POTENTIAL CONFLICT BTWN A B767 ON A VECTORED APCH AND AN MD11 IN A TURN; SAME ALT. QUICK REACTIONARY CLRNC GIVEN BY APCH CTLR TO B767 WITH TURN AND FURTHER DSCNT TO 5000 FT. TCASII RA GIVES CLB WHICH B767 FLC IGNORES. BOTH ACFT IN A TURN WITH B767 PIC HAVING A VISUAL ON THE MD11.

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WHILE BEING RADAR VECTORED FOR AN ILS TO ATL RWY 27L AND DSNDING TO 5000 FT; WE WERE TOLD TO LEVEL OFF AT 6000 FT AND TURN TO '270 DEGS (L TURN); INTERCEPT RWY 27L LOC.' IN THE L TURN AROUND 330 DEGS ACFT HDG; WE WERE ISSUED A R TURN 270 DEGS; DSND TO 5000 FT; EXPEDITE; TURN L 270 DEGS -- ALL IN SHORT ORDER. DURING THESE CTLR ISSUED CLRNCS WE RECEIVED A 'CLB RA.' AS I WAS IN A R TURN BACK THROUGH ABOUT 030 DEGS AND IN A DSCNT TO 5000 FT; I COULD NOT SEE TO THE L OF THE ACFT. THE CAPT IMMEDIATELY PICKED THE CONFLICTING ACFT UP VISUALLY AND INFORMED ATC WE COULD NOT TURN L AND THAT WE WOULD CONTINUE THE TURN R TO 270 DEGS. THE CAPT ALSO CONCLUDED IT TO BE SAFEST TO CONTINUE THE DSCNT TO 5000 FT AS PREVIOUSLY CLRED INSTEAD OF FOLLOWING THE RA CLB. WE REMAINED S OF THE RWY 27L LOC AT ALL TIMES. THE CONFLICTING MD11 WAS NOT ON OUR FREQ. THERE WAS SEVERE WX IN THE AREA BUT NOT AT THE ARPT. WE HEARD ONE ACFT (IDENT UNKNOWN) DECLARE MINIMUM FUEL JUST MOMENTS BEFORE THE INCIDENT. UNEVENTFUL APCH AND LNDG. SUPPLEMENTAL INFO FROM ACN 378582: DSNDING TO 5000 FT; WE WERE TOLD TO LEVEL OFF AT 6000 FT; HDG ABOUT 330 DEGS. ATC EXCITEDLY TOLD US TO TURN E. I THEN SAW AN MD11 IN A SHARP BANK TO THE W; AT OUR ALT. TCASII ADVISED US TO TURN L (INTO THE MD11). I HAD THE MD11 IN SIGHT UNTIL WE HEADED OPPOSITE DIRECTIONS.