Sycamore - very interesting background on the Gazelle jacks and jackstall response - never heard that before
Georg1na - a very similar experience happened to a Valley Wessex SAR pilot in about 1989/90 - he came into our crewroom next door looking for a QHI to ask if it was possible to lose control of a helicopter in the hover.
He described an almost identical winching scenario on Tryfan in very strong winds and updraughts and fortunately they hadn't deployed the winchman when the aerobatics started - I told him I was pretty convinced it was RBS