Decent responses,
The real reason I posted the question was because I was bored 5hitless sitting here in the office waiting for the proverbial launch codes...... but having said that, this exact thing did happened to a bloke I know..... many moons ago now though.
He was flying along doing a wonderful job of being fat, dumb and happy, when the shaft let go due to a small crack that originated at the bolt holes under the flex plate.
His reaction was obviously correct because he put it down without a scratch from a couple of hundred feet.
The thing he recalls the most is the major engine overspeed (may be due to the fact that we were flying un-governed 22's at this stage).
Having a study of the problem it was noted that the tail rotor was still being driven by the engine but as there was no longer any drag from the main drive system the tail rotor was literally free to spin in sympathy with the increased engine RPM.
All other indications were synonomous with a basic belt come donk failure.
It has always stood out in my mind as a great story to get the head thinking as to what to expect. If the engine RPM isn't brought into check due to the excitement and maybe concentration with getting RRPM sorted out first then there could well be a conflict of indicators that would otherwise help to put a picture in your head as to what is going on behind you. How will the tail rotor react at the flare if you forget to roll the throttle all the way into the detent? Have I just had a catestrophic failure that has taken out the tail rotor controls as well? etc etc........
Just passing the time.....