CAPT OF AN MLG ACR ACFT INADVERTENTLY TUNED THE ILS TO THE WRONG PARALLEL RWY RESULTING IN A CONFLICT WITH ANOTHER ACFT ON APCH TO THE OTHER RWY AND A MISSED APCH FOR THE RPTING ACFT.

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APCHING CHARLOTTE; WE WERE TOLD TO EXPECT RWY 36L. THERE WERE TSTMS JUST OVER MARJO; SO WE REQUESTED A TURN IN CLOSE ON FINAL. DUE TO TFC WE WERE KEPT AT 7000 FT UNTIL 2 MI FROM INTERCEPTING RWY 36L. WE WERE THEN TOLD WE WOULD BE TAKEN ACROSS RWY 36L FOR A R DOWNWIND TO RWY 36R. THE FREQ WAS VERY CONGESTED WITH THE EARLY MORNING RECOVERY INTO CHARLOTTE. THERE WAS AT LEAST ONE OTHER ACFT WITH A CALL SIGN ENDING IN NUMBER '1' LIKE OUR CALL SIGN. I WAS FLYING THE ACFT AND THE CAPT WAS SETTING UP THE RADIOS; FMC; AND COMMUNICATING. HE PUT IN RWY 36R FREQ AND I BRIEFED APCH FREQ; COURSE; MINIMUMS; MISSED APCH ALT. HE HAD SOME DIFFICULTY GETTING IN THE RWY 36R APCH INTO THE FMC. WHILE HE WAS DOING THIS; I WAS BEING SLAMMED FROM 7000 FT TO 2400 FT AND INTERCEPTING RWY 36R JUST OVER HAYOU; THE MARKER. WHILE I WAS DOING THIS; WE WERE SWITCHED TO TWR 118.1 AND CLRED RWY 36R APCH. THE CAPT SAID '118.1 IS NOT RWY 36L TWR!' I SAID WE WERE CLRED FOR RWY 36R AND HE SAID NO; WE HAD BEEN SWITCHED BACK TO RWY 36L. I NOTICED RWY 36L TFC WE WERE RAPIDLY CONVERGING WITH AND I IMMEDIATELY CORRECTED R. THE CAPT SAID HE HAD PUT RWY 36L IN THE ILS; WHICH IS WHAT I HAD BEEN INTERCEPTING. ALL OF THIS HAPPENED NEARLY; SIMULTANEOUSLY. HE PUT RWY 36R BACK INTO THE ILS; ALTHOUGH THE FMC HAD RWY 36R SINCE THE ORIGINAL CHANGE. I USED THE NAV TO AVOID THE CONFLICT. I ENDED UP BEING HIGH AND R ON RWY 36R AND ENDED UP EXECUTING A TWR DIRECTED MISSED APCH AT APPROX 2400 FT. THE CAPT WAS UPSET I DID NOT RAPIDLY GET BACK ON GS AND COMPLETE APCH; AS HE HAD PUT RWY 36R BACK IN TIME; IF I HAD ACTED IMMEDIATELY. I FEEL HIS SITUATIONAL AWARENESS DUE TO CHANGING RADIOS; COMMUNICATING; PREVENTED HIM FROM SEEING OR APPRECIATING THE PROX TO THE RWY 36L TFC. APCH APOLOGIZED FOR ANY CONFUSION. ALTHOUGH I UNDERSTOOD RWY 36R AS THE CTLR HAD CLRED US; IT WAS UNSAFE FOR ME TO CONTINUE AN APCH TO MINIMUMS WHEN THERE IS DOUBT AND NAV RADIOS BEING CHANGED OVER THE MARKER. WE BROKE OUT AT MINIMUMS ON THE FOLLOWING RWY 36R APCH. APCH SHOULD MINIMIZE CLOSE IN RWY CHANGES ON PARALLEL APCHS IN SEVER WX WHEN RADIO COMS ARE EXTREMELY BUSY.