Narrative:

We were level at FL250 in IMC. We were expecting a climb to FL260 as a final cruising altitude. The first officer and myself heard the controller clear us to FL260. I accepted the climb and read back our flight number and 'climb to FL260.' the first officer set it in the altitude select and we both verified the altitude and then began a slow climb approximately 500 FPM to FL260. As we were approaching FL255, the controller told us to 'verify altitude of FL250.' I said 'no, we're at FL255, we accepted a climb to FL260.' then we proceeded to reverse direction and descended back down to FL250. There was another airplane above us at FL260. We never received a TCASII warning. The problem occurred due to miscom. I accepted a climb that was meant for a company airplane with a similar call sign. The controller did not correct me of my mistake. These 2 mistakes on our part, coupled with the close proximity of a second airplane, made for an uncomfortable situation. Both airplanes were also in IMC.

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Original NASA ASRS Text

Title: POTENTIAL CONFLICT OCCURS BTWN 2 ACR FLTS WHEN THE PIC OF ONE ANSWERS TO THE WRONG CALL SIGN FOR THE OTHER COMPANY FLT ON FREQ WITH ZKC, MO.

Narrative: WE WERE LEVEL AT FL250 IN IMC. WE WERE EXPECTING A CLB TO FL260 AS A FINAL CRUISING ALT. THE FO AND MYSELF HEARD THE CTLR CLR US TO FL260. I ACCEPTED THE CLB AND READ BACK OUR FLT NUMBER AND 'CLB TO FL260.' THE FO SET IT IN THE ALT SELECT AND WE BOTH VERIFIED THE ALT AND THEN BEGAN A SLOW CLB APPROX 500 FPM TO FL260. AS WE WERE APCHING FL255, THE CTLR TOLD US TO 'VERIFY ALT OF FL250.' I SAID 'NO, WE'RE AT FL255, WE ACCEPTED A CLB TO FL260.' THEN WE PROCEEDED TO REVERSE DIRECTION AND DSNDED BACK DOWN TO FL250. THERE WAS ANOTHER AIRPLANE ABOVE US AT FL260. WE NEVER RECEIVED A TCASII WARNING. THE PROB OCCURRED DUE TO MISCOM. I ACCEPTED A CLB THAT WAS MEANT FOR A COMPANY AIRPLANE WITH A SIMILAR CALL SIGN. THE CTLR DID NOT CORRECT ME OF MY MISTAKE. THESE 2 MISTAKES ON OUR PART, COUPLED WITH THE CLOSE PROX OF A SECOND AIRPLANE, MADE FOR AN UNCOMFORTABLE SIT. BOTH AIRPLANES WERE ALSO IN IMC.

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.