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Helicopter down outside Leicester City Football Club

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Helicopter down outside Leicester City Football Club

Old 7th Nov 2018, 07:33
  #681 (permalink)  
 
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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
  #682 (permalink)  
 
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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, 467 views)
File Type: pdf
GVSKP_All_CrashSite.pdf (116.1 KB, 283 views)
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Old 7th Nov 2018, 08:12
  #683 (permalink)  
 
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Originally Posted by Mitchaa View Post
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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Old 7th Nov 2018, 08:12
  #684 (permalink)  
 
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Originally Posted by Mitchaa View Post
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?
I understand. I think what I was getting at was whether pedal input in one direction (yaw left) might not be affected by the absence of the nut but that in the other direction (at the top of the climb for the first time) it would, as the absence of the nut would not affect a 'pushing input' but would allow the lever to pull itself away from shaft. If this were true, perhaps it could allow for the fact that control seemed normal in the climb - with no right yaw demanded - even if the nut was already on the ground. (Despite your excellent explanation of the mechanics I'm afraid I'm simply too stupid to fully understand).

As to this thread being full of "absolute bo££ox", IMHO I'd echo the point made earlier (which I can't now find) that for inexperienced pilots (such as me), the amount of insight from those who are far more knowledgeable has a value that far outweighs the obvious nonsense - which we can easily choose to skip.
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Old 7th Nov 2018, 08:46
  #685 (permalink)  
 
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Originally Posted by Gustosomerset View Post
I understand. I think what I was getting at was whether pedal input in one direction (yaw left) might not be affected by the absence of the nut but that in the other direction (at the top of the climb for the first time) it would, as the absence of the nut would not affect a 'pushing input' but would allow the lever to pull itself away from shaft. If this were true, perhaps it could allow for the fact that control seemed normal in the climb - with no right yaw demanded - even if the nut was already on the ground.


The amount of pedal deflection will be proportionate to the amount of movement of the pitch shaft, small inputs left and right may well have been enough to keep the 2 connected. As a larger input is made there's more deflection on the pitch change shaft and that would be enough to disconnect the shaft from the link. From viewing the video I believe he put in a large yaw input to turn the aircraft and at that point, the servo was at a large deflection from centre and the connection then failed, keeping the servo most probably at the hard stop.
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Old 7th Nov 2018, 11:05
  #686 (permalink)  
 
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EC will also tell you that SBs for 225 and 365s are precaution. But we all know how did this board went about it.
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Old 7th Nov 2018, 12:05
  #687 (permalink)  
 
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[QUOTE=noooby;10303760]Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

I remember delivering a new EC135 T1 to a new owner, during a walk round of the aircraft with him he commented that the tail rotor seemed to be missing a fairing, I pointed out it never had one, to facilitate preflight inspection and daily maintenance. 2 years later I flew the new P2 version that did have a fairing covering the important bits. Being old school I'd rather be able to cast an eye and a torch over the Tail rotor components, the P2 looked tidier but I always thought it was an improvement that actually made things worse.

My only accident was a tail rotor drive failure, thankfully only from a high hover taxi, due to servicing error. The intermediate gearbox came off the tailboom with most of the drive shafts and tail fairings. I'd already completed 4 ground runs to track and vibe the Tail rotor which had had components replaced. The 5 bolts holding the shaft to the IGB had been replaced but the engineer had not replaced the nuts. The supervisor signed off the job and secured the fairings, from that point on the aircraft was doomed. I felt a slight vibe through the pedals for around 2 seconds before it went bang just as I moved forward after the post take off checks. Thankfully the non handling pilot got the ECLs back just as I got the collective down and we had rotated through a full 360 turn.

The missing nuts were still on the bench in the hangar, I've had a very wary approach to tail rotors ever since, particularly when they've been tinkered with!
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Old 7th Nov 2018, 12:17
  #688 (permalink)  
 
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Art....‘‘twas not the tail rotor that let you down!
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Old 7th Nov 2018, 12:31
  #689 (permalink)  
 
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Originally Posted by SASless View Post
Art....‘‘twas not the tail rotor that let you down!
very true SAS!
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Old 7th Nov 2018, 13:44
  #690 (permalink)  
 
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Originally Posted by sycamore View Post
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..?
First off, I'm just relaying what Leonardo is telling the operators when they ask about this SB. That the AAIB have not (as yet) given them any info about possible or probable causes of this accident.

Sycamore, the TR is duplex hydraulic. It is controlled with a single push-pull cable. Unlike previous Leo machines that have relied on control tubes. Hydraulics cannot be selected off as the aircraft cannot be flown without hydraulics.

I know as much as any 169 operator who asks the right questions
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Old 7th Nov 2018, 15:08
  #691 (permalink)  
 
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Originally Posted by noooby View Post
First off, I'm just relaying what Leonardo is telling the operators when they ask about this SB. That the AAIB have not (as yet) given them any info about possible or probable causes of this accident.

Sycamore, the TR is duplex hydraulic. It is controlled with a single push-pull cable. Unlike previous Leo machines that have relied on control tubes. Hydraulics cannot be selected off as the aircraft cannot be flown without hydraulics.

I know as much as any 169 operator who asks the right questions
From the picture it seems improbable that both locking means were missing/misinstalled.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.

Not discernible from the drawing but appears that the shoulder the washer sits on is probably just a bit larger than the hole in the hinge bracket (90). Lack of washer would allow the system to operate normally but might cause high stress on the hinge bracket leading to a fracture. Even without a fracture it could dig a hole in the hinge bracket resulting in play that could cause other issues such as the nut being loose which in turn could cause other damage.
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Old 7th Nov 2018, 16:27
  #692 (permalink)  
 
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[QUOTE=MurphyWasRight;10304564]From the picture it seems improbable that both locking means were missing/misinstalled.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.

I have no experience on this helicopter type (but 43 years on many others).

In most mechanical assembly situations a washer is placed "under" a nut, and looks "correctly assembled" when inspected, but it is the opposite in this case.
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Old 7th Nov 2018, 16:56
  #693 (permalink)  
 
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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.


Murphy, there are possibilities as you suggest. The wording of the SD is perhaps not ideal and certainly doesn't detail any specific potential fault or assembly mistake, and maybe that is for a reason; the intention being to ensure that all ships have the components in place and correctly installed in good condition, not to support speculation about actual cause of the accident. However the SD also doesn't mention that washer with the other components.

Nothing to do but wait...
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Old 7th Nov 2018, 17:37
  #694 (permalink)  
 
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It has now been issued by EASA as an emergency AD for 169’s and 189’s

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Old 7th Nov 2018, 18:13
  #695 (permalink)  
 
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Interesting. As stated in the EAD, perhaps simply a precautionary measure based on what was observed in the accident. It would appear there is though, a way in which the mechanism can be incorrectly installed/assembled that has been either observed or imagined and is causing concern. Of course this may yet not apply in the case of this recent accident.
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Old 7th Nov 2018, 18:50
  #696 (permalink)  
 
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Nooby,thanks again...must be using `old newstock `teleflex` from Whirlwind days....
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Old 7th Nov 2018, 19:03
  #697 (permalink)  
 
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you can guarantee they found a missing nut on the accident helicopter at this point.
what they cant guarantee yet is if it was an isolated incident or not. Hence the SB and AD.
this is the data gathering stage where they find out if it's a widespread issue or not.

Ive been reading others posts about the two stages of locking. This is a must on any flight control. Dont forget though that they are only safety nets to the initial locking, which is the correct torque on the nut. Continual inspections offer the final net of safety.

In essence what I am saying is there was 4 failures here.
The torque was lost/incorrect or was never applied, allowing the nut to un-thread.
either faulty cotterpin/lockwire, or missing cotterpin/lockwire the failure was just a matter of time.
and the 4th, the inspections, didn't catch the impending loss.
Personally I think the loss of the nut would have happened quickly once torque was lost and the safety features failed to retain it.
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Old 7th Nov 2018, 19:06
  #698 (permalink)  
 
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Originally Posted by Overdrive View Post
Interesting. As stated in the EAD, perhaps simply a precautionary measure based on what was observed in the accident. It would appear there is though, a way in which the mechanism can be incorrectly installed/assembled that has been either observed or imagined and is causing concern. Of course this may yet not apply in the case of this recent accident.
Lots of components in the TR control system, looks very specific.
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Old 7th Nov 2018, 19:20
  #699 (permalink)  
 
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Originally Posted by GrayHorizonsHeli View Post
you can guarantee they found a missing nut ...
Personally I think the loss of the nut would have happened quickly once torque was lost and the safety features failed to retain it.
I wonder whether an incorrect assembly, rather than lose a nut, could cause a misalignment or deformation of the link/control rod, resulting in a jamming of the control rod.
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Old 7th Nov 2018, 19:27
  #700 (permalink)  
 
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GRAYHORIZONSHELI Do you actually mean “they found a missing nut” or “they found that a nut is missing”?

I would assume (and surely at this stage of the game, it’s still an assumption) it would be the latter.

I stress again, I am not a pilot, but I am a mech engineer (albeit from a different discipline). As a slight aside, I have used split pins and wire locks on many a track motorcycle in my time, so as well as those two safety measures, there is (as you stated) the correct torque setting for the nut. On top of that, I don’t know if the aviation world use it or not, but on track bikes, it was also common practice to apply a further safeguard in the form of an appropriate thread locking fluid (yes, usually from the Loctite company).
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