ACFT ON APCH TO ORL MADE A MISSED APCH CAUSING MLG TCASII TO GIVE RA AND TWR CTLR ALSO GAVE MISSED APCH TO MLG ON ILS TO RWY 18 AT MCO.

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OUR DEST WAS MCO. MCO WX 8 OVCST VISIBILITY 8 WIND 270/10. TOPS OF CEILING 1800 FT MSL. I (FO) WAS FLYING ILS 18R MCO WITH AUTOPLT AND AUTOTHROTTLES OFF. WE WERE CLRED APCH AND CLRED TO LAND BY MCO TWR. WE WERE ON COURSE GS; 141 KIAS; 700 FPM SINK; 2100-2200 FT MSL. TCASII RA SUDDENLY DIRECTED 'REDUCE DSCNT.' NO TA. THE VVI INDICATED A RED TARGET -500 NEAR THE CENTER OF THE INDICATOR. VVI RA DIRECTED A RED ARC FOR DSCNT AND GREEN ARC OF 0 TO 300 FPM CLB. I LEVELED AT APPROX 2000 FT MSL IN COMPLIANCE WITH TCASII RA. THE CAPT ATTEMPTED TO CONTACT TWR FOR CLARIFICATION; BUT THEY XMITTED SIMULTANEOUSLY AND BLOCKED EACH OTHER. TWR'S NEXT XMISSION INSTRUCTED US TO GAR IMMEDIATELY; CANCEL LNDG CLRNC; MAINTAIN PRESENT HDG AND 2500 FT. WE COMPLIED. LATER WE WERE INFORMED THAT AN ACFT HAD EXECUTED A MISSED APCH AT EXECUTIVE ARPT (ORL) AND WAS CLBING THROUGH OUR FLT PATH. WE NEVER SAW THE ACFT NOR DID ATC INDICATE OUR PROX TO IT. TCASII WORKED WELL! COORD SHOULD BE IMPROVED BTWN TWRS AT ORL AND MCO.