Narrative:

We were operating air carrier X. Company air carrier Y was behind us on a similar route. Controller had multiple frequencys and multiple aircraft deviating for WX. He was working very quickly. I heard a climb issued to us. The controller said the readback was stepped on and reissued the climb. I heard him say something like 'everybody listen, this is for climb to 17000 ft.' after that, our company tried 2 or 3 times to say that someone had taken their climb. I thought 'no dude, you took ours.' the first officer wisely leveled off. The controller said he saw us climbing and realized we took the clearance. The mistake was caught. Luckily, we had only climbed 200 ft or so (less than 300 ft). Besides congestion, the other factors are similar call signs, especially when spoken fast. Also, controller workload -- I swear the second time he said our flight number. (At least that is what I heard.) since we were on similar rtes, the instructions would've been appropriate for both of us, this knocking down another barrier preventing mistakes. In fact, later, he cleared the other flight to our destination. He could've been confused as well. In the end, it was probably a bunch of factors that contributed. Luckily, the other crew, the first officer with me, and the controller were all able to step back and fix the situation before safety was compromised. Also, I read the clearance back with flight number both times, but it was likely at least partially blocked.

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Original NASA ASRS Text

Title: CALL SIGN CONFUSION RESULTED IN FLT CREW LEAVING ASSIGNED ALT.

Narrative: WE WERE OPERATING ACR X. COMPANY ACR Y WAS BEHIND US ON A SIMILAR RTE. CTLR HAD MULTIPLE FREQS AND MULTIPLE ACFT DEVIATING FOR WX. HE WAS WORKING VERY QUICKLY. I HEARD A CLB ISSUED TO US. THE CTLR SAID THE READBACK WAS STEPPED ON AND REISSUED THE CLB. I HEARD HIM SAY SOMETHING LIKE 'EVERYBODY LISTEN, THIS IS FOR CLB TO 17000 FT.' AFTER THAT, OUR COMPANY TRIED 2 OR 3 TIMES TO SAY THAT SOMEONE HAD TAKEN THEIR CLB. I THOUGHT 'NO DUDE, YOU TOOK OURS.' THE FO WISELY LEVELED OFF. THE CTLR SAID HE SAW US CLBING AND REALIZED WE TOOK THE CLRNC. THE MISTAKE WAS CAUGHT. LUCKILY, WE HAD ONLY CLBED 200 FT OR SO (LESS THAN 300 FT). BESIDES CONGESTION, THE OTHER FACTORS ARE SIMILAR CALL SIGNS, ESPECIALLY WHEN SPOKEN FAST. ALSO, CTLR WORKLOAD -- I SWEAR THE SECOND TIME HE SAID OUR FLT NUMBER. (AT LEAST THAT IS WHAT I HEARD.) SINCE WE WERE ON SIMILAR RTES, THE INSTRUCTIONS WOULD'VE BEEN APPROPRIATE FOR BOTH OF US, THIS KNOCKING DOWN ANOTHER BARRIER PREVENTING MISTAKES. IN FACT, LATER, HE CLRED THE OTHER FLT TO OUR DEST. HE COULD'VE BEEN CONFUSED AS WELL. IN THE END, IT WAS PROBABLY A BUNCH OF FACTORS THAT CONTRIBUTED. LUCKILY, THE OTHER CREW, THE FO WITH ME, AND THE CTLR WERE ALL ABLE TO STEP BACK AND FIX THE SIT BEFORE SAFETY WAS COMPROMISED. ALSO, I READ THE CLRNC BACK WITH FLT NUMBER BOTH TIMES, BUT IT WAS LIKELY AT LEAST PARTIALLY BLOCKED.

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.