Narrative:

During descent into chicago midway airport, at approximately 5 NM southeast jot VOR, at approximately 7000' and while on a radar vector heading of 050 degree assigned by chicago approach, we passed through a group of 3 gliders. 2 gliders passed directly below us approximately 500' below, and the 3RD glider passed on our right side, at our altitude, and less than 200' away. No radar traffic warning was issued by chicago approach because the gliders did not appear on his radar scope. We initiated a left turn to evade the glider on the right, but still passed less than 200' from the glider. An air carrier X medium large transport on the same route ahead of us reported a light aircraft to chicago approach. Chicago did not have the aircraft on radar and advised us of the possibility of light aircraft activity on our route of flight. Both the captain and myself were actively looking for light aircraft traffic when we passed through the group of 3 gliders. Just prior to the near midair collision, we spotted what appeared to be a tow aircraft spiraling down below us, and then we passed through the group of three gliders. We saw the gliders only about 3 seconds before we passed by them. Air carrier Y aircraft behind us confirmed the location and altitude of the 3 gliders to chicago approach. It is important to note that both the captain and myself were actively looking for light aircraft when this near midair collision occurred, and our evasive left turn only provided 200' or less separation from the glider on our right. The concept of 'see and avoid' does not work for an airliner traveling at 250 KTS indicated airspeed. Chicago approach did not have any of the 4 light aircraft on radar. How to prevent recurrence: all aircraft, including balloons and gliders should be required to use altitude reporting transponders and strobe lights. We had 105 people on board our aircraft, and were less than 200' away from disaster.

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Original NASA ASRS Text

Title: CLOSE PROX ACR-MLG GA-SPN NEAR JOT VOR.

Narrative: DURING DESCENT INTO CHICAGO MIDWAY ARPT, AT APPROX 5 NM SE JOT VOR, AT APPROX 7000' AND WHILE ON A RADAR VECTOR HEADING OF 050 DEG ASSIGNED BY CHICAGO APCH, WE PASSED THROUGH A GROUP OF 3 GLIDERS. 2 GLIDERS PASSED DIRECTLY BELOW US APPROX 500' BELOW, AND THE 3RD GLIDER PASSED ON OUR RIGHT SIDE, AT OUR ALT, AND LESS THAN 200' AWAY. NO RADAR TFC WARNING WAS ISSUED BY CHICAGO APCH BECAUSE THE GLIDERS DID NOT APPEAR ON HIS RADAR SCOPE. WE INITIATED A LEFT TURN TO EVADE THE GLIDER ON THE RIGHT, BUT STILL PASSED LESS THAN 200' FROM THE GLIDER. AN ACR X MLG ON THE SAME ROUTE AHEAD OF US REPORTED A LIGHT ACFT TO CHICAGO APCH. CHICAGO DID NOT HAVE THE ACFT ON RADAR AND ADVISED US OF THE POSSIBILITY OF LIGHT ACFT ACTIVITY ON OUR ROUTE OF FLT. BOTH THE CAPT AND MYSELF WERE ACTIVELY LOOKING FOR LIGHT ACFT TFC WHEN WE PASSED THROUGH THE GROUP OF 3 GLIDERS. JUST PRIOR TO THE NEAR MIDAIR COLLISION, WE SPOTTED WHAT APPEARED TO BE A TOW ACFT SPIRALING DOWN BELOW US, AND THEN WE PASSED THROUGH THE GROUP OF THREE GLIDERS. WE SAW THE GLIDERS ONLY ABOUT 3 SECONDS BEFORE WE PASSED BY THEM. ACR Y ACFT BEHIND US CONFIRMED THE LOCATION AND ALT OF THE 3 GLIDERS TO CHICAGO APCH. IT IS IMPORTANT TO NOTE THAT BOTH THE CAPT AND MYSELF WERE ACTIVELY LOOKING FOR LIGHT ACFT WHEN THIS NEAR MIDAIR COLLISION OCCURRED, AND OUR EVASIVE LEFT TURN ONLY PROVIDED 200' OR LESS SEPARATION FROM THE GLIDER ON OUR RIGHT. THE CONCEPT OF 'SEE AND AVOID' DOES NOT WORK FOR AN AIRLINER TRAVELING AT 250 KTS INDICATED AIRSPEED. CHICAGO APCH DID NOT HAVE ANY OF THE 4 LIGHT ACFT ON RADAR. HOW TO PREVENT RECURRENCE: ALL ACFT, INCLUDING BALLOONS AND GLIDERS SHOULD BE REQUIRED TO USE ALT REPORTING TRANSPONDERS AND STROBE LIGHTS. WE HAD 105 PEOPLE ON BOARD OUR ACFT, AND WERE LESS THAN 200' AWAY FROM DISASTER.

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.