells!
If BOTH transfer pumps failed would that not leave about 95 liters of Unusable fuel in the lower Main fuel Cell??
Therfore... NO Fuel in the two aft SUPPLY fuel cells!
Last edited by earth2mars; 10th Dec 2013 at 01:26. Reason: add
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reading this thread one idea that i have not seen is the idea of complete electrical system failure.
No Batt, No gens, no power at all.
Would not explain why none of the "witnesses" seen any lights and would it also explain the engines sputtering as there is no fuel being pumped in to the engines?
I'm not a Roterhead, just a fixed wing pilot.
Could that be the case?
No Batt, No gens, no power at all.
Would not explain why none of the "witnesses" seen any lights and would it also explain the engines sputtering as there is no fuel being pumped in to the engines?
I'm not a Roterhead, just a fixed wing pilot.
Could that be the case?
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AAIB preliminary report indicated no mechanical failure in engines or drivetrain and fuel still in system. No fleet grounding or mandated inspections either immediately or after preliminary inspection. My belief is that AAIB have a pretty clear understanding of the sequence of events and my money, sadly, is on human 'factors' being key.
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I may be the only remaining member of this forum who hasn't had a go yet, so here is my question.
In a prior life flying EMS in the BK117, a not too dissimilar aircraft, at about 1.5 NM from the pad at night I would be starting to slow things down, so I would not be in cruise. In an earlier post there was mention of arming floats, my question is if the approach was over water (river) to the pad and arming floats for that landing was SOP, what is close to the Floats Arm Switch on the panel/collective?
Obviously, if floats not required, this post is like many others and a waste of electrons.
In a prior life flying EMS in the BK117, a not too dissimilar aircraft, at about 1.5 NM from the pad at night I would be starting to slow things down, so I would not be in cruise. In an earlier post there was mention of arming floats, my question is if the approach was over water (river) to the pad and arming floats for that landing was SOP, what is close to the Floats Arm Switch on the panel/collective?
Obviously, if floats not required, this post is like many others and a waste of electrons.
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Still Possible Fuel Starvation
In reference to the fuel system diagram in post #1026.......
If BOTH transfer pumps failed would that not leave about 95 liters of Unusable fuel in the lower Main fuel Cell??
Therfore... NO Fuel in the two aft SUPPLY fuel cells!
In reference to the fuel system diagram in post #1026.......
If BOTH transfer pumps failed would that not leave about 95 liters of Unusable fuel in the lower Main fuel Cell??
Therfore... NO Fuel in the two aft SUPPLY fuel cells!
Not possible! SUPPLY tanks are always full (44 kg and 40 kg) and do not need XFER pumps to supply the engines ("the engine driven fuel pumps alone provides enough suction capacity to draw fuel from supply tank via supply lines...")
Sometimes you land with 4kg in MAIN tank (or 0 kg ... and F.XFER pump CAD caution light ON) with 40 kg in one and 36 kg in another supply tank. If the average fuel flow is 3-3.5 kg/min, it´s enough fuel for 21-25 min...and FUEL LOW is still not ON.
When FUEL LOW warning light is ON, you have to land in 10 minutes.
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Return to the question of "tumbling"
If the rotor was stopped, then there's no gyroscopic stabilization, and it would be possible for the aircraft to have been "tumbling" as witnesses suggested.
While eyewitnesses are not necessarily able to assess or report the true motion in 3D, the helicopter "tumbling" is not ruled out as it would be by the presence of angular momentum with the rotors turning.
Turning at 20 radians/s the 200kg 10-m-diameter rotor has an angular momentum of order 100,000 kg m^2 s^-1, requiring a huge torque of order a million Newton-metres to make it turn end-over-end at a radian per second.
With the rotor stopped, the whole helicopter has a moment of inertia of only a few 1000 kg m^2, turning quickly in any axis when a torque of only ~10,000 Newton-meters was applied.
While eyewitnesses are not necessarily able to assess or report the true motion in 3D, the helicopter "tumbling" is not ruled out as it would be by the presence of angular momentum with the rotors turning.
Turning at 20 radians/s the 200kg 10-m-diameter rotor has an angular momentum of order 100,000 kg m^2 s^-1, requiring a huge torque of order a million Newton-metres to make it turn end-over-end at a radian per second.
With the rotor stopped, the whole helicopter has a moment of inertia of only a few 1000 kg m^2, turning quickly in any axis when a torque of only ~10,000 Newton-meters was applied.
Not possible! SUPPLY tanks are always full (44 kg and 40 kg) and do not need XFER pumps to supply the engines
The Original Whirly
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Thomas Coupling wrote:
I'm far from an expert on the 135, but this sounds plausible to me. Or, at any rate, something along these lines - ie, something goes wrong, tired pilot makes mistake, then he tries to sort it out but too late. In other words, it's beginning to look as though this tragic accident was due to a combination of unexpected malfunction combined with human error.
I realise this probably leaves us with an almost infinite number of possible scenarios, limited only by our collective knowledge of helicopter aerodynamics and human factors. Well, we have several months....
The pilot is coming to the end of his task having spent some considerable time doing the same old, same old. I recall getting bored/tired towards the end of some monotonous sorties and my mind wandering.
At some challenging stage in his flight he experienced a potentially benign run down or torque fluctuation caused by one of the ECU's stalling/surging (as witnessed by outsiders). "Normally" one determines the duff engine by comparing Nr movement with the suspect engine Ng. The duff engine drives the Nr out of its governed range thus enabling the pilot to select the correct engine for shut down. Perhaps this time the wrong engine was shut down whilst tired/confused. This left the duff engine driving the Nr and if that engine was providing less than nominal output the Nr will droop or even worse. He may have instinctively raised the collective to maintain his cruise height anyway (or tried to stop his increasing descent) and the Nr would continue to decay - ever closer towards its point of no return (what is it in the 135? 82%?). He sees this and tries in vain to salvage the decaying Nr by chopping the remaining engine and lowering the collective but too late, he sees the looming deck and pulls for all its worth to salvage some of the RoD. By then there is very little Nr left, but what is left is washed out by that final application of lever. RoD continues unchecked and the cab hits hard with no engines or little minimal Nr.
At some challenging stage in his flight he experienced a potentially benign run down or torque fluctuation caused by one of the ECU's stalling/surging (as witnessed by outsiders). "Normally" one determines the duff engine by comparing Nr movement with the suspect engine Ng. The duff engine drives the Nr out of its governed range thus enabling the pilot to select the correct engine for shut down. Perhaps this time the wrong engine was shut down whilst tired/confused. This left the duff engine driving the Nr and if that engine was providing less than nominal output the Nr will droop or even worse. He may have instinctively raised the collective to maintain his cruise height anyway (or tried to stop his increasing descent) and the Nr would continue to decay - ever closer towards its point of no return (what is it in the 135? 82%?). He sees this and tries in vain to salvage the decaying Nr by chopping the remaining engine and lowering the collective but too late, he sees the looming deck and pulls for all its worth to salvage some of the RoD. By then there is very little Nr left, but what is left is washed out by that final application of lever. RoD continues unchecked and the cab hits hard with no engines or little minimal Nr.
I realise this probably leaves us with an almost infinite number of possible scenarios, limited only by our collective knowledge of helicopter aerodynamics and human factors. Well, we have several months....
Shy Torque:
Your post mirrored my thinking. I remember when I was flying 330’s; the aircraft was on the ground and the engines at ground idle when something sheared on the TR pitch assembly and the tail rotor went to full pitch setting – can’t remember which way. The force was sufficient to yaw the fuselage, even though on the ground at a low power setting.
Many discussions in the crew room on how to cope with that failure in the air – and no positive answer, particularly if the aircraft was at low airspeed at the time.
Only way to stop the yaw is autorotation – and pull collective to slow the NR ……….?
Your post mirrored my thinking. I remember when I was flying 330’s; the aircraft was on the ground and the engines at ground idle when something sheared on the TR pitch assembly and the tail rotor went to full pitch setting – can’t remember which way. The force was sufficient to yaw the fuselage, even though on the ground at a low power setting.
Many discussions in the crew room on how to cope with that failure in the air – and no positive answer, particularly if the aircraft was at low airspeed at the time.
Only way to stop the yaw is autorotation – and pull collective to slow the NR ……….?
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Prawn2King4 - with a tail rotor hardcover to full pitch autorotation will make things much worse. In this situation, at low speed, you need as much torque on the rotor to counteract the maximum anti torque from the TR.
As the TR is at maximum pitch, AUW, MR torque, density Altitude and wind direction against the anti torque moment are all relevant but combined, may not be enough to overcome the anti torque moment being generated and a yawing spin may be inevitable.
Turning the engines off removes all the MR torque and the yaw rate would dramatically increase and most likely result in an uncontrolled crash.
As the TR is at maximum pitch, AUW, MR torque, density Altitude and wind direction against the anti torque moment are all relevant but combined, may not be enough to overcome the anti torque moment being generated and a yawing spin may be inevitable.
Turning the engines off removes all the MR torque and the yaw rate would dramatically increase and most likely result in an uncontrolled crash.