B190 CREW HAD A TCASI TA WITH A DC9 IN MKE CLASS C AIRSPACE.

Narrative

I WAS THE PF. WE WERE ON VECTORS FOR DSCNT INTO MKE. ATC CLRED US FROM 8000 FT TO 6000 FT. WE WERE APPROX 10 MI SE OF THE ARPT ON ABOUT A 340 DEG HDG. ATC THEN CLRED US TO 2800 FT AND ASKED IF WE HAD THE ARPT IN SIGHT. (AT THIS POINT WE WERE DSNDING THROUGH APPROX 7000 FT.) THE CAPT REPLIED THAT WE DID. ATC THEN TOLD US THE INSTRUCTIONS WERE NOT FOR US BUT A DIFFERENT ACFT. AT THIS TIME WE RECEIVED A TA ON TCASI. WE HAD VISUAL CONTACT WITH THE OTHER ACFT WHICH WAS APPROX 2-4 MI AHEAD OF US XING OUR L TO R DEPARTING FROM MKE. NO EVASIVE ACTION WAS NEEDED. ATC SAID WE WERE ANSWERING FOR THE WRONG ACFT AND WERE NEVER CLRED FROM 8000 FT. THE CAPT AND I; HOWEVER; WERE SURE HE WAS USING OUR CALL SIGN AND THE MISTAKE WAS HIS. (HE MEANT TO SAY A DIFFERENT CALL SIGN). THIS WAS CONFIRMED AFTER WE LANDED AND THE CAPT TALKED TO HIM ON THE PHONE. THE CTLR SAID HE LISTENED BACK TO THE TAPES AND HE WAS IN FACT USING OUR CALL SIGN WHEN HE ACTUALLY MEANT TO BE TALKING TO A DIFFERENT ACFT (SAME COMPANY). I BELIEVE THE CTLR MADE THE MISTAKE BECAUSE HE WAS OVERLOADED. THIS WAS EVIDENT AS WE WERE APCHING THE ARPT. THE TFC VOLUME WAS BUSY AND YOU COULD TELL FROM THE URGENCY IN HIS VOICE; NOT ONLY TO US BUT ALL OF THE TFC HE WAS COMMUNICATING WITH; THAT HE WAS HANDLING ALL OF THE TFC THAT HE COULD.