havoc,
That helo link is the Canadian Military 412 that had a scratched TR blade which cracked and eventually failed, causing tail boom separation and then the crash.
It is an example of why flaw tolerance is a wise idea, but it isn't the same mode as the EH-101 problem, which Labpilot explains a bit for us.
Regarding how these things happen, it is not easy to engineer anything, and especially a helicopter. I believe computers have made things far better, by a long shot. For that, and other reasons, I believe these incidents are fewer and fewer than they used to be (there were over 75 main rotor separations in Hueys, folks!) but that is still no real explanation. I guess I could wax on about our collective inability to be perfect, but we all know that already. Most folks have their mistakes show up in a file drawer, or a mailbox, or perhaps in a courtroom. Aviation is so very unforgiving, far more so than even the Sea, and so even the minor mistakes good people make end up very badly. Is it any consolation that in the world of aviation, three accidents occur for crew error for every one that is the fault of the machine or designers? I think not, because we all share the blame when an aircraft goes in.
Labpilot, thanks for the details about the 101 TR, I am sure my friends there are working hard to fix this.