.....ANYWAY, back on topic, so far we have a few interim reports that DO seem to raise more questions than answers. There is an obvious reliance on HUMS which in my mind is simply a tool that we must use, and the chemists are looking at the materials used.......
bigglesbutler- Just one last comment about the change in material for the EC225 spiral bevel gear shaft (and then I'll go away for a while). The AAIB special bulletin S7/2012 actually gave fairly detailed information about the shaft material/heat treatment. The shaft material was changed from 16NCD13 VAC-ARC (AMS 6263) to 32CDV13 VAR (AMS 6481). Regarding weldability, the only difference is that 16NCD13 has a lower carbon content than 32CDV13, 0.15% vs. 0.32%. While both alloys should produce sound welds using EB or laser, the 0.32% carbon content of 32CDV13 is getting close to the limit of what is generally considered weldable using a fusion welding process. Steel alloys that have a carbon content of around 0.40% or more can be prone to cracking when fusion welded, unless the parts are very carefully pre-heated before welding and post-heated after welding.
I'm sure EC has some very competent engineers working for them, and I'm sure they spent lots of time and effort developing this part design and manufacturing process. From what I have seen in the published reports, the basic design seems sound. And it's most likely there is a quality control issue on the manufacturing side of things.
For some perspective, here is a report describing a somewhat similar fracture issue with an EB welded gear shaft:
http://products.asminternational.org...rd=409&search=
Lastly, in the spirit of disclosure, while I would not consider myself an "expert" in aircraft drivetrain engineering, I have spent the better part of two decades designing aircraft mechanical systems, including a couple of gearboxes. While I have no intimate knowledge of the EC225 MGB design and I have never worked for EC, I am quite familiar with the technical issues involved because I have had to deal with these same issues many times myself in my job. I hope no one has misinterpreted what I posted in this thread. I never intended to place blame, nor did I claim to have indisputable proof of what caused the problem. My only intent was to provide some technical perspective, based on my personal experiences, of the many possible factors that may have contributed to the problem.
Best regards to you all. I hope this problem is resolved quickly and satisfactorily for all parties involved.
riff_raff