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Helicopter down outside Leicester City Football Club

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Helicopter down outside Leicester City Football Club

Old 11th Nov 2018, 20:00
  #741 (permalink)  
 
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Totti, OK,I`ll` add a couple of other bits as your calculator is warmed up;
IF the helo now enters a full autorotation,how much aft stick movement is produced at a variety of airspeeds,to keep a level attitude;
now do it all at a fwd C o G...
now consider the fact that the aircraft has yawed(depending on airspeed and fin size)which may also have a `pitch` effect..
now consider where the stick/disc relationship is to tail- boom.....and your stick margins vs control stops

Answers on a postcard,,,...or sheets of A4.....
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Old 11th Nov 2018, 20:22
  #742 (permalink)  
 
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Not rocket science to suggest that the longer the tailboom, the further from the C of G is the TRGB and the more marked effect its loss will have on longitudinal C of G.
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Old 11th Nov 2018, 20:30
  #743 (permalink)  
 
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Originally Posted by sycamore View Post
Totti, OK,I`ll` add a couple of other bits as your calculator is warmed up;
IF the helo now enters a full autorotation,how much aft stick movement is produced at a variety of airspeeds,to keep a level attitude;
now do it all at a fwd C o G...
now consider the fact that the aircraft has yawed(depending on airspeed and fin size)which may also have a `pitch` effect..
now consider where the stick/disc relationship is to tail- boom.....and your stick margins vs control stops

Answers on a postcard,,,...or sheets of A4.....
I don't need to calculate anything,read my post again.
Crab, you are absolutely correct.
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Old 11th Nov 2018, 20:32
  #744 (permalink)  
 
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Originally Posted by HarryMann View Post
MWR ... If you are in any way correct, this implies a really poor original design... a prime goal in mechanical components design just as important as stessing and robustness is clarity of assembly whilst minimising potential for mis-assembly...
e.g. all bolts in a locality doing much the same job being of the same length, usually arranged by say stepping a casting thickness .. EVEN IF IT COSTS WEIGHT..
Totally agree, I sincerely hope that my conjecture on misplaced washer is way off. I mentioned it only because at least as presented in the AD it is hard to see how both the split pin and lockwire could be missing without being noticed and was pondering what else could be mi-assembled.

GeordiMike also responded that lack of washer would likely affect the centering of the control system enough that it would at least be noticed if not totally unserviceable.
(My thoughts based on his feedback)

Again most likely they suspect something in that mechanism but do not know (or cannot say with certainty) exactly what so the goal is to have it looked at for anything suspicious.
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Old 12th Nov 2018, 07:17
  #745 (permalink)  
 
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Originally Posted by sycamore View Post
For; Blade Slap,totti,M3- perhaps I should have put the phrase about the CG` beyond the nose`` in italics/commas,or a couple of smilies.
Dont worry, that was blatantly clear to anybody who didnít bother to respond.
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Old 12th Nov 2018, 13:02
  #746 (permalink)  
 
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Originally Posted by MurphyWasRight View Post
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).

did you magnify the photo?
If you haven't, please do. I see the arrangement in the photo as indicated in the drawing.
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Old 12th Nov 2018, 14:31
  #747 (permalink)  
 
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Quote:
Originally Posted by MurphyWasRight
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).
did you magnify the photo?
If you haven't, please do. I see the arrangement in the photo as indicated in the drawing.
I saw that the photo matches the drawing as expected since the photo is of a correct assembly. My question was about possibility of an incorrect assembly with the washer on the wrong side, under the nut, and if that was even possible without causing an obvious problem. If it is possible then the hardened rod shoulder could stress the 'hinge bracket element (90)' and cause a failure,especially if the shoulder was significantly smaller than the outside diameter of the washer.

Without detailed drawings and system knowledge whether misassembly is even possible is an open question though feed back from GeordiMike suggests it probably would be obvious due to offsets in the servo loop.
Also if washer misplacement (or missing) is possible seems that it would have been an explicit check in the AD which does not mention the washer.
Then again something did go wrong, as others have said will be clear in final report.
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Old 12th Nov 2018, 17:54
  #748 (permalink)  
 
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thats why I asked, I figured that as well, if the washer was suspect for any reason it would be part of the AD.

Incidentally for simple random information totally unrelated to this case, I was disassembling some AS350 control rods today, and while cutting the lockwire, the nut started turning. the lockwasher design didn't stop the nut as it was just a place for the lockwire to terminate.
The "double locking" in this case did its job although the proper torque was not on the nut.
However, nothing further would have happened because the lockwire, torgue and locktabs, on the other end would have all had to fail too before bad things happened.
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Old 13th Nov 2018, 01:29
  #749 (permalink)  
 
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Originally Posted by GrayHorizonsHeli View Post
thats why I asked, I figured that as well, if the washer was suspect for any reason it would be part of the AD.

Incidentally for simple random information totally unrelated to this case, I was disassembling some AS350 control rods today, and while cutting the lockwire, the nut started turning. the lockwasher design didn't stop the nut as it was just a place for the lockwire to terminate.
The "double locking" in this case did its job although the proper torque was not on the nut.
However, nothing further would have happened because the lockwire, torgue and locktabs, on the other end would have all had to fail too before bad things happened.
This is a dangerous assumption, in part led by a pervasive culture that safety wire, cotter pins, etc. actually help keep a joint together. Proper torque keeps it together, and absence of torque can lead to high loads from vibration even on parts that are not thought of as load carrying, wear on threads can be just as bad and can lead to loss of control. That rod should be replaced, or possibly NDI inspected for damage, but at minimum raise awareness... do not ignore "loose nuts found on good parts".

earlier posters describe uncommanded full actuation which would certainly be possible probably likely, with failures on the subject side of servo. A neutral tail rotor would not cause aircraft to keep spinning after main rotor torque was dropped, it would slow down, and if biased it would actually turn the aircraft to the left. Yes, a missing nut could do this, but for all we know, they found a fractured end of servo. One cause of that could be... incorrect or inadequate torque on the nut. An initial inspection is prudent.
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Old 13th Nov 2018, 05:26
  #750 (permalink)  
 
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Further to OPR's comments -

Certification Specifications contain the following statement -

Fasteners

(a) Each removable bolt, screw, nut, pin or other fastener whose loss could jeopardise the safe operation of the rotorcraft must incorporate two separate locking devices.
The fastener and its locking devices may not be adversely affected by the environmental conditions associated with the particular installation.

(b) No self-locking nut may be used on any bolt subject to rotation in operation unless a non-friction locking device is used in addition to the self-locking device.
At the outset this seems to be prudent and simple but there are other subtleties. Installation of locking devices implies that someone has made the effort to install things correctly and
when doing a "duplicate inspection" the second inspector can at least see that the locking is in place.

As quoted by OPR the locking devices do NOT have anything to do with the integrity of the fastener. If the fastener has become loose and it is relying upon the locking device
something is wrong with the connection and the safety system works.

There are numerous issues that safety locking can overcome and incorrect torque is only one of them.

Incorrect hardware
Worn hardware
incorrect assembly of the fastener etc etc.

Nuts and bolts can be more complex than a lot of people appreciate.

I know of one particular large manufacturer who does not comply with the above statement but that is another story.......................
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Old 13th Nov 2018, 09:24
  #751 (permalink)  
 
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FAA Follows EASA with Stricter AW169 Emergency AD

by Mark Huber
- November 9, 2018, 1:49 PMThe FAA has issued a more comprehensive Emergency Airworthiness Directive (AD 2018-23-52) to cover Leonardo AW169 and AW189 twin-engine helicopter tail rotor servo-actuator assemblies, following the issuance of an EASA Emergency AD earlier this week. The FAA said it “determined the unsafe condition exists and is likely to exist or develop on other helicopters of the same type design.”

The FAA Emergency AD requires inspecting the nut, cotter pin, lock-wire, hinge bracket connected to the tail rotor servo-actuator feedback lever link, and each connection of the tail rotor servo-actuator feedback lever link. It also requires applying a paint stripe or torque seal on the nut and reporting certain information to Leonardo.

The EASA AD specifies visually inspecting the nut, cotter pin, lock wire, and hinge bracket for condition and absence of damage, while the FAA Emergency AD requires inspecting those parts for correct installation and loose, broken, and missing parts. While the EASA AD specifies visually inspecting the connection elements of the tail rotor servo-actuator feedback lever link, the FAA Emergency AD requires inspecting all three connections of the tail rotor servo-actuator feedback lever link for correct installation and loose, broken, and missing parts. The inspections specified by the FAA Emergency AD are not limited to visual inspections.

The EASA AD requires contacting Leonardo for approved instructions if there is any damage or other finding, while the FAA Emergency AD requires performing any necessary repairs in accordance with FAA-approved procedures. The FAA AD covers seven helicopters on the FAA registry and estimates the cost of compliance at $255 per helicopter. Leonardo has produced approximately 70 AW169s and 55 AW189s to date.
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    Old 14th Nov 2018, 11:10
      #752 (permalink)  
     
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    No real news but AAIB special bulletin....
    https://assets.publishing.service.go...018_G-VSKP.pdf
    212man is offline  
    Old 14th Nov 2018, 11:29
      #753 (permalink)  
     
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    The helicopter ....... did not respond to the pilot's command, initial findings show.

    https://www.bbc.co.uk/news/uk-englan...shire-46208494
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    Old 14th Nov 2018, 11:33
      #754 (permalink)  
     
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    BBC news just posting that the "helicopter did not respond to pedal inputs".
    Beat me to it.
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    Old 14th Nov 2018, 11:51
      #755 (permalink)  
     
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    Its is interesting that the Landing Gear was retracted! On a structure RFM profile should this not be done at Vy + 200 feet?
    The aircraft impacted upright. If the gear was down maybe some energy would have been absorbed......maybe it would not have rolled!
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    Old 14th Nov 2018, 13:34
      #756 (permalink)  
     
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    I think landing on the stone wall/fence was the deciding factor to the aircrafts eventual resting place, regardless of gear up or down.
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    Old 14th Nov 2018, 14:03
      #757 (permalink)  
     
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    Originally Posted by GrayHorizonsHeli View Post
    I think landing on the stone wall/fence was the deciding factor to the aircrafts eventual resting place, regardless of gear up or down.
    And the gear speed restrictions tend to make most people hoik it up pretty quick.

    SND
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    Old 14th Nov 2018, 14:12
      #758 (permalink)  
     
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    And the gear speed restrictions tend to make most people hoik it up pretty quick
    Interesting, as without doors you would not associate that kind of gear with a IAS low restriction - is it because it's electrically actuated?
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    Old 14th Nov 2018, 14:34
      #759 (permalink)  
     
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    Interesting that after loss of TR authority, the aircraft continued to climb. Why would the pilot increase the power when he lost the TR?
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    Old 14th Nov 2018, 15:01
      #760 (permalink)  
     
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    Originally Posted by asdf1234 View Post
    Interesting that after loss of TR authority, the aircraft continued to climb. Why would the pilot increase the power when he lost the TR?
    I would guess at an involuntarily input caused by either the startle factor or bio-mechanical due to the sudden forces being experienced. It wasn't much.
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