ACR MLG WAS CLOSE ENOUGH TO OTHER TFC DURING A CIRCLING APCH TO MDW TO ACTIVATE THE TCASII RA.

Narrative

THE APCH WAS AN ILS 31 CIRCLE TO 2R. SPD WAS REDUCED BY ATC THROUGH THE APCH CAUSING US TO BE HIGH ON THE GLIDE PATH IN VISUAL CONDITIONS STARTING THE CIRCLE. JUST AFTER STARTING THE CIRCLE TWR CALLED TFC TO OUR R AND ASKED US TO EXPEDITE THROUGH 2000 FT. THE TCASII ISSUED A TA FOLLOWED ALMOST IMMEDIATELY BY AN RA. I WAS FOLLOWING THE RA WHEN THE CAPT SAID TO LEVEL OFF. THE RA WAS COMMANDING 'MONITOR RATE' AND INDICATING 1000 FPM DSCNT MIN. SHORTLY THEREAFTER (THE CAPT INFORMED ME LATER) THE TWR ALSO SAID LEVEL OFF. I DID NOT SEE THE TFC; THE CAPT DID; AND SO WITH THE CONFLICTING COMMANDS; I COMMENTED YOU HAVE THE ACFT. ALMOST IMMEDIATELY THE TCASII INDICATED THE CONFLICT WAS RESOLVED AND THE CAPT TOLD THE TWR THE TFC WAS PASSING BEHIND. I REGAINED CTL FROM THE CAPT AND LANDED WITHOUT FURTHER INCIDENT. I DO NOT BELIEVE SAFETY WAS COMPROMISED BUT I HAVE COME TO SOME INTERESTING CONCLUSIONS. THE TWR'S DIRECTIONS; THE RA DIRECTIONS; AND THE CAPT'S DIRECTIONS WERE AT DIFFERENT TIMES CONFLICTING; AND I BELIEVE THE RESULTING INFO OVERLOAD KEPT ME FROM VISUALLY ACQUIRING THE TFC. NOT SEEING THE TFC AND NOT REALIZING IT WOULD CROSS BEHIND; I BELIEVED MY BEST COURSE OF ACTION WAS TO FOLLOW THE RA. THOUGH SEE AND AVOID SHOULD TAKE PRECEDENCE; THE TCASII CAN HELP AVOID A 'MEXICAN STANDOFF' IN THE VERT. THE CIRCLING APCH IS A VISUAL MANEUVER; ATC SHOULD NOT RELY ON ALT FOR SEPARATION IN A CIRCLING APCH UNLESS THEY HAVE DIRECTED AN ALT.