RPTR IN SMA ACFT ENCOUNTERED SNOW AND LOW VISIBILITY ON APCH WHEN VFR WAS EXPECTED.

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AFTER BEING HANDED OFF TO A SECOND CTLR ABOUT 25 NM FROM TOUCHDOWN I WAS ADVISED TO EXPECT A VOR CIRCLE TO LAND APCH AND TO SLOW TO 100 KTS FOR SPACING. THAT WAS A BIT UNUSUAL BUT COULD BE DONE. HOWEVER; THE SUBSTANTIAL PWR REDUCTION REQUIRED RESULTED IN A SIGNIFICANT AMOUNT OF CARB ICE -- AT LEAST THE APPLICATION OF CARB HEAT REMEDIED THE PROBLEM AFTER A BIT OF VERY ROUGH ENG OP. THE OP WAS ROUGH ENOUGH THAT IT CAUSED ME TO BE SOMEWHAT PREOCCUPIED WITH THE ENG. I ALSO WAS SURPRISED AND UNEASY THAT NO FURTHER CLRNC; HDG OR VECTORS WERE GIVEN TO ME AS I APCHED THE VOR UPON WHICH THE APCH IS BASED; PARTICULARLY SINCE THEY USUALLY ARE AND I HAD FILED MO20/A. AFTER SOME REFLECTION I DECIDED TO PROCEED WITH THE 'DIRECT BED' THAT HAD BEEN IMPLIED BY THE LAST CLRNC I HAD RECEIVED. AFTER BEING CLRED FOR THE APCH THINGS WENT SMOOTHLY AND I KEPT AHEAD OF THE AIRPLANE UNTIL THE FINAL APCH FIX EVEN THOUGH THE SNOW WAS INTENSIFYING AND THE FORWARD VISIBILITY WAS DETERIORATING MARKEDLY. UP TO THIS POINT I HAD NEITHER REVIEWED THE APCH PLATE NOR REALLY SET MY MIND TO THE TASK OF FLYING THE APCH. I WOULD NORMALLY DO BOTH OF THESE EVEN THOUGH I AM QUITE FAMILIAR WITH THE APCH. I THINK MY FAILURE TO DO SO WAS CAUSED PARTLY BY MY EXPECTATION OF VMC CONDITIONS ON THE INITIAL APCH SEGMENT AT 1500 FT MSL AND PARTLY BY MY PREOCCUPATION WITH THE EVENTS MENTIONED ABOVE. IT IS A FAILURE I WILL NOT REPEAT. AS I DSNDED TO MDA I STILL WAS IN A VMC STATE OF MIND SPENDING TOO MUCH TIME PEERING INTO THE SNOW FOR THE ARPT AND TOO LITTLE TIME FLYING THE AIRPLANE BY REF TO INSTS -- PARTICULARLY WITH REF TO THE ALTIMETER. PERHAPS THAT WAS BECAUSE I COULD SEE THE GND BELOW AND STILL 'BELIEVED' THAT I WAS IN VMC BUT I SURELY DIDN'T HAVE THE RWY ENVIRONMENT IN SIGHT. IN FACT THE VISIBILITY WAS SO BAD THAT I ASKED FOR FIELD LIGHTS TO BE TURNED UP ONLY TO BE TOLD THAT THEY HAD NO OBSTRUCTIONS TO VISION THERE. THE SNOW SHOWER WAS A VERY LCL BUT INTENSE ONE THAT I FLEW OUT OF ABOUT 2 MI FROM THE FIELD. THE ONLY REAL DAMAGE THAT RESULTED FROM THIS WAS TO MY EGO; BUT IT COULD HAVE TURNED OUT DIFFERENTLY. WRITING ABOUT IT HELPS ME PUT IT IN PERSPECTIVE AND FIX THE LESSONS TO BE LEARNED FROM IT IN MY MIND. HOPE IT HELPS YOUR PROGRAM TOO.