Narrative:

We were at 7000 ft MSL under control of chicago approach control on a 360 degree heading being vectored for an ILS approach to runway 22R at ord. We were communicating with approach on frequency 119.0 and voice traffic was very heavy. Both my first officer (who was PNF) and I both heard the controller say, 'air carrier eih turn right to 040 degree and descend to 4000 ft'. My first officer read back the clearance verbatim with no response from the controller. I started a right turn and announced 'cleared to 4000' and started to descend. At about 6500 ft the controller said, 'air carrier eih maintain 6000 ft and turn to 020 degree, your last clearance was to maintain 7000 ft'. I immediately responded to ATC. 'Air carrier eih was descending to 4000 ft which is what we read back that we had been cleared to. We will maintain 6000 ft'. ATC again repeated 'air carrier eih maintain 6000 ft heading 020 degree, you have heavy traffic at your 10 O'clock and 5000 ft'. We replied 'traffic in sight, maintaining 6000 ft'. A few seconds later we were again cleared to descend to 4000 ft and the flight continued to a landing without further incident. Although ord approach is a very busy place most of the time, there still needs to be some sort of backup for the busy controller who often does not hear and/or respond to aircraft readbacks that are wrong. I have been an 'earwitness' to this occurrence at O'hare many times and it is potentially a very dangerous situation. The controllers basically do an outstanding job at ord but they often are just too busy to catch all the mistakes. In our case today I believe that the clearance was issued prematurely or perhaps was meant for another aircraft but given to us instead. Supplemental information from acn 183915: the problem seemed to be a result of the fact that ATC did not confirm any of our readbacks, and apparently did not listen closely to our readbacks.

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Original NASA ASRS Text

Title: ACR READ BACK AND COMPLIED WITH CLRNC. LATER TOLD MAINTAIN ALT.

Narrative: WE WERE AT 7000 FT MSL UNDER CTL OF CHICAGO APCH CTL ON A 360 DEG HDG BEING VECTORED FOR AN ILS APCH TO RWY 22R AT ORD. WE WERE COMMUNICATING WITH APCH ON FREQ 119.0 AND VOICE TFC WAS VERY HVY. BOTH MY FO (WHO WAS PNF) AND I BOTH HEARD THE CTLR SAY, 'ACR EIH TURN R TO 040 DEG AND DSND TO 4000 FT'. MY FO READ BACK THE CLRNC VERBATIM WITH NO RESPONSE FROM THE CTLR. I STARTED A R TURN AND ANNOUNCED 'CLRED TO 4000' AND STARTED TO DSND. AT ABOUT 6500 FT THE CTLR SAID, 'ACR EIH MAINTAIN 6000 FT AND TURN TO 020 DEG, YOUR LAST CLRNC WAS TO MAINTAIN 7000 FT'. I IMMEDIATELY RESPONDED TO ATC. 'ACR EIH WAS DSNDING TO 4000 FT WHICH IS WHAT WE READ BACK THAT WE HAD BEEN CLRED TO. WE WILL MAINTAIN 6000 FT'. ATC AGAIN REPEATED 'ACR EIH MAINTAIN 6000 FT HDG 020 DEG, YOU HAVE HVY TFC AT YOUR 10 O'CLOCK AND 5000 FT'. WE REPLIED 'TFC IN SIGHT, MAINTAINING 6000 FT'. A FEW SECONDS LATER WE WERE AGAIN CLRED TO DSND TO 4000 FT AND THE FLT CONTINUED TO A LNDG WITHOUT FURTHER INCIDENT. ALTHOUGH ORD APCH IS A VERY BUSY PLACE MOST OF THE TIME, THERE STILL NEEDS TO BE SOME SORT OF BACKUP FOR THE BUSY CTLR WHO OFTEN DOES NOT HEAR AND/OR RESPOND TO ACFT READBACKS THAT ARE WRONG. I HAVE BEEN AN 'EARWITNESS' TO THIS OCCURRENCE AT O'HARE MANY TIMES AND IT IS POTENTIALLY A VERY DANGEROUS SITUATION. THE CTLRS BASICALLY DO AN OUTSTANDING JOB AT ORD BUT THEY OFTEN ARE JUST TOO BUSY TO CATCH ALL THE MISTAKES. IN OUR CASE TODAY I BELIEVE THAT THE CLRNC WAS ISSUED PREMATURELY OR PERHAPS WAS MEANT FOR ANOTHER ACFT BUT GIVEN TO US INSTEAD. SUPPLEMENTAL INFO FROM ACN 183915: THE PROBLEM SEEMED TO BE A RESULT OF THE FACT THAT ATC DID NOT CONFIRM ANY OF OUR READBACKS, AND APPARENTLY DID NOT LISTEN CLOSELY TO OUR READBACKS.

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.