Hi spinwing
You say the manufacturer says
these de-bonding issues are only prevalent on machines operating in the middle east
Regretably these issues have been reported elsewhere. Reference NTSB A08-25_29 dated 09 Jun 2008. Interfacial degradation is exacerbated by hot and wet environments. Hence, a number of OEMs have incorrectly blamed tropical environments for similar failures. I am also aware of manufacturers blaming wash fluids, bird crap, whatever. The real reason is a failure of resistance to environmental degradation at the interface and this relates directly back to the failure of the FARs (or other regulations such as JARs, DEF STAN 00 970, MIL STD 1530 etc.) to require demonstration of the durability of the interfacial chemical bonds in the operating environment.
The current FARs require that bonds use "processes known to produce a sound structure". But what constitutes a sound structure? If it passes NDI is it a sound structure? Not necessarily because NDI can not interrogate bad interfaces. If it passes bond strength tests, is it a sound structure? Not necessarily because if the test is conducted before the interface is degraded, then there will be a false-positive result. If it passes fatigue testing is it a sound structure? Not necessarily because if the test is conducted before the interface is degraded, then there will be a false-positive result. None of these requirements address the time-dependent degradation of the chemical bonds at the interface. Hence, the FARs and other reg's which require strength and fatigue tests and the use of processes that produce a sound structure do not prevent a common (dare I say the most dominant) failure mechanism in adhesive bonded structures.
I stress again that it is NOT the manufacturers who are liable, it is the regulators who permit certification of structures which are susceptible to a known deficiency. Eventually some smart lawyer will stop sueing the manufacturers and realise that it really is the regulations themselves which permit structures to be certified such that they fail to prevent a known, common failure mechanism. I published a paper on this in 1996 and I am aware that the regulators have seen this paper ( see my web site at adhesionassociates.com ).
I have been trying since 1996 to have this deficiency rectified. If it takes a smart lawyer to defend a manufacturer or another even smarter lawyer to seek damages for defcient regulations, I would be available for discussions. My objective is not to make money from other's demise, but to prevent further needless loss of life. In the case of this specific aircraft, the on-ground failure avoided loss of life. It does not mean that the structure which in all probability met certification requirments was actually airworthy. I am well aware of other cases where "rotorheads" have not been so fortunate. The problem is not just limited to rotary wing aircraft. There are examples from fixed wing structures as well.
And can I stress again, if ANYONE has ANY testing evidence that injection repairs for disbonds actually restore ANY strength, I'd be very interested. The difference between removing the NDI signature and actually restoring strength is critical. Similarly, if an adhesive disbond exhibits interfacial failure (metal or composite) this is a processing and certification issue, not a loads issue.
On a related issue, I have data (admittedly old data) which shows that injection repair for delaminations in composites actually REDUCES fatigue life compared to doing absoultely nothing. I actually forced one OEM to admit that injection repairs for delaminations could not restore ultimate strength and at best slowed down delamination growth. Any comments?
Regards
Blakmax