What was found
PILOT OBSERVED ENGINE RPM DROOPED TO APPROX 98 PERCENT N2 AND WOULD NOT BEEP UP. THIS CAUSING LOW ROTOR WARNING TO ILLUMINATE, AS WELL AS AUDIO WARNING TO SOUND. PILOT ENTERED AN AUTO ROTATION AND OBSERVED THE ENGINE SURGING AS HE APPROACHED THE GROUND. NORMAL AUTO ROTATION LANDING WAS MADE WITH NO DAMAGE TO AIRCRAFT OR INJURY TO PERSONS. FOR TROUBLESHOOTING PURPOSE MAINTENANCE CONDUCTED AN ENGINE START AND OBSERVED THE ENGINE WOULD NOT BEEP ABOVE 98 PERCENT N2 AND MINOR SURGING OF THE ENGINE. MAINTENANCE REPLACED THE PT GOVERNOR. ENGINE AND AIRCRAFT PERFORMED NORMAL. AIRCRAFT RETURNED TO SERVICE FOLLOWING OPS FLIGHT CHECK. (K)