riff raff and buzz66, you are both spot on.
Failure to detect sufficiently is the one bold claim made in the preliminary report.
The gear design does not account for a rim fracture as a design point, relies on this mode to simply never show up. An overtorque test is the standard used, but that would not consider degradation of raceway over time, just tooth bending primarily. Other factors could still include mis-assembly leading to uneven load share (although at least two planets have the cracks. Worse, there may not be enough control of planet load share. We really speculate without knowing details, but fatigue can still happen in a matter of hours if loads are unusually high. In that case - would we not expect severe loads to be picked up by the HUMS? I said early on that I suspect that we have multiple failed oppurtunities that would have prevented this. We have an idea on two, details will follow, but it will take a couple months anyway. Urgency to report initially is about maintaining fleet safety. Only urgency now is money, and the investigators are not losing any, so they are not the ones in a hurry. We won't be seeing more tidbits until someone inside the investigation leaks it. Until then, we rumor anyway.