CAPT OF AN MLG CLBED DURING AN ILS APCH OVER THE OM IN RESPONSE TO A TCASII RA.

Narrative

FLT X; B737-200 ORD-ATL. REGARDING CREW INITIATED A RAPID CLB IN RESPONSE TO A TCASII RA. DURING INITIAL CONTACT WITH ATLANTA APCH CTL; WE WERE CLRED ON ILS APCH TO RWY 9R WITH A SUBSEQUENT VISUAL APCH CLRNC. THE WX DURING THE APCH AND AT THE ATL ARPT WAS IFR. APPROX 15 NM W OF THE APCH END OF RWY 9R WE REQUESTED CLRNC TO LAND ON RWY 9L. APCH CTL CLRED OUR REQUEST DUE TO TFC XING AHEAD FROM R TO L AND BELOW. WE WERE RECLRED VISUAL TO RWY 9R AND ADVISED TO CONTACT TWR AT THE 'OM' (BRUNY). AS WE CROSSED OVERHEAD THE OM; OUR TCASII ALERTED US TO CLB 2000 FPM DUE TO AN RA AT OUR POS AND 100 FT BELOW; THE CAPT EXECUTED AN IMMEDIATE CLB TO AVOID TFC ON TCASII. THE TCASII WAS ON THE 5 NM SCALE AND SCANNING BELOW. DURING OUR CLB THE TARGET WAS AT OUR POS AND INDICATED MINUS 01; 100 FT BELOW OUR ALT. WE ADVISED THE TWR OF THE SIT AND HE RECLRED US TO LAND. THE TWR SAID HE SAW NO TFC WHICH CONFLICTED WITH OUR FLT PATH. WE DID HOWEVER SEE THE TCASII TARGET MOVE TO OUR L AND LAND ON THE PARALLEL RWY 8L ATL. WE LANDED WITH NO FURTHER COMMENTS WITH THE ATC'S.