As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED NO LOW ROTOR RPM WARNING HORN (HEADSET BEEP) NR GAUGE INDICATIONS WAS NORMAL. SENSOR IS DUAL ELEMENT WITH ONE PORTION PROVIDING EACH SIGNAL FOR WARNING HORN AND NR INDICATION. INTERNAL WIRES ARE SO FINE THIS UNIT IS FAILURE PRONE, SUGGEST OPTIC SENSOR DESIGN. (K)