Narrative:

At 4000 ft on an easterly heading to intercept the runway 4R localizer at mdw, mdw approach called VFR traffic at 1 O'clock position, 5 mi, altitude 4000 ft, type unknown. The controller said 'let me know when you have him in sight.' the bases of the clouds were approximately 3600 ft and visibility was good looking down at an angle but was 0 ft horizontally. We looked for the aircraft but could not see it because of the clouds. We did see it on TCASII and it had already turned into a white target. I told the controller we were in the clouds and could not see the traffic, but he was very busy and I am not sure if he heard me. I told my first officer to get ready for an 'RA' and told the controller we were in the clouds and could not see the traffic. The controller gave us a 10 degree turn to the left which we complied with. At this point, the traffic was only 2 mi away and closing. The controller issued an immediate left 140 degree turn and a climb to 5000 ft. At this very moment, the TCASII gave an RA to 'descend.' I told the controller we were complying with an RA. My first officer had already disconnected the autoplt and autothrottles and was descending and turning left. The traffic passed overhead on TCASII at +100 ft. We continued our descent until TCASII said clear of conflict and then we climbed back to 4000 ft. I thought we were going to hit, although I never saw the traffic. I told the controller that it was very close! He cleared us for the visual to runway 4R and we landed without further incident. Supplemental information from acn 668964: judging off TCASII we cleared by 150-200 ft. 500-600 ft altitude was lost and we climbed back to 4000 ft to intercept the arrival.

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Original NASA ASRS Text

Title: AN A320 APCHING MDW RESPONDED TO A VFR RA CONFLICTING WITH AN ATC COMMAND.

Narrative: AT 4000 FT ON AN EASTERLY HDG TO INTERCEPT THE RWY 4R LOC AT MDW, MDW APCH CALLED VFR TFC AT 1 O'CLOCK POS, 5 MI, ALT 4000 FT, TYPE UNKNOWN. THE CTLR SAID 'LET ME KNOW WHEN YOU HAVE HIM IN SIGHT.' THE BASES OF THE CLOUDS WERE APPROX 3600 FT AND VISIBILITY WAS GOOD LOOKING DOWN AT AN ANGLE BUT WAS 0 FT HORIZLY. WE LOOKED FOR THE ACFT BUT COULD NOT SEE IT BECAUSE OF THE CLOUDS. WE DID SEE IT ON TCASII AND IT HAD ALREADY TURNED INTO A WHITE TARGET. I TOLD THE CTLR WE WERE IN THE CLOUDS AND COULD NOT SEE THE TFC, BUT HE WAS VERY BUSY AND I AM NOT SURE IF HE HEARD ME. I TOLD MY FO TO GET READY FOR AN 'RA' AND TOLD THE CTLR WE WERE IN THE CLOUDS AND COULD NOT SEE THE TFC. THE CTLR GAVE US A 10 DEG TURN TO THE L WHICH WE COMPLIED WITH. AT THIS POINT, THE TFC WAS ONLY 2 MI AWAY AND CLOSING. THE CTLR ISSUED AN IMMEDIATE L 140 DEG TURN AND A CLB TO 5000 FT. AT THIS VERY MOMENT, THE TCASII GAVE AN RA TO 'DSND.' I TOLD THE CTLR WE WERE COMPLYING WITH AN RA. MY FO HAD ALREADY DISCONNECTED THE AUTOPLT AND AUTOTHROTTLES AND WAS DSNDING AND TURNING L. THE TFC PASSED OVERHEAD ON TCASII AT +100 FT. WE CONTINUED OUR DSCNT UNTIL TCASII SAID CLR OF CONFLICT AND THEN WE CLBED BACK TO 4000 FT. I THOUGHT WE WERE GOING TO HIT, ALTHOUGH I NEVER SAW THE TFC. I TOLD THE CTLR THAT IT WAS VERY CLOSE! HE CLRED US FOR THE VISUAL TO RWY 4R AND WE LANDED WITHOUT FURTHER INCIDENT. SUPPLEMENTAL INFO FROM ACN 668964: JUDGING OFF TCASII WE CLRED BY 150-200 FT. 500-600 FT ALT WAS LOST AND WE CLBED BACK TO 4000 FT TO INTERCEPT THE ARR.

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.