UNAUTHORIZED RWY XING BY COMMUTER.

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I FEEL CONTRIBUTING CAUSES WERE FATIGUE AND POOR COCKPIT COM. FO WAS GIVEN CLRNC TO TAXI FOR 32 BUT FOR SOME REASON; I (PIC); THOUGHT THE CLRNC WAS FOR 24. I TAXIED FOR RWY 24 AND CROSSED RWY 32 TO GET THERE. THE FO DID NOT REALIZE IT SINCE HE WAS BUSY WITH LAST MIN CHANGES FOR WT AND BAL. THE GND CTLR ALSO DID NOT REALIZE IT UNTIL I RADIOED HIM FOR NEW TAXI INSTRUCTIONS AFTER REALIZING MY MISTAKE. DURING THE FO'S CALL FOR GND TAXI INSTRUCTIONS; I WAS BUSY CHKING FIRST FLT OF THE DAY ITEMS. THIS ALSO CONTRIBUTED TO THE ERROR SINCE I WAS DISTRACTED DURING THE ORIGINAL TAXI CLRNC REQUEST AND READBACK. SUPPLEMENTAL INFO FROM ACN 198441: CAPT COPIED THE ATIS. I OBTAINED IFR CLRNC. THE CHKLIST WAS RUN. I CALLED FOR TAXI CLRNC. WE WERE CLRED TO TAXI TO RWY 32. I TOLD THE CAPT I WAS OFF TO BRIEF THE PAX AND COPY THE CHANGES. HE ACKNOWLEDGED. I BRIEFED THE PAX AND AFTER RAISING MY HEAD FROM COPYING THE CHANGES I SAW WE WERE NEARLY ACROSS 32. I SAID TO THE CAPT THAT I THOUGHT WE WERE CLRED TO 32 WONDERING IF THE RWY ASSIGNMENT WAS CHANGED. HE SAID THAT HE THOUGHT OUR CLRNC WAS TO TAXI TO 24. HE THEN QUERIED GND AND THEY SAID TO TAXI TO RWY 32 VIA 24 AND BACK TAXI ON 32. POSSIBLE CAUSES: CAPT MISUNDERSTOOD TAXI INSTRUCTION. FO UNABLE TO ASSIST BECAUSE OF PERFORMING DUTIES. FATIGUE (CONTINUOUS DUTY OVER NIGHT). COMPLACENCY. LUCKILY CAPT OBSERVED CLRED RWY AND FINAL BEFORE XING RWY 32. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR PARTICIPATED IN STRUCTURED CALLBACK FOR RWY INCURSION STUDY. RPTR DESCRIBED WORK SCHEDULE. SAYS THAT ON THIS MORNING HE VARIED FROM NORMAL ROUTINE SOMEWHAT. NORMALLY COMPLETED ALL OF THE 'FIRST FLT OF THE DAY' CHKS BEFORE CALLING FOR TAXI CLRNC. IN THIS CASE THE FO CALLED TOO SOON FOR TAXI AND PIC (PF) WAS STILL DOING FIRST FLT CHKS. PF DID NOT CONCENTRATE ON LISTENING TO ATC RWY ASSIGNMENT AND FOR SOME UNKNOWN REASON HAD RWY 24 IN MIND AS HE TAXIED. BOTH PF AND PNF WERE DISTRACTED BY OTHER TASKS AS THEY CROSSED RWY 32. SAYS THAT FLC FATIGUE WAS A MAJOR FACTOR IN INCIDENT.