Narrative:

I was flying at 10000' MSL from boston, ma, to burlington, vt. About 20 mi northwest of leb VOR established on V-141, I noticed the left engine propeller RPM indicator decreasing. Both engines were set at 80 percent torque and the propeller RPM's were set at 97.0. I shut off the propeller syncrophaser and torque limiter. However, the propeller RPM's continued to slowly decrease. I then told boston center that we would like to divert to lebanon, nh. I retarded the left power lever to see if this would have any effect on the decreasing propeller RPM's. When I did so, the left engine torque did not change. At this point, I realized I had no control over the left engine. By this time the leb airport was in sight. We were approximately 15 mi northwest at 10000'. In order to descend and remain within my maximum airspeed (200 KIAS), I had to reduce the power on both my engines. The only way to do this was to shut down the left engine. My first officer and I discussed the shut down and what to expect, I informed our 3 passengers. Propeller RPM at this point was 92 percent. The landing at lebanon went well and the aircraft taxied to the gate under its own power. I did request emergency vehs to be standing by just in case, however,K they were not needed. It is my belief that the problem with the engine was either in the propeller governor unit and/or fuel control unit.

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Original NASA ASRS Text

Title: COMMUTER SMT HAD TOO SHUT LEFT ENGINE DOWN AT CRUISE ALT BECAUSE OF LOSS OF POWER CTL.

Narrative: I WAS FLYING AT 10000' MSL FROM BOSTON, MA, TO BURLINGTON, VT. ABOUT 20 MI NW OF LEB VOR ESTABLISHED ON V-141, I NOTICED THE L ENG PROP RPM INDICATOR DECREASING. BOTH ENGS WERE SET AT 80 PERCENT TORQUE AND THE PROP RPM'S WERE SET AT 97.0. I SHUT OFF THE PROP SYNCROPHASER AND TORQUE LIMITER. HOWEVER, THE PROP RPM'S CONTINUED TO SLOWLY DECREASE. I THEN TOLD BOSTON CTR THAT WE WOULD LIKE TO DIVERT TO LEBANON, NH. I RETARDED THE L PWR LEVER TO SEE IF THIS WOULD HAVE ANY EFFECT ON THE DECREASING PROP RPM'S. WHEN I DID SO, THE L ENG TORQUE DID NOT CHANGE. AT THIS POINT, I REALIZED I HAD NO CTL OVER THE L ENG. BY THIS TIME THE LEB ARPT WAS IN SIGHT. WE WERE APPROX 15 MI NW AT 10000'. IN ORDER TO DSND AND REMAIN WITHIN MY MAX AIRSPD (200 KIAS), I HAD TO REDUCE THE PWR ON BOTH MY ENGS. THE ONLY WAY TO DO THIS WAS TO SHUT DOWN THE L ENG. MY F/O AND I DISCUSSED THE SHUT DOWN AND WHAT TO EXPECT, I INFORMED OUR 3 PAXS. PROP RPM AT THIS POINT WAS 92 PERCENT. THE LNDG AT LEBANON WENT WELL AND THE ACFT TAXIED TO THE GATE UNDER ITS OWN PWR. I DID REQUEST EMER VEHS TO BE STANDING BY JUST IN CASE, HOWEVER,K THEY WERE NOT NEEDED. IT IS MY BELIEF THAT THE PROB WITH THE ENG WAS EITHER IN THE PROP GOVERNOR UNIT AND/OR FUEL CTL UNIT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.