While hover taxiing for takeoff, the pilot reported that the helicopter suddenly pitched nose-up and as he was unable to regain control he lowered the collective allowing the aircraft to descend to the ground where it rolled onto its side. The investigation was unable to establish the reason for the loss of control, but it is possible that there was a restriction in one of the flying control servo-jack control valves leading to higher control forces required to control the helicopter in the hover.
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Published 9 February 2017