North Sea heli ditching: Oct 2012
HC, while we discuss ways of measuring shaft crack magnitude, I suspect that the reall issue for EC to resolve is the thing cracking in the first place. 
I do appreciate your points on adding parts and circuits and sensors inside the box regarding a risk of failure profile.
I do appreciate your points on adding parts and circuits and sensors inside the box regarding a risk of failure profile.
HC, while we discuss ways of measuring shaft crack magnitude, I suspect that the real issue for EC to resolve is the thing cracking in the first place.
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.....With your scheme, for each shaft you need at least a pair of sensors in quadrature, probably more for multi-bearing shafts. Whereas for external vibe sensors, one can share a number of shaft/gears/bearings and/or more than 1 sensor can look at the same element to give corroboration. With the amazing "power" of signal averaging, current hums technology is pretty good at detecting the sort of shaft breathing you are referring to. Sorry but I remain unconvinced that proximity/position sensing is a better way to do it..........
It was not my intent to propose using the technique shown in that image as a fix for the EC225 MGB. I only meant to demonstrate that there are methods to monitor for such failures. As you correctly noted, it would be difficult to implement such a system for each rotating shaft in the MGB.
In practice, there is typically no monitoring for these types of failure modes. While it may seem illogical, especially given what occurred with the EC225 MGB bevel shaft, the reason for this is that such failure modes are not considered to be "credible" in a classic failure mode/effects analysis. In theory, these failures are prevented from occurring by a combination of careful design and analysis, use of special materials, tightly controlled manufacturing processes, special inspections, etc.
Regards,
riff_raff
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"Eurocopter Closing In On Gearbox Issue Solution"
"Eurocopter Closing In On Gearbox Issue Solution"
From: Eurocopter Closing In On Gearbox Issue Solution | Aviation International News
From: Eurocopter Closing In On Gearbox Issue Solution | Aviation International News
332L.....not a 225?
If it had been the same problem in an L instead of a 225...it would have ruined EC's Day......mine doesn't get ruined in any case.
What I do take out of all the recent news is that the problem is not limited to a particular set of shafts as no mention has been made to enumerate the particular shafts in question....and the testing program seems designed to confirm the problem, identify the cause, and find a fix for it.....rather than just do a recall on particular Marks of shaft.
That would also tend to explain the length of time all this is taking.
What I do take out of all the recent news is that the problem is not limited to a particular set of shafts as no mention has been made to enumerate the particular shafts in question....and the testing program seems designed to confirm the problem, identify the cause, and find a fix for it.....rather than just do a recall on particular Marks of shaft.
That would also tend to explain the length of time all this is taking.
EADS CEO comments
These guys sum up comments from the CEO:-
Eurocopter develops ?interim fix? for EC225 issue - News - Shephard
You can read for yourselves but it really is confusing language.
For example:-
‘The final fix will include partial changes in the design of the shaft. It is not a very significant change – we can do it with the same raw material. The root cause is residual stresses from the manufacturing process combined with… other things. But the final fix is a slight change of the
design,’ Bertling said
Then he continues with:-
He noted that the crack was caused by unavoidable corrosion of the bevel gear shaft in combination with a ‘very specific’ set of circumstances, in a ‘worst of worst case scenario’.
If we have a "very specific" set of circumstances then isn't the fix best resolved with training? Surely if re-training or further education then its not "very specific" enough?
Whilst it might sound very fancy to have HUMS data available to the crew as they fly if they can isolate the cause to a specific set of circumstances then avoiding such circumstances has to be safer than simply making an assumption that HUMS alarms are now relating only to this issue.
Eurocopter develops ?interim fix? for EC225 issue - News - Shephard
You can read for yourselves but it really is confusing language.
For example:-
‘The final fix will include partial changes in the design of the shaft. It is not a very significant change – we can do it with the same raw material. The root cause is residual stresses from the manufacturing process combined with… other things. But the final fix is a slight change of the
design,’ Bertling said
Then he continues with:-
He noted that the crack was caused by unavoidable corrosion of the bevel gear shaft in combination with a ‘very specific’ set of circumstances, in a ‘worst of worst case scenario’.
If we have a "very specific" set of circumstances then isn't the fix best resolved with training? Surely if re-training or further education then its not "very specific" enough?
Whilst it might sound very fancy to have HUMS data available to the crew as they fly if they can isolate the cause to a specific set of circumstances then avoiding such circumstances has to be safer than simply making an assumption that HUMS alarms are now relating only to this issue.
Last edited by Pittsextra; 18th Apr 2013 at 09:12.
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I read Pitts post scratched my head and read the article and I think second time round it made sense, no offense meant Pitts.
That sounds positive and even my little knowledge of manufacturing processes gives me hope for a permanent fix. Lets get the software and sensors and get going again, I want to get back in the 225.
Si
That sounds positive and even my little knowledge of manufacturing processes gives me hope for a permanent fix. Lets get the software and sensors and get going again, I want to get back in the 225.
Si
No offence taken.
If this is such a "very specific" set of circumstances and EC have identified that X, Y and Z together = crack then surely the easiest thing (prior to any redesign) to do is avoid X, Y and Z together??
My point being if you can't avoid it then its not "very specific" is it.
Edit to add: - Also having identified this issue - seemingly a few weeks ago - when will EASA (and others) modify the airworthiness directive to formalise any change in operation for those EC225's not currently grounded?
If this is such a "very specific" set of circumstances and EC have identified that X, Y and Z together = crack then surely the easiest thing (prior to any redesign) to do is avoid X, Y and Z together??
My point being if you can't avoid it then its not "very specific" is it.
Edit to add: - Also having identified this issue - seemingly a few weeks ago - when will EASA (and others) modify the airworthiness directive to formalise any change in operation for those EC225's not currently grounded?
Last edited by Pittsextra; 18th Apr 2013 at 08:43.
Yep...so like I said why wait to formalise this? EASA AD 2012-0087 came out what? 9 days after the 1st issue. So why wait 27days (and counting) to highlight these specific circumstances that presumably its advisable to avoid.
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Originally Posted by Pittsextra
So why wait 27days (and counting) to highlight these specific circumstances that presumably its advisable to avoid.
In short I have no idea but the lack of information is more than slightly frustrating.
Si
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I have no idea Pitts. I have nothing to do with EC, I am just a customer who pays the ultimate bills. But the cause(s) are residual stress caused by the welding process and other manufacturing processes and corrosion.
The short term fix will be additional HUMS data acquisition. It will activate a (probably temporary) cockpit warning. EOP will probably be reduce MCP by 15% and continue to land as soon as possible.
The new shaft will probably not be welded and if it does have a weld, it will be done at a lower temperature to reduce stress. New shafts are predicted to be available mid 2014.
The short term fix will be additional HUMS data acquisition. It will activate a (probably temporary) cockpit warning. EOP will probably be reduce MCP by 15% and continue to land as soon as possible.
The new shaft will probably not be welded and if it does have a weld, it will be done at a lower temperature to reduce stress. New shafts are predicted to be available mid 2014.
I feel for those in the thick of this. I'm sure the issues are all the things you sasy TM but when you have a CEO coming out with comments like ..."corrosion....and other things" and "very specific set of circumstances" it will be interesting to see how the story gets spun for the punters at the HSSG.