SAAB 340 CROSSED RWY 17C WITHOUT TWR CLRNC. FO WAS ON ANOTHER FREQ DISCUSSING A MECHANICAL PROB AND THE CAPT BECAME CONCERNED WITH THIS CONVERSATION.

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MY CAPT CROSSED AN ACTIVE RWY WITHOUT PERMISSION FROM THE TWR. WE HAD A MAINT PROB WITH THE ACFT. I GAVE CHARGE OF THE #1 COM TO THE CAPT WHILE I WAS ON THE #2 COM TRYING TO GET AHOLD OF MAINT. THE CAPT WAS IN CHARGE OF ALL GND AND TWR COM WHILE I WAS ON THE #2 COM. I HEARD NOTHING THAT WAS BEING SAID ON THE #1 COM. WE WERE XING RWY 17C WHEN I CAME BACK AND SAID 'I AM ON ONE' WHICH MEANT I WAS NO LONGER COMMUNICATING WITH MAINT OR RAMP CTL; BUT NOW AM IN CHARGE OF GND AND TWR COM. THE INSTANT I TOOK OVER THE #1 COM I HEARD THE TWR SAY 'ARE YOU XING RWY 17C?' MY CAPT SAID 'OH BLEEP' AND THEN REPLIED TO THE TWR BY SAYING 'YES.' TWR'S RESPONSE WAS OK; NO PROB; CLRED TO CROSS RWY 17C AND HOLD SHORT OF THE R. THE CAPT WAS THINKING ABOUT OUR MAINT PROB AND SPACED OUT HIS HOLD SHORT CLRNC. THE ONLY CORRECTIVE ACTION I CAN OFFER IS THE PLT WHO IS IN CHARGE OF WHICH EVER RADIO MUST CONCENTRATE AND HIS DUTY AT HAND AND NOT WORRY OR BE CONCERNED WITH WHAT THE OTHER PLT IS DOING. IT IS IMPOSSIBLE FOR ONE PLT TO DO THE DUTIES OF BOTH PLTS.