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EC225 crash near Bergen, Norway April 2016

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EC225 crash near Bergen, Norway April 2016

Old 5th Jul 2018, 12:30
  #1841 (permalink)  
 
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"The Accident Investigation Board Norway recommends that Airbus Helicopters revise the type design to improve the robustness, reliability and safety of the main gearbox in AS 332 L2 and EC 225 LP."
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Old 5th Jul 2018, 12:32
  #1842 (permalink)  

 
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Very interesting. For laypeople, I strongly recommend the 4mins 34secs video which you can download from the end of the list of downloadable appendices - or from the end of the 'downloads' column on the right.

airsound
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Old 5th Jul 2018, 12:39
  #1843 (permalink)  
 
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What the Certification Authorities and AH (....and other designers) do now shall be very interesting.

The Report points out some issues that affect the Industry as a whole.

AH has some “splaining” to do about the success rate of second stage components making it to Design Life.
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Old 5th Jul 2018, 12:50
  #1844 (permalink)  
 
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This is what AH is saying https://www.airbus.com/helicopters/i...on-status.html
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Old 5th Jul 2018, 14:31
  #1845 (permalink)  
 
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Originally Posted by SASless View Post
What the Certification Authorities and AH (....and other designers) do now shall be very interesting.

The Report points out some issues that affect the Industry as a whole.

AH has some “splaining” to do about the success rate of second stage components making it to Design Life.
PLM, Product Lifecycle Management, is the favoured design regime of modern times. This, or some other term with a more aviation flavour may start to be heard more widely and taken more seriously if this report gets the attention it deserves.

And yes, implications for the industry as a whole, especially since this is the most examined helicopter type in history so we don't know what we don't know yet in respect of other types.
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Old 5th Jul 2018, 14:56
  #1846 (permalink)  
 
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Originally Posted by jimf671 View Post
And yes, implications for the industry as a whole, especially since this is the most examined helicopter type in history so we don't know what we don't know yet in respect of other types.
err ...
exactly, what we do know is that COMPLEXITY has a cost (not knowing what you don't know being one of them).
It is part of the price paid to buy engine redundancy.
That cost should be accounted for, you cant take the credit for the upside of engine redundancy without taking responsibility for the downside.
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Old 5th Jul 2018, 15:18
  #1847 (permalink)  
 
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Originally Posted by AnFI View Post
err ...
exactly, what we do know is that COMPLEXITY has a cost (not knowing what you don't know being one of them).
It is part of the price paid to buy engine redundancy.
That cost should be accounted for, you cant take the credit for the upside of engine redundancy without taking responsibility for the downside.
We will take that into account everytime a combining gearbox fails catastrophically. Irrelevant in this case, but even you know that. I hope.
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Old 5th Jul 2018, 16:25
  #1848 (permalink)  
 
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Originally Posted by SASless View Post

AH has some “splaining” to do about the success rate of second stage components making it to Design Life.
The tables around page 25 of the report go into some detail and as you would expect the situation is somewhat more nuanced. After REDL for example Heli One adopted a policy of replacing on first overhaul. They also most usually fitted the NTN-SNR variant which proved more resilient. Nevertheless, only 10% of both types combined made it to operational life.

What would be interesting is if any of our helicopter maintenance colleagues could take a look at the tables and tell us if the level of damage from in service operations is very different from other types?.
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Old 5th Jul 2018, 20:23
  #1849 (permalink)  
 
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You can call me a cynic but in my experience, large organisations, whether public or private, have the necessary power-base to ensure that their version of events prevails and that the external dermis of such organisations is so Teflon-like that they will contrive to escape censure. We have already seen, I believe, their influence on the certification process that has seen national aviation authorities apparently bullied into accepting an analysis of the events that is in line with one of Europes largest and most powerful industrial entities wishes, not the truth. WTHIH !!!

G

Last edited by Senior Pilot; 5th Jul 2018 at 22:43. Reason: Remove OT stuff
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Old 6th Jul 2018, 10:48
  #1850 (permalink)  
 
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Seems like a very good report. I note that AH and EASA both come in for some stick for being obstructive in taking months to release relevant documents, and in AH's case not allowing the documents out of the factory due to their commercial sensitivity. Seems sad that once again commercial interest/secrecy/bureaucracy is put ahead of safety. AH also get some stick for smoke screening with their suspension bar theory. And how often have we heard about unreliable parts just being binned and replaced, without the cause of their unreliability being explored? (answer: often!).
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Old 6th Jul 2018, 13:44
  #1851 (permalink)  
 
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AH also get some stick for smoke screening with their suspension bar theory
Where do you see that? I looked and can only see reference to it be one of the options to be looked at and the quickly ruled out as they shown to be correctly mounted at the time of the break up.
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Old 6th Jul 2018, 14:39
  #1852 (permalink)  
 
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Not investigating why so many items failed to reach their design life will be gratefully accepted by the negligent lawyers.
i note ERA have already settled - agreeing to hold no one to blame....
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Old 8th Jul 2018, 14:03
  #1853 (permalink)  
 
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Originally Posted by EESDL View Post
Not investigating why so many items failed to reach their design life will be gratefully accepted by the negligent lawyers.
i note ERA have already settled - agreeing to hold no one to blame....
The type is clearly still persona non grate in the North Sea. The unions still regard the unresolved issues too significant to rehabilitate the type.

Unite the Union: recent report shows Super Pumas should be banned from North Sea - Original 106
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Old 8th Jul 2018, 19:42
  #1854 (permalink)  
 
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Now What!

So!
Were does it go from here? The once so super Puma!
Are the new regime good enough for all N-CAAs and a bit like the 737-rudderhardover that got solved!
Or should the bird be grounded.
According to some here in Norway it must never fly again.
Any toughts
Regards
Cpt B
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Old 8th Jul 2018, 21:53
  #1855 (permalink)  
 
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Separate rotor support and gearbox?

Every helicopter has components that must not fail in flight if disaster is to be avoided. It would appear that minimising these would be a desirable design goal.

It seems that it might not be essential to include pretty much the entire gearbox in the list of these critical components. Clearly any gearbox failure is likely to result in a loss of drive and a subsequent autorotation, however there seems no essential need to combine the gearbox with the support of the main rotor as seems to be commonly done.

The two EC225 crashes may have had a better outcome if these functions were separated.

I am fairly sure for example the the Robinson R22 separates the reduction gearbox (belts:-) from the rotor support structure.

It may of course be more challenging to arrange a 3,000HP helicopter that way as opposed to the 100HP Robinson but I don't see that it would be impossible or even impractical.
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Old 9th Jul 2018, 00:12
  #1856 (permalink)  
 
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Originally Posted by jimjim1 View Post
Every helicopter has components that must not fail in flight if disaster is to be avoided. It would appear that minimising these would be a desirable design goal.

It seems that it might not be essential to include pretty much the entire gearbox in the list of these critical components. Clearly any gearbox failure is likely to result in a loss of drive and a subsequent autorotation, however there seems no essential need to combine the gearbox with the support of the main rotor as seems to be commonly done.

The two EC225 crashes may have had a better outcome if these functions were separated.

I am fairly sure for example the the Robinson R22 separates the reduction gearbox (belts:-) from the rotor support structure.

It may of course be more challenging to arrange a 3,000HP helicopter that way as opposed to the 100HP Robinson but I don't see that it would be impossible or even impractical.
Only one crash was a 225, the other a 332L2.
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Old 9th Jul 2018, 00:43
  #1857 (permalink)  
 
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Yes we know....but there are some amazing similarities between the two types and the cause and result of the crashes would you not agree?
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Old 9th Jul 2018, 01:50
  #1858 (permalink)  
 
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The S76 MGB emergency procedure flows into monitoring for increase in vibration, torque and noise level.. I wonder if this failure has caused a rethink and if the design differences in gearboxes would change the result in a catastrophic failure of a sun gear? Over the years the loss of oil and dry run time on a gearbox have been topical but again, if any of those cracks exist and you have to contend with a run dry situation, (now things are really becoming very hypothetical..) then how would those sun gears or any other component with subsurface cracks respond?
The comment below has just started me thinking..
"Following that, given that it might not be possible to assess the fatigue reliability of internal gearbox components, it recommends EASA require a fail-safe main gearbox, in which no failure of an internal component leads to a catastrophic failure." (https://www.verticalmag.com/news/nor...a-type-design/)
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Old 9th Jul 2018, 03:43
  #1859 (permalink)  
 
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I have some experience with epicyclic gear drive design. And when I looked at a cross section drawing of this gearbox, one thing that seemed questionable to me was the rim section thickness of the 2nd stage planet gears. The radial section thickness at the face width center appears to be less than 1x the gear tooth whole depth. I recall being given a stern lecture by a very experienced gearbox designer about making sure to provide plenty of rim section thickness with planet gear configurations like this. The alternating 2/rev tension/compression stress cycles at the bearing race surface resulting from "bending" of the rim will be more of a problem than you would think. There is a great illustration on page 8 of appendix H that shows how the planet gear rim deforms under load

It is also important to apply a suitable analysis factor to account for unequal load distribution between the planet gears. For this particular arrangement of eight planet gears with good accuracy mounted on fixed carrier pins, AGMA recommends using an analysis load factor of 1.3. Unfortunately, the analysis report produced by Romax Technology in appendix H assumes equal load sharing between all eight planet gears, which would be much lower loading than industry recommendations.
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Old 9th Jul 2018, 05:57
  #1860 (permalink)  
 
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Originally Posted by riff_raff View Post
I have some experience with epicyclic gear drive design. And when I looked at a cross section drawing of this gearbox, one thing that seemed questionable to me was the rim section thickness of the 2nd stage planet gears. The radial section thickness at the face width center appears to be less than 1x the gear tooth whole depth. I recall being given a stern lecture by a very experienced gearbox designer about making sure to provide plenty of rim section thickness with planet gear configurations like this. The alternating 2/rev tension/compression stress cycles at the bearing race surface resulting from "bending" of the rim will be more of a problem than you would think. There is a great illustration on page 8 of appendix H that shows how the planet gear rim deforms under load

It is also important to apply a suitable analysis factor to account for unequal load distribution between the planet gears. For this particular arrangement of eight planet gears with good accuracy mounted on fixed carrier pins, AGMA recommends using an analysis load factor of 1.3. Unfortunately, the analysis report produced by Romax Technology in appendix H assumes equal load sharing between all eight planet gears, which would be much lower loading than industry recommendations.
So for a layman would the required redesign be a new gearbox or could they redesign the inside whilst not increasing the gearbox outside dimensions too much?
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