PLT OF AN ATX AMB SMT TWIN TURBOPROP MADE AN ILS APCH AND LNDG BELOW RPTED LNDG MINIMUMS REQUIRED UNDER PART 135 OF THE FARS. THE RPTR STATED THAT HE COULD VISUALLY SEE BETTER THAN RPTED DURING APCH AND LNDG.

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I FILED A LIFEGUARD FLT FROM IEN; SD; TO SPF; SD. WE ARE BASED IN RAP; SD; AND DUE TO RPTED FOG 100 FT AND 1/4 MI VISIBILITY; WE PLANNED TO LAND IN SPEARFISH; SD; WITH A POSSIBILITY OF LNDG IN 49B; SD; IF THERE WAS NO FOG AT THIS ARPT. SPEARFISH IS A 55 MIN DRIVE BY AMBULANCE TO RAP AND STURGIS IS A 35 MIN DRIVE TO RAP. AFTER LEAVING PINE RIDGE; I CLBED TO 12000 FT. AFTER LEVELING OFF; I COULD SEE RAPID CITY CITY LIGHTS IN FRONT OF ME. AFTER BEING HANDED OFF FROM ZDV TO ELLSWORTH APCH; I WAS GIVEN DSCNT CLRNC FOR THE APCH AT RAP (POSSIBLY DUE TO THE FACT WE ALWAYS COME BACK TO RAP). I ASKED THE WX AT RAP AND AT ELLSWORTH. RAP WAS 100 FT; 1/4 MI VISIBILITY VERSUS ELLSWORTH 100 FT 1/16 MI VISIBILITY. AT THIS POINT I CLICKED UP THE LIGHTS AT RAP ARPT SINCE TWR WAS CLOSED. I COULD SEE THE RWY AND OCCASIONALLY THE LEAD-IN LIGHTS. I THEN TOLD ELLSWORTH APCH THAT I WOULD TRY THE ILS AND IF I MISSED THEN GO TO STURGIS WITH POSSIBILITY OF ENDING UP IN SPEARFISH. AFTER XING THE MIDDLE MARKER; I COULD SEE PART OF THE LEAD-IN LIGHTS AND SOME OF THE RWY LIGHTS. AT DECISION HT; I COULD SEE MOST; IF NOT ALL; OF THE RWY LIGHTS AND LANDED WITH NO PROB OR INCIDENT. THE PROB WAS THE DIFFERENCE BTWN RPTED WX AND MY OBSERVED WX. I OBSERVED MUCH BETTER WX THAN RPTED. IT SEEMED MORE LIKE A THICK HAZE LAYER VERSUS A FOG LAYER; AND LOOKED BY MY JUDGEMENT 3/4 MI VISIBILITY.