AW139 lost tail taxying DOH
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Testing for repair surface preparation
Just in case there are any sceptics left out there, here are some results of a test to evaluate surface preparation procedures. The test is based on ASTM D3762. Two panels are bonded together using the candidate process and then specimens 25mm wide are cut from the blank. A standard wedge is driven into the end of the specimen and it is placed in a hostile test environment, typically 50C and 95% RH. The faster the crack in the adhesive grows, together with the locus of failure (interface or through the adhesive layer) will give an indication of the relative performance of the surface preparation process. The closer to horizontal the graph is, the better.
This is a far more reliable test than just strength testing or fatigue testing.
Sorry for the poor resolution. The image was scanned from a photocopy of an old paper (Repair of Mirage III Aircraft Using the BFRP Crack Patching Technique, Baker, A.A., et al, Int. J. of Case Studies in Eng. Mech. and Matls., 1983). Suffice it to say that the highest line is hand abrasion, in a manner simialr if not identical to that specified by AW. The slightly better but still bad result is grit blasting. The two lower (acceptable) lines are phosphoric acid anodising.
This is old data and shows just how long ago it was known that hand abrasion produces poor bond durability. (Almost back to the days of the horse-drawn zepplin!) Nowdays there are at least two alternative processes which produce results comparable to phosphoric acid anodising and which are far easier to apply under field conditions than anodising. We have used one of those processes for well over four thousand repairs with only three failures (due to operator errors/laziness).
Now poor old AW has copped a flogging from me about this subject lately, but to be fair, they are not the only manufacturer using such antiquated repair methods. I am told that there is at least one other large OEM who use similar methods and I am sure that there are others. I think it is time that the regulators stepped in and requried that all OEM repair processes produce reliably sound structures.
I could fax the image if anyone wants it. It may come out better.
Regards
blakmax
This is a far more reliable test than just strength testing or fatigue testing.
Sorry for the poor resolution. The image was scanned from a photocopy of an old paper (Repair of Mirage III Aircraft Using the BFRP Crack Patching Technique, Baker, A.A., et al, Int. J. of Case Studies in Eng. Mech. and Matls., 1983). Suffice it to say that the highest line is hand abrasion, in a manner simialr if not identical to that specified by AW. The slightly better but still bad result is grit blasting. The two lower (acceptable) lines are phosphoric acid anodising.
This is old data and shows just how long ago it was known that hand abrasion produces poor bond durability. (Almost back to the days of the horse-drawn zepplin!) Nowdays there are at least two alternative processes which produce results comparable to phosphoric acid anodising and which are far easier to apply under field conditions than anodising. We have used one of those processes for well over four thousand repairs with only three failures (due to operator errors/laziness).
Now poor old AW has copped a flogging from me about this subject lately, but to be fair, they are not the only manufacturer using such antiquated repair methods. I am told that there is at least one other large OEM who use similar methods and I am sure that there are others. I think it is time that the regulators stepped in and requried that all OEM repair processes produce reliably sound structures.
I could fax the image if anyone wants it. It may come out better.
Regards
blakmax
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blakmax,
I was wondering if there might be a chance you could write a book about bonding practices.
Something an average mechanic or pilot could use and understand.
I would buy the book. (assuming the price is reasonable)
I was wondering if there might be a chance you could write a book about bonding practices.
Something an average mechanic or pilot could use and understand.
I would buy the book. (assuming the price is reasonable)
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Hi Slowrotor
I have produced a document for the FAA called BEST PRACTICE IN ADHESIVE BONDED STRUCTURES AND REPAIRS which is DOT/FAA/AR – TN06/07, Apr 2007.
It is available through the FAA Tech Center Library. Unfortunately you must email them because access to the FAA web site with the document is not available outside the US because of homeland security restrictions to government web sites. The address is [email protected] That is actlibrary at faa dot gov .
That document addresses surface preparation as well as a number of other issues including the correct methods for hot bonded repairs.
The best part is that it is free!!
Regards
blakmax
I have produced a document for the FAA called BEST PRACTICE IN ADHESIVE BONDED STRUCTURES AND REPAIRS which is DOT/FAA/AR – TN06/07, Apr 2007.
It is available through the FAA Tech Center Library. Unfortunately you must email them because access to the FAA web site with the document is not available outside the US because of homeland security restrictions to government web sites. The address is [email protected] That is actlibrary at faa dot gov .
That document addresses surface preparation as well as a number of other issues including the correct methods for hot bonded repairs.
The best part is that it is free!!
Regards
blakmax
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Hi Blakmax
Very good, however I feel that as being that 99 % readers/contributers of this web site are pilots why are you seeming to run a composite repair course on-line?
Being in commercial aviation (also military to an extent) I feel it can be contradictory to certain interests to make the statements that you do, yes you are very correct in your composite repair comments, but you are influencing people to make decisions, commercial, that you are not qualified to make, I would also suggest an engineering site would be best suited for your extremely valuable contribution.
Best Regards
An old! structural engineer
Very good, however I feel that as being that 99 % readers/contributers of this web site are pilots why are you seeming to run a composite repair course on-line?
Being in commercial aviation (also military to an extent) I feel it can be contradictory to certain interests to make the statements that you do, yes you are very correct in your composite repair comments, but you are influencing people to make decisions, commercial, that you are not qualified to make, I would also suggest an engineering site would be best suited for your extremely valuable contribution.
Best Regards
An old! structural engineer
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No suprise
...on the delamination of the repair. I have a great picture of the repair being done in an open "clamp shell hangar" (tent) with the sand blowing in the distance.
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stacey_s
Hi Blakmax
Very good, however I feel that as being that 99 % readers/contributers of this web site are pilots why are you seeming to run a composite repair course on-line?
Being in commercial aviation (also military to an extent) I feel it can be contradictory to certain interests to make the statements that you do, yes you are very correct in your composite repair comments, but you are influencing people to make decisions, commercial, that you are not qualified to make, I would also suggest an engineering site would be best suited for your extremely valuable contribution.
Best Regards
An old! structural engineer
Hi Blakmax
Very good, however I feel that as being that 99 % readers/contributers of this web site are pilots why are you seeming to run a composite repair course on-line?
Being in commercial aviation (also military to an extent) I feel it can be contradictory to certain interests to make the statements that you do, yes you are very correct in your composite repair comments, but you are influencing people to make decisions, commercial, that you are not qualified to make, I would also suggest an engineering site would be best suited for your extremely valuable contribution.
Best Regards
An old! structural engineer
If you feel his information is adversely affecting some people's decision making skills, then perhaps those same people should not be in aviation, much less make decisions related to aviation.
Blakmax's information has been nothing but informative, detailed and consistently objective and as such, will no doubt IMPROVE many people's decision making skills.
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I agree, the decision makers I refer too are the our clients, not Engineers or Pilots. but people who decide if their employees ride in your machines or a competitors!
S
S
Safety First...
Remember?!
Crew and Customers included, than final commercial result can be lucrative too.
But can fully understand operators concerns after such huge investment in something new, nice and shiny.... reminds me on Titanic case, no more orchestra ready to play while.....
Any way things must be settled properly soon or later.
Remember?!
Crew and Customers included, than final commercial result can be lucrative too.
But can fully understand operators concerns after such huge investment in something new, nice and shiny.... reminds me on Titanic case, no more orchestra ready to play while.....
Any way things must be settled properly soon or later.
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Hi Stacey
I have tried all avenues to talk directly with the engineers at AW but to no avail. Perhaps you have some contacts who would be prepared to talk to me? Without that dialog, I am left to communicate publically. I have tried other forums, but they simply don't have the focus. As well, I have also had a number of responses from repair technicians and other people who also read PPRuNe. Many have supported my comments and found them helpful.
My personal objective in running these discussions is to foster an improvement in repair and construction bonding technology with the goal of improved air safety. Much of the bonded structure on helicopters is primary, flight critical structure. If I am aware of deficient practices such as voided adhesive bonds or ineffective repair surface preparation methods I feel I have a duty of care to raise these issues.
Regards
blakmax
I have tried all avenues to talk directly with the engineers at AW but to no avail. Perhaps you have some contacts who would be prepared to talk to me? Without that dialog, I am left to communicate publically. I have tried other forums, but they simply don't have the focus. As well, I have also had a number of responses from repair technicians and other people who also read PPRuNe. Many have supported my comments and found them helpful.
My personal objective in running these discussions is to foster an improvement in repair and construction bonding technology with the goal of improved air safety. Much of the bonded structure on helicopters is primary, flight critical structure. If I am aware of deficient practices such as voided adhesive bonds or ineffective repair surface preparation methods I feel I have a duty of care to raise these issues.
Regards
blakmax
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Blakmax, I have been viewing your input into this discussion and have found it totally enthralling. It’s like a on line training exercise and given by a professional with knowledge. I hope this thread continues and develops as I feel it can only befit the industry and the people involved in this type of technology.
Your last post indicating the lack of response from Augusta should not be a surprise, it is not to me. The I assume investigation into the event in question will soon reach the public domain and feed the thread and further discussion. Until then it’s un-lightly any meaning full information will be available.
Outhouse.
Your last post indicating the lack of response from Augusta should not be a surprise, it is not to me. The I assume investigation into the event in question will soon reach the public domain and feed the thread and further discussion. Until then it’s un-lightly any meaning full information will be available.
Outhouse.
Stacey _s Today there appears to be a fragmented understanding of technology, each subject in its own box, and no real connection between each box, I find your comment rather strange , the more the user knows & understands about his ride the safer he should be, the same for engineers
"Being in commercial aviation (also military to an extent) I feel it can be contradictory to certain interests to make the statements that you do, yes you are very correct in your composite repair comments, but you are influencing people to make decisions, commercial, that you are not qualified to make, I would also suggest an engineering site would be best suited for your extremely valuable contribution".(my bold)
Surely a commercial decision starts with safety, & if it does not I REALLY want to know.Some time ago I suggested a repair method we were using (not on aircraft) BM sent me a PM pointing out the pitfalls of the method we were using, it was totally unsolicited, a gesture that we found informative & helpful, and improved our repairs, he also suggested. how to find further information.
We have to remember that this is field of expertise & his living, any information we receive will be evaluated and used if thought relevant.
"Being in commercial aviation (also military to an extent) I feel it can be contradictory to certain interests to make the statements that you do, yes you are very correct in your composite repair comments, but you are influencing people to make decisions, commercial, that you are not qualified to make, I would also suggest an engineering site would be best suited for your extremely valuable contribution".(my bold)
Surely a commercial decision starts with safety, & if it does not I REALLY want to know.Some time ago I suggested a repair method we were using (not on aircraft) BM sent me a PM pointing out the pitfalls of the method we were using, it was totally unsolicited, a gesture that we found informative & helpful, and improved our repairs, he also suggested. how to find further information.
We have to remember that this is field of expertise & his living, any information we receive will be evaluated and used if thought relevant.
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Don't know if it happens to others, but if someone posts to a thread while I am drafting a response, my web browser crashes. Thanks 500e!
Thanks for the support guys. (Outhouse, down under you would be called "Dunny")
I understand Stacey's point and I did take some time out to consider an appropriate response. By chance I watched some TV and the program ended with a quotation I think is relevant: Our lives begin to end the day we become silent about things that matter. (Martin Luther King) (We have some deep and meaningful TV down under. Lots of crap but some D and M).
There are two ways I can change things; by educating people about the deficiencies (preferrably the manufacturers) or by helping lawyers get rich. The sad fact is that the latter option involves someone (possibly one of the 99% of readers) being a potential victim.
John R81, I have been working on educating crash investigators with some success (Google A08_25_29 and see if you recognise some similarities in the content.) I have also had favourable responses from local airworthiness authorities on some occasions when I have addressed some issues with crash reports. I have looked at creating a short course and I have even prepared a draft, but the economics don't stack up. With such a small target audience, I would not recover even my travel costs from down under, let alone any fees.
Some of my comments have been addressed in the FAA's latest version of AC20-107B, but regretably as long as the FAA continue to confuse the term "composites" by including adhesive bonding (which is a different technology altogether) and as long as the FAA persists with addressing a known and common adhesive bond failure mode by information which is only advisory, not regulatory, I don't hold out much hope for early improvement. If you read A08_25_29, keep in mind that the specific company mentioned has probably fully complied with the current regulations, yet disbonds occur in service. Surely something which can result in a loss of an aircraft should be mandatory, not advisory.
Regards
blakmax
Thanks for the support guys. (Outhouse, down under you would be called "Dunny")
I understand Stacey's point and I did take some time out to consider an appropriate response. By chance I watched some TV and the program ended with a quotation I think is relevant: Our lives begin to end the day we become silent about things that matter. (Martin Luther King) (We have some deep and meaningful TV down under. Lots of crap but some D and M).
There are two ways I can change things; by educating people about the deficiencies (preferrably the manufacturers) or by helping lawyers get rich. The sad fact is that the latter option involves someone (possibly one of the 99% of readers) being a potential victim.
John R81, I have been working on educating crash investigators with some success (Google A08_25_29 and see if you recognise some similarities in the content.) I have also had favourable responses from local airworthiness authorities on some occasions when I have addressed some issues with crash reports. I have looked at creating a short course and I have even prepared a draft, but the economics don't stack up. With such a small target audience, I would not recover even my travel costs from down under, let alone any fees.
Some of my comments have been addressed in the FAA's latest version of AC20-107B, but regretably as long as the FAA continue to confuse the term "composites" by including adhesive bonding (which is a different technology altogether) and as long as the FAA persists with addressing a known and common adhesive bond failure mode by information which is only advisory, not regulatory, I don't hold out much hope for early improvement. If you read A08_25_29, keep in mind that the specific company mentioned has probably fully complied with the current regulations, yet disbonds occur in service. Surely something which can result in a loss of an aircraft should be mandatory, not advisory.
Regards
blakmax
Both documents are available for direct download:
DOT/FAA/AR-TN06/57
http://www.tc.faa.gov/its/worldpac/techrpt/artn0657.pdf
http://www.ntsb.gov/Recs/letters/2008/A08_25_29.pdf
DOT/FAA/AR-TN06/57
http://www.tc.faa.gov/its/worldpac/techrpt/artn0657.pdf
http://www.ntsb.gov/Recs/letters/2008/A08_25_29.pdf
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Mmmm ...
Gentleman...
Whilst I think we are very lucky to have some excellent input from blackmax I also think that we have to appreciate that there might be some input from others (stace) that might also be input effectively from "the horses mouth" .. perhaps we should wait and see what develops ... Agusta WILL sort this out and they will do it accurately ... lets wait and see what they come up with .... I'm sure they have this problem sorted ...
I'm flying these machines atm and I am confident in the info that is coming my way ... They (the 139) are a great bit of kit ... and as a LAME since 1976 I am quite happy for the time being to give Agusta the benefit of doubt ... I am happy with the new (?) tail booms lets see what develops ...
Cheers
Gentleman...
Whilst I think we are very lucky to have some excellent input from blackmax I also think that we have to appreciate that there might be some input from others (stace) that might also be input effectively from "the horses mouth" .. perhaps we should wait and see what develops ... Agusta WILL sort this out and they will do it accurately ... lets wait and see what they come up with .... I'm sure they have this problem sorted ...
I'm flying these machines atm and I am confident in the info that is coming my way ... They (the 139) are a great bit of kit ... and as a LAME since 1976 I am quite happy for the time being to give Agusta the benefit of doubt ... I am happy with the new (?) tail booms lets see what develops ...
Cheers
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Saudi Aramco
Saudi Aramco has issued a written notice to Agusta Westland that they will not accept delievery of Phase II of the Purchase Agreement (9 AW139's) until the tailboom issue has been resolved.
Other than the tailboom issue, we have been very satisfied with the five AW139's that we are currently operating. As noted in previous threads, there have been some minor issues with this aircraft, but as a helicopter pilot since 1970, I could go on and on about helicopter problems.
Other than the tailboom issue, we have been very satisfied with the five AW139's that we are currently operating. As noted in previous threads, there have been some minor issues with this aircraft, but as a helicopter pilot since 1970, I could go on and on about helicopter problems.
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Moving discussions about micro-voiding
Fellow PPRuNers
I have thought long and hard about stacey_s's comments of 2nd Dec and I have taken note. I have started a new, more generic thread at http://www.pprune.org/tech-log/39913...ng-issues.html
You will note from that new thread that AW is NOT the only company with the micro-voiding problem. I also provide my advice at that thread on how to manage micro-voiding for FREE so there is no excuse for AW or any other OEM for not addressing this issue.
I also invite interest in other topics which have appeared on this thread, but which are just as relevant to other manufacturer's repairs.
Regards and Merry Christmas
blakmax
I have thought long and hard about stacey_s's comments of 2nd Dec and I have taken note. I have started a new, more generic thread at http://www.pprune.org/tech-log/39913...ng-issues.html
You will note from that new thread that AW is NOT the only company with the micro-voiding problem. I also provide my advice at that thread on how to manage micro-voiding for FREE so there is no excuse for AW or any other OEM for not addressing this issue.
I also invite interest in other topics which have appeared on this thread, but which are just as relevant to other manufacturer's repairs.
Regards and Merry Christmas
blakmax