LOW VISIBILITY APCH GAR TOO LATE ACFT LANDED OFF RWY.

Narrative

I WAS A COPLT ON A LR-55 CHARTER FLT FROM ADS TO BGM. ON DSCNT INTO BGM; ATIS WAS RPTING 3/4 MI VISIBILITY WITH FOG. ILS RWY 16 WAS IN USE. WE (THE CREW) OVERHEARD APCH CTL SAY THAT THE VISIBILITY WAS 3/16 MI. WHEN THE CAPT QUESTIONED THE CTLR ABOUT THE VISIBILITY; THE CTLR RESPONDED THAT THE OFFICIAL VISIBILITY WAS 3/4 MI; BUT AN ACFT AHEAD OF US RPTED THE RWY LIGHTS IN SIGHT 8-9 MI OUT ON FINAL FOR RWY 16. APCH ASKED US FOR OUR INTENTIONS. CAPT RESPONDED BY STATING THAT WE WOULD LIKE TO SHOOT THE APCH WHILE THE VISIBILITY WAS STILL ABOVE MINIMUMS (1/2 MI). APCH GAVE US VECTORS FOR THE ILS RWY 16 AND CLRED US FOR THE APCH. UPON TURNING ON THE LOC; I SPOTTED THE APCH LIGHTS FOR THE RWY. UPON REACHING DECISION HT; THE CAPT TRANSITIONED TO THE VISUAL LNDG PHASE OF THE APCH. UPON STARING HIS LEVEL OFF; WE RAN INTO A DENSE FOG; LOSING SIGHT OF THE RWY. WE DRIFTED L; I PICKED UP THE RWY EDGE LIGHTS; AND STARTED TO CALL ATTN TO THE CAPT. AT THIS POINT HE ALSO REALIZED WE WERE DRIFTING OFF THE RWY; AND STARTED TO INITIATE A GAR. AT THIS POINT THE ACFT SETTLED ON THE GND A FEW FT L OF THE RWY. UPON TOUCHING DOWN; THE CAPT MANEUVERED THE ACFT BACK ON THE RWY; CLOSING THE THROTTLES COMPLETELY; APPLYING REVERSE THRUST AND BRAKING. AFTER STOPPING ON THE RWY; WE NOTIFIED TWR; INSPECTED THE ACFT; ASKED FOR TAXI CLRNC; AND TAXIED TO THE RAMP. AFTER SHUTDOWN; THE CAPT CALLED THE TWR BY TELEPHONE. THERE WERE NO INJURIES IN THE INCIDENT. I THINK; ATC WAS TRYING TO DO US A FAVOR BY RPTING THE VISIBILITY AT 3/4 MI WHEN IT WAS 3/16 MI. THE CAPT DID WANT THE MINIMUMS TO BE LEGAL; KNOWING THAT ANOTHER ACFT PICKED UP THE APCH LIGHTS 8-9 MI OUT. THE VISIBILITY WAS GOOD UNTIL LEVELING OFF WHEN THE HORIZ VISIBILITY WENT TO ALMOST ZERO. AT THAT POINT; IT WAS TOO LATE TO DO A MISSED APCH. BY THE TIME WE WERE SHUT DOWN; THE WHOLE ARPT WAS COVERED WITH DENSE FOG. (BEFORE STARTING APCH; WE DID ASK ATC FOR AN RVR RPT ON RWY 34 BUT WERE UNABLE TO OBTAIN ONE.)