Narrative:

For ATC purposes, our call sign is limited to the last 3 numbers (ie, air carrier XXX). Because of thunderstorms in and around chicago, we had been holding at bradford on the bradford arrival into chicago. Although 'holding,' my workload as the PNF was high. Because of fuel considerations, I had been listening to ATIS at pia, spi, bmi, and mli. Furthermore, I had been attempting to reach company dispatch on ground/air frequency and common radio, finally succeeding on that facility. While I was attending to these duties, the captain had assumed communication #1 while flying the airplane. We were cleared direct ord and maintain 6000 ft. I acknowledged the captain exiting the hold and setting the altitude selector to 6000 ft. I did not actually hear the ATC clearance. Everything so far was ok. With the heavy workload of our crew, the approach controller, the WX, and the arrival of another air carrier flight yxx on the approach frequency, a breakdown of communication began to occur. ATC began calling us, 'air carrier XXX, air carrier yxx,' and 'other air carrier yxx as other air carrier XXX.' ATC had now cleared 'other air carrier XXX' to 4000 ft. The controller meant for 'other air carrier yxx' to descend to 4000 ft. My captain heard '...XXX' and dialed in 4000 ft, I acknowledged (not having ATC because of garble on communication #2) and we began to descend to 4000 ft. The crew of 'other air carrier yxx' was the first to pick up on the growing confusion. He quickly queried ATC to clarify the last clearance. My captain arrested the descent immediately and climbed back to 6000 ft. Everything happened quickly except our descent, which revealed a total altitude deviation of about -300 ft. Once back at altitude, ATC said 'I guess you have discovered that clearance wasn't for you.' the tone was one that simply stated, both my crew and ATC erred equally. 'Other air carrier yxx' saved the day. The airspace around chicago was not congested because of ground holds at ord and mdw due to WX. At no time was the safety of any aircraft at risk. Finally, a solution could be ACARS which could have sped up my duties on communication #2 and would have allowed me to listen to xmissions on communication #1. ACARS does not exist on our aircraft fleet.

Related reports:

Google
 

Original NASA ASRS Text

Title: A HOLDING CRJ200 STARTS A DSCNT MEANT FOR ANOTHER ACR FLT WHEN THE PIC ANSWERS TO THE WRONG CALL SIGN WHILE HOLDING SW OF ORD, IL.

Narrative: FOR ATC PURPOSES, OUR CALL SIGN IS LIMITED TO THE LAST 3 NUMBERS (IE, ACR XXX). BECAUSE OF TSTMS IN AND AROUND CHICAGO, WE HAD BEEN HOLDING AT BRADFORD ON THE BRADFORD ARR INTO CHICAGO. ALTHOUGH 'HOLDING,' MY WORKLOAD AS THE PNF WAS HIGH. BECAUSE OF FUEL CONSIDERATIONS, I HAD BEEN LISTENING TO ATIS AT PIA, SPI, BMI, AND MLI. FURTHERMORE, I HAD BEEN ATTEMPTING TO REACH COMPANY DISPATCH ON GND/AIR FREQ AND COMMON RADIO, FINALLY SUCCEEDING ON THAT FACILITY. WHILE I WAS ATTENDING TO THESE DUTIES, THE CAPT HAD ASSUMED COM #1 WHILE FLYING THE AIRPLANE. WE WERE CLRED DIRECT ORD AND MAINTAIN 6000 FT. I ACKNOWLEDGED THE CAPT EXITING THE HOLD AND SETTING THE ALT SELECTOR TO 6000 FT. I DID NOT ACTUALLY HEAR THE ATC CLRNC. EVERYTHING SO FAR WAS OK. WITH THE HVY WORKLOAD OF OUR CREW, THE APCH CTLR, THE WX, AND THE ARR OF ANOTHER ACR FLT YXX ON THE APCH FREQ, A BREAKDOWN OF COM BEGAN TO OCCUR. ATC BEGAN CALLING US, 'ACR XXX, ACR YXX,' AND 'OTHER ACR YXX AS OTHER ACR XXX.' ATC HAD NOW CLRED 'OTHER ACR XXX' TO 4000 FT. THE CTLR MEANT FOR 'OTHER ACR YXX' TO DSND TO 4000 FT. MY CAPT HEARD '...XXX' AND DIALED IN 4000 FT, I ACKNOWLEDGED (NOT HAVING ATC BECAUSE OF GARBLE ON COM #2) AND WE BEGAN TO DSND TO 4000 FT. THE CREW OF 'OTHER ACR YXX' WAS THE FIRST TO PICK UP ON THE GROWING CONFUSION. HE QUICKLY QUERIED ATC TO CLARIFY THE LAST CLRNC. MY CAPT ARRESTED THE DSCNT IMMEDIATELY AND CLBED BACK TO 6000 FT. EVERYTHING HAPPENED QUICKLY EXCEPT OUR DSCNT, WHICH REVEALED A TOTAL ALTDEV OF ABOUT -300 FT. ONCE BACK AT ALT, ATC SAID 'I GUESS YOU HAVE DISCOVERED THAT CLRNC WASN'T FOR YOU.' THE TONE WAS ONE THAT SIMPLY STATED, BOTH MY CREW AND ATC ERRED EQUALLY. 'OTHER ACR YXX' SAVED THE DAY. THE AIRSPACE AROUND CHICAGO WAS NOT CONGESTED BECAUSE OF GND HOLDS AT ORD AND MDW DUE TO WX. AT NO TIME WAS THE SAFETY OF ANY ACFT AT RISK. FINALLY, A SOLUTION COULD BE ACARS WHICH COULD HAVE SPED UP MY DUTIES ON COM #2 AND WOULD HAVE ALLOWED ME TO LISTEN TO XMISSIONS ON COM #1. ACARS DOES NOT EXIST ON OUR ACFT FLEET.

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.