WITH ROUGH RUNNING ENG RPTR APPLIED CARB HEAT; BUT APPARENTLY IT DIDN'T IMMEDIATELY IMPROVE THE ENG PROB AND RPTR PLT TURNED IT OFF. AS RPM'S CONTINUED TO DECREASE; RPTR HEADED FOR THE NEAREST ARPT; BUT COULDN'T MAKE IT AND LANDED IN A PARKING LOT. INVESTIGATED BY THE NTSB. SUSPECTED TO BE CARB ICE.

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I DEPARTED HICKORY; NC; AT APPROX XA40 (VFR CONDITIONS). BECAUSE OF STRONG TURB; THE INITIAL ALT WAS 4500 FT. DURING THE FLT AT CRUISING SPD; I REALIZED THE ENG WAS RUNNING ROUGH. I USED CARB HEAT TO CHK FOR CARB ICING BUT THE ENG WAS STILL RUNNING ROUGH; WITH NO CHANGE IN PERFORMANCE. AT APPROX 9 MI FROM ROA ARPT AT 11500 FT; I LOST SIGNIFICANT RPM'S (FROM 2600 TO 1600 RPM'S) AND THE ENG WAS SOUNDING DIFFERENT. I CONTACTED ROA APCH EXPLAINING THAT I WAS 10 MI FROM ROA ARPT; HAD LOST RPM'S AND REQUESTED A FULL STOP. WX CONDITIONS WERE GOOD VFR. AT 4 MI OUT I TESTED THE THROTTLE AND THERE SEEMED TO BE NO PWR. I DID NECESSARY EMER PROCS AND AT APPROX 1/2 MI BEFORE THE ARPT AT 2500 FT; WITH WIND 330 DEGS; 13 KTS AND HAVING TO LAND DIRECTLY INTO THE WIND; I RADIOED APCH SAYING; 'I AM MAKING A L TURN; I CAN'T MAKE IT.' I HEADED FOR THE VALLEY VIEW MALL PARKING LOT BECAUSE OF THE GOOD LIGHTING. BECAUSE OF HAVING TO MAKE A SHARP L TURN TO LAND AT MY DESIGNATED SPOT; MY L WINGTIP CLIPPED A LIGHT POLE. MY STALL BUZZER WENT OFF AND I DROPPED MY NOSE FOR AIRSPD AND HEADED TO MY LNDG SPOT; GLIDING ALL THE WAY. BECAUSE OF LNDG DOWNWIND; I AIMED FOR THE BEST STOPPING SPOT WHICH WAS AWAY FROM THE CARS AND ENDING UP AGAINST A SMALL TREE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ACFT TYPE C172 WITH A 180 ENG. RPTR SAYS CAUSE COULDN'T BE FOUND AND WAS PROBABLY CARB ICE. AS RPM DETERIORATED THE PLT HEADED FOR ROA ARPT AND CONTACTED APCH CTL FOR CLRNC. AIRSPD DETERIORATED TO THE POINT RPTR WAS GETTING STALL WARNING AND HAD TO LAND IN A PARKING LOT WHICH WAS LIGHTED. (IT WAS NIGHT.) ON THE LNDG HE HIT A CURB WHICH DAMAGED THE NOSEGEAR AND THE L WING HIT A TREE. THE L WING HAD TO BE REPLACED. ALSO; DURING THE LNDG HIS ACFT HIT A PARKED VAN AND KNOCKED THE MIRROR OFF; FOR WHICH HE WAS BILLED. RPTR SAYS HE SENT $25 TO THE NTSB TO GET A COPY OF THEIR RPT; BUT HASN'T HEARD FROM THEM YET. HE SUSPECTS NOBODY REALLY KNOWS WHAT THE PROB WAS; BUT CARB ICE WAS SUSPECTED. WHEN THE ENG FIRST STARTED RUNNING ROUGH; HE TURNED ON THE CARB HEAT; BUT WHEN IT DIDN'T SEEM TO HELP; HE TURNED IT OFF. THE ENG PROGRESSIVELY GOT ROUGHER AND RPM DECREASED.