What was found
FUEL CONTROL DRIVE BEARINGS FAILED ALLOWING FUEL CONTROL SHAFT TO WOBBLE & FUEL PUMP TO FUEL CONTROL DRIVE ADAPTER TO DISTORT & DISENGAGE FROM FUEL CONTROL WITH ACFT IN CRUISE. THE DRIVE BEARINGS & ADAPTER FAILURE RESULTED IN AN UNCONTROLLED ACCELERATION OF THE ENG AS INDICATED BY A MAIN ROTOR RPM INCREASE. ATTEMPTED TO CONTAIN RPM BY RAISING COLLECTIVE WITH NO EFFECT. SHUT THE ACFT MAIN FUEL VLV OFF & AUTO ROTATED INTO A FIELD RESULTING IN MINOR DAMAGE TO THE ACFT BUT NO INJURIES TO PERSONS ON BOARD. FUEL CONTROL COMPLIED WITH SERVICE BULLETIN LT 101-73-20-0272 645. 7 HOURS PRIOR.