A CRJ200 ON APCH TO MCI RWY 18R IS CLRED TO LAND RWY 18L BUT MISTAKES IT FOR RWY 17L AND EXPERIENCES A CONFLICT WITH AN ACFT APCHING RWY 17L.

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I WAS THE PNF INBOUND TO MCO. APCH TOLD US TO EXPECT RWY 18R. CAPT REMARKED WE WOULD PROBABLY GET SWITCHED TO RWY 17L AND BRIEFED THE APCH FOR RWY 18R. WE CAPTURED THE LOC. I CALLED APCH AND ADVISED WE HAD THE FIELD. WE WERE CLRED FOR THE VISUAL AND HANDED OVER TO TWR. TWR ASKED IF WE WANTED RWY 18L. WE SAID YES AND TWR CLRED US FOR RWY 18L. I READ BACK THE CLRNC AND THE CAPT STARTED A L TURN. AS WE WERE XING RWY 17R; I ASKED 'WEREN'T WE CLRED FOR RWY 18L?' THE CAPT RESPONDED WE NORMALLY GET RWY 17L. BEFORE I COULD CONFIRM THE CLRNC; WE GOT A TCAS ALERT. THE OTHER ACFT WAS HIGH AND TO OUR L REAR. THE CAPT STARTED TO DSND AT A FASTER RATE AND NOW WE WERE GETTING A TCAS RA. THE CAPT RESPONDED TO THE RA AND THE TCAS WAS NOW WARNING; 'MONITOR VERT SPD.' I LOOKED AT THE TCAS AND THE OTHER ACFT IS ABOUT 1000 FT ABOVE US AND DSNDING. IN THE CONFUSION THAT FOLLOWED; WE HEARD THE OTHER ACFT DISCUSSING THE CURRENT SIT WITH TWR. TWR CALLED US AND ASKED WHERE WE WERE. THEY REALIZED WE WERE NOT LNDG RWY 18L BUT RWY 17L; AND CLRED US TO LAND RWY 17L. AFTER LNDG; THE TWR CALLED BOTH ACFT AND GAVE A PHONE NUMBER TO CALL. THE OTHER CAPT WANTED THE EVENT NOTED. IN RETROSPECT; WE WERE NOT IN THE RIGHT PLACE. TWR DID NOT NOTICE WE HAD STRAYED OFF COURSE AND THE OTHER CAPT CHOSE TO DSND; WHICH COMPOUNDED THE SIT. ALL OF THESE EVENTS OCCURRED IN RAPID SUCCESSION WHICH CAUSED THE SIT TO DEVELOP RAPIDLY. AT THAT POINT; THE ONLY SAFE COURSE OF ACTION IN MY OPINION WAS TO LAND ON RWY 17L. SUPPLEMENTAL INFO FROM ACN 675386: UPON ARR; I CALLED THE TWR AND WAS INFORMED THE OTHER ACFT'S CAPT WAS PRESSING FOR A 'NEAR MISS' RPT TO BE FILED. I COMPLIED WITH TWR'S REQUESTS FOR INFO AND ADMITTED MY ERROR. ALTHOUGH I WAS ON THE WRONG APCH PATH; I DID EXERCISE PROPER TCAS AND 'SEE AND AUDIO' PROTOCOL. THERE WAS NO 'NEAR MISS' BECAUSE I WAS DOING MY BEST TO GET OUT OF HIS WAY. IN RETROSPECT; IT IS CLR THAT THE OTHER PLT WAS NOT MANEUVERING WELL TO AVOID ME WHILE WE BOTH MUST HAVE BEEN HEADED TO THE SAME RWY; I WRONGLY SO. I WAS ESTABLISHED ON FINAL BEFORE THE CONFLICT. HE COULD HAVE BETTER AVOIDED ME. WHAT WAS HIS TCAS TELLING HIM? DID HE COMPLY? AS TO MY ORIGINAL ERROR; MY FAULT. I LET MY EXPECTATIONS SPEAK LOUDER THAN WORDS. HOWEVER; WHAT POSSIBLE REASON WOULD ATC HAVE FOR OFFERING ME RWY 18L? IT SERVES ME NO PURPOSE TO GIVE UP AN ILS BACKED UP VISUAL TO GO TO AN ADJACENT RWY WHICH IS PRACTICALLY JUST AS FAR FROM MY PARKING. THE TRAP WAS SET AND I STEPPED RIGHT INTO IT. I MUST DO BETTER!