What was found
DURING CRUISE, PILOT FELT A VERY MILD VIBRATION AND NOTICED THE NR WAS 1 PERCENT LOW, PILOT THEN LOWERED THE COLLECTIVE TO MAKE A LT TURN FOR LANDING. THE NR DECREASED AS PILOT LOWERED THE COLLECTIVE TO THE POINT WHERE THE NR HORN SOUNDED AND THE VIBRATION GOT WORSE THEN SUBSIDED. THROTTLE WAS THEN PLACED IN MANUAL POSITION AND INCREASED THE NR INTO THE GREEN AND RAISED THE COLLECTIVE WITH NO NR DROP. COLLECTIVE WAS THEN LOWERED AND THE THROTTLE WAS MANIPULATED TO MAINTAIN NR FOR LANDING. AFTER LANDING NOTICED THE THROTTLE WAS WELL ABOVE THE FLT POSITION. RIGGING WAS VERIFIED ON THE RVDT, MECHANICAL GOVERNOR AND THE PC LINKS AND ALL WERE RIGGED PROPERLY, THE FCU WAS THEN CHANGED AND A OPERATION TEST FLIGHT WAS PERFORMED WITH NO FURTHER NR DROP.