AN SMA PLT IS FORCED TO PROCEED TO AN ALTERNATE ARPT WHEN ROA APCH CTLR ADVISES PLT THAT THE GPS APCH TO RWY 12 AT BCB IS NOT AUTH. PLT ELECTS TO GO TO ROA AS HE CANNOT GET VMC DURING VECTORS AROUND THE BCB AREA.

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OUR IFR FLT ORIGINATED AT STAFFORD ARPT IN WEATHERFORD; OK. THIS WAS A 4 HR 50 MIN FLT TO BCB AND WAS CONDUCTED MOSTLY IN IMC CONDITIONS. AS WE WERE APCHING BCB TRAVELING NE ON V16 AFTER PASSING HMV; I REQUESTED THE GPS RWY 12 APCH AT BCB FROM THE CTLR AT ROA APCH (126.9). THE CTLR SAID HE WOULD PASS THAT INFO TO THE NEXT CTLR. PASSING PSK WE TURNED N (021 DEGS) ON V37 TO INTERCEPT THE HAWTO WAYPOINT ON THE GPS RWY 12 APCH; WHEN THE FINAL CTLR STATED THAT THE GPS RWY 12 APCH 'WAS NOT AN AUTH APCH FOR BCB.' THE CTLR THEN BEGAN TO VECTOR AND DSND US TO VARIOUS HDGS AND ALTS. I BECAME UNCOMFORTABLE BEING VECTORED IN IMC CONDITIONS AT LOWER ALTS IN WHAT I KNEW TO BE MOUNTAINOUS TERRAIN. HE WANTED US TO GO VISUAL BUT CONDITIONS REMAINED IMC. AT THAT POINT I DECIDED THAT I WANTED VECTORS TO THE NEAREST VFR ARPT AS FUEL WOULD SOON BECOME A FACTOR (DEPENDING ON HOW FAR THE NEAREST VFR ARPT MIGHT BE). I HAD CONSIDERABLE DIFFICULTY GETTING THE ATTN OF THE CTLR THAT I NEEDED; TO GET VECTORS TO THE NEAREST VFR RWY BECAUSE HE WAS CTLING A NUMBER OF OTHER ACFT. VECTORS TO ROA WERE EVENTUALLY GIVEN BY A FINAL CTLR. I WAS ONLY 30 MI FROM ROA. AT NO TIME DURING THE APCH TO BCB AND ROA DID OUR FUEL RESERVE FALL BELOW LEGAL MINIMUMS AS THIS PARAMETER IS CONTINUOUSLY DISPLAYED ON MY FMS SYS (KFC 200 FLT DIRECTOR COUPLED TO BOTH AN IFR CERTIFIED APCH CERTIFIED GPS NAVIGATOR AND AN IFR CERTIFIED AND COUPLED TO GPS FUEL COMPUTER THAT READS OUT/DISPLAYS 'GALLONS REMAINING AT DEST' THROUGHOUT THE DURATION OF THE FLT). A NORMAL VISUAL APCH AND LNDG WAS EXECUTED AT ROA WITHOUT INCIDENT.