ACR LGT TOOK EVASIVE ACTION TO AVOID COLLISION WITH SMA.

Narrative

WHILE ON BASE BWI APCH CALLED OUT TFC AT 2 O'CLOCK AND 4 MI; ALT UNKNOWN AND AN LTT JET AT 12 O'CLOCK; 5000' MSL ON FINAL TO RWY 33L. THE F/O (PNF) CALLED THE 2 O'CLOCK; SMA Y; IN SIGHT. APCH SUBSEQUENTLY CLRED LGT X FOR A VISUAL APCH TO FOLLOW THE JET TFC AT 12 O'CLOCK. THE CAPT (PF) STATED HE DID NOT HAVE THE 12 O'CLOCK TFC IN SIGHT AND REFUSED THE VISUAL. THE CTLR RESUMED RADAR VECTORS TO THE FINAL APCH COURSE TO RWY 33L BWI. MEANWHILE; SMA Y WAS MANEUVERING BELOW AT APPROX 2000' MSL AND HDG IN A S WESTERLY DIRECTION. IT BECAME APPARENT TO THE F/O THAT SMA Y COULD STILL POSE A FACTOR ONCE LGT X TURNED FINAL FOR RWY 33L BWI AND SO STATED THIS TO THE CAPT. ONCE LGT X HAD TURNED INBND AND AT ABOUT 5 MI OUT; DSNDING ON G/S AT APPROX 2000'; SMA Y WAS STILL MAKING UNPREDICTABLE TURNS WHILE DRIFTING TOWARD LGT X'S FINAL APCH PATH. APCH CTL CLRED LGT X FOR THE APCH FOLLOWING THE JET ON A 3 1/2 MI FINAL. IT BECAME APPARENT TO BOTH F/E AND F/O THAT SMA Y WAS STILL A FACTOR AND THE F/O FOR THE SECOND TIME SO STATED TO THE CAPT. SMA Y STILL DRIFTING RIGHT TO LEFT STARTED TO TURN TOWARD LGT X AND WHEN THE ACFT WAS APPROX 2000' HORIZ AND CLOSING; THE S/O AGGRESSIVELY STATED 'TURN RIGHT.' THE COPLT SIMULTANEOUSLY SUGGESTED AN EVASIVE MANEUVER. THE CAPT TOLD US BOTH TO 'SHUT UP.' HE FINALLY SIGHTED SMA Y AND PAUSED WHILE BOTH ACFT WERE CLOSING ON ONE ANOTHER. HE INITIALLY STARTED A LEFT TURN INTO SMA Y; THEN ABRUPTLY MADE A 30 DEG BANK TO THE RIGHT AND SUBSEQUENTLY RETURNED ON COURSE. BOTH ACFT CAME WITHIN 300-500' HORIZ AND 100' VERT BEFORE EVASIVE ACTION WAS TAKEN BY LGT X. LGT X; AT THE REQUEST OF THE CAPT; TOLD THE CTLR OF A NEAR MISS. THE CTLR'S RESPONSE WAS; 'A NEAR MISS? I THOUGHT YOU HAD THE TFC IN SIGHT!' LGT X WAS HANDED OVER TO THE TWR AT BWI AND CLRED TO LAND.