What a sad thing to happen.
B models have a design flaw that allows something like this to happen. The tail rotor control cables run alongside the tail rotor drive shaft, in the upper tunnel of the boom. D and H models moved it into the lower tunnel.
In August 1981, a RAAF B model had one cable somehow come off its pulley and make contact with the drive shaft. It wrapped around it and was pulled to an extreme position. The tail rotor went to maximum pitch and flapped so much it hit the vertical fin. One blade separated, then the whole gearbox pulled out.
With the loss of the anti-torque and 90 lbs weight from 30 feet back, the cabin yawed and pitched nose down. The main rotor stayed where it was, so there was a mast bump, the blade separated, but before it did so, it came down through the cabin, and sliced off the left side and tail boom. The remains fluttered to the ground from 1500', with three fatalities.
No official reason was found for the cable's behaviour, and within a year, all B models were pensioned off.