Narrative:

While on chicago approach frequency on a heading of 270 degrees, was given a clearance to descend from 5000 to 3000'. We were given a frequency change at that same time or shortly after starting descent. After changing frequencys I saw traffic just to the left of 12 O'clock and level, about 1/2 mi away and coming towards us. The traffic was a single engine, low wing, aircraft apparently cruising at 3500' MSL. I pointed out the traffic to captain, who was flying, and I put my hands on the yoke to take control if required. The captain saw the traffic immediately and started a bank to the right as traffic passed on our left as we passed about 3400' MSL. After checking in on frequency we learned that the traffic was VFR on radar advisory with this same controller. Contributing factors: we were given a descent through an altitude where there was known conflicting traffic, who was talking to the same controling agency (different frequency). We were never issued a traffic advisory or given an avoidance vector. Visibility was reduced heading west due to setting sun and haze. Chicago approach control was unusually busy this pm. Note: I made a near miss report to chicago approach control. Area supervisor took the report.

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Original NASA ASRS Text

Title: CLOSE PROX ACR-MLG GA-SMA NEAR ORD TCA MDW ARSA.

Narrative: WHILE ON CHICAGO APCH FREQ ON A HDG OF 270 DEGS, WAS GIVEN A CLRNC TO DSND FROM 5000 TO 3000'. WE WERE GIVEN A FREQ CHANGE AT THAT SAME TIME OR SHORTLY AFTER STARTING DSCNT. AFTER CHANGING FREQS I SAW TFC JUST TO THE LEFT OF 12 O'CLOCK AND LEVEL, ABOUT 1/2 MI AWAY AND COMING TOWARDS US. THE TFC WAS A SINGLE ENG, LOW WING, ACFT APPARENTLY CRUISING AT 3500' MSL. I POINTED OUT THE TFC TO CAPT, WHO WAS FLYING, AND I PUT MY HANDS ON THE YOKE TO TAKE CTL IF REQUIRED. THE CAPT SAW THE TFC IMMEDIATELY AND STARTED A BANK TO THE RIGHT AS TFC PASSED ON OUR LEFT AS WE PASSED ABOUT 3400' MSL. AFTER CHKING IN ON FREQ WE LEARNED THAT THE TFC WAS VFR ON RADAR ADVISORY WITH THIS SAME CTLR. CONTRIBUTING FACTORS: WE WERE GIVEN A DSCNT THROUGH AN ALT WHERE THERE WAS KNOWN CONFLICTING TFC, WHO WAS TALKING TO THE SAME CTLING AGENCY (DIFFERENT FREQ). WE WERE NEVER ISSUED A TFC ADVISORY OR GIVEN AN AVOIDANCE VECTOR. VIS WAS REDUCED HDG W DUE TO SETTING SUN AND HAZE. CHICAGO APCH CTL WAS UNUSUALLY BUSY THIS PM. NOTE: I MADE A NEAR MISS RPT TO CHICAGO APCH CTL. AREA SUPVR TOOK THE RPT.

Data retrieved from NASA's ASRS site as of August 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.