AW139 lost tail taxying DOH
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Heard a rumour (hey it's a rumour network) ...
Heard a rumour that the airframe in question not only had a previous tail strike which was repaired but had a 2nd tail strike leaving a platform on the same day of the incident.
Also, the operator is refusing to release HUMS and other data to AAC.
The tail strike was enabled by a take-off without the autopilots engaged...
Comments?
Heard a rumour that the airframe in question not only had a previous tail strike which was repaired but had a 2nd tail strike leaving a platform on the same day of the incident.
Also, the operator is refusing to release HUMS and other data to AAC.
The tail strike was enabled by a take-off without the autopilots engaged...
Comments?
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Mmmm ...
wde ....
Care to clarify that .... do you mean that on the day of the tail-boom fold the a/c suffered a boom strike on a prior flight .... OR that the original strike was caused by a failure to engage the auto pilot?
It is common knowledge in the Arabian Gulf that the original boom damage was caused by an attempted T/Off with A/P not engaged and the then 'hard landing' that ensued. The t'boom damage from that landing subsequently was repaired and then returned to service.
Are you saying that there was a second Auto Pilot off incident?
wde ....
Care to clarify that .... do you mean that on the day of the tail-boom fold the a/c suffered a boom strike on a prior flight .... OR that the original strike was caused by a failure to engage the auto pilot?
It is common knowledge in the Arabian Gulf that the original boom damage was caused by an attempted T/Off with A/P not engaged and the then 'hard landing' that ensued. The t'boom damage from that landing subsequently was repaired and then returned to service.
Are you saying that there was a second Auto Pilot off incident?
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Good rumour, but totally wrong all data supplied to relevant authorities and full co-operation given to manufacturer and authorities carrying out the investigation, report will come early January.
Stace
Stace
hope to see that in action not in "rumors"
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Sorry to say it guys, but changing to aluminium for the boom is not going to address the problem. These failures and the rash of disbonds which have occurred on aircraft which I believe have not had tail strikes are almost certainly due to weakening of the bond caused by micro-voids. I posted photos on the thread about the recent AW109 ground resonance incident that show a significant degradation of the bond. I suggest that readers look at these to see the example of a good bond and compare that with the AW139 disbond example.
Changing the skins or the core material without addressing the moisture contamination of the bond prior to and during production will still produce sub-standard adhesive bonds.
Secondly, if the repairs referred to used a scuff sand and solvent contaminate process as the surface preparation (as I am told is the standard process) then I am prepared to wager the family jewels on the fact that these repairs will disbond. Unless there is some chemical treatment of the metallic surface to develop proper bond durability, whatever strength is achieved in the short term will dissipate with time until the bond completely fails. The rivets will only act to hold the ineffective repair in place so it looks good.
Thirdly, my rumour network tells me the latest version of the repair leaves the disbonded skin intact. The recommended (mandated?) repair involves injection of adhesive into the disbond and rivetting a doubler over the area. What a joke! For an adhesive to form a structural bond to a metal the surface must be clean, chemically active and treated to resist hydration of the interface. You can not do any of these steps by drilling a hole and squeezing fresh adhesive in. Two things will happen: 1. the air gap will be filled with ineffective adhesive such that the tap test suggests it is no longer disbonded, and 2. The technician will get a warm fuzzy feeling that he has performed the repair IAW the OEM instructions. The difference to bond strength will be dead set ZERO.
Here is a better repair
. Carefully map the disbond extremities. Prepare the area for painting IAW the OEM procedures. Apply a coating of bright pink paint to carefully map the disbond. Return to service.
Here are the advantages of this repair:
For nearly twenty five years, I have been advocating the total prohibition of injection repairs for disbonds. I have openly challenged OEMs to show me one single test result (other than meaningless NDI which shows the disbond has "dissapeared").
So, AW, do you have any structural tests which show ANY restoration of bond strength after injection repair? Do you have any evidence which shows scuff sand and solvent cleaning for repair actually restores structural integrity AND bond durability?
AW has not responded to any of my approaches through this forum or from direct and indirect e-mails. So I suggest that you, the operators, owners and crew start asking the same questions. You have a legal right to have assurance that 1. The structure as manufactured is sound and 2. Any repair actually restores the certification basis for the aircraft.
Regards
Blakmax
Changing the skins or the core material without addressing the moisture contamination of the bond prior to and during production will still produce sub-standard adhesive bonds.
Secondly, if the repairs referred to used a scuff sand and solvent contaminate process as the surface preparation (as I am told is the standard process) then I am prepared to wager the family jewels on the fact that these repairs will disbond. Unless there is some chemical treatment of the metallic surface to develop proper bond durability, whatever strength is achieved in the short term will dissipate with time until the bond completely fails. The rivets will only act to hold the ineffective repair in place so it looks good.
Thirdly, my rumour network tells me the latest version of the repair leaves the disbonded skin intact. The recommended (mandated?) repair involves injection of adhesive into the disbond and rivetting a doubler over the area. What a joke! For an adhesive to form a structural bond to a metal the surface must be clean, chemically active and treated to resist hydration of the interface. You can not do any of these steps by drilling a hole and squeezing fresh adhesive in. Two things will happen: 1. the air gap will be filled with ineffective adhesive such that the tap test suggests it is no longer disbonded, and 2. The technician will get a warm fuzzy feeling that he has performed the repair IAW the OEM instructions. The difference to bond strength will be dead set ZERO.
Here is a better repair
. Carefully map the disbond extremities. Prepare the area for painting IAW the OEM procedures. Apply a coating of bright pink paint to carefully map the disbond. Return to service.Here are the advantages of this repair:
- This repair is just as effective in restoring bond strength (i.e. it will achieve nothing, the same as injection achieves)
- It does not involve penetration of the skin, so core and skin corrosion risks are reduced substantially.
- It will be easy to find the disbonded area during the next inspection.
- If the area is accurately mapped, you can plot the growth of the disbond
- There is an additional layer of fresh paint which will improve corrosion resistance of the skin.
For nearly twenty five years, I have been advocating the total prohibition of injection repairs for disbonds. I have openly challenged OEMs to show me one single test result (other than meaningless NDI which shows the disbond has "dissapeared").
So, AW, do you have any structural tests which show ANY restoration of bond strength after injection repair? Do you have any evidence which shows scuff sand and solvent cleaning for repair actually restores structural integrity AND bond durability?
AW has not responded to any of my approaches through this forum or from direct and indirect e-mails. So I suggest that you, the operators, owners and crew start asking the same questions. You have a legal right to have assurance that 1. The structure as manufactured is sound and 2. Any repair actually restores the certification basis for the aircraft.
Regards
Blakmax
BMAX you are my idol, agree just core change will make no springtime tobonding over all...but it seems that we must wait for another trouble in paradise
to gain some evidence.
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posted photos on the thread about the recent AW109 ground resonance incident that show a significant degradation of the bond.
I've read the post and I think you don't have sufficent information to say that the bond was degraded...
AW has not responded to any of my approaches through this forum
AW has not responded to any of my approaches through this forum or from direct and indirect e-mails.
and you think that AW or EC or AIRBUS give you this informations on a public forum just because Mr."None" asking for ???
of his scientific contributions to "art of composite bonding" over the past 20 years.
AW (Finmeccanica) is just bit arrogant (not just in this case)...and you missing
major point. FYI even some native Italian operators decide not to take AW139
in operations recently and YOP 2008 AW139 paid approx 16M $ now can be
purchased for less than 10M $ (FH 100 t/t). Can you imagine why?!
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Blakmax has been kind and gracious enough to share some of the theory with me. He knows what he's talking about - and he isn't asking the OEM to come here and share information, he's asking them to review their procedures in light of obvious problems.
It doesn't matter whether the OEM ever posts a single word on this forum or any other; what matters is the safety of the aircraft and the people inside.
It doesn't matter whether the OEM ever posts a single word on this forum or any other; what matters is the safety of the aircraft and the people inside.
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Hi makrider
With regard to the AW109 incident, if you read my postings you will easily see that I DO NOT SAY this is the cause. I simply ask that my theory be evaluated and if necessary discarded. Again, my postings state that this is not a widely recognised phenomenum and may well be outside the experiences of many investigators. I raised it because I have seen this form of failure in a number of crash investigation reports and it was not even considered. When I raised this theory with one major safety investigation organisation the response I got was "Wow, didn't even think of that!".
The reason I added the AW139 photos was to show that there is a history of bonding issues with AW components as evidenced by the photographs I supplied. If the blades in question were manufactured by the same contractor using the same facilities and same quality management processes, there is at least justification to require the possibility is at least considered.
The rest of your posting is a response I often get and I am not surprised or offended by it. Many people (and this obviously includes you) have total faith in manufacturers to have a very high level of technical competence in every aspect of aviation, and in many areas this confidence is well founded. Unfortunately with adhesive bonding almost without exception processes are grandfathered from what passed certification testing, QA testing and NDI last time. This is combined with a failure by manufacturers, regulators and investigators to recognise the significance of bond failure characteristics. Add to that regulations which do not prevent the most common cause of bond failure (interfacial degradation) and you have a recipe for problems.
I guess this issue requires a level of credibility. My understanding of this technology has resulted in a reduction from 43% repeat bonded repair rate in one large defence facility to almost zero since 1992. I instigated and managed a major review of an entire repair manual for a very large US manufacturer of fast jets by an international committee which addressed every aspect of composite and adhesive bonded repairs and that committee made major changes to these publications addressing 75 deficiencies to which the manufacturer agreed. I wrote the world's first engineering standard on composite and adhesive bonded repairs and I also wrote two associated handbooks. I established three training courses and assisted in the development of two other courses. I wrote a document on best practices in composite and adhesive bonded repairs which is lodged with the FAA Tech Centre and is available from there. I know my subject.
Now please revisit the photographs and honestly tell me: Which aircraft would you prefer to fly on; one with the brown coloured adhesive where the bond was strong enough to tear the core, or one with the red coloured adhesive where the failure was weaker than the core and actually occured under service loads?
By the way, I never expect any manufacturer or regulator to respond to me through this or any other public forum unless it is by PM to make initial contact, after which I will correspond in a professional and confidential manner. I actually do try to make contact in a professional manner through other channels but if you get no response, you use the avenues available to you.
Regards
blakmax
With regard to the AW109 incident, if you read my postings you will easily see that I DO NOT SAY this is the cause. I simply ask that my theory be evaluated and if necessary discarded. Again, my postings state that this is not a widely recognised phenomenum and may well be outside the experiences of many investigators. I raised it because I have seen this form of failure in a number of crash investigation reports and it was not even considered. When I raised this theory with one major safety investigation organisation the response I got was "Wow, didn't even think of that!".
The reason I added the AW139 photos was to show that there is a history of bonding issues with AW components as evidenced by the photographs I supplied. If the blades in question were manufactured by the same contractor using the same facilities and same quality management processes, there is at least justification to require the possibility is at least considered.
The rest of your posting is a response I often get and I am not surprised or offended by it. Many people (and this obviously includes you) have total faith in manufacturers to have a very high level of technical competence in every aspect of aviation, and in many areas this confidence is well founded. Unfortunately with adhesive bonding almost without exception processes are grandfathered from what passed certification testing, QA testing and NDI last time. This is combined with a failure by manufacturers, regulators and investigators to recognise the significance of bond failure characteristics. Add to that regulations which do not prevent the most common cause of bond failure (interfacial degradation) and you have a recipe for problems.
I guess this issue requires a level of credibility. My understanding of this technology has resulted in a reduction from 43% repeat bonded repair rate in one large defence facility to almost zero since 1992. I instigated and managed a major review of an entire repair manual for a very large US manufacturer of fast jets by an international committee which addressed every aspect of composite and adhesive bonded repairs and that committee made major changes to these publications addressing 75 deficiencies to which the manufacturer agreed. I wrote the world's first engineering standard on composite and adhesive bonded repairs and I also wrote two associated handbooks. I established three training courses and assisted in the development of two other courses. I wrote a document on best practices in composite and adhesive bonded repairs which is lodged with the FAA Tech Centre and is available from there. I know my subject.
Now please revisit the photographs and honestly tell me: Which aircraft would you prefer to fly on; one with the brown coloured adhesive where the bond was strong enough to tear the core, or one with the red coloured adhesive where the failure was weaker than the core and actually occured under service loads?
By the way, I never expect any manufacturer or regulator to respond to me through this or any other public forum unless it is by PM to make initial contact, after which I will correspond in a professional and confidential manner. I actually do try to make contact in a professional manner through other channels but if you get no response, you use the avenues available to you.
Regards
blakmax
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And here are the pics of the aircraft mentioned, sans the tailboom
Enjoy
Tail Boom Separates From AW139
EnjoyTail Boom Separates From AW139
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Mmmm ....
.... And here are the pics of the aircraft mentioned, sans the tailboom
And if you had spent the time to review this thread you would have found those pictures have already been included ....
.... And here are the pics of the aircraft mentioned, sans the tailboom
And if you had spent the time to review this thread you would have found those pictures have already been included ....
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Disbonding repairs
G'day bandit19. Like spinwing, I knew this would happen. I am surprised that it happened so soon, but it would have happened anyway, given the scuff sand and solvent contaminate process specified by AW. When you pull it apart, take photos for me. I bet that at any given location, there is adhesive on one surface and none on the other with the failure propagating along the interface between the adhesive and the metal. There may still be regions where you actually fracture the adhesive geting the repair off, but this only a short term bond.
It would be prudent if other operators inspected their repairs as well.
Next wait for the response "you must have done it wrong". Let me assure you that there is a chance that there was less than optimum peformance of the processes, but in reality the best technician in the world doing his very best efforts would still produce the same results. It is the process which is deficient and the deficiencies in this process have been known for at least 25 years in my case.
Then the next response from AW will be "It is OK. The fasteners will carry the load." Well, they may or they may not. AW is in possession of loading data and should be able to work that out. I am not strong on fasteners, but to my eye, there are far too few fasteners spaced too far apart to assure load capacity. I am also concerned about the bearing loads being transferred through such thin skin. These appear also to be fasteners fitted into holes with clearance to install them. That will reduce fastener efficiency and add to bolt rotation which in turn will reduce efficiency even further.
However, what happens to the large stress concentration in the structure caused by the cut-out with the now ineffective repair and the fasteners? If my assessment of the degradation of the strength of the core to skin bond is correct, then the additional stress caused by the defective repair combined with the reduced bond strength caused by the micro-voids may lead to further disbonding of the surrounding structure. even if that doesn't happen, then the loss of local moment of intertia coupled with the local eccentricity of the neutral axis of the structure could precipitate buckling collapse of the boom similar to what happened at Doha.
There are three things AW should do:
Regards
Blakmax
It would be prudent if other operators inspected their repairs as well.
Next wait for the response "you must have done it wrong". Let me assure you that there is a chance that there was less than optimum peformance of the processes, but in reality the best technician in the world doing his very best efforts would still produce the same results. It is the process which is deficient and the deficiencies in this process have been known for at least 25 years in my case.
Then the next response from AW will be "It is OK. The fasteners will carry the load." Well, they may or they may not. AW is in possession of loading data and should be able to work that out. I am not strong on fasteners, but to my eye, there are far too few fasteners spaced too far apart to assure load capacity. I am also concerned about the bearing loads being transferred through such thin skin. These appear also to be fasteners fitted into holes with clearance to install them. That will reduce fastener efficiency and add to bolt rotation which in turn will reduce efficiency even further.
However, what happens to the large stress concentration in the structure caused by the cut-out with the now ineffective repair and the fasteners? If my assessment of the degradation of the strength of the core to skin bond is correct, then the additional stress caused by the defective repair combined with the reduced bond strength caused by the micro-voids may lead to further disbonding of the surrounding structure. even if that doesn't happen, then the loss of local moment of intertia coupled with the local eccentricity of the neutral axis of the structure could precipitate buckling collapse of the boom similar to what happened at Doha.
There are three things AW should do:
- Address the micro-voiding issue during manufacture, because this is the source of all of the problems. Changing to aluminium core may only slightly reduce the problem. The real solution is to addressthe sources and effects of moisture contamination of the adhesive and bonding surfaces prior to and during adhesive cure.
- Specify VALID repair processes, not antiquated ineffective methods.
- Stop specifying injection repairs because they can never restore bond strength.
Regards
Blakmax
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Mmmmm ....
....where can I see the pictures of the 109 ground resonance incident?
Errrr ..... on the Polish HEMS Agusta 109 thread ...
Try this ...
http://www.pprune.org/rotorheads/396...-incident.html
....where can I see the pictures of the 109 ground resonance incident?
Errrr ..... on the Polish HEMS Agusta 109 thread ...
Try this ...
http://www.pprune.org/rotorheads/396...-incident.html