Narrative:

I was on an IFR flight plan from detroit city airport to wittman field, oshkosh, wi. On V450, about 75 NM from mkg while on top at 10000', there was a line of build-ups in my flight path. I asked for a heading of 240 degrees to deviate from the WX, which was granted by ZAU. My clearance was to fly 240 degrees, when clear of WX proceed direct mkg. On the 240 degree heading it looked like the tops of the build-ups were declining and I would be clear of the WX. I then turned to the west to proceed direct mkg. About 5 mins later I went into the clouds. The ride was smooth with no turbulence. A few mins later I flew into an embedded thunderstorm. There was lightning, heavy rain, hail and severe turbulence. I lost 4000' in one downdraft. I could not maintain my heading or altitude. I called ZAU and told them of my problem. They had me contact lansing approach who gave me a heading to try and fly to get out. I did and broke out of the thunderstorm. They asked me what my intentions were. I said I would like to continue on to osh. They had me contact ZAU. Center said to climb back to 10000', and I believe a 360 degree heading. About that time my carburetor ice warning light came on. I tried to apply carburetor heat, but it wouldn't come out. The engine started to run rough and lose power. Finally I managed to pull the carburetor heat knob out and the engine smoothed out and the carburetor ice light went out. I tried to push in the carburetor heat knob at that time, but it wouldn't't go back in. With full carburetor heat on, the engine wouldn't't produce full power and I couldn't maintain altitude or climb, so I called ZAU and declared an emergency. They handed me off to lansing approach, who gave me a vector back to their airport. After landing and looking over the airplane, I noticed hail damage to the leading edge of the wings, propeller spinner and the plastic strut fairings. The carburetor heat worked on the ground, but was very stiff. This problem has not been looked into yet. Prior to leaving home that morning, after watching the WX channel on tv and checking WX with FSS, I filed a flight plan route right.V.SM V2 direct mkg, V510 direct osh, which was south of an area of potential WX. Upon receiving my clearance at detroit city prior to takeoff ATC had changed my route of flight to right.V.-V337 direct hockey V450 direct mkg, then as filed; which was more to the north and closer to potential WX. I think if ATC changes your route of flight, especially with potentially hazardous WX, they should assume more responsibility for keeping you away from it. I am aware that they don't do that, so I do not plan to fly into clouds again west/O my own means of detecting severe WX.

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Original NASA ASRS Text

Title: EMERGENCY DECLARED AS SMA PLT HAS AN INFLT ENCOUNTER WITH WX. AFTER EMERGENCY LNDG DISCOVERED THAT ACFT SUFFERED DAMAGE DUE TO HAIL FROM TSTM.

Narrative: I WAS ON AN IFR FLT PLAN FROM DETROIT CITY ARPT TO WITTMAN FIELD, OSHKOSH, WI. ON V450, ABOUT 75 NM FROM MKG WHILE ON TOP AT 10000', THERE WAS A LINE OF BUILD-UPS IN MY FLT PATH. I ASKED FOR A HDG OF 240 DEGS TO DEVIATE FROM THE WX, WHICH WAS GRANTED BY ZAU. MY CLRNC WAS TO FLY 240 DEGS, WHEN CLR OF WX PROCEED DIRECT MKG. ON THE 240 DEG HDG IT LOOKED LIKE THE TOPS OF THE BUILD-UPS WERE DECLINING AND I WOULD BE CLR OF THE WX. I THEN TURNED TO THE W TO PROCEED DIRECT MKG. ABOUT 5 MINS LATER I WENT INTO THE CLOUDS. THE RIDE WAS SMOOTH WITH NO TURB. A FEW MINS LATER I FLEW INTO AN EMBEDDED TSTM. THERE WAS LIGHTNING, HEAVY RAIN, HAIL AND SEVERE TURB. I LOST 4000' IN ONE DOWNDRAFT. I COULD NOT MAINTAIN MY HDG OR ALT. I CALLED ZAU AND TOLD THEM OF MY PROB. THEY HAD ME CONTACT LANSING APCH WHO GAVE ME A HDG TO TRY AND FLY TO GET OUT. I DID AND BROKE OUT OF THE TSTM. THEY ASKED ME WHAT MY INTENTIONS WERE. I SAID I WOULD LIKE TO CONTINUE ON TO OSH. THEY HAD ME CONTACT ZAU. CENTER SAID TO CLB BACK TO 10000', AND I BELIEVE A 360 DEG HDG. ABOUT THAT TIME MY CARB ICE WARNING LIGHT CAME ON. I TRIED TO APPLY CARB HEAT, BUT IT WOULDN'T COME OUT. THE ENG STARTED TO RUN ROUGH AND LOSE PWR. FINALLY I MANAGED TO PULL THE CARB HEAT KNOB OUT AND THE ENG SMOOTHED OUT AND THE CARB ICE LIGHT WENT OUT. I TRIED TO PUSH IN THE CARB HEAT KNOB AT THAT TIME, BUT IT WOULDN'T'T GO BACK IN. WITH FULL CARB HEAT ON, THE ENG WOULDN'T'T PRODUCE FULL PWR AND I COULDN'T MAINTAIN ALT OR CLB, SO I CALLED ZAU AND DECLARED AN EMER. THEY HANDED ME OFF TO LANSING APCH, WHO GAVE ME A VECTOR BACK TO THEIR ARPT. AFTER LNDG AND LOOKING OVER THE AIRPLANE, I NOTICED HAIL DAMAGE TO THE LEADING EDGE OF THE WINGS, PROP SPINNER AND THE PLASTIC STRUT FAIRINGS. THE CARB HEAT WORKED ON THE GND, BUT WAS VERY STIFF. THIS PROB HAS NOT BEEN LOOKED INTO YET. PRIOR TO LEAVING HOME THAT MORNING, AFTER WATCHING THE WX CHANNEL ON TV AND CHKING WX WITH FSS, I FILED A FLT PLAN ROUTE R.V.SM V2 DIRECT MKG, V510 DIRECT OSH, WHICH WAS S OF AN AREA OF POTENTIAL WX. UPON RECEIVING MY CLRNC AT DETROIT CITY PRIOR TO TKOF ATC HAD CHANGED MY ROUTE OF FLT TO R.V.-V337 DIRECT HOCKEY V450 DIRECT MKG, THEN AS FILED; WHICH WAS MORE TO THE N AND CLOSER TO POTENTIAL WX. I THINK IF ATC CHANGES YOUR ROUTE OF FLT, ESPECIALLY WITH POTENTIALLY HAZARDOUS WX, THEY SHOULD ASSUME MORE RESPONSIBILITY FOR KEEPING YOU AWAY FROM IT. I AM AWARE THAT THEY DON'T DO THAT, SO I DO NOT PLAN TO FLY INTO CLOUDS AGAIN W/O MY OWN MEANS OF DETECTING SEVERE WX.

Data retrieved from NASA's ASRS site as of August 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.