Narrative:

I was on an IFR flight plan. Flying VMC at 11000 ft MSL, I flew south around an area of snow showers. Once east of the mountains, I did not see any clouds, but the air was very moist laden. I requested 15000 ft thinking I could climb on top of any thin cloud layers. I was given clearance, but while climbing I encountered IMC with moisture in the air. During the climb, I flew into a cloud for what seemed to be 30 seconds and picked up a very thin ice coat on 50% of my windshield. I was between layers at 13000 ft so I requested to remain level. Clearance granted so I stayed at 13000 ft MSL for some 15 mins. The temperature was 10 degrees below zero. I became concerned over the fact that thin rime ice was now on my leading edge. Because I did not want any ice to build up, I requested 9000 ft and was granted 10000 ft. Upon descending through 11000 ft MSL, my engine began to lose some power. I noticed the cylinder heat temperature was 50 degrees cool. Suddenly, the engine power dropped off drastically, faltered, gained power momentarily, and then dropped off drastically again. I increased RPM's to 2600 RPM, and fuel to rich. Boost pump on. I declared an emergency. Another aircraft asked center if they heard me. Center contacted me and I declared an emergency stating that power loss was occurring multiple times and I was not sure if the aircraft would maintain intermittent power or not. I turned the aircraft to a 180 degree heading and requested lower clearance. I cannot remember what was granted -- maybe 9000 ft or 8000 ft. I noticed that the egt on all 4 cylinders was peaking at maximum egt multiple times. I suspected fuel blockage. Upon descending through something less than 9500 ft MSL, I regained consistent power. By this time conversations as to alternative airports were discussed including santa rosa and chonchas lake. My heading was now 210 degrees to 240 degrees and my altitude was below what I thought was the MEA. I declared I was going to tucumcarri (tcc). I asked for a minimum altitude and was granted 7700. Being the engine had regained power, I climbed back from what I remember to be some 7300 ft or so MSL to 7700 ft MSL. I picked tcc because it was in lower territory, had an approach I could fly in protected airspace and rain which indicated warmer air. I considered, but did not want to switch fuel tanks because of a fear of losing all power. I left all settings alone as I did not want to troubleshoot while continuing IMC. I headed for the victor route 12. I did not want to attempt to fly below the MEA to locate the 2 VFR airports mentioned above. Upon landing at tcc and closing flight plan, I checked for water and found none in the left tank. However, in the other unused right tank, I did find water -- 3 drops. Because I neglected to check for water during my preflight by draining fuel, I suggest that ice formed in the fuel line creating a blockage of fuel to the engine. It is possible that the rapid descent from 13000 ft to 10000 ft MSL contributed to super cooling of the airframe and engine. It is possible that thin ice may have formed on the air intake. Conclusion: always drain fuel for water or contamination prior to each flight. Never skip this test even once. Do not assume that flying between layers will avoid ice buildup. Be aware of MEA's -- even during emergencys.

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Original NASA ASRS Text

Title: SMA PLT EXPERIENCE PWR LOSS DURING IFR FLT AND DIVERTED TO ANOTHER ARPT UNDER INTERMITTENT PWR. FUEL LINE ICE AND ENG INTAKE BLOCKAGE IS SUSPECTED.

Narrative: I WAS ON AN IFR FLT PLAN. FLYING VMC AT 11000 FT MSL, I FLEW S AROUND AN AREA OF SNOW SHOWERS. ONCE E OF THE MOUNTAINS, I DID NOT SEE ANY CLOUDS, BUT THE AIR WAS VERY MOIST LADEN. I REQUESTED 15000 FT THINKING I COULD CLB ON TOP OF ANY THIN CLOUD LAYERS. I WAS GIVEN CLRNC, BUT WHILE CLBING I ENCOUNTERED IMC WITH MOISTURE IN THE AIR. DURING THE CLB, I FLEW INTO A CLOUD FOR WHAT SEEMED TO BE 30 SECONDS AND PICKED UP A VERY THIN ICE COAT ON 50% OF MY WINDSHIELD. I WAS BTWN LAYERS AT 13000 FT SO I REQUESTED TO REMAIN LEVEL. CLRNC GRANTED SO I STAYED AT 13000 FT MSL FOR SOME 15 MINS. THE TEMP WAS 10 DEGS BELOW ZERO. I BECAME CONCERNED OVER THE FACT THAT THIN RIME ICE WAS NOW ON MY LEADING EDGE. BECAUSE I DID NOT WANT ANY ICE TO BUILD UP, I REQUESTED 9000 FT AND WAS GRANTED 10000 FT. UPON DSNDING THROUGH 11000 FT MSL, MY ENG BEGAN TO LOSE SOME PWR. I NOTICED THE CYLINDER HEAT TEMP WAS 50 DEGS COOL. SUDDENLY, THE ENG PWR DROPPED OFF DRASTICALLY, FALTERED, GAINED PWR MOMENTARILY, AND THEN DROPPED OFF DRASTICALLY AGAIN. I INCREASED RPM'S TO 2600 RPM, AND FUEL TO RICH. BOOST PUMP ON. I DECLARED AN EMER. ANOTHER ACFT ASKED CTR IF THEY HEARD ME. CTR CONTACTED ME AND I DECLARED AN EMER STATING THAT PWR LOSS WAS OCCURRING MULTIPLE TIMES AND I WAS NOT SURE IF THE ACFT WOULD MAINTAIN INTERMITTENT PWR OR NOT. I TURNED THE ACFT TO A 180 DEG HDG AND REQUESTED LOWER CLRNC. I CANNOT REMEMBER WHAT WAS GRANTED -- MAYBE 9000 FT OR 8000 FT. I NOTICED THAT THE EGT ON ALL 4 CYLINDERS WAS PEAKING AT MAX EGT MULTIPLE TIMES. I SUSPECTED FUEL BLOCKAGE. UPON DSNDING THROUGH SOMETHING LESS THAN 9500 FT MSL, I REGAINED CONSISTENT PWR. BY THIS TIME CONVERSATIONS AS TO ALTERNATIVE ARPTS WERE DISCUSSED INCLUDING SANTA ROSA AND CHONCHAS LAKE. MY HDG WAS NOW 210 DEGS TO 240 DEGS AND MY ALT WAS BELOW WHAT I THOUGHT WAS THE MEA. I DECLARED I WAS GOING TO TUCUMCARRI (TCC). I ASKED FOR A MINIMUM ALT AND WAS GRANTED 7700. BEING THE ENG HAD REGAINED PWR, I CLBED BACK FROM WHAT I REMEMBER TO BE SOME 7300 FT OR SO MSL TO 7700 FT MSL. I PICKED TCC BECAUSE IT WAS IN LOWER TERRITORY, HAD AN APCH I COULD FLY IN PROTECTED AIRSPACE AND RAIN WHICH INDICATED WARMER AIR. I CONSIDERED, BUT DID NOT WANT TO SWITCH FUEL TANKS BECAUSE OF A FEAR OF LOSING ALL PWR. I LEFT ALL SETTINGS ALONE AS I DID NOT WANT TO TROUBLESHOOT WHILE CONTINUING IMC. I HEADED FOR THE VICTOR RTE 12. I DID NOT WANT TO ATTEMPT TO FLY BELOW THE MEA TO LOCATE THE 2 VFR ARPTS MENTIONED ABOVE. UPON LNDG AT TCC AND CLOSING FLT PLAN, I CHKED FOR WATER AND FOUND NONE IN THE L TANK. HOWEVER, IN THE OTHER UNUSED R TANK, I DID FIND WATER -- 3 DROPS. BECAUSE I NEGLECTED TO CHK FOR WATER DURING MY PREFLT BY DRAINING FUEL, I SUGGEST THAT ICE FORMED IN THE FUEL LINE CREATING A BLOCKAGE OF FUEL TO THE ENG. IT IS POSSIBLE THAT THE RAPID DSCNT FROM 13000 FT TO 10000 FT MSL CONTRIBUTED TO SUPER COOLING OF THE AIRFRAME AND ENG. IT IS POSSIBLE THAT THIN ICE MAY HAVE FORMED ON THE AIR INTAKE. CONCLUSION: ALWAYS DRAIN FUEL FOR WATER OR CONTAMINATION PRIOR TO EACH FLT. NEVER SKIP THIS TEST EVEN ONCE. DO NOT ASSUME THAT FLYING BTWN LAYERS WILL AVOID ICE BUILDUP. BE AWARE OF MEA'S -- EVEN DURING EMERS.

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.