Narrative:

The following occurred while flying the ILS runway 4R circle to land runway 13C at mdw. Prior to intercepting the localizer, we were cleared for the ILS runway 4R, circle to land runway 13C. The approach phase prior to passing the FAF was normal. We descended to 1600 ft MSL at the FAF and switched to tower frequency as directed by chicago approach. Passing the FAF (ermin - hk), we began our circling approach to remain within the terps airspace (ie, 2.3 NM from the runway). We made our radio call to tower informing them that we had begun our circling approach. Tower did not reply. We were about 1/3 - 1/2 way through the circling maneuver when tower called and asked if we were on frequency -- we immediately realized that something was wrong from the tone of the controller's voice. We replied, 'affirmative, we are circling to land runway 13C.' the tower controller transmitted 'turn left immediately, you have traffic on final for runway 13C at your 1 O'clock position.' I rolled the aircraft from 15 degrees of right bank to 30-35 degrees of left bank. We spotted the aircraft on final at about 1 mi and 1 O'clock position. Our B737-300 responded sluggishly due to being configured with 40 degrees flaps (our highest drag confign for the short runways at mdw). I asked the captain to select 30 degrees flaps and then our B737's performance improved -- we accelerated and began to turn away from the final approach course of runway 13C. Tower then informed us that there was a second aircraft on final behind the first one that had been a potential conflict. These aircraft were cleared ILS runway 4R circle-to-land runway 13. However, they both flew well outside of the terps circling criteria with their turns to final looking more like a 7 mi straight-in approach. We maneuvered to align ourselves on final for runway 13C behind the second aircraft (both aircraft were cpr bizjets). No further conflicts developed and we landed without further incident.

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Original NASA ASRS Text

Title: A B737-300 CREW, FLYING A CIRCLING APCH TO MDW, TOOK EVASIVE ACTION WHEN ATC ADVISED OF A TFC CONFLICT.

Narrative: THE FOLLOWING OCCURRED WHILE FLYING THE ILS RWY 4R CIRCLE TO LAND RWY 13C AT MDW. PRIOR TO INTERCEPTING THE LOC, WE WERE CLRED FOR THE ILS RWY 4R, CIRCLE TO LAND RWY 13C. THE APCH PHASE PRIOR TO PASSING THE FAF WAS NORMAL. WE DSNDED TO 1600 FT MSL AT THE FAF AND SWITCHED TO TWR FREQ AS DIRECTED BY CHICAGO APCH. PASSING THE FAF (ERMIN - HK), WE BEGAN OUR CIRCLING APCH TO REMAIN WITHIN THE TERPS AIRSPACE (IE, 2.3 NM FROM THE RWY). WE MADE OUR RADIO CALL TO TWR INFORMING THEM THAT WE HAD BEGUN OUR CIRCLING APCH. TWR DID NOT REPLY. WE WERE ABOUT 1/3 - 1/2 WAY THROUGH THE CIRCLING MANEUVER WHEN TWR CALLED AND ASKED IF WE WERE ON FREQ -- WE IMMEDIATELY REALIZED THAT SOMETHING WAS WRONG FROM THE TONE OF THE CTLR'S VOICE. WE REPLIED, 'AFFIRMATIVE, WE ARE CIRCLING TO LAND RWY 13C.' THE TWR CTLR XMITTED 'TURN L IMMEDIATELY, YOU HAVE TFC ON FINAL FOR RWY 13C AT YOUR 1 O'CLOCK POS.' I ROLLED THE ACFT FROM 15 DEGS OF R BANK TO 30-35 DEGS OF L BANK. WE SPOTTED THE ACFT ON FINAL AT ABOUT 1 MI AND 1 O'CLOCK POS. OUR B737-300 RESPONDED SLUGGISHLY DUE TO BEING CONFIGURED WITH 40 DEGS FLAPS (OUR HIGHEST DRAG CONFIGN FOR THE SHORT RWYS AT MDW). I ASKED THE CAPT TO SELECT 30 DEGS FLAPS AND THEN OUR B737'S PERFORMANCE IMPROVED -- WE ACCELERATED AND BEGAN TO TURN AWAY FROM THE FINAL APCH COURSE OF RWY 13C. TWR THEN INFORMED US THAT THERE WAS A SECOND ACFT ON FINAL BEHIND THE FIRST ONE THAT HAD BEEN A POTENTIAL CONFLICT. THESE ACFT WERE CLRED ILS RWY 4R CIRCLE-TO-LAND RWY 13. HOWEVER, THEY BOTH FLEW WELL OUTSIDE OF THE TERPS CIRCLING CRITERIA WITH THEIR TURNS TO FINAL LOOKING MORE LIKE A 7 MI STRAIGHT-IN APCH. WE MANEUVERED TO ALIGN OURSELVES ON FINAL FOR RWY 13C BEHIND THE SECOND ACFT (BOTH ACFT WERE CPR BIZJETS). NO FURTHER CONFLICTS DEVELOPED AND WE LANDED WITHOUT FURTHER INCIDENT.

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.