Narrative:

While we were in cruise flight; the left engine lost power. I had switched from the left auxiliary tank to the left main tanks. I had flown about 1 hour 50 mins on the left auxiliary tanks when I switched back to the left main tank. I recall potomac approach gave me a lower altitude from 11000 ft to 10000 ft. I noticed after leveling off at 10000 ft; with the same propeller and throttle position; the left fuel flow started fluctuating more than normal. I did note that I had been flying for 5-7 mins when I switched tanks. I noticed the fuel flow was decreasing more and the left engine began to surge. After the power loss; I made sure the throttles were full forward and I pushed the mixtures slightly more rich and I pushed the propellers forward to 2500 RPM. I checked my fuel selector and made sure I was on the left main fuel tank -- and I was on the left main fuel tank -- also turned the fuel boost pump to low. I then checked both magnetos and this did not help. I then switched back to the left auxiliary tank and this did not help; and then switched back to the left main tank. The engine was still turning at 2200 RPM's and when I moved the throttle; the RPM's would change and the plane would yaw more to the left; so I knew the engine was making some power. I then moved the fuel boost pump to high and at this time the engine completely lost power. I turned the boost pump off and moved the fuel selector to xfeed to see if this would help. After a moment; the left engine regained power and surged 2 more times before regaining normal power. After I was sure the plane was running normal; I continued my flight to ZZZ on the xfeed. At this time the plane was running normal and I knew I had enough fuel in the right main fuel tank to continue my 20-25 min flight to ZZZ. In the meantime; I declare an emergency and was standing by for vectors to ZZZ2. I continued to ZZZ with no more problems. The next day I had an aviation mechanic look at my problem. The mechanic did feel it was a fuel problem and did a complete check of the fuel system to his knowledge and per a maintenance manual noting no abnormal problem. He feels like it was air in the fuel system that caused the engine to surge. He did an engine run-up and cleared the plane was safe for flight. When I fueled up; the left auxiliary tank was filled with 28.8 gallons with 2.2 left in a 31.0 usable gallon. The left main tank was filled with around 7 gallons out of 37 usable gallons in the left main fuel tank.

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Original NASA ASRS Text

Title: BE55 PLT SUFFERS PARTIAL POWER LOSS OF LEFT ENGINE.

Narrative: WHILE WE WERE IN CRUISE FLT; THE L ENG LOST PWR. I HAD SWITCHED FROM THE L AUX TANK TO THE L MAIN TANKS. I HAD FLOWN ABOUT 1 HR 50 MINS ON THE L AUX TANKS WHEN I SWITCHED BACK TO THE L MAIN TANK. I RECALL POTOMAC APCH GAVE ME A LOWER ALT FROM 11000 FT TO 10000 FT. I NOTICED AFTER LEVELING OFF AT 10000 FT; WITH THE SAME PROP AND THROTTLE POS; THE L FUEL FLOW STARTED FLUCTUATING MORE THAN NORMAL. I DID NOTE THAT I HAD BEEN FLYING FOR 5-7 MINS WHEN I SWITCHED TANKS. I NOTICED THE FUEL FLOW WAS DECREASING MORE AND THE L ENG BEGAN TO SURGE. AFTER THE PWR LOSS; I MADE SURE THE THROTTLES WERE FULL FORWARD AND I PUSHED THE MIXTURES SLIGHTLY MORE RICH AND I PUSHED THE PROPS FORWARD TO 2500 RPM. I CHKED MY FUEL SELECTOR AND MADE SURE I WAS ON THE L MAIN FUEL TANK -- AND I WAS ON THE L MAIN FUEL TANK -- ALSO TURNED THE FUEL BOOST PUMP TO LOW. I THEN CHKED BOTH MAGNETOS AND THIS DID NOT HELP. I THEN SWITCHED BACK TO THE L AUX TANK AND THIS DID NOT HELP; AND THEN SWITCHED BACK TO THE L MAIN TANK. THE ENG WAS STILL TURNING AT 2200 RPM'S AND WHEN I MOVED THE THROTTLE; THE RPM'S WOULD CHANGE AND THE PLANE WOULD YAW MORE TO THE L; SO I KNEW THE ENG WAS MAKING SOME PWR. I THEN MOVED THE FUEL BOOST PUMP TO HIGH AND AT THIS TIME THE ENG COMPLETELY LOST PWR. I TURNED THE BOOST PUMP OFF AND MOVED THE FUEL SELECTOR TO XFEED TO SEE IF THIS WOULD HELP. AFTER A MOMENT; THE L ENG REGAINED PWR AND SURGED 2 MORE TIMES BEFORE REGAINING NORMAL PWR. AFTER I WAS SURE THE PLANE WAS RUNNING NORMAL; I CONTINUED MY FLT TO ZZZ ON THE XFEED. AT THIS TIME THE PLANE WAS RUNNING NORMAL AND I KNEW I HAD ENOUGH FUEL IN THE R MAIN FUEL TANK TO CONTINUE MY 20-25 MIN FLT TO ZZZ. IN THE MEANTIME; I DECLARE AN EMER AND WAS STANDING BY FOR VECTORS TO ZZZ2. I CONTINUED TO ZZZ WITH NO MORE PROBS. THE NEXT DAY I HAD AN AVIATION MECH LOOK AT MY PROB. THE MECH DID FEEL IT WAS A FUEL PROB AND DID A COMPLETE CHK OF THE FUEL SYS TO HIS KNOWLEDGE AND PER A MAINT MANUAL NOTING NO ABNORMAL PROB. HE FEELS LIKE IT WAS AIR IN THE FUEL SYS THAT CAUSED THE ENG TO SURGE. HE DID AN ENG RUN-UP AND CLRED THE PLANE WAS SAFE FOR FLT. WHEN I FUELED UP; THE L AUX TANK WAS FILLED WITH 28.8 GALLONS WITH 2.2 LEFT IN A 31.0 USABLE GALLON. THE L MAIN TANK WAS FILLED WITH AROUND 7 GALLONS OUT OF 37 USABLE GALLONS IN THE L MAIN FUEL TANK.

Data retrieved from NASA's ASRS site as of May 2009 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.