LTT CROSSED AN ACTIVE RWY AND THEN TAXIED INTO POSITION ON THE WRONG RWY CAUSING A MISSED APCH AT PIT.

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WHILE TAXIING FOR TKOF AT PIT; GND CTL ASSIGNED US RWY 28C. I WAS ACTING AS SECOND IN COMMAND AND RESPONDED WITH THE ACFT CALL SIGN. I DID NOT REPEAT THE RWY NUMBER. IT WAS SNOWING PRETTY HARD THAT DAY. THE TWR IS A TALL ONE AND THEY COULD NOT SEE THE END OF THE RWY THAT WE WERE ON DUE TO THE SNOW RESTRICTING THE VIS. AS THE CAPT WAS TAXIING THE AIRPLANE; I HAD MY HEAD DOWN WHILE READING THE TAXI CHKLIST. I DID NOT NOTICE THAT THE CAPT TAXIED ACROSS RWY 28C. HE WAS ON HIS WAY TO 28L. PRIOR TO REACHING THE HOLD LINE OF 28L; THE TWR ASKED US IF WE WERE 'AT THE END?' WE RESPONDED THAT WE WERE AT THE END. WE WERE AT THE END OF RWY 28L. THE CAPT THOUGHT THAT RWY 28L WAS HIS ASSIGNED RWY. I THOUGHT WE WERE AT THE END OF 28C. THE TWR TOLD US TO TAXI INTO POS AND HOLD. AFTER TAXIING INTO POS I HEARD AN AIRPLANE SAY THAT THERE WAS AN AIRPLANE ON THE RWY AND THAT THEY COULD NOT LAND ON IT. I REALIZED AT THAT POINT THAT WE WERE ON THE WRONG RWY. I THEN TOLD THE CAPT THAT WE MUST GET OFF OF THE RWY IMMEDIATELY. WE DID SO; BUT IT WAS TOO LATE. I WATCHED AS THE ACFT EXECUTED A MISSED APCH SEVERAL HUNDRED FT ABOVE US. WE THEN WERE RECLRED TO TKOF ON RWY 28C. THE FACT THAT I WAS RELATIVELY UNFAMILIAR WITH THE SOUTHERN PORTION OF THE ARPT; AND THE POOR VIS; CAUSED ME TO NOT REALIZE WHAT PORTION OF THE FIELD THE CAPT HAD TAXIED TO. I ALSO WAS OVER CONFIDENT IN THE CAPT. I WAS NOT WATCHING WHERE THE CAPT WAS TAXIING. I FEEL THAT THE PROB COULD HAVE BEEN ELIMINATED IF THE TWR WOULD HAVE ASKED IF WE WERE AT THE END OF 28C; INSTEAD OF JUST ASKING IF WE WERE 'AT THE END.' THIS WOULD NOT HAVE HAPPENED IF THE TWR HAD THE ABILITY TO MONITOR GND OPS THROUGH THE USE OF RADAR. THE PROB MAY ALSO HAVE BEEN SOLVED IF THE TAXI CHK HAD BEEN COMPLETED EITHER BEFORE THE ACFT WAS MOVING OR AFTER IT STOPPED. ATTN WOULD NOT HAVE BEEN SPLIT IF IT WAS DONE THIS WAY.