E120 CREW TAXIED INTO POS WITHOUT CLRNC.

Narrative

WHEN WE STARTED OUR LONG TAXI AT XA30L FROM THE GATE; WE WERE INSTRUCTED TO TAXI TO RWY 1R FOR OUR DEP TO FAT ON THE SFO8 DEP. AT XB00L (APPROX) WE WERE NEXT FOR TKOF. TWR SAID ACR XXX HOLD SHORT OF RWY 1R FOR WAKE TURB AVOIDANCE. I; THE FO; READ BACK THE INSTRUCTIONS. 15-20 SECONDS LATER; I HEARD 'ACR XXX TAXI INTO POS AND HOLD RWY 1R.' I READ BACK THE INSTRUCTIONS 'TAXI INTO POS AND HOLD RWY 1R.' WE STARTED OUR TAXI; CLRING R AND L INTO POS ON RWY 1R. SFO TWR SAID; 'ACR XXX YOU WERE NOT INSTRUCTED TO TAXI INTO POS; YOU WERE INSTRUCTED TO HOLD SHORT RWY 1R.' MY CAPT SAID TO THE TWR 'WE READ BACK THE INSTRUCTION TO TAXI INTO POS; AND SORRY ABOUT THAT.' THE SFO TWR CAME BACK AND SAID 'ACR XXX CONTINUE HOLDING IN POS ON RWY 1R.' WE HELD IN POS ON THE RWY UNTIL WE WERE CLRED FOR TKOF. THE CAPT AND I TALKED ABOUT WHAT HAPPENED DURING OUR CRUISE TO FAT. I BELIEVE I MISTOOK THE CALL SIGN OF COMPANY SAME ACR XX FOR THE CALL SIGN OF COMPANY ACR XXX. THE TWR PROBABLY SAID 'SAME ACR XX TAXI INTO POS AND HOLD RWY 1L' AND I HEARD 'ACR XXX TAXI INTO POS AND HOLD RWY 1R.' I WAS WRONG IN WHAT I HEARD. CONTRIBUTING FACTORS: A LONG TAXI; BUSY ARPT; BUSY RADIO TFC; SIMILAR COMPANY CALL SIGNS; SAME ACR XX TO ACR XXX. CREW NEEDS TO PAY CLOSER ATTN TO THE FREQ. HOW IT WAS DISCOVERED: SFO TWR SAW US TAXI INTO POS RWY 1R. CORRECTIVE ACTION: WE APOLOGIZED TO THE CTLR. I CALLED AND ASKED FOR THE TWR SUPVR; BUT SPOKE TO A CTLR AB. HE SAID THAT THEY (CTLRS) LISTENED TO THE TAPES AND THEY HEARD ME READ BACK 'ACR XXX; TAXI INTO POS AND HOLD RWY 1R.' SO THE CTLR AT THE TIME DID NOT HEAR OUR XMISSION. AB TOLD ME THAT THERE WAS NOT ANY PROB AND ASKED US TO LISTEN MORE CAREFULLY WHEN THE RADIO GETS REAL BUSY. I TOLD HIM THANK YOU AND I WAS SORRY FOR THE MISTAKE. THE CAPT AND I BOTH AGREED THAT IN OUR FUTURE COMS WE WILL TALK SLOWER. SOMETIMES CTLRS ARE VERY BUSY AND BEGIN TO TALK FAST AND AS PLTS WE BEGIN TO DO THE SAME. THIS IS WHEN IMPORTANT INFO CAN GET LOST IN THE RADIO COM. AS A PLT; I WILL SLOW DOWN AND ASK FOR CLARIFICATION WHEN NOT ABSOLUTELY SURE.