lomapaseo:
So, how many times had it gone through overhaul and repair where such a massive propagation had gone undetected even as the fracture surface may have been discolored by cleaning agents etc.
This factor has showed up in a number of uncontained engine failures. The UAL CF6 fan disc (Sioux City) is a notorious example; UAL's NDT inspection was shown to be "lightweight" and a major contributor, in that the incipient failure was readily detectable by best practices.