COMMUTER ACFT OVERSHOOTS LOC ON APCH WITH PARALLEL RWYS IN USE.

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WE WERE 20 MI OUTSIDE OF CVG WHEN APCH TOLD US TO MAINTAIN 230 KIAS. I SAW THE ARPT AND ASKED THE FO IF HE 'SAW THE ARPT.' HE REPLIED 'YES THAT HE SAW THE ARPT AND BEACON.' I TOLD APCH 'WE HAVE THE ARPT IN SIGHT.' APCH CLRED US FOR THE VISUAL APCH TO JOIN FINAL OUTSIDE OF TROYF. TROYF IS 5.6 DME ON THE RWY 36R LOC. THE FO REMAINED ON A 300 DEG HDG TO JOIN THE FINAL. APCH THEN CLRED US FOR THE VISUAL AGAIN USING THE SAME INSTRUCTIONS AS BEFORE. AS WE APCHED THE FINAL APCH COURSE I TOLD THE FO 'YOU ARE GOING TO BLOW THROUGH THE COURSE.' HE DID NOT RESPOND. AS HE PASSED THROUGH THE LOC I REPEATED 'YOU ARE BLOWING THROUGH THE LOC.' THE FO THEN STARTED A 5-10 DEG BANK TURN TO THE R. BECOMING ALARMED I SAID 'YOU HAVE BLOWN THROUGH THE COURSE ARE YOU GOING TO THE WRONG RWY.' I THEN REPEATED 'YOU ARE GOING FOR THE WRONG RWY.' THE FO STILL REMAINED IN A 5-10 DEG BANK TURN. I PROCEEDED TO REACH FOR THE CTLS AND SAID 'CRANK IT OVER INTO A HARD BANK NOW!' THE FO THEN ROLLED INTO A 30 DEG BANK TURN THEN LINED UP ON THE CORRECT RWY. THERE WAS A B-767 LINING UP ON THE CORRECT RWY. THERE WAS A B-767 LINING UP ON THE RWY 36L FINAL THAT CAUGHT MINE AND THE CTLRS ATTN. THERE WAS NO CONFLICT AT ANYTIME BUT I DID NOT WANT THE FO TO DRIFT ANY FURTHER. AS WE SWITCHED TO TWR I THOUGHT I HAD HEARD OUR CALL SIGN BEING CALLED BY THE APCH CTLR. TWR CLRED US TO LAND AND NOTHING WAS SAID ABOUT THE SIT. AFTER LNDG I ASKED THE FO WHAT HE WAS DOING AND HE SAID 'I LOST THE RWY AND COULD NOT FIND IT.' I ASKED WHY HE DIDN'T TELL ME AND I COULD HAVE GUIDED HIM TO THE ARPT. I ALSO STATED THAT WHEN I SAID YOU WERE BLOWING THROUGH THE LOC THAT THE LOC WAS CURRENTLY CTRED ON COURSE. HE REPLIED 'HE WAS LOOKING OUTSIDE FOR THE RWY.' THE BIGGEST PROB IN THIS CASE WAS THE FO'S FAILURE TO TELL ME THAT HE HAD LOST THE ARPT IN THE DARK AND HIS NOT PAYING ATTN TO MY PROMPT THAT HE WAS BLOWING THROUGH COURSE. I SHOULD HAVE TAKEN THE ACFT OVER SOONER THAN I WAS GOING TO; BUT I THOUGHT HE WOULD TURN.