As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT, ROTOR RPM INDICATION DROPPED TO 0 THEN RETURNED TO NORMAL FOUR TIMES TOTAL. TROUBLESHOOTING FOUND THE MAIN ROTOR RPM SENSOR INDICATED INTERMITTENTLY. TRIPLE TACHOMETER INDICATOR FUNCTIONED NORMALLY ON SIGNAL GENERATOR. REMOVED AND REPLACED SPEED PICK-UP SENSOR IAW AMM 62-41-00, 4-1.