AN MD11 CREW; TAXIING FOR TKOF AT LAX; TO THE CHAGRIN OF ATC; CROSSED RWY 25L AFTER HEARING WHAT THEY THOUGHT WAS A CLRNC TO DO SO.

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DURING TAXI FROM RAMP AT A2; OUR DEP RWY WAS CHANGED FROM RWY 25R TO RWY 24L. AS WE TAXIED W ON TXWY A; AS DIRECTED BY GND. THE FO WAS WORKING NEW TKOF DATA FOR FMS INPUT ON OUR PERFORMANCE LAPTOP WHILE I TAXIED AND MONITORED THE RADIOS. PASSING TXWY G; WE SWITCHED TO TWR; AS DIRECTED; AND WAS TOLD TO 'HOLD SHORT OF RWY 25L AT TXWY P.' I READ BACK 'ROGER; ACR X HOLD SHORT OF RWY 25L AT TXWY P.' AS WE PASSED TXWY A7 I HEARD SEVERAL CALLS TO AN ACR Y JET (BY TWR) TO 'TAXI INTO POS AND HOLD; TFC XING DOWNFIELD.' APCHING TXWY N; MY FO SAID 'I'M PUTTING THE LAPTOP AWAY FOR NOW TO LISTEN FOR OUR CLRNC TO CROSS.' AFTER SEVERAL MORE CALLS TO ACR Y AND AS WE APCHED TXWY P; WE BOTH HEARD 'ACR X CLRNC TO CROSS RWY 25L; HOLD SHORT OF RWY 25R.' THE FO READ BACK 'ROGER; ACR X XING RWY 25L; HOLD SHORT OF RWY 25R.' I THEN ASKED HIM AS WE TURNED ON TXWY P TO CROSS 'DID YOU SAY ACR Y XING RWY 25L?' HE SAID 'NO; I DON'T THINK SO!' AFTER XING; WE WERE TOLD BY GND TO CALL THE TWR UPON OUR ARR IN OAK. AFTER ARRIVING OAK; WE WERE INFORMED THAT WE CROSSED RWY 25L WITHOUT CLRNC. THE RESULTS OF THE INVESTIGATION ARE PENDING A REVIEW OF THE TAPES. CONTRIBUTING FACTORS TO THIS EVENT ARE: CONGESTED RADIO TFC; POOR VISIBILITY DUE TO RAIN AND DARKNESS; AND THE FO WAS ON HIS THIRD LEG OF IOE COMING FROM SO DC10. SUPPLEMENTAL INFO FROM ACN 564933: RECEIVED CLRNC TO CROSS RWY 25L; HOLD SHORT OF RWY 25R. READ BACK THE CLRNC AND TAXIED.