ACR X TCASII TA HAD NMAC WITH Y. EVASIVE ACTION TAKEN. ACR X FLEW THROUGH THE LOC NON ADHERENCE TO ATC INSTRUCTIONS. PLTDEV.

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WE WERE ON A 180 DEG HDG FOR A BASE LEG TO THE ILS 10R AT CMH AND CLRED TO 4000 FT MSL. A SCATTERED TO BROKEN LAYER OF CLOUDS WAS BTWN 4000 FT TO 5000 FT MSL. AS WE WENT INTO THE CLOUDS; WE RECEIVED A 'TFC; TFC' WARNING FROM THE TCASII. THE YELLOW TARGET DID NOT SHOW ANY ALT OR DSNDING ASCENDING ARROW. THE TFC WAS SHOWN BEING 5 MI ON OUR NOSE. SHORTLY AFTER THE TCASII ALERT. CMH APCH CALLED OUT THE TFC BUT ALSO DID NOT HAVE ANY ALT INFO. AS WE BROKE OUT OF THE CLOUDS (APPROX 4300 FT MSL) I SAW THE ACFT ON OUR NOSE AND BECAUSE WE WERE DSNDING WE WERE ON A COLLISION COURSE. I DIRECTED THE CAPT TO PULL UP TO AVOID THE OTHER ACFT. THE OTHER ACFT WAS OPERATING VFR AND NOT IN CONTACT WITH ATC; HOWEVER; IT APPEARED THE ACFT WAS VERY CLOSE TO OUR LEVEL OFF ALT OF 4000 FT MSL. DURING THIS PERIOD; APCH GAVE US A VECTOR TO INTERCEPT THE LOC TO 10R. WE MISSED THIS CALL DUE TO OUR PREOCCUPATION WITH AVOIDING THE OTHER ACFT. AS WE WERE FLYING THROUGH THE CTRLINE OF THE LOC (ON OUR 180 DEG VECTOR) WE REALIZED SOMETHING WASN'T RIGHT BUT WERE UNABLE TO QUERY APCH DUE TO OTHER RADIO TRANSMISSIONS. WE EVENTUALLY WERE VECTORED BACK TO THE LOC AND LANDED UNEVENTFULLY. SUPPLEMENTAL INFO FROM ACN 207551: WHILE BEING RADAR VECTORED TO THE CMH ARPT; OUR CLRNC WAS TO FLY 180 DEG HDG AND DSND TO 4000 FT. WHILE DSNDING WE FLEW THROUGH A CLOUD DECK. SHORTLY AFTER BREAKING OUT OF THE CLOUDS; WHILE STILL DSNDING; OUR TCASII SYS GAVE US A TA. I THEN RESET OUR TCASII SYS TO READOUT ON THE MOST SENSITIVE; 5 MI RANGE. A YELLOW DOT (NO ALT READOUT) APPEARED AT 12 O'CLOCK AND ABOUT 3 MI. BOTH CAPT AND FO LOOKED OUT THE WINDOW FOR TFC. I BEGAN MY LEVEL OFF AT 4000 FT WHEN THE FO ABRUPTLY YELLED; 'PULL UP.' I IMMEDIATELY LOOKED OUT THE WINDSHIELD; PULLED UP AND BANKED R; NARROWLY MISSING THE TFC.