Narrative:

While in cruise at FL350 we received a clearance for what we heard to be for our aircraft to turn left 10 degrees and descend to FL310. There were many thunderstorms in the area and other aircraft were deviating for them, so it did not seem unusual for ATC to make this request. My first officer acknowledged the ATC request and I turned the aircraft 10 degrees and began a descent to FL310. At approximately FL343, ZAB asked our altitude. We replied that we were passing FL340 for FL310 as previously requested. The controller then ordered 20 degree right turn and a descent to FL310. I did not see any other aircraft on TCASII until one appeared 1100 ft below and approximately 10 mi behind us. No problems were perceived until several mins later, after we had been deviating extensively for WX -- with ATC approval -- that we were advised to call ZAB on landing for a possible pilot deviation. We remembered hearing another aircraft with a similar call sign, which we later found out to be aircraft #2. If the turn and descent clearance were for aircraft #2 and not aircraft #1, he may have stepped on our readback, or we may have stepped on his. At no time were we ever advised that there was another aircraft on frequency with a similar sounding call sign. The similar call signs, extensive deviation for WX, and congested radio communications were all contributing factors to this possible deviation. Supplemental information from acn 409090: the occurrence happened while we were cleared direct to zuni VOR at FL350. While we were on this frequency, we heard aircraft #2. We were never told about a conflicting call sign.

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Original NASA ASRS Text

Title: B737 FLC ACKNOWLEDGES AND INITIATES CTL INSTRUCTIONS FOR ANOTHER ACFT WHILE DEVIATING AROUND WX. FLC ALLEGES ATC NEVER ADVISED TO EXPECT SIMILAR SOUNDING CALL SIGNS.

Narrative: WHILE IN CRUISE AT FL350 WE RECEIVED A CLRNC FOR WHAT WE HEARD TO BE FOR OUR ACFT TO TURN L 10 DEGS AND DSND TO FL310. THERE WERE MANY TSTMS IN THE AREA AND OTHER ACFT WERE DEVIATING FOR THEM, SO IT DID NOT SEEM UNUSUAL FOR ATC TO MAKE THIS REQUEST. MY FO ACKNOWLEDGED THE ATC REQUEST AND I TURNED THE ACFT 10 DEGS AND BEGAN A DSCNT TO FL310. AT APPROX FL343, ZAB ASKED OUR ALT. WE REPLIED THAT WE WERE PASSING FL340 FOR FL310 AS PREVIOUSLY REQUESTED. THE CTLR THEN ORDERED 20 DEG R TURN AND A DSCNT TO FL310. I DID NOT SEE ANY OTHER ACFT ON TCASII UNTIL ONE APPEARED 1100 FT BELOW AND APPROX 10 MI BEHIND US. NO PROBS WERE PERCEIVED UNTIL SEVERAL MINS LATER, AFTER WE HAD BEEN DEVIATING EXTENSIVELY FOR WX -- WITH ATC APPROVAL -- THAT WE WERE ADVISED TO CALL ZAB ON LNDG FOR A POSSIBLE PLTDEV. WE REMEMBERED HEARING ANOTHER ACFT WITH A SIMILAR CALL SIGN, WHICH WE LATER FOUND OUT TO BE ACFT #2. IF THE TURN AND DSCNT CLRNC WERE FOR ACFT #2 AND NOT ACFT #1, HE MAY HAVE STEPPED ON OUR READBACK, OR WE MAY HAVE STEPPED ON HIS. AT NO TIME WERE WE EVER ADVISED THAT THERE WAS ANOTHER ACFT ON FREQ WITH A SIMILAR SOUNDING CALL SIGN. THE SIMILAR CALL SIGNS, EXTENSIVE DEV FOR WX, AND CONGESTED RADIO COMS WERE ALL CONTRIBUTING FACTORS TO THIS POSSIBLE DEV. SUPPLEMENTAL INFO FROM ACN 409090: THE OCCURRENCE HAPPENED WHILE WE WERE CLRED DIRECT TO ZUNI VOR AT FL350. WHILE WE WERE ON THIS FREQ, WE HEARD ACFT #2. WE WERE NEVER TOLD ABOUT A CONFLICTING CALL SIGN.

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.