Robinson Helicopter CEO Kurt Robinson said the company has been working with the FAA for “some time” to address concerns about “mast-rocking” or “chugging” on its R44 helicopters. On August 22 the NTSB issued several safety recommendations (A-11-82 through -86) related to the condition in the wake of several mast-rocking accidents/incidents dating back to 2006. “We are working with the FAA to address any concerns or recommendations the NTSB has,” Robinson told AIN.
Pilots of the incident/accident aircraft reported yaw and pitch oscillations so severe that they elected to make emergency landings, several of them hard enough to cause substantial aircraft damage. The condition appears to be exacerbated by a forward cg that can still be within the flight envelope and is more readily entered during descending and banking turns of 30 degrees. Flight-test reports dating back to 2006 found that certain combinations of transmission mount and vibration isolator mitigate the problem, as did stopping turns while adding power, especially during practice autorotations.
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