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Old 2nd Oct 2015, 06:51   #101 (permalink)
 
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Quote:
Originally Posted by SASless View Post
OK....we have a pre-impact failure of a rod end....and an un-contained engine failure in the same crashed aircraft. Two completely different components in two different areas of the aircraft.

Just what do we take out of that situation?

Are we overlooking something in all of the wild assed guessing that is going on about what caused the Crash?
The engine blowing up was most likely the result of the engine decoupling from the Mgb and overspeeding.
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Old 2nd Oct 2015, 10:21   #102 (permalink)
 
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SASLESS your back, I have not seen a post from you in a very long time.


Is it not possible the engine failure ( eruption) was after the aircraft impacted the water??


Looking at the pictures of the engine most if not all of the bolts that hold on the power module were gone, indicated they broke. Which could have occurred post crash.


As SAS mentions is quite hard to believe two totally different failures happen at the same time in flight.
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Old 2nd Oct 2015, 15:21   #103 (permalink)
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Yes "twisted wrench" that's what I'm also thinking as a possibility .... I have had an uncontroled ditching once, and on impact, engines didn't immediatly stop by themselves, and instead stabilised at an intermediate regime, but the "flexible couplings" linking their power shafts to the gear box, broke .... we can imagine that this condition may, as well, have caused a sudden uncontained overspeed. Or else,as you say, the forces of impact, caused a displacement of the power turbine out of its shield while the engine was still running.

Once again, just pilots sharing ideas ! Investigators probably already have a clearer picture now.
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Old 2nd Oct 2015, 17:39   #104 (permalink)
 
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AND... there we go again.
Where, exactly, does the report even HINT at a possible engine/gearbox de-couple?
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Old 2nd Oct 2015, 19:01   #105 (permalink)
 
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I would vote for the engine being a post impact event.....but that is purely an assumption.

I do wonder what the Rod End failure would have done to the controllability of the aircraft....and what that might prompt in the way of a Crew Reaction?

Perhaps we can start with a simple query....and focus upon the results of the Rod End issue rather than the "why".....and see where that leads us.

Or....let's start with the simple assumption the Engine did its thing and a crew reaction resulted in the control rod failure.

Not faulting the Crew or in any way suggesting they caused the tragedy....but as we all know our Emergency Procedure Training is for the expected and common place....and not the absolutely weird things that can happen.
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Old 2nd Oct 2015, 20:22   #106 (permalink)
 
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The weight of the servo input rod (when detached from lower rod end) is enough to ramp the servo down under static loads.
No idea what the dynamic loads would do, but the whole purpose of a servo is to isolate flight control loading from the pilot, so there cannot be much feedback.
In flight, a movement down on this servo - alone - causes right roll and nose down.
This is not what the report says happened in this case.
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Old 2nd Oct 2015, 22:01   #107 (permalink)
 
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Are my tired old eyes deceiving me or does the Nigerian AIB Report's photo of the Bell Crank Assy and Rod End not show some thread defamation/wear which would suggest it had been on its way out for some time?

The Question that begs is when was the last time it was inspected as being as it should be and by whom?
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Old 3rd Oct 2015, 00:12   #108 (permalink)
 
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Hi lynnx;

The servo would go full extension when the input disconnected and after seeing the pictures of the mangled helicopter in the report there is a strong possibility that the engine decoupled after the crash.
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Old 3rd Oct 2015, 03:04   #109 (permalink)
 
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The Engine did not seem to exhibit "Shrapnel" damage as one would expect from a genuine "Un-contained Failure".
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Old 3rd Oct 2015, 09:39   #110 (permalink)
 
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Hi Wizard,
I grant you, there may well have been a decouple following impact but the report does not state that.
A servo does not move unless there is an input - IF it is working correctly.
A servo mounted the way they are in the s76 should not go to full extension/retraction if you disconnect the imput unless the input is moved. The weight of the imput lever itself will normally ramp it down. With the control rod attached it will almost certainly ramp down under weight alone.
But thats static - with rotors running who knows.
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Old 3rd Oct 2015, 10:24   #111 (permalink)
 
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Lynnx you might be very correct but that only accounts for the one with the link that is disconnected there are two other servo´s that are connected and being moved by the pilot who is wondering what has happened to his controls.


So if two servo´s are moving and one is not imagine what that is doing with the swashplate and control of the helicopter?
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Old 3rd Oct 2015, 11:37   #112 (permalink)
 
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Unhappy Imagination

I,m trying very hard NOT to imagine !

I was exploring SASless' comment about the effect of the rod end detaching
and its consequences.
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Old 3rd Oct 2015, 18:13   #113 (permalink)
 
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I did not study the picture of the engine in the report very much. The rod end is much more disturbing. My memory says the containment ring for the power turbine was deformed, and I have seen that before in an Arriel 2. A. Sudden stoppage caused a main drive shaft coupling failure, and a TR DS coupling failure, the engine did not shut down, until the fuel supply was shut off, even though the power turbine had disintegrated and departed out the exhaust. The containment ring did its job and then started to melt I guess- it was tear drop shaped by the time it was all over.
To me all evidence points to the rod end including the resulting bulletins. I'm sure a corresponding action would have been taken if the engine were thought to be a contributing cause, and as far as I know all post accident bulletis, ADs, and MM amendment.
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Old 4th Oct 2015, 06:41   #114 (permalink)
 
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Quote:
The Engine did not seem to exhibit "Shrapnel" damage as one would expect from a genuine "Un-contained Failure".
SAS, have had two blow em up failures with this engine (same failure mode, turbine blade breaking off at root). One had shrapnel damage all over, while the other just spat it all out the exhaust.
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Old 4th Oct 2015, 08:23   #115 (permalink)
 
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Hi Lynx
I'm 100% sure the servo will go to full extension when there is no input connected.
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Old 4th Oct 2015, 12:51   #116 (permalink)
 
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Why would any kind of engine failure cause the aircraft to become uncontrollable?

It is easy to accept such a control rod failure could make the aircraft uncontrollable.

If the one Servo went to full extension and could not be moved in the other direction by Flight Control Inputs....what effect would it cause?

Perhaps Brother Dixson could offer some thoughts on this?
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Old 5th Oct 2015, 04:53   #117 (permalink)
 
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Quote:
A servo does not move unless there is an input - IF it is working correctly.
Flown a Bell medium at all?

Ever thought about the weight of the disconnected parts?
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Old 5th Oct 2015, 08:55   #118 (permalink)
 
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Hi RVDT,
Did you read past that line?
If servos moved without inputs you,d have a hard job flying.
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Old 5th Oct 2015, 09:06   #119 (permalink)
 
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Lynnx,

I did read your comments - just having difficulty understanding them.
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Old 5th Oct 2015, 10:21   #120 (permalink)
 
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Fair enough.

You asked about the weight of the disconnected rod?
I posted"with the control rod attached it will almost certainly ramp down under weight alone"
The rod in question had disconnected at the bottom. I,m presuming(!) that the AIB had disconnected it from the servo at the top for photo purposes - hence the "weight alone" - the remaining rod would be hanging off the servo input.

If your servo,s were moving WITHOUT an input (from the controls)then they would be continuously "running away" the whole time and the pilot would continuously fighting them the whole time!!

Does this make sense?
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