POTENTIAL CONFLICT IN A NIGHT OP. ALT HDG TRACK DEV.

Narrative

WE WERE FLT (M-88); 20 NM NE OF ATL; BEING VECTORED FOR APCH (ILS 26R) BY ATL APCH. WE WERE AT 8000 FT; 210 KIAS; HDG 230 DEGS. APCH DIRECTED US TO TURN TO A 180 DEG HDG; TO DSND TO 6000 FT AND THEN SLOW TO 180 KIAS. WE WERE THEN GIVEN A FREQ CHANGE. WE WERE UNABLE TO 'CHK IN' IMMEDIATELY DUE TO THE HIGH VOLUME OF COM. AT THIS POINT WE WERE ASKED OUR ASSIGNED HDG BY APCH CTL AND SIMULTANEOUSLY RECEIVED A TCASII TA. THE TCASII SHOWED TFC AT 1 O'CLOCK AND 100 FT LOW. THE RANGE WAS JUST OUTSIDE THE 'MID-SCALE' RING ON THE RADAR SCREEN DISPLAY. I DON'T RECALL IF I WAS IN 5 OR 10 MI SCALE. WE BEGAN TO INITIATE A L TURN; AND WERE DIRECTED BY APCH TO IMMEDIATELY TURN L TO HDG 090 DEGS AND CLB TO 7000 FT. WE DID AS INSTRUCTED AND AFTER THE TURN AND CLB NO FURTHER ACTION WAS TAKEN OR NECESSARY. I DO NOT RECALL RECEIVING A TCASII RA. I DID SEE ACFT LIGHTS AT OUR 1 O'CLOCK POS WHEN INITIATING THE EVASIVE TURN; BUT DUE TO NIGHT/IMC CONDITIONS (OVCST BUT THIN) AND FLYING THE ACFT I AM UNABLE TO ESTIMATE THE HORIZ RANGE TO THE TFC ACCURATELY. I ESTIMATE IT WAS ABOUT 1-2 NM AT THE CLOSEST POINT. A CONTRIBUTING FACTOR WAS THAT OUR ACR Y WAS ALSO ON FREQ. THERE MAY HAVE BEEN SOME CONFUSION; WITH THE CTLR BTWN ACR X AND ACR Y.