COMMERCIAL PILOT REPORTS LANDING AT RCA AND GOING OFF THE RWY WHILE ATTEMPTING TO LAND AT RAP.

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I WAS ON AN IFR FLT PLAN TO RAP. I DEPARTED AROUND XA15 VFR AND PICKED MY CLRNC UP WHILE AIRBORNE. THE FLT WENT WELL AND I RECEIVED CLRNC FROM ELLSWORTH APCH FOR THE GPS 14 APCH INTO RAP. HE CLRED ME TO ASUVE AT OR ABOVE 5500 FT MSL THEN FOR THE APCH. WHEN I ACTIVATED THE APCH ON THE GNS 530 IT SOMEHOW DROPPED ASUVE SO I PUT IN A DIRECT TO COURSE TO ASUVE THEN TURNED TO THE INBOUND COURSE OF 141 DEGS AND PUNCHED IN DIRECT TO ZUDIM. AS I WAS APCHING ZUDIM; I LOOKED UP AND SAW THE RWY RIGHT BEFORE ME; EARLIER THAN I EXPECTED. I TOOK OVER VISUALLY AND LANDED ON RWY 14. UPON LNDG ON THE CTRLINE I LOST DIRECTIONAL CTL AND EXITED THE RWY ON THE R ONTO THE GRASS. NO DAMAGE OCCURRED EITHER TO THE ACFT OR TO THE RWY LIGHTING. RAP TWR ASKED WHERE I WAS AND I TOLD THEM I JUST LANDED AND WENT OFF THE RWY ONTO THE GRASS. THEY XFERRED ME TO ELLSWORTH TWR WHO TOLD ME TO SHUT DOWN THE AIRPLANE; WHICH I DID. SHORTLY THEREAFTER; I WAS GREETED BY MULTIPLE MIL PERSONNEL. AFTER I AND MY AIRPLANE WERE CLRED; I WAS TOLD TO START THE ENG AND TAXI BACK ONTO THE RWY AND FOLLOW THE TRUCK TO PARKING; WHICH I DID. FOR ABOUT THE NEXT 2 HRS I WAS QUESTIONED BY A NUMBER OF PEOPLE AND FILLED OUT VARIOUS FORMS. WHEN THAT WAS FINISHED I WAS GRANTED PERMISSION TO START THE AIRPLANE AND FLY TO RAP; WHICH I DID. UPON REFLECTING HOW THIS HAPPENED; I HAVE DECIDED IT WAS A CHAIN OF ERRORS ON MY PART. I HAD FLOWN MY AIRPLANE VERY LITTLE OVER THE PRIOR 3 MONTHS. I HAD BECOME LESS THAN PROFICIENT WITH THE GWS530 AS WELL. BEFORE DEPARTING; I WAS STAYING IN A LODGE THAT HAD NO INTERNET. MOST OF MY FLT PLANNING TAKES PLACE 24 HRS PRIOR TO DEP AND I USE THE INTERNET TO CHK WX AND CHARTS AS WELL AS IAP'S. I WAS NOT ABLE TO DO THIS AND DID AN ABBREVIATED PREPARATION AFTER ARRIVING AT THE ARPT SINCE I HAD LEFT ALL MY CHARTS IN THE ACFT. IN MY PREPARATION I SHOULD HAVE NOTICED ELLSWORTH AFB NEXT TO THE FAF APPROX 5 MI NE OF RAP. HAD I DONE THIS; I WOULD HAVE AVOIDED THIS EMBARRASSING INCIDENT.