Narrative:

Air carrier X level at 8000 ft, wbound on the pullman arrival (heading 270 degrees assigned) when I observed eastbound traffic at 12:00- 12:30 O'clock near or slightly below our altitude. The night was very dark but at the same time the air was very clear. The traffic appeared to be some miles away. I assumed it was VFR traffic at 7500 ft. As the traffic moved nearer it became obvious it would pass off our right wing and slightly below us. Simultaneously, ATC gave us a traffic report and immediate left turn to 180 degrees and descent to 7000 ft. On the ground, I talked to the approach control supervisor who said that on his initial investigation it looked as if air carrier Y was given a 280 degree heading but instead turned around to 080 degrees. Notes: 1) air carrier X was not TCASII equipped. 2) I believe ATC twice tried to issue TA's but each time was blocked by numerous xmissions from other aircraft. 3) traffic into ord was very heavy and the radio frequency was saturated. Supplemental information from acn 228943: I was working ord approach control during heavy inbound eastbound rush. I was training a developmental at the time. O'hare was landing runways 14L/right. We were vectoring to runway 14L. Air carrier Y was 20 mi northeast of ord heading 220 degrees on pullman 1 arrival. We gave air carrier Y a 'turn right heading 280 degrees.' we believed air carrier Y to acknowledge heading. Approximately 1.5 mins later, air carrier Y is heading easterly into heavy inbound east arrival fix at 8000 ft. Air carrier X was inbound from same fix also at 8000 ft. I gave air carrier X an immediate turn (sbound) and descent. Air carrier X said he had visual contact with air carrier Y. I told air carrier X to maintain visual separation and then turned air carrier Y northbound away from air carrier X. As it turned out, air carrier Y thought we gave him a 080 degree heading as opposed to a 280 degree heading. The readback was somewhat difficult to distinguish because it was read back very quickly. At the time, it sounded like a 280 degree heading in the readback. On tape afterwards, after 3 or 4 times listened to, it was determined to be a 080 degree heading in air carrier Y readback.

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Original NASA ASRS Text

Title: ACR Y READ BACK AND FLEW WRONG HDG HAD LTSS FROM ACR X. SYS ERROR.

Narrative: ACR X LEVEL AT 8000 FT, WBOUND ON THE PULLMAN ARR (HDG 270 DEGS ASSIGNED) WHEN I OBSERVED EBOUND TFC AT 12:00- 12:30 O'CLOCK NEAR OR SLIGHTLY BELOW OUR ALT. THE NIGHT WAS VERY DARK BUT AT THE SAME TIME THE AIR WAS VERY CLR. THE TFC APPEARED TO BE SOME MILES AWAY. I ASSUMED IT WAS VFR TFC AT 7500 FT. AS THE TFC MOVED NEARER IT BECAME OBVIOUS IT WOULD PASS OFF OUR R WING AND SLIGHTLY BELOW US. SIMULTANEOUSLY, ATC GAVE US A TFC RPT AND IMMEDIATE L TURN TO 180 DEGS AND DSCNT TO 7000 FT. ON THE GND, I TALKED TO THE APCH CTL SUPVR WHO SAID THAT ON HIS INITIAL INVESTIGATION IT LOOKED AS IF ACR Y WAS GIVEN A 280 DEG HDG BUT INSTEAD TURNED AROUND TO 080 DEGS. NOTES: 1) ACR X WAS NOT TCASII EQUIPPED. 2) I BELIEVE ATC TWICE TRIED TO ISSUE TA'S BUT EACH TIME WAS BLOCKED BY NUMEROUS XMISSIONS FROM OTHER ACFT. 3) TFC INTO ORD WAS VERY HVY AND THE RADIO FREQ WAS SATURATED. SUPPLEMENTAL INFO FROM ACN 228943: I WAS WORKING ORD APCH CTL DURING HVY INBOUND EBOUND RUSH. I WAS TRAINING A DEVELOPMENTAL AT THE TIME. O'HARE WAS LNDG RWYS 14L/R. WE WERE VECTORING TO RWY 14L. ACR Y WAS 20 MI NE OF ORD HDG 220 DEGS ON PULLMAN 1 ARR. WE GAVE ACR Y A 'TURN R HDG 280 DEGS.' WE BELIEVED ACR Y TO ACKNOWLEDGE HDG. APPROX 1.5 MINS LATER, ACR Y IS HDG EASTERLY INTO HVY INBOUND E ARR FIX AT 8000 FT. ACR X WAS INBOUND FROM SAME FIX ALSO AT 8000 FT. I GAVE ACR X AN IMMEDIATE TURN (SBOUND) AND DSCNT. ACR X SAID HE HAD VISUAL CONTACT WITH ACR Y. I TOLD ACR X TO MAINTAIN VISUAL SEPARATION AND THEN TURNED ACR Y NBOUND AWAY FROM ACR X. AS IT TURNED OUT, ACR Y THOUGHT WE GAVE HIM A 080 DEG HDG AS OPPOSED TO A 280 DEG HDG. THE READBACK WAS SOMEWHAT DIFFICULT TO DISTINGUISH BECAUSE IT WAS READ BACK VERY QUICKLY. AT THE TIME, IT SOUNDED LIKE A 280 DEG HDG IN THE READBACK. ON TAPE AFTERWARDS, AFTER 3 OR 4 TIMES LISTENED TO, IT WAS DETERMINED TO BE A 080 DEG HDG IN ACR Y READBACK.

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.