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Helicopter down outside Leicester City Football Club

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Helicopter down outside Leicester City Football Club

Old 6th Nov 2018, 18:32
  #641 (permalink)  
 
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Originally Posted by Barcli
Trouble is JJ , the SB isnt really relevant to a servo runaway. Its relevant to a structural failure of the parts concerned or even more explicit of a missing split pin / nut/ wirelocking procedure. I hope they are also looking at security at Fairoaks.
'The security at Fairoaks'.................... as a retired LAE, I am wondering about the possibility of sabotage, locking pins and wire locking do not fail simultaneously.
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Old 6th Nov 2018, 18:48
  #642 (permalink)  
 
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I have never even met a billionaire but I have worked for several millionaires. They had some nasty enemies - they didnt become millionaires by being nice in business. I know nothing of Thai politics.
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Old 6th Nov 2018, 19:23
  #643 (permalink)  

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Jellycopter,

My speculation from experience of other designs; if the T/R control became disconnected, the blades would revert to a pre determined position by design. This position is a balance between aerodynamic and centrifugal turning moments which are usually designed to apply some positive pitch to the blades to allow a running landing. In a vertical climb OGE, this pitch setting would not be sufficient to prevent yaw developing (quite rapidly).
That might be true for smaller helicopters but if there is a flying control hydraulic system driving the tail rotor servo to either full positive or full negative pitch, that can't possibly happen. Some aircraft do have a centreing device to hold the servo at a pre-set mid range pitch position if the flying control run disconnects (e.g. control cable break), others don't. In a situation where the control mechanism fails, any number of things might happen. If the servo puts the tail rotor pitch to a medium or neutral position, you might be able to control the aircraft in yaw by either varying the main rotor torque, by changing the airspeed, or a combination of both. If the tail rotor pitch ends up at either full positive (anti-torque) pitch, or as possibly happened in this case, somewhere near maximum negative (pro-torque) position, you are in a very dire situation indeed. The fixed wing equivalent would be a rudder hard over and an engine failure on the same side that the rudder surface had moved to.

To put some typical figures on this, an aircraft you might remember very well (Puma) has a tail rotor pitch range of something like +35 degrees to -17 degrees astride the "zero pitch" datum. The RAF HC1 had no tail rotor pitch centreing device fitted, whereas the civilian Super Pumas did.
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Old 6th Nov 2018, 20:25
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Are all these components covered by a cowling/in the fin ,or exposed,on view....?
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Old 6th Nov 2018, 20:27
  #645 (permalink)  
 
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Originally Posted by Gustosomerset
Well no, quite. Which is really my point. However incredible the proposed method, there's probably someone mad enough to believe it's a clever idea...
Got you. Indeed. If a potential assassin had gained access to the aircraft, then there would be better methods of securing a successful outcome for them.
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Old 6th Nov 2018, 20:39
  #646 (permalink)  
 
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Originally Posted by Mitchaa
If you wanted to bring down a 169 and it’s billionaire owner and make it look like an accident then this would be the perfect way to do it. Not glaringly obvious and not an instant failure.
Quite. There is no guarantee that the target was in the aircraft when the nut falls off. I’m sure that the people down in Farnborough will get to the cause soon enough and involve the relevant authorities of foul play is a possibility.

Misty.
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Old 6th Nov 2018, 20:45
  #647 (permalink)  
 
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Originally Posted by sycamore
Are all these components covered by a cowling/in the fin ,or exposed,on view....?
Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

For those reading the SB and thinking this is directly related to this incident, it is not. AAIB have not given Leonardo any information that leads Leonardo to believe this to be the cause of the crash. Leonardo are being proactive. That is what Leonardo Customer Support are advising 169 owners.

Has Leonardo looked at the videos? You bet. Have they looked at all the possible mechanical issues that may cause this? You bet. And this would seem to be the most likely scenario that they have come up with on their own.

Doesn't mean it is the actual cause of this accident though.
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Old 6th Nov 2018, 20:51
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Originally Posted by Cows getting bigger
Silly old me, I thought we were in the business of reducing/mitigating risk and not just accepting the status quo. Is a split pin and a locking wire really the best way? Clearly someone has recognised the importance of this nut. Perhaps the whole linkage could be redesigned.
What do you think holds on the complete main rotor on a Jetranger? One big nut (not self locking) and two pieces of lock wire. THAT IS IT. And the fact that the nut is effing tight.

So how, pray tell, would you redesign it? Make the whole helicopter one piece???? There are only three methods that are easily used to lock a nut. Lockwire, split pin and tab washer. For critical components you should use two of the three or repeat one twice. Although it you use a self locking nut you can legally get away with only one.

And go.......
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Old 6th Nov 2018, 20:59
  #649 (permalink)  
 
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Originally Posted by MurphyWasRight
Thanks, that is roughly what I guessed from the diagram, works by balancing the control input and servo output to a "zero'' at the pilot valve, in electronics same as an op-amp.

So Is this roughly correct?
If the control path disconnects the system could be rigged to settle on the 'aerodynamic neutral' mentioned above.
If the feedback path fails then the servo will likely continue to be driven to a stop since there is no (or at least incorrect) input at the pilot valve.
I believe you are correct though I'm not entirely sure about the 169 TR Servo. Often the servos are made so that the pilot valve is spring loaded (for want of a better term) to neutral. That doesn't mean the servo goes to neutral. It means the servo stops moving, wherever it may be at the time.

If the feedback path fails, as I see it on the diagrams, then there is nothing to tell the pilot valve to stop porting fluid to the servo. So it would, in theory at least, go full one way. What I don't know is if manipulation of the pedals could still operate (albeit very roughly) the pilot valve, thereby controlling the servo to a certain extent. You'd have to try that on a 169 with a hydraulic cart hooked up. I also don't know if the servo will self-center if the feedback loop is disconnected.

In other words, if the lever is no longer connected to the servo through the feedback attachment, is any self centering force on the pilot valve enough to overcome the weight of the lever? If yes, then the servo should stop where it is. If no, then it may be possible for it to keep on moving to full extension.

I do not however know the answer to that.
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Old 6th Nov 2018, 21:47
  #650 (permalink)  
 
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Nooby,thanks for that.
Does the a/c have single or duplex hydraulics to the t/r servo, is it cable /pushrod actuated,and if duplex mains ,single system to t/r..ie could the t/r hyds be selected off...??..if you know..?
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Old 6th Nov 2018, 22:13
  #651 (permalink)  
 
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Originally Posted by noooby
Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

For those reading the SB and thinking this is directly related to this incident, it is not. AAIB have not given Leonardo any information that leads Leonardo to believe this to be the cause of the crash. Leonardo are being proactive. That is what Leonardo Customer Support are advising 169 owners.

Has Leonardo looked at the videos? You bet. Have they looked at all the possible mechanical issues that may cause this? You bet. And this would seem to be the most likely scenario that they have come up with on their own.

Doesn't mean it is the actual cause of this accident though.

Can you please link us to the actual 'in-service' event to which this sb applies? Odd that it does actually apply to an 'in-service' "event" so close to this accident. I, for one, can't say that I believe in coincidences of this nature. If you say Leonardo are being proactive, that doesn't imply that an Sb is released due to an in service event.
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Old 6th Nov 2018, 23:03
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Originally Posted by 212man
I would tend to disagree. A TR Servo problem could include an uncommanded full input in either direction, which is the equivalent of applying full yaw pedal - which is very much like what we see in this incident. I fail to see how that can be considered 'controllable'. The S92 referred to earlier may have had a similar outcome if not a few feet above the deck.
Agree. It was obvious as a possibility from the beginning.
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Old 6th Nov 2018, 23:13
  #653 (permalink)  
 
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Originally Posted by EGPI10BR


Quite. There is no guarantee that the target was in the aircraft when the nut falls off. I’m sure that the people down in Farnborough will get to the cause soon enough and involve the relevant authorities of foul play is a possibility.

Misty.
Surely Occam's Razor suggests not, though. I'm no assassination expert, but there are plenty of ways to kill people in undetectable ways that also happily avoid killing lots of other people.
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Old 6th Nov 2018, 23:14
  #654 (permalink)  
 
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Originally Posted by Mitchaa


I’ve heard a couple of people mention this today and just thought don’t be so ridiculous.

There was a billionaire on board, it wouldnt be hard to snip the lockwire, remove the pin and back the nut off. Those actions can be done in less than a minute if there’s access. It wouldn’t result in an instant failure but it would work it’s way loose over time. Too far fetched bordering on madness although anything is possible.

Wise words.
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Old 7th Nov 2018, 01:12
  #655 (permalink)  
 
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Originally Posted by noooby
Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

For those reading the SB and thinking this is directly related to this incident, it is not. AAIB have not given Leonardo any information that leads Leonardo to believe this to be the cause of the crash. Leonardo are being proactive. That is what Leonardo Customer Support are advising 169 owners.

Has Leonardo looked at the videos? You bet. Have they looked at all the possible mechanical issues that may cause this? You bet. And this would seem to be the most likely scenario that they have come up with on their own.

Doesn't mean it is the actual cause of this accident though.

if you're part of AAIB or Leonardo, then their might be some weight to your claims...
Otherwise, I'm pretty sure Leonardo staff are working alongside AAIB staff and the information is flowing freely amongst them.
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Old 7th Nov 2018, 01:37
  #656 (permalink)  
 
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Quote:
Originally Posted by noooby
Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

For those reading the SB and thinking this is directly related to this incident, it is not. AAIB have not given Leonardo any information that leads Leonardo to believe this to be the cause of the crash. Leonardo are being proactive. That is what Leonardo Customer Support are advising 169 owners.
if you're part of AAIB or Leonardo, then their might be some weight to your claims...
Otherwise, I'm pretty sure Leonardo staff are working alongside AAIB staff and the information is flowing freely amongst them.
Nooby does not need to be part of AAIB or Leonardo, just needs access to what Leonardo tech support is saying about the SB. He is also not stating that there is not a flow of information, although I have heard unless it is an immediate safety action the flow can be mostly towards the investigators. (Added bold/italics in quote)
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Old 7th Nov 2018, 06:54
  #657 (permalink)  
 
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Originally Posted by Mitchaa
Looking at the diagram of how the pitch change shaft is locked to the feedback lever bracket, if the nut was missing something would have had to initiate the extension or retraction of the pitch change shaft for the feedback lever bracket to disconnect from the pitch change shaft. (Namely a commanded yaw action)
It never happened on the ground, nor in the climb. It looks to have happened as the pilot turns the aircraft to transition to forward flight.

Is there any significance to be drawn from the observation that the failure appeared to happen at the first point that the pilot commanded a yaw to the right (i.e. counter the MR rotation) as opposed to the slight yaw to the left observed (and explained earlier) during the climb?
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Old 7th Nov 2018, 07:33
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I’m led to believe, that this part isn’t something that would necessarily have been touched by the maintenance organisation since new. So unless work had been carried out on it for some other reason recently, it shouldn’t have needed touching. I’m certain the 145 op and aaib will be aware. This will be an interesting report no doubt. I have to say that I’ve read some absolute bo££ox on pprune accident threads but this one has it all. From Russian conspiracy theories to garbage expert witness statements to theorised pilot error and non existent SB which are SB, but not related to this event but related to a recent event. Wow.
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Old 7th Nov 2018, 07:49
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To help the discussion on the pitch of the TR blades, I attach again a close-up of the TR at the crash site, plus the original it was taken from (as pdfs, I can't post images yet). The blades seem to be at a roughly neutral postion.

This may mean absolutely nothing, as, for example, the blades may be self-centred when hydraulic power is lost with or without the servo connected.
Attached Files
File Type: pdf
GVSKP_TailRotor_CrashSite.pdf (171.0 KB, 474 views)
File Type: pdf
GVSKP_All_CrashSite.pdf (116.1 KB, 284 views)
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Old 7th Nov 2018, 08:12
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Originally Posted by Mitchaa
Does anyone know the hours on the airframe? All I can see from a quick google is that it was delivered in August 2016. What are VIP aircraft doing per year? 2-300 hours? Likely hours to be around 5-600? (or more?)

The reason I ask, it may never have been disturbed by the Part 145 organisation? If the airframe is low hours, that particular part may never have been disturbed, fitted from factory and untouched? I guess it would still fall under calendar ops, 1 or 2 yearly inspection, but would that involve disconnecting that link? Perhaps they had an unscheduled removal which resulted in its disconnection? Again, only the Part 145 and AAIB will have the answers to that.
G-INFO reports registered in July 2016 and 283 total hours as at 28-Jun-2018 (not sure how reliable the G-INFO database is)
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