Narrative:

The approach was an ILS 31 circle to 2R. Speed was reduced by ATC through the approach causing us to be high on the glide path in visual conditions starting the circle. Just after starting the circle tower called traffic to our right 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 captain said to level off. The RA was commanding 'monitor rate' and indicating 1000 FPM descent min. Shortly thereafter (the captain informed me later) the tower also said level off. I did not see the traffic, the captain did, and so with the conflicting commands, I commented you have the aircraft. Almost immediately the TCASII indicated the conflict was resolved and the captain told the tower the traffic was passing behind. I regained control from the captain and landed without further incident. I do not believe safety was compromised but I have come to some interesting conclusions. The tower's directions, the RA directions, and the captain's directions were at different times conflicting, and I believe the resulting information overload kept me from visually acquiring the traffic. Not seeing the traffic 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 vertical. The circling approach is a visual maneuver, ATC should not rely on altitude for separation in a circling approach unless they have directed an altitude.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.