What was found
AN ABNORMAL INTERMITTENT VIBRATION WAS FELT DURING CRUISE FLIGHT. THE CAUSE WAS DETERMINED TO BE THE OUTBOARD MAIN ROTOR GRIP ELASTOMERIC BEARING ON ONE BLADE GRIP TO HAVE SEPARATED. THE OTHER THREE ELASTOMERIC BEARING WERE INSPECTED, AND FOUND TO HAVE VARIOUS STAGES OF SEPARATION. ALL FOUR OUTBOARD ELASTOMERIC BEARING WERE REPLACED. THE MAIN ROTOR HUB ASSEMBLY HAD ONLY 275 HOURS REMAINING UNTIL THE FIRST SCHEDULED OVERHAUL. THE INBOARD ELASTOMERIC BEARING WERE ALSO CHANGED DURING THIS MAINTENANCE EVENT DUE TO DETERIORATION OF THE RUBBER BONDING.