Narrative:

On an IFR trip from plattsburg, ny to roc, I had been in IMC conditions for approximately 1.5 hours at 6000'. Because the OAT was below freezing, I had been keeping a constant eye out for air frame icing of which there had been not a trace. Shortly after being handed off from syr to roc approach, the engine began to lose power--very subtly at first. But within a 2 min period it felt as if it were going to quit, even though I had done all the required steps. At this time I asked to be vectored to the nearest airport, which was sodus-williamson for a landing. With an engine only producing partial power, I definitely wanted to land. Upon descending out of the clouds at 4000' and with excellent vectors from roc approach, the airport was located and I continued descent toward it. Approach gave me the option of cancelling IFR (which I did), and asked that I contact them either by radio or landline upon landing. After a successful landing on the airport runway 10, I shut the engine down and immediately began to investigate what had caused the problem. Fluid was profusely dripping from the cowl and I at first thought it was fuel. Further checking showed it to be water, at which time the upper cowl was removed to discover huge amounts of slush type ice had accumulated within the engine cowl. I stress that there was not a trace of air frame ice on the aircraft during and after the flight. But now I was looking at 1-2' accumulations in the engine compartment, mostly on the inside of the upper cowl, the fire wall and various nooks and crannies of the engine downdraft baffling. The amount I would estimate to have been 1 1/2-3 gals if placed in a container. There was no sign of impact icing as you would expect to find from snow--just this very slushy ice. The intake for the induction air which is located above #4 cylinder was clear, but upon removal of the filter cover the filter was found to be almost totally blocked by the ice slush. I should mention at this point that I had checked with people at sodus as to my status with roc ATC and was told that they had called the airport and monitored the phone till I was on the ground at the airport and safe. And as long as I had landed they were satisfied and I did not have to call them. Having now found the cause of my power loss, I went about removing all traces of the ice and particularly cleaning the air filter and checking the induction system out thoroughly. After allowing the aircraft to dry out (surface temperature 45 degrees F), and carefully replacing the filter and assembly, I started the engine and gave it a 5 min run-up just to be sure it was producing full power with magnetic-propeller-alternate and fully checked out. I then proceeded to takeoff and fly the aircraft once around the pattern and was satisfied it was fully airworthy. At this point I taxied in and loaded my 2 passenger, and after another careful run-up, proceeded to depart the airport and continue to roc with no further problems. My analysis: it was induction icing but of an uncommon occurrence. There was at no time a trace of air frame ice, nor at the time of power loss was there any sign of snow. It was not something I was prepared for, nor have I heard or read about. I have over 100 hours actual IMC time and I read everything about flying I can find. I always assumed induction icing went hand in hand with air frame icing or snow conditions, neither of which was present on this flight. Although the engine did have partial power on descent, I was fortunate there was an airport within 5 NM. Callback conversation with reporter revealed the following: reporter states aircraft is fuel injected engine and has no engine induction heat function. (Analyst checked with mechanic and learned that the alternate air function opens a door up inside the cowling and uses unfiltered air.) the propeller stopped on landing when power to idle. Local folks assisted in pulling aircraft onto ramp and off taxiway. Flight began in heavy snow conditions, but out of it in about 10 mins. Reporter had just given a pilot report indicating negative icing. He has talked to many people and many don't believe him. FAA upset because he took off west/O a mechanic inspection. Reporter felt his run-ups and test flight indicated engine performing properly.

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Original NASA ASRS Text

Title: SMA PLT IN IMC EXPERIENCES ENG PROBLEMS. DIVERTS FOR EMERGENCY LNDG.

Narrative: ON AN IFR TRIP FROM PLATTSBURG, NY TO ROC, I HAD BEEN IN IMC CONDITIONS FOR APPROX 1.5 HRS AT 6000'. BECAUSE THE OAT WAS BELOW FREEZING, I HAD BEEN KEEPING A CONSTANT EYE OUT FOR AIR FRAME ICING OF WHICH THERE HAD BEEN NOT A TRACE. SHORTLY AFTER BEING HANDED OFF FROM SYR TO ROC APCH, THE ENG BEGAN TO LOSE PWR--VERY SUBTLY AT FIRST. BUT WITHIN A 2 MIN PERIOD IT FELT AS IF IT WERE GOING TO QUIT, EVEN THOUGH I HAD DONE ALL THE REQUIRED STEPS. AT THIS TIME I ASKED TO BE VECTORED TO THE NEAREST ARPT, WHICH WAS SODUS-WILLIAMSON FOR A LNDG. WITH AN ENG ONLY PRODUCING PARTIAL PWR, I DEFINITELY WANTED TO LAND. UPON DSNDING OUT OF THE CLOUDS AT 4000' AND WITH EXCELLENT VECTORS FROM ROC APCH, THE ARPT WAS LOCATED AND I CONTINUED DSNT TOWARD IT. APCH GAVE ME THE OPTION OF CANCELLING IFR (WHICH I DID), AND ASKED THAT I CONTACT THEM EITHER BY RADIO OR LANDLINE UPON LNDG. AFTER A SUCCESSFUL LNDG ON THE ARPT RWY 10, I SHUT THE ENG DOWN AND IMMEDIATELY BEGAN TO INVESTIGATE WHAT HAD CAUSED THE PROB. FLUID WAS PROFUSELY DRIPPING FROM THE COWL AND I AT FIRST THOUGHT IT WAS FUEL. FURTHER CHKING SHOWED IT TO BE WATER, AT WHICH TIME THE UPPER COWL WAS REMOVED TO DISCOVER HUGE AMOUNTS OF SLUSH TYPE ICE HAD ACCUMULATED WITHIN THE ENG COWL. I STRESS THAT THERE WAS NOT A TRACE OF AIR FRAME ICE ON THE ACFT DURING AND AFTER THE FLT. BUT NOW I WAS LOOKING AT 1-2' ACCUMULATIONS IN THE ENG COMPARTMENT, MOSTLY ON THE INSIDE OF THE UPPER COWL, THE FIRE WALL AND VARIOUS NOOKS AND CRANNIES OF THE ENG DOWNDRAFT BAFFLING. THE AMOUNT I WOULD ESTIMATE TO HAVE BEEN 1 1/2-3 GALS IF PLACED IN A CONTAINER. THERE WAS NO SIGN OF IMPACT ICING AS YOU WOULD EXPECT TO FIND FROM SNOW--JUST THIS VERY SLUSHY ICE. THE INTAKE FOR THE INDUCTION AIR WHICH IS LOCATED ABOVE #4 CYLINDER WAS CLR, BUT UPON REMOVAL OF THE FILTER COVER THE FILTER WAS FOUND TO BE ALMOST TOTALLY BLOCKED BY THE ICE SLUSH. I SHOULD MENTION AT THIS POINT THAT I HAD CHKED WITH PEOPLE AT SODUS AS TO MY STATUS WITH ROC ATC AND WAS TOLD THAT THEY HAD CALLED THE ARPT AND MONITORED THE PHONE TILL I WAS ON THE GND AT THE ARPT AND SAFE. AND AS LONG AS I HAD LANDED THEY WERE SATISFIED AND I DID NOT HAVE TO CALL THEM. HAVING NOW FOUND THE CAUSE OF MY PWR LOSS, I WENT ABOUT REMOVING ALL TRACES OF THE ICE AND PARTICULARLY CLEANING THE AIR FILTER AND CHKING THE INDUCTION SYS OUT THOROUGHLY. AFTER ALLOWING THE ACFT TO DRY OUT (SURFACE TEMP 45 DEGS F), AND CAREFULLY REPLACING THE FILTER AND ASSEMBLY, I STARTED THE ENG AND GAVE IT A 5 MIN RUN-UP JUST TO BE SURE IT WAS PRODUCING FULL PWR WITH MAG-PROP-ALTERNATE AND FULLY CHKED OUT. I THEN PROCEEDED TO TKOF AND FLY THE ACFT ONCE AROUND THE PATTERN AND WAS SATISFIED IT WAS FULLY AIRWORTHY. AT THIS POINT I TAXIED IN AND LOADED MY 2 PAX, AND AFTER ANOTHER CAREFUL RUN-UP, PROCEEDED TO DEPART THE ARPT AND CONTINUE TO ROC WITH NO FURTHER PROBS. MY ANALYSIS: IT WAS INDUCTION ICING BUT OF AN UNCOMMON OCCURRENCE. THERE WAS AT NO TIME A TRACE OF AIR FRAME ICE, NOR AT THE TIME OF PWR LOSS WAS THERE ANY SIGN OF SNOW. IT WAS NOT SOMETHING I WAS PREPARED FOR, NOR HAVE I HEARD OR READ ABOUT. I HAVE OVER 100 HRS ACTUAL IMC TIME AND I READ EVERYTHING ABOUT FLYING I CAN FIND. I ALWAYS ASSUMED INDUCTION ICING WENT HAND IN HAND WITH AIR FRAME ICING OR SNOW CONDITIONS, NEITHER OF WHICH WAS PRESENT ON THIS FLT. ALTHOUGH THE ENG DID HAVE PARTIAL PWR ON DSNT, I WAS FORTUNATE THERE WAS AN ARPT WITHIN 5 NM. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATES ACFT IS FUEL INJECTED ENG AND HAS NO ENG INDUCTION HEAT FUNCTION. (ANALYST CHKED WITH MECH AND LEARNED THAT THE ALTERNATE AIR FUNCTION OPENS A DOOR UP INSIDE THE COWLING AND USES UNFILTERED AIR.) THE PROP STOPPED ON LNDG WHEN PWR TO IDLE. LCL FOLKS ASSISTED IN PULLING ACFT ONTO RAMP AND OFF TXWY. FLT BEGAN IN HEAVY SNOW CONDITIONS, BUT OUT OF IT IN ABOUT 10 MINS. RPTR HAD JUST GIVEN A PLT RPT INDICATING NEGATIVE ICING. HE HAS TALKED TO MANY PEOPLE AND MANY DON'T BELIEVE HIM. FAA UPSET BECAUSE HE TOOK OFF W/O A MECH INSPECTION. RPTR FELT HIS RUN-UPS AND TEST FLT INDICATED ENG PERFORMING PROPERLY.

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.