Narrative:

Flight from sfo to bur. About 10 mins prior to planned descent on the fim.fern 5 arrival, I had turned down ATC volume to make a predscnt PA (more lengthy than normal because we explain our short field landing procedures at bur). While this was occurring, I heard the captain respond to ATC 'out of FL290 for FL240.' I set FL240 in our altitude window (as per SOP) but I did not actually hear ATC's directive. 1 controller at ZLA was controling several sectors on different frequencys. (We heard several of his calls on simulcast, but no aircraft response.) while we thought it was early to start the descent, and we usually were given pilot's discretion, it was not unknown to descend early for future conflicts, and center did not countermand our call that we were descending. About 6-7 mins later (we had been at FL240 1 min or so) ZLA gave us 'pilot's discretion to FL240.' when I said we were already directed to FL240 and were there, controller said we had not been cleared earlier. I suggested he review his tapes. Later, in socal approach airspace, another aircraft with a similar call sign came on frequency, but arrived from the nne. We had not heard this aircraft call sign while on ZLA frequency earlier, but the controller may have been controling him on another frequency in another sector, and directed him to FL240. Our response may have mirrored the other aircraft's call on the other frequency, so the controller did not hear our call. By the way, we were not advised of a similar call sign by either ZLA controller or socal approach controller, but the other aircraft was advised of us by socal approach. No traffic conflict resulted from this confusion and our early descent to FL240.

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Original NASA ASRS Text

Title: FLC ACCEPTED DSCNT CLRNC INTENDED FOR ANOTHER ACFT.

Narrative: FLT FROM SFO TO BUR. ABOUT 10 MINS PRIOR TO PLANNED DSCNT ON THE FIM.FERN 5 ARR, I HAD TURNED DOWN ATC VOLUME TO MAKE A PREDSCNT PA (MORE LENGTHY THAN NORMAL BECAUSE WE EXPLAIN OUR SHORT FIELD LNDG PROCS AT BUR). WHILE THIS WAS OCCURRING, I HEARD THE CAPT RESPOND TO ATC 'OUT OF FL290 FOR FL240.' I SET FL240 IN OUR ALT WINDOW (AS PER SOP) BUT I DID NOT ACTUALLY HEAR ATC'S DIRECTIVE. 1 CTLR AT ZLA WAS CTLING SEVERAL SECTORS ON DIFFERENT FREQS. (WE HEARD SEVERAL OF HIS CALLS ON SIMULCAST, BUT NO ACFT RESPONSE.) WHILE WE THOUGHT IT WAS EARLY TO START THE DSCNT, AND WE USUALLY WERE GIVEN PLT'S DISCRETION, IT WAS NOT UNKNOWN TO DSND EARLY FOR FUTURE CONFLICTS, AND CTR DID NOT COUNTERMAND OUR CALL THAT WE WERE DSNDING. ABOUT 6-7 MINS LATER (WE HAD BEEN AT FL240 1 MIN OR SO) ZLA GAVE US 'PLT'S DISCRETION TO FL240.' WHEN I SAID WE WERE ALREADY DIRECTED TO FL240 AND WERE THERE, CTLR SAID WE HAD NOT BEEN CLRED EARLIER. I SUGGESTED HE REVIEW HIS TAPES. LATER, IN SOCAL APCH AIRSPACE, ANOTHER ACFT WITH A SIMILAR CALL SIGN CAME ON FREQ, BUT ARRIVED FROM THE NNE. WE HAD NOT HEARD THIS ACFT CALL SIGN WHILE ON ZLA FREQ EARLIER, BUT THE CTLR MAY HAVE BEEN CTLING HIM ON ANOTHER FREQ IN ANOTHER SECTOR, AND DIRECTED HIM TO FL240. OUR RESPONSE MAY HAVE MIRRORED THE OTHER ACFT'S CALL ON THE OTHER FREQ, SO THE CTLR DID NOT HEAR OUR CALL. BY THE WAY, WE WERE NOT ADVISED OF A SIMILAR CALL SIGN BY EITHER ZLA CTLR OR SOCAL APCH CTLR, BUT THE OTHER ACFT WAS ADVISED OF US BY SOCAL APCH. NO TFC CONFLICT RESULTED FROM THIS CONFUSION AND OUR EARLY DSCNT TO FL240.

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.