A LEAR 25 FLC FAILS TO IDENT THE FREQ OF THE ILS FOR RWY 17R AND ENDS UP LINING UP ON ILS FOR RWY 17L. APCH CTLR INTERVENES AND SETS THEM STRAIGHT.

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WE WERE ON AN IFR FLT PLAN FROM COS TO OKC. WE WERE ON VECTORS FOR THE ILS TO RWY 17R. THE APCH HAD BEEN BRIEFED AND ALL FREQS HAD BEEN SET FOR THE APCH. WE RECEIVED VECTORS WHICH APPEARED TO CARRY US THROUGH THE FINAL APCH COURSE AND THEN WERE TOLD TO TURN R; INTERCEPT THE LOC AND WAS CLRED FOR THE APCH. DURING THE TURN TO INTERCEPT; THE COURSE INDICATOR SHOWED THAT THE COURSE WAS TO THE L INSTEAD OF THE R. THIS CONFUSED ME AND I TOLD THE SIC THAT SOMETHING WAS NOT RIGHT BUT I TURNED L TO INTERCEPT. IT WAS A VERY SMALL CORRECTION BECAUSE WE WERE ALMOST ON THE LOC FOR RWY 17L. THE APCH CTLR THEN EITHER ASKED OUR POS OR OUR HEADING AND SAID THAT IT LOOKED LIKE WE WERE ON FINAL TO RWY 17L INSTEAD OF RWY 17R. ABOUT THE SAME TIME I LOOKED AT THE APCH PLATE AND REALIZED THAT WE HAD THE ONE FOR RWY 17L INSTEAD OF RWY 17R. WE CORRECTED THE FREQ AND COMPLETED THE APCH TO RWY 17R. AFTER LNDG WE DISCUSSED THE INCIDENT TO TRY TO DETERMINE WHAT HAPPENED AND HOW TO KEEP IT FROM HAPPENING IN THE FUTURE. SINCE WE HAD PLANNED FOR AND BRIEFED THE APCH FOR RWY 17R WE DIDN'T UNDERSTAND HOW WE ENDED UP WITH THE FREQ FOR RWY 17L. THIS IS WHAT I THINK HAPPENED: 1) SINCE THE COCKPIT OF A LEAR 25 IS SO SMALL OUR NORMAL SOP IS TO USE ONLY ONE SET OF APCH PLATES AND CHARTS. THIS DOESN'T ALLOW FOR EACH PLT TO XCHK THE OTHER. IN THE FUTURE BOTH PLTS WILL HAVE APCH PLATES FOR THE APCH BEING EXECUTED. 2) THE APCH FOR RWY 17R IS ON THE BACK OF THE SAME PIECE OF PAPER AS RWY 17L. DURING THE APCH BRIEF WE WERE INTERRUPTED BY ATC AND THE APCH PLATE WAS PLACED ON THE CTR CONSOLE. WHEN I RESUMED THE BRIEFING I LOOKED AT THE WRONG SIDE OF THE PLATE AND SET 110.9 (ILS RWY 17L) INSTEAD 110.7 (ILS RWY 17R). IN THE FUTURE WHEN AN APCH BRIEF IS INTERRUPTED I WILL START THE BRIEF OVER TO INSURE THAT I STILL HAVE THE CORRECT APCH PLATE.