FO OCCUPYING THE CAPT'S L SEAT WAS TAXIING THE ACFT AND WAS SUPPOSED TO TAXI ACROSS RWY 29 AT SDF. FOLLOWING THE PIC'S TAXI DIRECTIONS; HE TURNED L AND TAXIED ONTO THE RWY INSTEAD OF XING IT FIRST. FO DID NOT HAVE ARPT CHART OUT. PIC WAS NOT WATCHING. CTLR DIRECTED ACFT OFF THE RWY.

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AFTER CLRING RWY 17 AT SDF; ACFT WAS CLRED 'TO THE RAMP.' BECAUSE SDF IS AN ARPT FREQUENTLY USED BY THE COMPANY; PIC IN R SEAT TOLD SIC IN L SEAT THAT TAXI RTE WOULD INVOLVE 'A L TURN; THEN A R TURN.' ARPT DIAGRAM WAS ATTACHED TO COPLT'S YOKE. THE REQUIRED PIC'S INTENDED TAXI RTE INVOLVED XING APCH END OF RWY 29 THEN TURNING L ON TXWY TO PARALLEL RWY 29 FOR SHORT DISTANCE; THEN R TURN ON TXWY TO PARALLEL RWY 35 TO RAMP. APCHING RWY 29; PIC (IN R SEAT) CALLED 'CLR R;' SIC CALLED 'CLR L.' PIC THEN DIRECTED ATTN INSIDE COCKPIT TO COMPLETE AFTER LNDG CHKLIST. AFTER SEVERAL SECONDS; GND CTL TOLD ACFT TO 'HOLD SHORT OF RWY 35;' THEN 'MAKE 180 DEG TURN; TAXI BACK TO CLR RWY 15 TXWY G(?).' PIC LOOKED UP AND DISCOVERED THAT SIC HAD TURNED L ONTO RWY 29; INSTEAD OF XING RWY 17. ACFT COMPLIED WITH GND CTLR'S INSTRUCTIONS. NO CONFLICTS NOTED. BOTH PLTS NEED TO BE HEADS OUT OF COCKPIT APCHING ANY TXWY/RWY INTXN. DO NOT ASSUME PLT AT CTLS IS FAMILIAR WITH ARPT. EVEN IN A SMALL COCKPIT; BOTH PLTS SHOULD HAVE OWN CHARTS. ESPECIALLY CRITICAL IN HIGH WORKLOAD ENVIRONMENT.