B767 EXPERIENCED NMAC WITH MD80 AT 4000 FT IN ATL.

Narrative

ON FINAL FOR A VISUAL APCH TO RWY 8L AT ATL. LEVEL AT 4000 FT MSL AND ABOUT TO INTERCEPT THE ILS GS ON THE LOC. GOT 'TFC; TFC' FROM TCASII AND SPOTTED AN MD-80 IN A R TURN; APCHING FROM OUR R SIDE. MD-80 APPEARED TO BE TURNING TO INTERCEPT FINAL TO RWY 9R (PARALLEL); BUT OVER-SHOOTING. ALL 3 OF US IN COCKPIT (INCLUDING RELIEF PLT) SAW THE MD-80. MD-80 STAYED IN SHALLOW R TURN; BUT CONTINUED TO APCH OUR ACFT. I DISCONNECTED THE AUTOPLT TO PREVENT OUR ACFT FROM STARTING DOWN THE GS. (MD-80 WAS SLIGHTLY LOWER). SOMEWHERE IN HERE; APCH CTL ADVISED ABOUT OVERSHOOTING ACFT; BUT DID NOT ISSUE ANY INSTRUCTIONS. AS MD-80 CLOSED; I BEGAN A CLB (SHALLOW) TO ENSURE SOME VERT SEPARATION. TCASII RA SAID 'MONITOR VERT SPD;' BUT I DON'T KNOW WHAT VERT SPD WAS ADVISED; BECAUSE I WAS WATCHING THE MD-80; NOT THE VSI. THE MD-80 CONTINUED TO CLOSE AND FLEW UNDER OUR ACFT. IT DISAPPEARED THERE FOR 5-10 SECONDS; THEN RE-APPEARED ON OUR R IN A R TURN BACK TOWARD THE RWY 9R FINAL. CONSIDER THIS A TCASII SAVE. I WILL BE INTERESTED TO SEE WHAT THE RADAR TAPES SHOW FOR VERT SEPARATION. LATERAL SEPARATION WAS ZERO. LONG STORY SHORT -- MD-80 OVERSHOT FINAL; EVENTUALLY LINING UP ON THE PARALLEL RWY. ACFT ON PARALLEL FINAL IS CUED BY TCASII; GETS A VISUAL; AND AVOIDS COLLISION. CREW COORD IN OUR ACFT WAS EXCELLENT. RELIEF PLT UNSTRAPPED AND MOVED TO THE WINDOW BEHIND ME IN ORDER TO MAINTAIN VISUAL ON TFC. CAPT HELPED MONITOR SPD. CONFIGN; AND ALT.