Narrative:

ZAU had cleared flight to 12000 ft direct to ord VOR, advised to contact chicago approach on appropriate frequency. I attempted several times to contact approach but the controller was talking continuously, and I was apparently blocked on each transmission as the controller never acknowledged my transmission. A TCASII TA appeared suddenly at 3 O'clock showing approximately 12500 ft, followed shortly by an RA which was followed, resulting in a climb of approximately 300 ft before the clear of traffic advisory was given. The traffic was not sighted visually. I contacted approach immediately to advise of the RA. The controller had a different voice, indicating a change of controllers at the approach position. He acknowledged my call and requested our location, suggesting that the previous controller had either failed to advise him of our location, or had never positively idented our flight. The RA was probably due to our remaining at the center assigned altitude of 12000 ft, while we were unable to contact approach control due to the congestion on the frequency. Pilots flying into ord on a regular basis are aware of the congestion on the frequencys and tend to wait for the controller to call them if previous xmissions have been unanswered. In this case, my flight seems to have slipped through the cracks, and TCASII avoided a potential near miss.

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Original NASA ASRS Text

Title: FLC OF AN ACR MLG ACFT TOOK EVASIVE ACTION IN RESPONSE TO A TCASII RA RESULTING IN EXCURSION FROM ASSIGNED ALT.

Narrative: ZAU HAD CLRED FLT TO 12000 FT DIRECT TO ORD VOR, ADVISED TO CONTACT CHICAGO APCH ON APPROPRIATE FREQ. I ATTEMPTED SEVERAL TIMES TO CONTACT APCH BUT THE CTLR WAS TALKING CONTINUOUSLY, AND I WAS APPARENTLY BLOCKED ON EACH XMISSION AS THE CTLR NEVER ACKNOWLEDGED MY XMISSION. A TCASII TA APPEARED SUDDENLY AT 3 O'CLOCK SHOWING APPROX 12500 FT, FOLLOWED SHORTLY BY AN RA WHICH WAS FOLLOWED, RESULTING IN A CLB OF APPROX 300 FT BEFORE THE CLR OF TFC ADVISORY WAS GIVEN. THE TFC WAS NOT SIGHTED VISUALLY. I CONTACTED APCH IMMEDIATELY TO ADVISE OF THE RA. THE CTLR HAD A DIFFERENT VOICE, INDICATING A CHANGE OF CTLRS AT THE APCH POS. HE ACKNOWLEDGED MY CALL AND REQUESTED OUR LOCATION, SUGGESTING THAT THE PREVIOUS CTLR HAD EITHER FAILED TO ADVISE HIM OF OUR LOCATION, OR HAD NEVER POSITIVELY IDENTED OUR FLT. THE RA WAS PROBABLY DUE TO OUR REMAINING AT THE CTR ASSIGNED ALT OF 12000 FT, WHILE WE WERE UNABLE TO CONTACT APCH CTL DUE TO THE CONGESTION ON THE FREQ. PLTS FLYING INTO ORD ON A REGULAR BASIS ARE AWARE OF THE CONGESTION ON THE FREQS AND TEND TO WAIT FOR THE CTLR TO CALL THEM IF PREVIOUS XMISSIONS HAVE BEEN UNANSWERED. IN THIS CASE, MY FLT SEEMS TO HAVE SLIPPED THROUGH THE CRACKS, AND TCASII AVOIDED A POTENTIAL NEAR MISS.

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.