ACR X TCASII TA/RA WITH ACFT Y. ACR X ON VISUAL APCH FAILED TO KEEP ACFT Y IN SIGHT.

Narrative

ACR X APCHING KLEX FROM THE SSE; ON A VECTORED DSCNT DIRECT TO KLEX; ANTICIPATING CLRNC FOR AN ILS RWY 22 APCH. VISIBILITY WAS GOOD; VMC NIGHT CONDITIONS. LEX APCH ASKED US IF WE HAD TFC IN SIGHT AT OUR 1 O'CLOCK POS OVER THE CITY. WE CHKED OUR TCASII PRESENTATION. TFC WAS CONFIRMED IN THAT DIRECTION AND WE BOTH SAW AN ACFT Y LIGHT OVER THE CITY. WE RESPONDED 'AFFIRMATIVE' AND THE APCH CTLR SAID TO MAINTAIN VISUAL SEPARATION FROM THE ACFT Y. THE APCH CTLR THEN ASKED IF WE HAD THE ARPT IN SIGHT AT OUR 11 O'CLOCK POS. WHEN WE REPLIED 'AFFIRMATIVE;' HE CLRED US FOR THE VISUAL APCH TO RWY 22 AND TO KEEP TFC IN SIGHT. I BEGAN SLOWING THE ACFT; CONFIGURING FOR APCH; THEN TURNED R TO 040 DEGS (L DOWNWIND) AND BEGAN DSCNT TO OM FIX ALT. AFTER BEGINNING L TURN TO BASE LEG (HDG APPROX 020 DEGS) APCH CTLR ADVISED US TO START OUR TURN TO BASE LEG. WE SAID WE WERE ALREADY TURNING BASE. AS OUR HDG PASSED APPROX 360 DEGS WE GOT TCASII TA/RA ON TFC AT OUR 2 O'CLOCK POS. TCASII DIRECTED US TO DSND. CAPT SAW TFC IN THAT DIRECTION AND POINTED IT OUT. I ALSO SAW THE TFC ABOUT 1 - 1 1/2 MI AS I STARTED MAKING TCASII CORRECTION TO SPECIFIED DSCNT RATE. I SAID THE ACFT WOULD PASS OFF OUR R SIDE; BEHIND US AND BE NO FACTOR. BEFORE REACHING TCASII DSCNT RATE AND IN A CONTINUING L TURN TO BASE (APPROX 310 DEG HDG) WE RECEIVED A SECOND TCASII TA/RA. A NEW ACFT 'POPPED UP' AT OUR 11 O'CLOCK POS; APPROX 300 FT BELOW US. TCASII COMMANDED A CLB; THEN LEVEL OFF WHICH I COMPLIED WITH. BOTH OF US THEN SPOTTED THE ACFT Y APPROX 300 FT BELOW AND 1000-1500 FT HORIZ; PASSING OFF L SIDE OF ACFT. THE ACFT APPEARED TO BE IN A TURN TO THE S. CAPT CALLED APCH CTLR WITH NMAC RPT AND CTLR SAID THAT TFC WAS WHAT WE WERE INITIALLY DIRECTED TO REMAIN CLR OF. WE WERE THEN TURNING ONTO FINAL APCH AT APPROX 4 1/2 MI ON GS AND TOLD TO SWITCH TO TWR.