Narrative:

Air carrier a flight was at level flight at FL250 when ATC asked us if we could be level at FL290 in 1 1/2 mins. ATC called us as air carrier a 123. We accepted the clearance with the restrs. Passing about FL275 we were told by ATC to immediately descend to FL240. We complied and then were told by ATC that there was air carrier B 123 on the frequency. We never heard air carrier B 123 on the frequency. ATC indicated that he probably said 'air carrier a' when he meant 'air carrier B.' ATC was working more than 1 frequency at the time. We also were never advised about air carrier B 123 being around. I don't believe there was a traffic conflict later on with ord approach there again was some confusion with our call signs. Again air carrier B 123 was on a different frequency that we couldn't hear. Both times ATC was surprised about the confusion. Frequency congestion was not necessarily that busy, at least the ones we were listening to. There was a comment on the radio by ATC that he was very busy with 'all' the frequencys he was working. The solution to this problem is very simple -- controllers shouldn't operate more than 1 frequency at a time.

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Original NASA ASRS Text

Title: MLG FLC ACKNOWLEDGED CLB CLRNC ONLY TO BE DISPUTED BY ZAU CTLR. CTLR XMITTING ON MULTIPLE FREQS WITH SIMILAR SOUNDING CALL SIGN.

Narrative: ACR A FLT WAS AT LEVEL FLT AT FL250 WHEN ATC ASKED US IF WE COULD BE LEVEL AT FL290 IN 1 1/2 MINS. ATC CALLED US AS ACR A 123. WE ACCEPTED THE CLRNC WITH THE RESTRS. PASSING ABOUT FL275 WE WERE TOLD BY ATC TO IMMEDIATELY DSND TO FL240. WE COMPLIED AND THEN WERE TOLD BY ATC THAT THERE WAS ACR B 123 ON THE FREQ. WE NEVER HEARD ACR B 123 ON THE FREQ. ATC INDICATED THAT HE PROBABLY SAID 'ACR A' WHEN HE MEANT 'ACR B.' ATC WAS WORKING MORE THAN 1 FREQ AT THE TIME. WE ALSO WERE NEVER ADVISED ABOUT ACR B 123 BEING AROUND. I DON'T BELIEVE THERE WAS A TFC CONFLICT LATER ON WITH ORD APCH THERE AGAIN WAS SOME CONFUSION WITH OUR CALL SIGNS. AGAIN ACR B 123 WAS ON A DIFFERENT FREQ THAT WE COULDN'T HEAR. BOTH TIMES ATC WAS SURPRISED ABOUT THE CONFUSION. FREQ CONGESTION WAS NOT NECESSARILY THAT BUSY, AT LEAST THE ONES WE WERE LISTENING TO. THERE WAS A COMMENT ON THE RADIO BY ATC THAT HE WAS VERY BUSY WITH 'ALL' THE FREQS HE WAS WORKING. THE SOLUTION TO THIS PROB IS VERY SIMPLE -- CTLRS SHOULDN'T OPERATE MORE THAN 1 FREQ AT A TIME.

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.