EC225
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I am back to work on Tuesday and when I'm away from work I don't hear anything, only down side of living in Australia really. I only ever step in when you go off on one grinding your axe.
Si
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You may be right Pablo, I can't see those paragraphs as I don't subscribe he Evening Express and I don't live in a place where I can get it. But, the return to service has not been implemented in a way which will instill or maintain passenger confidence.
From what I can recall of the meetings, it was mentioned that there will almost inevitably be software glitches associated with the introduction of mod 45 cockpit warning system. This is the nature of all software.
Bristow has anticipated this and is in no hurry to bring the EC225 back into service en masse. There is likely to be an initial period of relatively few flights, perhaps not carrying passengers, while experience is gained with new procedures and engineering practices.
All the colleagues I have spoken to are confident that the likelihood of an actual mechanical failure recurring in the bevel gear has now been reduced to virtually nil, due to rigorous anti-corrosion measures.
By "virtually nil" I mean no more prone now to failure with the existing shaft design than with the new shaft to be introduced in 2014. Personally I would feel more relaxed flying with a well-monitored old-style shaft.
Bristow has anticipated this and is in no hurry to bring the EC225 back into service en masse. There is likely to be an initial period of relatively few flights, perhaps not carrying passengers, while experience is gained with new procedures and engineering practices.
All the colleagues I have spoken to are confident that the likelihood of an actual mechanical failure recurring in the bevel gear has now been reduced to virtually nil, due to rigorous anti-corrosion measures.
By "virtually nil" I mean no more prone now to failure with the existing shaft design than with the new shaft to be introduced in 2014. Personally I would feel more relaxed flying with a well-monitored old-style shaft.
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All the colleagues I have spoken to are confident that the likelihood of an actual mechanical failure recurring in the bevel gear has now been reduced to virtually nil, due to rigorous anti-corrosion measures.
TM. No. As I understand it, by the time that all North Sea EC225 operations resume, every shaft will have been examined minutely not only by the techniques you mention but also by very close engineering inspection of the inside of shafts for any hint of "mud".
I believe that all shafts worldwide have already been scrutinised and the remainder of EC225s, flying elsewhere around the planet uninterrupted since last year's ditchings, have not been found to have any hint of stress corrosion or cracking.
According to EC, that's a collective total of over 20,000 hours of trouble free service from the other bevel gears in various countries.
I believe that all shafts worldwide have already been scrutinised and the remainder of EC225s, flying elsewhere around the planet uninterrupted since last year's ditchings, have not been found to have any hint of stress corrosion or cracking.
According to EC, that's a collective total of over 20,000 hours of trouble free service from the other bevel gears in various countries.
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As I understand it, by the time that all North Sea EC225 operations resume, every shaft will have been examined minutely not only by the techniques you mention but also by very close engineering inspection of the inside of shafts for any hint of "mud".
Last edited by terminus mos; 4th Aug 2013 at 11:33.
But I'm not sure that removing the shaft makes it any easier to inspect for corrosion. Either way, the access is from the bottom of the shaft and the relevant area is just a little way up. Therefore it can be seen with the naked eye, and I would presume that some sort of boroscope could easily give a magnified view. Looking at photos of the 2nd failed shaft, the corrosion was pretty obvious once it had been cleaned up.
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The degree and type of corrosion allegedly associated with the failed shafts was of such a minor nature that it didn’t raise any obvious alarm bells when the two incidents were compared.
Boroscope inspection in the field is only going to highlight plainly obvious corrosion. The boroscope inspection is carried out to confirm removal of the ‘ Mud’ and deposits not the type of corrosion EC are talking about.
There is no EC requirement to check for corrosion.
The chance of seeing the weld area with the naked eye from the bottom of the box is compromised due to the change in profile of the shaft and dripping oil.
Boroscope inspection in the field is only going to highlight plainly obvious corrosion. The boroscope inspection is carried out to confirm removal of the ‘ Mud’ and deposits not the type of corrosion EC are talking about.
There is no EC requirement to check for corrosion.
The chance of seeing the weld area with the naked eye from the bottom of the box is compromised due to the change in profile of the shaft and dripping oil.
Definitely not an Engineer or Metallurgist....but having the shaft completely removed from the Gearbox for an inspection certainly makes sense as far as being able to thoroughly examine the entire shaft in detail using advanced techniques beyond a MK I eyeball and flashlight by peering up into the gearbox from one end of the shaft with oil dripping into your eye.
Why if Corrosion is part of the cause for the cracking....why would there be no requirement by EC to Check for Corrosion.
I would think....any corrosion on any part of the aircraft would be of concern despite some corrosion not having the potential to cause loss of the aircraft.
Corrosion on a MGB Shaft seems an issue that would demand evaluation for cause and potential effect upon the serviceability of the Gear Box and thus the Aircraft.
Why if Corrosion is part of the cause for the cracking....why would there be no requirement by EC to Check for Corrosion.
I would think....any corrosion on any part of the aircraft would be of concern despite some corrosion not having the potential to cause loss of the aircraft.
Corrosion on a MGB Shaft seems an issue that would demand evaluation for cause and potential effect upon the serviceability of the Gear Box and thus the Aircraft.
Pablo, I'm no aircraft technician but from the photos published by EC, at modest magnification, the corrosion on the failed shaft was quite obvious compared to the smooth surface of an unaffected shaft.
I can't immediately find an SB requiring inspection of the surface for corrosion, but I do recall EC asking all the operators to look for it. Its such an obvious thing to do that I can't imagine that EC would not be sure that there weren't corroded shafts still in service, or that if they had omitted to do this, that EASA and CAA wouldn't have required it anyway.
If dripping oil is an issue, just remove the sump and leave for a couple of days until the drips stop - after all, these a/c haven't exactly been busy recently!
I can't immediately find an SB requiring inspection of the surface for corrosion, but I do recall EC asking all the operators to look for it. Its such an obvious thing to do that I can't imagine that EC would not be sure that there weren't corroded shafts still in service, or that if they had omitted to do this, that EASA and CAA wouldn't have required it anyway.
If dripping oil is an issue, just remove the sump and leave for a couple of days until the drips stop - after all, these a/c haven't exactly been busy recently!
Last edited by HeliComparator; 4th Aug 2013 at 19:33.
these a/c haven't exactly been busy recently!
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and I would presume that some sort of boroscope could easily give a magnified view. Looking at photos of the 2nd failed shaft, the corrosion was pretty obvious once it had been cleaned up.
So, I am back to where I started. Namely, the Bond failed shaft was the only one with corrosion at the plug shamfer, and it failed. The MGBs with the bad shamfer (known S/Ns) at the plug have been removed and re machined. Accepted.
The CHC gearbox was the only one which had corrosion under the sludge and it also failed. Other aircraft operating in the same environments have had sludge shown on NDI and cleaning, but have no corrosion, I am not sure about that.
Wasn't it the case that the CHC aircraft spent a lot of time shut down offshore? Much more so than other others in that fleet?
As I said, its such an easy thing to check that I really can't imagine that everyone has overlooked it. Surely you are in a position to ask the question of a more authoritative source than prune?
As I said, its such an easy thing to check that I really can't imagine that everyone has overlooked it. Surely you are in a position to ask the question of a more authoritative source than prune?
Last edited by HeliComparator; 5th Aug 2013 at 06:37.
In this document it contains on page 10 the following statement:-
is more severe than the certification standards
If the 14 false alarms in 2 weeks statistic is even remotely accurate how or what validates that statement?
The probability to have a bevel gear crack not detected by M’ARMS or NDI,
leading to in-flight rupture and ditching is
leading to in-flight rupture and ditching is
lower than 10-9/FH, (1 per billion) which
is more severe than the certification standards
If the 14 false alarms in 2 weeks statistic is even remotely accurate how or what validates that statement?
Precisely because they are FALSE alarms Pittsy. What validates it? I don't know but its probably based on previous MARMS detection information in both actual failure cases.
Add in the requirement for additional MOD 45 polling at 5 minute intervals, the requirement to have two consecutive alert polls, MARMS downloads after every flight and the NDI and you can get some idea where EC is coming from with this.
The problem is not that the MOD 45 warning is not detecting, the problem is that it thinks its detecting when its not really detecting anything bad.
Add in the requirement for additional MOD 45 polling at 5 minute intervals, the requirement to have two consecutive alert polls, MARMS downloads after every flight and the NDI and you can get some idea where EC is coming from with this.
The problem is not that the MOD 45 warning is not detecting, the problem is that it thinks its detecting when its not really detecting anything bad.
II - yes sure I hear you and sure its not to suggest that the physical problem isn't isolated but some of these claims are pretty big and to say that their HUMS is going to capture everything to a 1 in a billion but then that same system seems so un-robust that it false alarms 14 times in 2 weeks....
Obviously that might be 14 times from 14 billion but on the basis it isn't.... If I have an oil pressure light in my car that is constantly "on" then its not really a valid system or do we disagree?
Especially since this system seems to have the buy in of the CAA, EASA and the operators.....
Edited to add:-
Going back to your point about 1/1bn flight hours - obviously this isn't back tested because the entire fleet hasn't done this many hours so OK its an extrapolation which might be fine if a certain level of robustness had been demonstrated around the process, which a high % of false alarms wouldn't suggest (if in fact 14 false alarms is a high % of the total run ups).
Thing is when you read the AAIB report on the two accidents and the element around HUMS you do find that this system and its thresholds are very specific to each airframe (hence I believe there is a fleetwide maximum threshold within the "learned" limits).
That might seem to be OK if it was business as usual but here it seems that the use of this data is being used to overcome limitations.
Obviously that might be 14 times from 14 billion but on the basis it isn't.... If I have an oil pressure light in my car that is constantly "on" then its not really a valid system or do we disagree?
Especially since this system seems to have the buy in of the CAA, EASA and the operators.....
Edited to add:-
Going back to your point about 1/1bn flight hours - obviously this isn't back tested because the entire fleet hasn't done this many hours so OK its an extrapolation which might be fine if a certain level of robustness had been demonstrated around the process, which a high % of false alarms wouldn't suggest (if in fact 14 false alarms is a high % of the total run ups).
Thing is when you read the AAIB report on the two accidents and the element around HUMS you do find that this system and its thresholds are very specific to each airframe (hence I believe there is a fleetwide maximum threshold within the "learned" limits).
That might seem to be OK if it was business as usual but here it seems that the use of this data is being used to overcome limitations.
Last edited by Pittsextra; 5th Aug 2013 at 11:59.
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The crack in the shaft of G-REDW was initiated by a corrosion pit just over 2 thousands of an inch deep. Other corrosion pits were also discovered in the shaft, but only after using a scanning electron microscope.
Pitts, the one in a billion flight hours is of course a calculated probability, as it is for virtually all things to do with certification.
Clearly the false alarm rate is unacceptable, but fortunately we now know why its doing it a minor change to operational procedures will avoid it, although it would have been better if it hadn't done it in the first place!
Pablo, 2 thou depth doesn't sound a lot but in the context of a machined mirror finish, its obvious to the naked eye.
Clearly the false alarm rate is unacceptable, but fortunately we now know why its doing it a minor change to operational procedures will avoid it, although it would have been better if it hadn't done it in the first place!
Pablo, 2 thou depth doesn't sound a lot but in the context of a machined mirror finish, its obvious to the naked eye.