As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ROTOR RPM INDICATOR GAVE ERRATIC INDICATIONS FROM 101% TO 80% DURING FLIGHT. THE ROTOR LOW WARNING LIGHT INDICATION FLUCTUATED INTERMITTENTLY, NEVER STAYING ON. THE LOW ROTOR AUDIO NEVER SOUNDED OFF. REMOVED AND REPLACED THE SPEED PICKUP SENSOR IAW AMM 62-41-00, 4-1. MOC SUCCESSFULLY COMPLETED IAW 05-60-00, 6-1.