FLC OF AN MLG ACR ACFT TOOK EVASIVE ACTION BY CLBING TO AVOID A WDB ACR ACFT OVERSHOOTING FINAL FOR THE ADJACENT PARALLEL RWY DURING A VISUAL TURN-IN TO FINAL.

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WHILE CONDUCTING A VISUAL APCH TO ATL; I NOTICED A WDB JET MAKING AN APCH TO A PARALLEL RWY. WE WERE STILL N OF THE LOC TO RWY 26R. IT BECAME OBVIOUS THAT THE WDB WAS GETTING MUCH TOO CLOSE. WE THEN GOT A TA FROM THE TCASII FOLLOWED ALMOST IMMEDIATELY BY AN 'RA.' WE BEGAN A CLB WHILE VISUALLY WATCHING THE OTHER PLANE. HE CONTINUED TO CLOSE ON US. I QUESTIONED APCH CTL ABOUT THE OTHER PLANE AND WAS ADVISED THAT THE OTHER ACFT HAD US IN SIGHT. I SERIOUSLY QUESTION THAT FACT. IF WE HAD CONTINUED OUR ORIGINAL COURSE TO INTERCEPT THE LOC TO OUR RWY AND CONTINUED OUR DSCNT WE WOULD HAVE BEEN DANGEROUSLY CLOSE TO THE WDB. WHAT BOTHERS ME IS THAT; JUST BECAUSE THE OTHER ACFT WAS ON A VISUAL APCH AND HAD RPTED (SUPPOSEDLY) US IN SIGHT; APCH CTL ALLOWED HIM TO ENCROACH ON OUR AIRSPACE WAY BEYOND NORMAL SEPARATION LIMITS. IF IT WEREN'T FOR THE TCASII AND OUR MANEUVERING TO AVOID THE CONFLICT I'M NOT TOO SURE HOW CLOSE WE WOULD HAVE COME TO THE OTHER ACFT. SUPPLEMENTAL INFO FROM ACN 256889: WE OVERSHOT FINAL. ANOTHER ACFT WAS ON FINAL TO RWY 26R. WE HAD HIM IN SIGHT AT ALL TIMES AND NO EVASIVE ACTION WAS TAKEN BY EITHER ACFT. THE PF OVERSHOT FINAL WHILE ATTEMPTING TO RE-ENGAGE THE AUTOMATED ILS SYS OF THE WDB ACFT. CLOSEST APCH TO OTHER ACFT WAS 1500 FT HORIZ AND 500 FT VERT.