Narrative:

During cruise flight at 9000 ft MSL from wadsworth, oh (3g3), to college park, md (cgs), the engine began running rough, all of the sudden. The plane was shaking from the roughness and I had just changed ZOB sectors. On reporting on, I advised at 9000 ft and requested to land morgantown, wv (mgw). A check of the charts and LORAN verified mgw as 10.4 mi away. I tried to clear the engine and it still ran rough. Carburetor heat was added, the propeller was set to high RPM. To avoid any further potential damage to the engine or airframe, I decided on a precautionary landing with minimal power. Center gave a vector to the airport and xferred me to clarksburg approach who confirmed the situation and reaffirmed a vector and lower altitude. I arrived over the field with 4000 ft AGL, was given priority at the field by the tower and landed without incident after a very close pattern. Inspection on the ground revealed no airframe or engine problems. I refiled the IFR flight plan and continued on to cgs. I can only speculate that carburetor ice had formed and dislodged causing the roughness, no other cause has been found.

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Original NASA ASRS Text

Title: PLT OF A PIPER PA24 COMMANCHE DIVERTED TO LAND DURING AN IFR FLT DUE TO A ROUGH RUNNING ENG. CARB ICE WAS SUSPECTED.

Narrative: DURING CRUISE FLT AT 9000 FT MSL FROM WADSWORTH, OH (3G3), TO COLLEGE PARK, MD (CGS), THE ENG BEGAN RUNNING ROUGH, ALL OF THE SUDDEN. THE PLANE WAS SHAKING FROM THE ROUGHNESS AND I HAD JUST CHANGED ZOB SECTORS. ON RPTING ON, I ADVISED AT 9000 FT AND REQUESTED TO LAND MORGANTOWN, WV (MGW). A CHK OF THE CHARTS AND LORAN VERIFIED MGW AS 10.4 MI AWAY. I TRIED TO CLR THE ENG AND IT STILL RAN ROUGH. CARB HEAT WAS ADDED, THE PROP WAS SET TO HIGH RPM. TO AVOID ANY FURTHER POTENTIAL DAMAGE TO THE ENG OR AIRFRAME, I DECIDED ON A PRECAUTIONARY LNDG WITH MINIMAL PWR. CTR GAVE A VECTOR TO THE ARPT AND XFERRED ME TO CLARKSBURG APCH WHO CONFIRMED THE SIT AND REAFFIRMED A VECTOR AND LOWER ALT. I ARRIVED OVER THE FIELD WITH 4000 FT AGL, WAS GIVEN PRIORITY AT THE FIELD BY THE TWR AND LANDED WITHOUT INCIDENT AFTER A VERY CLOSE PATTERN. INSPECTION ON THE GND REVEALED NO AIRFRAME OR ENG PROBS. I REFILED THE IFR FLT PLAN AND CONTINUED ON TO CGS. I CAN ONLY SPECULATE THAT CARB ICE HAD FORMED AND DISLODGED CAUSING THE ROUGHNESS, NO OTHER CAUSE HAS BEEN FOUND.

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.