Narrative:

At approximately XA00 local time we were at 8000 ft MSL approximately 40 mi southwest of ord. The approach controller instructed us to slow to 180 KTS and descend to 5000 ft MSL. Being the PNF I acknowledged and readback the clearance, selected 5000 ft in the altimeter. Pre-selector, and confirmed with the first officer down to 5000 ft. There was no controller response from the readback. The first officer reduced power and started a slow descent. A few mins later, as we descended through 6700 ft MSL, the controller told us to climb back to 7000 ft MSL and then changed it to 8000 ft. He then inquired as to why we had left 8000 ft in the first place. I replied that he had cleared us and readback the original clearance to him. In retrospect, I believe that the controller might have been issuing the clearance to another flight with similar characters and mixed them up. Consequently he distinctly gave us a clearance intended for someone else.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION -- CLRNC DISPUTED -- THIS ACR COPIED AND READBACK A CLRNC TO DSND, BUT AFTER STARTING DOWN THE FLC WAS INSTRUCTED BY THE CTLR TO RETURN TO THE ORIGINAL ALT.

Narrative: AT APPROX XA00 LCL TIME WE WERE AT 8000 FT MSL APPROX 40 MI SW OF ORD. THE APCH CTLR INSTRUCTED US TO SLOW TO 180 KTS AND DSND TO 5000 FT MSL. BEING THE PNF I ACKNOWLEDGED AND READBACK THE CLRNC, SELECTED 5000 FT IN THE ALTIMETER. PRE-SELECTOR, AND CONFIRMED WITH THE FO DOWN TO 5000 FT. THERE WAS NO CTLR RESPONSE FROM THE READBACK. THE FO REDUCED PWR AND STARTED A SLOW DSCNT. A FEW MINS LATER, AS WE DSNDED THROUGH 6700 FT MSL, THE CTLR TOLD US TO CLB BACK TO 7000 FT MSL AND THEN CHANGED IT TO 8000 FT. HE THEN INQUIRED AS TO WHY WE HAD LEFT 8000 FT IN THE FIRST PLACE. I REPLIED THAT HE HAD CLRED US AND READBACK THE ORIGINAL CLRNC TO HIM. IN RETROSPECT, I BELIEVE THAT THE CTLR MIGHT HAVE BEEN ISSUING THE CLRNC TO ANOTHER FLT WITH SIMILAR CHARACTERS AND MIXED THEM UP. CONSEQUENTLY HE DISTINCTLY GAVE US A CLRNC INTENDED FOR SOMEONE ELSE.

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.