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Helicopter down outside Leicester City Football Club

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Helicopter down outside Leicester City Football Club

Old 16th Nov 2018, 09:11
  #761 (permalink)  
 
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Devil

Originally Posted by DOUBLE BOGEY
Apate, As I recall I facilitated his AS355 Line Training. I could be wrong. Apologies if I used the word "Student" which I guess is reserved more for ab-initio.

I am certainly not claiming any Kudos from his outstanding act of airmanship. However, fwhy is this such an issue for you?
Simples, you made a statement that I know not to be true.

You recollection regarding his AS355 Line Training is also incorrect!
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Old 16th Nov 2018, 09:20
  #762 (permalink)  
 
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Originally Posted by Apate
Simples, you made a statement that I know not to be true.

You recollection regarding his AS355 Line Training is also incorrect!
I think you are mistaken. As I recall 2 pilots came from CHC/Brintel to Police Ops with Veritiair as somewhat of an experiment to convince good P2s to remain in the Company group by giving them something interesting to do.. I completed the Line Training for both in Cardiff. I am almost 100% sure he was one of the pilots. Unless of course I am having a fantasy moment!!! Always possible at my age. I sent you a PM.
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Old 16th Nov 2018, 10:09
  #763 (permalink)  
 
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Overdrive

SASless - no magic! I think the thread looked to be going in a "Left unattended/not properly pre-flighted" direction, due to some of the stated (but not confirmed) timings.
Not at all, it would have made no difference here as any issues were probably not visible. It just seemed a short time to me but I am comparing it with larger types.
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Old 16th Nov 2018, 13:28
  #764 (permalink)  
 
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Uplinker.

Things that need to be checked regularly are either on the outside (control linkages to the tail rotor, the blades themselves, as examples) or can be inspected either through a specific hatch or other access (for my 120, opening the rear cargo hatch allows me to stand inside the tail and check the battery and look down the inside of the tail boom, for example). Typically the tail rotor drive shaft itself does not require daily inspection and so it (and any bearings along its length) are not made easily accessible. They are, however, subject to specific inspection regimes defined by the manufacturer and performed by mechanics. Where regular inspection is needed (some Rotorway designs have a belt-drive) inspection is facilitated.

There will be many flight-critical parts of a flixed-wing that are similarly treated (looking for corrosion on wing spars is not facilitated by a myriad of little hatches that you can open in a walk-around).

I have not seen a "twin tail rotor" design, and I am not imaginative enough to speculate how that might work; sorry
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Old 16th Nov 2018, 14:55
  #765 (permalink)  
 
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Thanks for your reply. I think I would want to be able to inspect all the bearings and CV couplings along the drive shaft to the tail rotor.

Take your point about wing spars, but corrosion is a slow process, amply covered during C and D checks, and the wing spars do not have moving parts requiring lubrication because they do not rotate during flight! The couplings and bearings driving a tail rotor do, and can potentially break up quickly. I think I would want to check there was no visual evidence of bearing or joint stress, given how critical the tail rotor seems to be.

Twin tail rotors would simply be two shafts running down the tail boom, each driving a tail rotor, so there would be one rotor on each side of the tail boom instead of just one on one side.
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Old 16th Nov 2018, 15:13
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Originally Posted by Uplinker
As a fixed wing pilot, can I ask; how do helicopter pilots inspect the tail rotor and its drive mechanism on the walk around? Are there inspection doors along the tail boom to enable inspection of every shaft joint? I donít recall seeing any in the helis we used to use for TV work. (Bolkow 105, Augusta 109, Twin Squirrel).

Given that the tail rotor seems to be so critical, why is there only one?. Would it not be safer if there were two separately driven tail rotors, or would that be overkill?
Most likely dual tail rotors would result in an overall reduction in safety given that some tail rotor failures such as a departed blade can cause other damage. The complexity and added weight would also have a detrimental effect. One comparison are the chances of surviving a (single) engine failure at takeoff in single and dual engine light aircraft, I have heard they are roughly the same.

IF the cause of this accident was a servo loop failure/run to a stop it is not clear that a second tail rotor would have helped, especially given the extremely limited time to take action.

Question for those who know: Would an immediate shutdown of both engines have stopped the tail rotor or is the transmission coupling such that it would continue to spin as long as the main rotor was spinning?
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Old 16th Nov 2018, 15:17
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Twin tail rotors would simply be two shafts running down the tail boom, each driving a tail rotor, so there would be one rotor on each side of the tail boom instead of just one on one side.
And contra rotating, it's not difficult to do, I designed and built one for a ROV. It worked great when one of the gearboxes failed...
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Old 16th Nov 2018, 15:37
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Originally Posted by Uplinker
Thanks for your reply. I think I would want to be able to inspect all the bearings and CV couplings along the drive shaft to the tail rotor.

Take your point about wing spars, but corrosion is a slow process, amply covered during C and D checks, and the wing spars do not have moving parts requiring lubrication because they do not rotate during flight! The couplings and bearings driving a tail rotor do, and can potentially break up quickly. I think I would want to check there was no visual evidence of bearing or joint stress, given how critical the tail rotor seems to be.

Twin tail rotors would simply be two shafts running down the tail boom, each driving a tail rotor, so there would be one rotor on each side of the tail boom instead of just one on one side.
Example of why it is important to inspect the tail rotor drive shaft : http://www.aaiu.ie/sites/default/fil...UGHLIN-0_0.PDF
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Old 16th Nov 2018, 17:12
  #769 (permalink)  

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Question for those who know: Would an immediate shutdown of both engines have stopped the tail rotor or is the transmission coupling such that it would continue to spin as long as the main rotor was spinning?




The tail rotor shaft is geared directly to the main rotor transmission, not to the engines.
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Old 16th Nov 2018, 22:54
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Does the AW169 have a any HUMS or condition monitoring system?
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Old 17th Nov 2018, 08:31
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Yes it does
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Old 20th Nov 2018, 13:30
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From the CAA website Tail rotor inspection

Specifically ATA 64 – Tail Rotor – Tail Rotor Flight Control System – Inspection
Since that AD was issued, EASA decided to require an inspection of the TR duplex bearing, as additional precautionary measure.
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Old 22nd Nov 2018, 06:27
  #773 (permalink)  
 
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When reading AAIB Bulletin S/1 2018 a few things catch my attention:

1). According to the bulletin the general wind direction was north-westerly with a strength of 10 to 12 kt at the surface and around 25 to 30 kt at 1000 ft.
2). The helicopter began a climb on a rearward flight path while maintaining a northerly heading.
3). The climb then paused. (somewhere above 320 ft)
4). Then the helicopter entered an increasing right yaw contrary to the pilot’s left pedal command
6). The helicopter reached a radio height of approximately 430 ft before descending with a high rotation rate.

— The climb out procedure was performed in downwind, (the heading was northerly, but the climb was rearward) so maybe the helicopter was following the same airmass with zero TAS so to speak?.. Somewhere above 320 ft the climb paused. Why?.. Did the helicopter reach a condition that sometimes is referred as ”settling with power” / climb in its own downwash? No descend was reported… If so, did the pilot manage to escape the situation with an unusual procedure by applying max power/max collective?-- The helicopter entered an increasing right yaw and reached 430 ft radio height before going down with high collective and power applied?
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Old 22nd Nov 2018, 07:27
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Originally Posted by arizona
3). The climb then paused. (somewhere above 320 ft)
4). Then the helicopter entered an increasing right yaw contrary to the pilotís left pedal command
6). The helicopter reached a radio height of approximately 430 ft before descending with a high rotation rate.
The wind direction for the take off couldn't have been much better, with it fore port side, it mitigates the likelihood of reduced tail rotor effectiveness while maximising forward wind component for a forced landing prior to tdp.

The report doesn't indicate the point at which the climb paused. It references undercarriage retraction at 320', and that maximum rad alt height was 430'. Aside from there being a pause, and that left pedal was applied to no effect, somewhere in the mix, we really know no more.
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Old 22nd Nov 2018, 07:56
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21 November, EASA issued AD No. 2018-0252-E, which now supersedes AD 2018-0250-E (of 19 November). AW169 & 189 (similar TR flight control systems).

"The incorrect installation of the TR servo-actuator, if not detected and corrected, depending on the flight condition, could possibly result in loss of control of the helicopter." Since the initial ASB from Leonardo, there has been further instruction to look at the duplex bearing.

Still an interim measure, but alters the inspection of the duplex bearing and servo-actuator within 5 flight hrs or 24 hrs.

1. Inspect TR duplex bearing in accordance with the accomplishment instructions - Part I of the ASB
2. Accomplish a breakaway torque check of the TR Duplex bearing in accordance with the accomplishment instructions - Part II of the ASB
3. Accomplish an inspection and reinstallation of the TR servo actuator castellated nut in accordance with the accomplishment instructions - Part III of the ASB

(CAA circulated 22 November, which I read this morning).
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Old 22nd Nov 2018, 10:58
  #776 (permalink)  
 
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Where is the duplex bearing in this assembly?
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Old 22nd Nov 2018, 11:11
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I'd say that the plot thickens...

Can we assume that it was still the factory issued one on this aircraft?
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Old 22nd Nov 2018, 14:43
  #778 (permalink)  
 
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Where is the duplex bearing in this assembly?
Ignore the fact that this is actually a 365 but the principal is near enough -

Item 16 is the Duplex bearing and Item 14 is where the nut is roughly.



I will let you work out the rest for what happens if the bearing fails and what could possibly happen to the nut.
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Old 22nd Nov 2018, 14:47
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Rather than concentrating too much on the rad alt height, couldnít this 100í anomaly be discounted due to the terrain below radalt changing rapidly due to the stadium contour below? Bar alt would give steady climb then level off if indeed that was the case.
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Old 22nd Nov 2018, 14:49
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14 is where the pitch change arm and the TR servo attachment is on a 365.

Gray - what they call a duplex bearing is what allows you to superimpose horizontal pitch change movement onto the rotating drive shaft - you probably already knew that but I though I'd clarify just in case.
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