As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INTERMITTENT FLUCTUATIONS ON NR GAUGE DURING OPERATION. FOLLOWED TROUBLESHOOTING STEPS AND FOUND NR TACH SENSOR TO BE IMPROPERLY SHIMMED BY MFG CAUSING CONTACT OF THE SENSOR AND THE PICK UP TEETH ON THE MAIN ROTOR MAST, DAMAGING THE NR TACH SENSOR AND MAIN ROTOR MAST PICK UP TEETH. RECOMMEND CHANGES TO QUALITY CONTROL PROGRAM TO ENSURE SENSOR IS PROPERLY INSTALLED, THIS COULD INCLUDE AN IN PROCESS INSPECTION DURING INSTALLATION.