Narrative:

On jan/sat/92, I made a precautionary landing almost immediately after takeoff from hanscom field, because of partial loss of engine power. I think the cause was water in the fuel, melted from ice pellets. I found nothing wrong when I checked the airplane on the ground and had no trouble in my subsequent flight home. I am an instrument rated pilot and CFI with about 1600 hours experience. My plan was to fly from bedford back to my home base in pittsfield, ma. I last refueled the airplane at pittsfield nearly 2 weeks before this takeoff. The airplane was tied down between jan X and jan Y. It sat through several large changes in temperature -- up to nearly 60 degrees F and down to near 0. Temperature changes like this cause water to condense inside of fuel tanks. On jan/thur/92 I flew the airplane from pittsfield to bedford. When I sampled the fuel prior to that flight, I was not surprised to find ice pellets in the fuel, but I did find so many that I made a comment about them to the linesman who was preheating the engine. (Actually, the pellets were more like compacted bits of snow than ice.) I drained the tanks until no more pellets appeared -- 1 or 2 cups full. I had no trouble at all on that flight. I did not refuel at bedford since I had more than enough to return to pittsfield. During my preflight at bedford, I found ice pellets in the fuel in both wings -- more than before. I drained 2 or 3 fuel sampler cups out of each wing tank before getting clear fuel. I also drained fuel from the fuel strainer, but since the handle for the fuel strainer drain valve is in the cockpit, I did not sample the fuel there for ice pellets. (In newer aircraft the handle is by the dip stick and you can sample fuel from the strainer.) the engine started without trouble and ran up ok. I let the engine warm up prior to taxi. At takeoff on sat, conditions at bedford were 3000 ft scattered, 50 mi visibility, 25 degrees F, wind 290 degrees at 16 gusting to 25. I took off from runway 29, for a straight-out departure. I had no trouble at all during the early part of the climb. There was moderate turbulence. But then, during the climb and while still over the airport, the engine lost 150-200 RPM. It seemed to me, from sound and from my intuition, like carburetor icing, except that it came on suddenly. I applied carburetor heat and the engine burbled and responded as it does with carburetor ice. But the application of carburetor heat did not fully resolve the problem, at least, not in the few seconds I gave it. Rather than climb away from the airport, I called the tower and asked to land. Had the engine failed completely, I was in a position to land on a runway without trouble. When I called the tower, I did not declare an 'emergency' or even an 'urgent' situation, but gave a sketchy description of partial loss of engine power. The controller in the tower responded promptly, telling me the wind and offering 2 runways. The engine returned to normal by the time I entered the downwind, and I made an uneventful landing. I taxied to the runup area, shut down, and sampled my fuel. I saw some ice pellets in the fuel from the wing tanks and drained them until no more pellets appeared. I also managed to sample fuel from the strainer drain, by pulling the handle in the cockpit, running around to the front of the aircraft, sampling the fuel, and then running back to shut the valve. This sample was clean. The engine compartment and oil looked ok. The engine ran up ok and delivered the right RPM at full power. I then took off and flew back to pittsfield without any problems. My theory is that the problem was what I first thought: water in the fuel. The water was frozen as ice pellets and while I managed to drain most of them, I did not get them all since ice pellets don't concentrate at the bottom of the tank as tightly as droplets of water. Also, I may have drawn some ice pellets from the wing tanks into the fuel strainer by draining it. I would not expect visible ice pellets to work their way through the fuel filter, but min particles may have come through. Also, I let the engine warm up prior to taxi. This may have warmed fuel near the engine, converting ice in it to water, which could then cause trouble. My primary theory is that liquid water in the fuel froze in the venturi in the carburetor, much as water vapor in the air can freeze to form carburetor ice. It is also possible that ice blocked the flow of fuel, but I don't think so. If ice had blocked the flow, I think I would have lost more and more power as more ice got in the way, unless the flow of fuel eroded the ice. Or engine vibration shook it away. Or possibly, water in the fuel simply caused a loss of power. Theory aside, there were ice pellets in the fuel, and when I applied carburetor heat, the engine burbled and sounded like it had carburetor ice. And the engine quickly regained normal power. There are 2 points I would like to make. When concerned about safety, I prefer to act promptly to land rather than attempt to carry on. (I once lost partial power from a broken cylinder and, more memorably, I once leaked engine oil and lost oil pressure, so I know that engines can fail.) since I was right over the airport, I was in an ideal location. I did not want to fly a few mi away from the airport, at 2000 ft, and then lose the engine. The controller in the tower did just right. However, I fear that I did not provide as much information as I might have -- although I consciously did not declare an emergency or even an 'urgency' it did not occur to me to explain directly that I did not think this event was too serious.

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Original NASA ASRS Text

Title: SMA PLT LOSES PWR ON TKOF AFTER SUSPICION OF ICE PELLETS IN FUEL TANKS.

Narrative: ON JAN/SAT/92, I MADE A PRECAUTIONARY LNDG ALMOST IMMEDIATELY AFTER TKOF FROM HANSCOM FIELD, BECAUSE OF PARTIAL LOSS OF ENG PWR. I THINK THE CAUSE WAS WATER IN THE FUEL, MELTED FROM ICE PELLETS. I FOUND NOTHING WRONG WHEN I CHKED THE AIRPLANE ON THE GND AND HAD NO TROUBLE IN MY SUBSEQUENT FLT HOME. I AM AN INST RATED PLT AND CFI WITH ABOUT 1600 HRS EXPERIENCE. MY PLAN WAS TO FLY FROM BEDFORD BACK TO MY HOME BASE IN PITTSFIELD, MA. I LAST REFUELED THE AIRPLANE AT PITTSFIELD NEARLY 2 WKS BEFORE THIS TKOF. THE AIRPLANE WAS TIED DOWN BTWN JAN X AND JAN Y. IT SAT THROUGH SEVERAL LARGE CHANGES IN TEMP -- UP TO NEARLY 60 DEGS F AND DOWN TO NEAR 0. TEMP CHANGES LIKE THIS CAUSE WATER TO CONDENSE INSIDE OF FUEL TANKS. ON JAN/THUR/92 I FLEW THE AIRPLANE FROM PITTSFIELD TO BEDFORD. WHEN I SAMPLED THE FUEL PRIOR TO THAT FLT, I WAS NOT SURPRISED TO FIND ICE PELLETS IN THE FUEL, BUT I DID FIND SO MANY THAT I MADE A COMMENT ABOUT THEM TO THE LINESMAN WHO WAS PREHEATING THE ENG. (ACTUALLY, THE PELLETS WERE MORE LIKE COMPACTED BITS OF SNOW THAN ICE.) I DRAINED THE TANKS UNTIL NO MORE PELLETS APPEARED -- 1 OR 2 CUPS FULL. I HAD NO TROUBLE AT ALL ON THAT FLT. I DID NOT REFUEL AT BEDFORD SINCE I HAD MORE THAN ENOUGH TO RETURN TO PITTSFIELD. DURING MY PREFLT AT BEDFORD, I FOUND ICE PELLETS IN THE FUEL IN BOTH WINGS -- MORE THAN BEFORE. I DRAINED 2 OR 3 FUEL SAMPLER CUPS OUT OF EACH WING TANK BEFORE GETTING CLR FUEL. I ALSO DRAINED FUEL FROM THE FUEL STRAINER, BUT SINCE THE HANDLE FOR THE FUEL STRAINER DRAIN VALVE IS IN THE COCKPIT, I DID NOT SAMPLE THE FUEL THERE FOR ICE PELLETS. (IN NEWER ACFT THE HANDLE IS BY THE DIP STICK AND YOU CAN SAMPLE FUEL FROM THE STRAINER.) THE ENG STARTED WITHOUT TROUBLE AND RAN UP OK. I LET THE ENG WARM UP PRIOR TO TAXI. AT TKOF ON SAT, CONDITIONS AT BEDFORD WERE 3000 FT SCATTERED, 50 MI VISIBILITY, 25 DEGS F, WIND 290 DEGS AT 16 GUSTING TO 25. I TOOK OFF FROM RWY 29, FOR A STRAIGHT-OUT DEP. I HAD NO TROUBLE AT ALL DURING THE EARLY PART OF THE CLB. THERE WAS MODERATE TURB. BUT THEN, DURING THE CLB AND WHILE STILL OVER THE ARPT, THE ENG LOST 150-200 RPM. IT SEEMED TO ME, FROM SOUND AND FROM MY INTUITION, LIKE CARB ICING, EXCEPT THAT IT CAME ON SUDDENLY. I APPLIED CARB HEAT AND THE ENG BURBLED AND RESPONDED AS IT DOES WITH CARB ICE. BUT THE APPLICATION OF CARB HEAT DID NOT FULLY RESOLVE THE PROBLEM, AT LEAST, NOT IN THE FEW SECONDS I GAVE IT. RATHER THAN CLB AWAY FROM THE ARPT, I CALLED THE TWR AND ASKED TO LAND. HAD THE ENG FAILED COMPLETELY, I WAS IN A POS TO LAND ON A RWY WITHOUT TROUBLE. WHEN I CALLED THE TWR, I DID NOT DECLARE AN 'EMER' OR EVEN AN 'URGENT' SITUATION, BUT GAVE A SKETCHY DESCRIPTION OF PARTIAL LOSS OF ENG PWR. THE CTLR IN THE TWR RESPONDED PROMPTLY, TELLING ME THE WIND AND OFFERING 2 RWYS. THE ENG RETURNED TO NORMAL BY THE TIME I ENTERED THE DOWNWIND, AND I MADE AN UNEVENTFUL LNDG. I TAXIED TO THE RUNUP AREA, SHUT DOWN, AND SAMPLED MY FUEL. I SAW SOME ICE PELLETS IN THE FUEL FROM THE WING TANKS AND DRAINED THEM UNTIL NO MORE PELLETS APPEARED. I ALSO MANAGED TO SAMPLE FUEL FROM THE STRAINER DRAIN, BY PULLING THE HANDLE IN THE COCKPIT, RUNNING AROUND TO THE FRONT OF THE ACFT, SAMPLING THE FUEL, AND THEN RUNNING BACK TO SHUT THE VALVE. THIS SAMPLE WAS CLEAN. THE ENG COMPARTMENT AND OIL LOOKED OK. THE ENG RAN UP OK AND DELIVERED THE RIGHT RPM AT FULL PWR. I THEN TOOK OFF AND FLEW BACK TO PITTSFIELD WITHOUT ANY PROBLEMS. MY THEORY IS THAT THE PROBLEM WAS WHAT I FIRST THOUGHT: WATER IN THE FUEL. THE WATER WAS FROZEN AS ICE PELLETS AND WHILE I MANAGED TO DRAIN MOST OF THEM, I DID NOT GET THEM ALL SINCE ICE PELLETS DON'T CONCENTRATE AT THE BOTTOM OF THE TANK AS TIGHTLY AS DROPLETS OF WATER. ALSO, I MAY HAVE DRAWN SOME ICE PELLETS FROM THE WING TANKS INTO THE FUEL STRAINER BY DRAINING IT. I WOULD NOT EXPECT VISIBLE ICE PELLETS TO WORK THEIR WAY THROUGH THE FUEL FILTER, BUT MIN PARTICLES MAY HAVE COME THROUGH. ALSO, I LET THE ENG WARM UP PRIOR TO TAXI. THIS MAY HAVE WARMED FUEL NEAR THE ENG, CONVERTING ICE IN IT TO WATER, WHICH COULD THEN CAUSE TROUBLE. MY PRIMARY THEORY IS THAT LIQUID WATER IN THE FUEL FROZE IN THE VENTURI IN THE CARB, MUCH AS WATER VAPOR IN THE AIR CAN FREEZE TO FORM CARB ICE. IT IS ALSO POSSIBLE THAT ICE BLOCKED THE FLOW OF FUEL, BUT I DON'T THINK SO. IF ICE HAD BLOCKED THE FLOW, I THINK I WOULD HAVE LOST MORE AND MORE PWR AS MORE ICE GOT IN THE WAY, UNLESS THE FLOW OF FUEL ERODED THE ICE. OR ENG VIBRATION SHOOK IT AWAY. OR POSSIBLY, WATER IN THE FUEL SIMPLY CAUSED A LOSS OF PWR. THEORY ASIDE, THERE WERE ICE PELLETS IN THE FUEL, AND WHEN I APPLIED CARB HEAT, THE ENG BURBLED AND SOUNDED LIKE IT HAD CARB ICE. AND THE ENG QUICKLY REGAINED NORMAL PWR. THERE ARE 2 POINTS I WOULD LIKE TO MAKE. WHEN CONCERNED ABOUT SAFETY, I PREFER TO ACT PROMPTLY TO LAND RATHER THAN ATTEMPT TO CARRY ON. (I ONCE LOST PARTIAL PWR FROM A BROKEN CYLINDER AND, MORE MEMORABLY, I ONCE LEAKED ENG OIL AND LOST OIL PRESSURE, SO I KNOW THAT ENGS CAN FAIL.) SINCE I WAS RIGHT OVER THE ARPT, I WAS IN AN IDEAL LOCATION. I DID NOT WANT TO FLY A FEW MI AWAY FROM THE ARPT, AT 2000 FT, AND THEN LOSE THE ENG. THE CTLR IN THE TWR DID JUST RIGHT. HOWEVER, I FEAR THAT I DID NOT PROVIDE AS MUCH INFO AS I MIGHT HAVE -- ALTHOUGH I CONSCIOUSLY DID NOT DECLARE AN EMER OR EVEN AN 'URGENCY' IT DID NOT OCCUR TO ME TO EXPLAIN DIRECTLY THAT I DID NOT THINK THIS EVENT WAS TOO SERIOUS.

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.