What was found
DURING CRUISE FLIGHT AC CWP RED AND YELLOW GOV GOVERNOR LIGHT SEGMENTS ILLUMINATED AND ROTOR RPM BEGAN TO DECAY WITH A LOW ROTOR WARNING AS PILOT ENTERED AUTOROTATION. A NORMAL AUTOROTATION WAS COMPLETED WITH NO DAMAGE SUSTAINED BY THE AIRCRAFT. THE VEMD INDICATED A FAULT WAS DETECTED WITH THE PUMP AND ADJUSTED VALVE METERING UNIT (HMU). AS THIS IDENTICAL EVENT WAS PREVIOUSLY CAUSED BY A RUPTURE OF THE DIAPHRAGM OF THE HMU CONSTANT DP VALVE ON 2 PREVIOUS OCCASIONS I FEEL THIS TO BE THE LIKELY CAUSE. A SERVICEABLE HMU WAS INSTALLED AND AC INSPECTED, LEAK AND OPERATIONALLY CHECKED AND RETURNED TO SERVICE. (K)