A B757-200 FLC MAKES A GAR WHEN THE ACFT TURNS ABOUT 40 DEGS BEYOND THE CORRECT ILS COURSE ON FINAL APCH TO RWY 10L AT BIL. THE FLC CONCLUDED THAT THEY HAD PUT THE WRONG COURSE IN THE ILS COURSE WINDOW DURING THE INTERRUPTED PREAPCH BRIEFING.

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WE WERE FLYING A COUPLED ILS APCH USING THE AUTOFLT SYS. THE CAPT WAS FLYING THE APCH AND I WAS THE PNF ON THIS LEG. APCH CTL HAD GIVEN US A VECTOR TO INTERCEPT THE ILS FINAL ABOUT 3 MI OUTSIDE THE OM. AS OUR RAW DATA CAME ALIVE; I CALLED OUT 'LOC ALIVE' AND THE CAPT CONFIRMED 'LOC ALIVE.' AS THE LOC CAME WITHIN 1 DOT; THE FLT DIRECTOR BARS DIRECTED THE ACFT TO A TURN TOWARDS FINAL; BUT INSTEAD OF ROLLING OUT ON FINAL; IT CONTINUED TO COMMAND A ROLL THROUGH FINAL AT A STANDARD RATE TURN. THE CAPT CLICKED OFF THE AUTOPLT AND ROLLED WINGS LEVEL. WHILE WE HAD GOOD RAW DATA; THE CAPT ELECTED TO ASK FOR A TURN DOWNWIND FOR ANOTHER VECTOR TO FINAL RATHER THAN TRY A RUSHED RAW DATA ILS. THE CAPT TRIED THE AUTOFLT SYS DOWNWIND AND EVERYTHING WORKED NORMALLY. APCH CTL GAVE US A QUICK TURN IN THE CIRCUIT WITH A VECTOR A FEW MI OUTSIDE THE OM. THE CAPT BRIEFED THAT IF THE AUTOFLT DID THE SAME THING HE WOULD CONTINUE WITH A MANUAL RAW DATA APCH. AS THE LOC CAME ALIVE ON THIS APCH WE NOTED THE HDG BUG IMMEDIATELY SLEWED TO A COURSE OTHER THAN THE INBOUND COURSE AND THE COMMAND BARS WERE COMMANDING TURN TO THE HDG BUG. THE CAPT CLICKED OFF THE AUTOFLT SYS AND FLEW AN UNEVENTFUL MANUAL RAW-DATA APCH. AFTER LNDG; WE WERE STILL BAFFLED WHY THE AUTOFLT SYS ACTED UP. THE AUTOFLT SYS CHKED OK BY MAINT. LATER THAT EVENING; WE WERE DISCUSSING WHAT WE COULD HAVE DONE TO CAUSE THIS PROB. MY EXPERIENCE IN AN ADVANCED COCKPIT IS THAT WHEN THE AUTOFLT SYS DOES SOMETHING YOU'RE NOT EXPECTING IT TO DO; IT'S USUALLY A WRONG INPUT BY THE PLT. COULD WE HAVE PUT THE WRONG INBOUND COURSE IN THE ILS COURSE WINDOW? THIS WOULD HAVE CAUSED THE HDG BUG TO SLEW TO A HDG OTHER THAN THE INBOUND COURSE ON LOC INTERCEPTION. BUT THE CAPT GAVE A COMPLETE APCH BRIEF WHICH INCLUDES VERIFYING FREQ AND COURSE IN THE ILS CTL PANEL. HOW COULD WE HAVE MISSED THIS? WE USUALLY TRY TO BRIEF THE APCH PRIOR TO TOP OF DSCNT SO WE ARE NOT INTERRUPTED DURING THE BRIEF. ON THIS LEG; WE HAD NOT RECEIVED ATIS PRIOR TO TOP OF DSCNT AND HAD TO SET UP FOR THE APCH AND BRIEF IT IN THE DSCNT. WHILE BRIEFING; THE CAPT'S BRIEF WAS INTERRUPTED SEVERAL TIMES WITH ATC ALT CHANGES; TFC CALLS AND A FREQ CHANGE. THE INTERRUPTIONS PROBABLY CAUSED US TO NOT PROPERLY VERIFY THE COURSE IN THE ILS CTL PANEL. WHAT COULD I HAVE DONE TO CATCH THIS OVERSIGHT? AS WE GOT CLOSER TO THE ARPT; I VERIFIED THE MORSE CODE IDENT OF THE LOC AND OM ADF AGAINST MY CHARTS AND RPTED TO THE CAPT I HAD A GOOD IDENT ON BOTH LOC AND ADF. I COULD HAVE ALSO CHKED THE COURSE ONE LAST TIME IN THE CTL BOX. FROM MY MANY YRS EXPERIENCE FLYING; INTERRUPTIONS ARE USUALLY THE CAUSE OF OVERLOOKING OR NOT DOING SOMETHING ON A PREFLT; FLOW OR CHKLIST. INTERRUPTIONS ARE SOMETHING WE ALL MUST LIVE WITH; WE JUST NEED TO BE EXTRA CAUTIOUS WHEN THEY HAPPEN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR WAS FLYING A B757-200 AND NOW ADMITS THAT THE FLC PROBABLY PUT THE WRONG COURSE IN THE ILS COURSE WINDOW. WHEN THE SAME OVERSHOOT PROB OCCURRED ON THE NEXT APCH; HE SAID THAT HE MANUALLY ADJUSTED THE HDG BUG TO THE CORRECT COURSE AND THE FLC COMPLETED THE APCH IN VISUAL CONDITIONS. THE FLC DID DISCUSS THE PROB EXTENSIVELY.