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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, 18:36
  #661 (permalink)  
 
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Originally Posted by Sky Sports View Post
It is also a possibility that the SB resulted from an observation on an aircraft on the other side of the world. Quite often, maintenance engineers, when they get a sense or a hunch of what caused an accident, will in the following days, take a stroll over to a similar machine in the hangar and just take another good look at the suspect system. Its sometimes at that point that things like anti-locking on components - that have been there since manufacture - suddenly become apparent.
That is very true, of course, none of us know anything concrete at the moment and are just theorising.

However, the wording in the SB copied and pasted below....

E. DESCRIPTION
Following an in service event, this Service Bulletin requires an urgent check of the
proper installation and functionality of the Tail Rotor servo-actuator feedback lever
installation and interface on the back end of the component.
Incorrect installation may lead to loss of Tail Rotor control which, depending on the
flight condition, could lead to loss of control of the aircraft.
Feedback on the compliance to this Service Bulletin is required


3. Perform a visual inspection of the input lever of the TR servo-actuator:
3.1 With reference to Figure 1 and Figure 2 perform an in situ inspection of the nut
(60), the cotter pin (50), the lock-wire and the hinge bracket element (90)
connected to the lever feedback link (110) for condition and absence of damage.
3.2 Check the connection elements of the input lever (110) of the TR servo-actuator
taking particular care on the lever feedback link.



Last edited by Mitchaa; 6th Nov 2018 at 18:47.
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Old 6th Nov 2018, 18:43
  #662 (permalink)  
 
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Originally Posted by Tony Mabelis View Post
'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.
Tony
Iíve heard a couple of people mention this today and just thought donít 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 thereís access. It wouldnít result in an instant failure but it would work itís way loose over time. Too far fetched bordering on madness although anything is possible.

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Old 6th Nov 2018, 18:48
  #663 (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
  #664 (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
  #665 (permalink)  
 
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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
  #666 (permalink)  
 
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Originally Posted by Gustosomerset View Post
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
  #667 (permalink)  
 
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Originally Posted by Mitchaa View Post
If you wanted to bring down a 169 and itís 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. Iím 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
  #668 (permalink)  
 
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Originally Posted by sycamore View Post
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
  #669 (permalink)  
 
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Originally Posted by Cows getting bigger View Post
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
  #670 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
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
  #671 (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
  #672 (permalink)  
 
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Originally Posted by noooby View Post
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, 22:21
  #673 (permalink)  
 
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Originally Posted by helimutt View Post
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.
I suspect Leonardo would also have listed a more thorough list of additional checks of the TR drivetrain if this was just a general pro active reaction.

-TGB and IGB chip detectors
-Driveshaft and flex coupling connections
-Blade and pitch link connections
-HUMS review
etc etc

SB is telling and it makes sense based on the video. Of course, it may just be coincidental, I guess we just need to hold out for more official detail.
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Old 6th Nov 2018, 23:03
  #674 (permalink)  
 
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Originally Posted by 212man View Post
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
  #675 (permalink)  
 
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Originally Posted by EGPI10BR View Post


Quite. There is no guarantee that the target was in the aircraft when the nut falls off. Iím 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
  #676 (permalink)  
 
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Originally Posted by Mitchaa View Post


Iíve heard a couple of people mention this today and just thought donít 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 thereís access. It wouldnít result in an instant failure but it would work itís 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
  #677 (permalink)  
 
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Originally Posted by noooby View Post
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
  #678 (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
  #679 (permalink)  
 
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Originally Posted by Mitchaa View Post
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, 07:18
  #680 (permalink)  
 
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Originally Posted by Gustosomerset View Post
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?
Only the extension/retraction of the pitch change shaft. It would appear once a full pedal input was made the feedback lever link disconnected itself from the pitch change shaft. It happened within 45 secs of take off and from the video, appeared to fail at the first significant yaw input. Was the nut in place before it lifted? Is the nut on the turf at the King power stadium? Did the pilot carry out a full left/right pedal check before lifting which caused the nut to depart on the ground? (It flew into the stadium okay)

The above (in my opinion anyway) is a plausible scenario based on the events that happened next with the video footage but I'm sure there are many more.

Only the AAIB will have an idea, we are just theorizing possible scenarios.



I have a few unrelated questions :-

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.
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