...no cracks started appearing until 2009 and then only on aircraft where MGB and or bolts had been replaced outside the factory environment. Until then, no foot cracks appeared indicating that there was nothing amiss with the load paths used on original testing.
Interesting point, 2700 TIS = 337 days @ 8 hours/day. S92 has been in service in Newfoundland since circa 2006. So even with non-stop daytime operations the MGBs would have been changed out at least 3 times prior to the cracking issue appearing. I'm assuming that the removed MGBs were sent back for overhaul and re-conditioning, which would then result in the re-use of the same housings, or are they scrapped?
MGB housing cracks started appearing post-MGB change-out by operators rather than SAC. Surely there is no difference in the procedure that SAC use versus the operator?
Was there any change to QA/QC on the MGB housings and/or supplier?
Perhaps something else is changing during "run-in" of the A/C e.g. alignment of the mounting points leading to additional stress points not seen in the MGB test rig?
How about thermal expansion effect on chassis versus MGB material, related to ambient and MGB operating temperatures? From memory I recall the original cracking was only seen in offshore operational areas, is there a link to the ambient operating conditions, and do SAC use an environmental simulator area when using the MGB test rig to temperature cycle as well as emulate TIS?
I'm sure that SAC design engineers have considered all these scenarios during the latest MGB upgrade and re-engineering.
For me it would be beneficial if a statement was released by SAC stating the root cause issue identified and the engineered solution arrived at. This would be a positive step forward in re-instilling confidence in the revised MGB design.
Safe flying
Max