Narrative:

ZAU 118.22 called us (air carrier X) to see if we could climb to FL350 for traffic. Captain answered yes, so ATC issued climb and I initiated climb. At that time, air carrier Y called ATC and said someone else had answered for them. ATC immediately issued 'air carrier X, maintain FL330,' as we were passing through FL340 in the climb. I immediately set FL330 and set for 'open descent.' airlines frequently use similar sounding flight numbers for departure and arrival banks, making it easy for miscom with ATC with similar sounding call signs. Supplemental information from acn 592864: our original filing was for FL370 which ZAU would not accept from ZMP. Both pilots are sure that ZAU said 'air carrier X' but maybe we were mistaken. I said we could take FL350 or FL370, our original request. I accepted FL350 as copilot initiated an open climb to FL350. Shortly after climb was initiated, there was interference on the frequency (118.22) with 2 talking at once. I would guess that air carrier Y and center were both talking. I suspected we had gotten the wrong clearance and motioned the copilot to return to FL330 as we were around FL338 before I could get a word in on the frequency to tell center that we were returning to FL330. We continued on at FL330, climbing to FL350 and FL370 shortly after on another frequency. Another case of overburdened frequency and similar call signs used by the same carrier. I am certain that I read back 'air carrier X' in the clearance to FL350, but heard no correction on what was a pretty busy frequency.

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Original NASA ASRS Text

Title: A319 FLT CREW TAKE CLB CLRNC OF COMPANY FLT WITH SIMILAR FLT NUMBER. AS ZAU AND OTHER COMPANY CLARIFY CLRNC, A319 BEGINS DSCNT TO ASSIGNED ALT.

Narrative: ZAU 118.22 CALLED US (ACR X) TO SEE IF WE COULD CLB TO FL350 FOR TFC. CAPT ANSWERED YES, SO ATC ISSUED CLB AND I INITIATED CLB. AT THAT TIME, ACR Y CALLED ATC AND SAID SOMEONE ELSE HAD ANSWERED FOR THEM. ATC IMMEDIATELY ISSUED 'ACR X, MAINTAIN FL330,' AS WE WERE PASSING THROUGH FL340 IN THE CLB. I IMMEDIATELY SET FL330 AND SET FOR 'OPEN DSCNT.' AIRLINES FREQUENTLY USE SIMILAR SOUNDING FLT NUMBERS FOR DEP AND ARR BANKS, MAKING IT EASY FOR MISCOM WITH ATC WITH SIMILAR SOUNDING CALL SIGNS. SUPPLEMENTAL INFO FROM ACN 592864: OUR ORIGINAL FILING WAS FOR FL370 WHICH ZAU WOULD NOT ACCEPT FROM ZMP. BOTH PLTS ARE SURE THAT ZAU SAID 'ACR X' BUT MAYBE WE WERE MISTAKEN. I SAID WE COULD TAKE FL350 OR FL370, OUR ORIGINAL REQUEST. I ACCEPTED FL350 AS COPLT INITIATED AN OPEN CLB TO FL350. SHORTLY AFTER CLB WAS INITIATED, THERE WAS INTERFERENCE ON THE FREQ (118.22) WITH 2 TALKING AT ONCE. I WOULD GUESS THAT ACR Y AND CTR WERE BOTH TALKING. I SUSPECTED WE HAD GOTTEN THE WRONG CLRNC AND MOTIONED THE COPLT TO RETURN TO FL330 AS WE WERE AROUND FL338 BEFORE I COULD GET A WORD IN ON THE FREQ TO TELL CTR THAT WE WERE RETURNING TO FL330. WE CONTINUED ON AT FL330, CLBING TO FL350 AND FL370 SHORTLY AFTER ON ANOTHER FREQ. ANOTHER CASE OF OVERBURDENED FREQ AND SIMILAR CALL SIGNS USED BY THE SAME CARRIER. I AM CERTAIN THAT I READ BACK 'ACR X' IN THE CLRNC TO FL350, BUT HEARD NO CORRECTION ON WHAT WAS A PRETTY BUSY FREQ.

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.