Heard of a similar one to that described by wrench1 involving a Bo105 on Northern Lighthouse Board duties over Scotland. Happened at several thou feet in transit - pilot (ex-SAR SeaQueen driver) had absolutely no control for several seconds. There was also a Royal Oman Police 214ST incident concerning the collective, which was effectively disconnected with the aircraft in either level or gently-descending flight. Fortunately, both occurrences led to safe arrivals - wish I knew more about each of them.