Heli ditch North Sea G-REDL: NOT condolences
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MGB Cross-Contamination
I am indebted to HC for the information that the LH accessory gearbox problem is fixed. But careful reading of AAIB Bulletin 8/2004 reveals that any accessory gearbox failure, left or right, can pass significant amounts of debris into the main gearbox via the common oil system. It seems unusual to permit a risk of consequential failure in a non-redundant system.
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EASA Airworthiness Directives Publishing Tool
All EASA-certified L2s and 225s grounded until the inspection is completed
All EASA-certified L2s and 225s grounded until the inspection is completed
If one certifying agency grounds an aircraft.....why would others not do the same? Likewise....if I know of the grounding order...why would I fly my machine until it had been inspected?
This ain't like an electrical relay that might cause a loss of air conditioning or something.....or am I missing something here?
This ain't like an electrical relay that might cause a loss of air conditioning or something.....or am I missing something here?
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Heli Ditch North Sea
I am surprised by the rapid turn round apparently achieved for gearbox examinations.
I have not helio experience, but have designed many gear boxes over the years, some safety critical. Apart from chip examination I would expect flaw detection of shafts and gears, this is not normally a very quick process even in AOG conditions
I have not helio experience, but have designed many gear boxes over the years, some safety critical. Apart from chip examination I would expect flaw detection of shafts and gears, this is not normally a very quick process even in AOG conditions
The EASA AD only grounds aircraft that have had a chip in the last 200 hours of operation.
No chip then carry on flying with a chip detector inspection every 10 hours.
This seems to be largely a tech records survey and probably wont ground many aircraft.
Does anybody know any different?
No chip then carry on flying with a chip detector inspection every 10 hours.
This seems to be largely a tech records survey and probably wont ground many aircraft.
Does anybody know any different?
Eric
That was last weeks AD, there was another one issued yesterday Numbered 2009-0095-E.
In essence the bit of the AD that has the teeth to effectively ground the aircraft is
The effective date of the AD is today 18th April 2009.
Gotta rush out, but hope this helps.
GS
That was last weeks AD, there was another one issued yesterday Numbered 2009-0095-E.
In essence the bit of the AD that has the teeth to effectively ground the aircraft is
In order to complement measures mandated by AD 2009-0087-E, this new AD
is issued to require a one-time inspection for absence of particles in the MGB
epicyclic reduction gear module on the entire fleet.
1) Before next flight after the effective date of this AD, unless already
accomplished per the requirements of AD 2009-0087-E, remove and
inspect the MGB epicyclic reduction gear module in accordance with the
instructions of paragraph 2.B.2 of Eurocopter Alert Service Bulletin (ASB)
No. 05.00.81 initial issue (for AS332 helicopters) or ASB No. 05A017 initial
issue (for EC225 helicopters).
is issued to require a one-time inspection for absence of particles in the MGB
epicyclic reduction gear module on the entire fleet.
1) Before next flight after the effective date of this AD, unless already
accomplished per the requirements of AD 2009-0087-E, remove and
inspect the MGB epicyclic reduction gear module in accordance with the
instructions of paragraph 2.B.2 of Eurocopter Alert Service Bulletin (ASB)
No. 05.00.81 initial issue (for AS332 helicopters) or ASB No. 05A017 initial
issue (for EC225 helicopters).
Gotta rush out, but hope this helps.
GS
I am out of the loop now but I imagine that each operator would have one or two zero timed MGB's ready to replace the initial units to be inspected thus minimising downtime. The gearboxes are not sealed units but can easily be dismantled in a workshop, I would think that Eurocopter engineers are on hand at the major operators to check out the epicyclics.
Has anyone got a copy of the 332 ASB 05-00-81?
Has anyone got a copy of the 332 ASB 05-00-81?
Last edited by Oldlae; 18th Apr 2009 at 17:55. Reason: Expansion for clarity.
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I am sure that if there was a bus crash that killed 16, there wouldn't be cries to stop the busses running - it would barely make the papers, despite the fact that for those directly affected, it would be no less dreadful than REDL.
N Sea workers are gravitating to this site because they are looking for comment (and probably comfort) beyond what is available in the Red Tops. For people to read that you believe this to be a PR exercise will do little to allay their fears. Many have learnt here that cracks are not necessarily accompanied by chips, therefore chip monitoring will not necessarily warn of cracks. I have to assume that the inspections mandate a minimum of CVI or MPI, or radiography for a more complete picture of what is going on today inside those gearboxes. Some of this has to be hugely time consuming (service to service) unless you have a significant stock of spare MGBs kicking around your storeroom.......not likely. REDL has a root cause. Until it is determined and eliminated, then it's difficult to think of a MGB inspection programme intended to provide assurance that there aren't undetected cracks propogating in key components as a "PR exercise",.It's sound engineering practice is it not?
bumpthump - PR was my feeling on Friday, but now the Manufacturer has modified its Alert Service Bulletin making further work mandatory. It seems that the manufacturer has an idea of how to improve fault detection within the epicyclic and want to implement it asap.
Regarding the point about the busses, what about a bus that crashed because its brakes failed - would the model be "grounded" in a flurry of prime time TV news and newspaper headlines? I somehow doubt it, because our perception of acceptable risk for road transport is quite different from our perception of that for air travel.
In the case of the Ford Pinto, there was certainly a fundamental design flaw and many burst into flames after a minor shunt. In the case of the L2/225 we have had one catastrophic failure in tens of millions of fleet hours over 17 years - hardly a fundamental design flaw.
This latest maintenance intervention does seem to be a good idea, but we have to be careful not to over-maintain since every maintenance intervention carries a potential hazard of human error etc.
HC
Regarding the point about the busses, what about a bus that crashed because its brakes failed - would the model be "grounded" in a flurry of prime time TV news and newspaper headlines? I somehow doubt it, because our perception of acceptable risk for road transport is quite different from our perception of that for air travel.
In the case of the Ford Pinto, there was certainly a fundamental design flaw and many burst into flames after a minor shunt. In the case of the L2/225 we have had one catastrophic failure in tens of millions of fleet hours over 17 years - hardly a fundamental design flaw.
This latest maintenance intervention does seem to be a good idea, but we have to be careful not to over-maintain since every maintenance intervention carries a potential hazard of human error etc.
HC
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RN,
it's inevitable that some remote possibilities will eventuate - but most will not. On this occasion it appears one has done so - as HC reiterates excellently above. To put it another way, it's very unlikely you'll be hit by lightning in the next 24 hours, but good odds it will happen to somebody somewhere. When it happens and is on the news, it doesn't make it any more likely it will happen to you or anyone else, nor does it mean we need to start an inquiry as to why we'd not all been warned to wear fireproof dielectric hats.
it's inevitable that some remote possibilities will eventuate - but most will not. On this occasion it appears one has done so - as HC reiterates excellently above. To put it another way, it's very unlikely you'll be hit by lightning in the next 24 hours, but good odds it will happen to somebody somewhere. When it happens and is on the news, it doesn't make it any more likely it will happen to you or anyone else, nor does it mean we need to start an inquiry as to why we'd not all been warned to wear fireproof dielectric hats.
It would appear that the clue is in the absence of precursors (just the one chip 34 hours before the failure). G-REDL was on heightened observation after this single precursor and, if there was to be an impending failure, more metal would have been anticipated - in the event, no more metal showed. Under normal circumstances that might have indicated that this metal could have been manufacturing swarf (realtively common in new gearboxes I am told).
In the EASA AD there was a hint that there might have been a reason that the mag-plug had not shown metal, hence the instruction to strip the epicyclic module and check for signs of MGB contamination (not check each gear for damage). The two ASBs from EC (one each for the EC225 and AS332L2) address the issue of absence of contamination and provide "enhancement of the means for detection of MGB contamination" by seeking to eliminate design features that could have resulted in the contamination being diverted away from the mag-plugs.
While the investigation is ongoing, it was absolutely necessary to ensure that there was no contamination in the gearboxes on other aircraft. It was also necessary to understand and address the issue of lack of precursors. EC and EASA appear to think they have found the reason (not the cause of the failure, but the inability to detect incipient failure).
Ramen - clearly it would be unlikely that any gearbox element could last for 10^9 flying hours. Achieving the extremely remote failure standard can therefore only be achieved by setting the inspection and overhaul periodicity and providing monitoring in the form of SOAP, mag-plugs and HUMS (I'm sure there are others - I'm not an engineer).
As 'The Sultan' pointed out to us several pages back, contamination detection is one of the principles tools for establishing the continuing health of rotating parts (as is HUMS). Normally, there is no failure without the precursors being seen and being confirmed by alternative monitoring methods. If, for some reason, the mag-plugs were not seeing metal (but it was being made) how much trust would have been placed in the alternative monitoring methods without this confirmation?
Jim
In the EASA AD there was a hint that there might have been a reason that the mag-plug had not shown metal, hence the instruction to strip the epicyclic module and check for signs of MGB contamination (not check each gear for damage). The two ASBs from EC (one each for the EC225 and AS332L2) address the issue of absence of contamination and provide "enhancement of the means for detection of MGB contamination" by seeking to eliminate design features that could have resulted in the contamination being diverted away from the mag-plugs.
While the investigation is ongoing, it was absolutely necessary to ensure that there was no contamination in the gearboxes on other aircraft. It was also necessary to understand and address the issue of lack of precursors. EC and EASA appear to think they have found the reason (not the cause of the failure, but the inability to detect incipient failure).
Ramen - clearly it would be unlikely that any gearbox element could last for 10^9 flying hours. Achieving the extremely remote failure standard can therefore only be achieved by setting the inspection and overhaul periodicity and providing monitoring in the form of SOAP, mag-plugs and HUMS (I'm sure there are others - I'm not an engineer).
As 'The Sultan' pointed out to us several pages back, contamination detection is one of the principles tools for establishing the continuing health of rotating parts (as is HUMS). Normally, there is no failure without the precursors being seen and being confirmed by alternative monitoring methods. If, for some reason, the mag-plugs were not seeing metal (but it was being made) how much trust would have been placed in the alternative monitoring methods without this confirmation?
Jim
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The lottery is an interesting comparison, but its reverse thinking. The lottery win is a forced, desired outcome. It's engineered to be that way. If the powers that be wanted it not to happen, and push out the likelihood of an occurance to the point where such an outcome could be considered nebulus, then there would be more than 49 numbers! In the case of MGBs, I'm pretty sure that passengers and crew alike want a repeat to be statistically speaking, as near as dammit, impossible. If the bus brakes failed because of an inherent design flaw, I reckon they'd be modified, and all types subject to a recall. I guess aviation is so exacting (and emotionally charged) simply because of the stark consequences in the event of something like an MGB failure. HUMS was being introduced jsut as I was leaving the N Sea. Doubtless a useful piece of kit, but equally, it has been shown to be not too smart (or perhaps the interpretation of its data) in the case of REDL. I guess only time will tell. Having worked in RBI and CBM for a good number of years, I have to agree with the concept of "the less intrusive maintenance the better". Bitter experience in rotating equipment (turbines and the likes) has shown a significant number of failures post intrusive maintenance were actually tied back to errors in the maintenance itself. Every time we take a wrench or screwdriver to a piece of healthy machinary, we introduce a risk that we can leave it in a worse (or potentially worse) state than we found it.
JimL, you have clarified something for me, in that you state that the inspections were to provide assurance that there was no contamination within the MGBs, as opposed to the component parts of the gearboxes.....is that correct? That would certainly make the inspections a whole lot less onerous than every cog in every box. I had assumed that there was a concern over cracks that may have preceded the catastrophic failure. A wrong assumption on my part.
JimL, you have clarified something for me, in that you state that the inspections were to provide assurance that there was no contamination within the MGBs, as opposed to the component parts of the gearboxes.....is that correct? That would certainly make the inspections a whole lot less onerous than every cog in every box. I had assumed that there was a concern over cracks that may have preceded the catastrophic failure. A wrong assumption on my part.
Last edited by bumpthump; 19th Apr 2009 at 19:38.
That's Life!!
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It 'appears' that part of the epicyclic gearing of the L2 and the 225 is 'potentially' magnetic, therefore there could be a case of 'metal making' being masked by this, rumours are that these components will be changed during the 'inspections' currently being conducted.
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Byte Jockey
Whether or not the box had been in another L2, I couldn't comment on but TIGF is an old 332L and as such has a earlier gearbox with different part number, not interchangeable with the L2 or 225.
HC
Tens of millions of fleet hours? Methinks you exaggerate somewhat. Even if you included the L and L1, (as well as the L2 and 225) I doubt that the Super Puma fleet hours would quite total "tens of millions"
Whether or not the box had been in another L2, I couldn't comment on but TIGF is an old 332L and as such has a earlier gearbox with different part number, not interchangeable with the L2 or 225.
HC
Tens of millions of fleet hours? Methinks you exaggerate somewhat. Even if you included the L and L1, (as well as the L2 and 225) I doubt that the Super Puma fleet hours would quite total "tens of millions"
Mark Twain's View of the Grand Lottery
Mark Twain, a great many years ago wrote an article that could very well apply to our situation today in regard the statistics and risk of flying out to the Rigs by helicopter.
The Danger Of Lying In Bed - Story by Mark Twain
The Danger Of Lying In Bed - Story by Mark Twain
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Mark Twain, a great many years ago wrote an article that could very well apply to our situation today in regard the statistics and risk of flying out to the Rigs by helicopter.
The Danger Of Lying In Bed - Story by Mark Twain
The Danger Of Lying In Bed - Story by Mark Twain
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Scotsheli
If a 332 pilot now gets an MGB chip light 100 miles offshore does he:-
a) Abandon the flight and land on the nearest platform
b) Abandon the flight and ditch immediately
c) Continue flight to base
a) Abandon the flight and land on the nearest platform
b) Abandon the flight and ditch immediately
c) Continue flight to base
G