I heard a story some years ago that the CH-46 had a tendency to break in half in its early days, prompting some macabre humour along the lines of "the CH-46 becomes a formation of two CH-23s"... Any truth in that?
I seem to remember a rotor at Coleman in Germany dephasing, passing through the fuselage and slicing an unfortunate crewman in half.
They grounded the fleet and initiated a fleetwide modification to fit a larger bolt in the combining box where the rotorshafts attached, there was I think three at Odious on a goodwill visit at the time ( one with the gear stuck at full extension on one side ) before we got ours, and a Rep came over to do the work and used a drill to ream the holes out, if memory serves me right he destroyed two before the crews stopped him getting near the third, they sat there for ages on the grass awaiting new gearboxes and shafts.
The problem was eventually found to be bad maintenance practice related as instead of turning the drives until they lined up and then installing the bolt, I think they were using a jacking handle against the shaft flange and against a frame to force it in, hence when they fitted the bolt it was under strain, the one in question failed, the rotors dephased, hit each other and sailed straight through the fuselage. But it was a long time ago and my memory is not what it was.
here you go, the incident in question.
https://aviation-safety.net/wikibase/wiki.php?id=56460