As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LOW ROTOR RPM LIGHT ON THE WU WITH ASSOCIATED TONE CAME ON INADVERTANTLY 6 TIMES DURING A 30 MINUTE FLIGHT. DURING TROUBLESHOOTING OF MAIN ROTOR RPM SYSTEM, FOUND RPM MONITORING SYSTEM TO BE WORKING. RPM SENSOR IS AT FAULT. REMOVED AND REPLACED SPEED PICK-UP (NR SENSOR) IAW AMM 62-41-00, 4-1. MOC SUCCESSFULLY C/W IAW AMM 05-60-00,6-1.