ACR-MLG FOLLOWED WRONG ACFT ON TURN TO FINAL AND CAUSED CONFLICT WITH SECOND LTT ON STRAIGHT IN APCH HE WAS SUPPOSED TO FOLLOW.

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APCHING ORF FLT WAS CLRED TO 5000' IFR (CAPT FLYING; F/O WORKING THE RADIOS). AT APPROX 5 MI S OF THE FIELD; VFR CONDITIONS; SET UP FOR A LEFT BASE TO A VISUAL. APCH CLRED US TO 2000' AND SAID THAT OUR TFC WAS ON A 10 MI FINAL STRAIGHT IN APCH TO RWY 23. THE TFC WAS NAMED BY TYPE; OF WHICH I CANNOT RECALL; BUT I NEVER HEARD IT IDENTED AS AN LTT. AT 2000' VFR; AND APPROX 2 MI N OF THE FIELD; WE RPTED OUR TFC (OR WHAT WE BELIEVED TO BE OUR TFC) AND THE FIELD IN SIGHT (THE TFC WAS 2-3 MI OUT). APCH AT THIS POINT SAID; 'FOLLOW THE TFC; CLRED FOR A VISUAL APCH;' (OR WORDS TO THAT EFFECT). AS WE STARTED OUR LEFT BASE TURN TO FINAL; FOLLOWING THE TFC THAT WE RPTED IN SIGHT; I CALLED APCH AT LEAST TWICE (MAYBE 3 TIMES) TO SEE IF HE WANTED US ON TWR FREQ. AFTER THE LAST CALL AND NO RESPONSE; AT THE 90 DEG POS; I SWITCHED TO TWR. NOW ON TWR; I HEARD TWR SAY TO AN LTT ACFT ON ABOUT A 5 MI INSTRUMENT FINAL; 'AN MLG WAS TURNING ON FINAL AND WAS NOT ON THE FREQ;' (OR WORDS TO THAT EFFECT). I QUICKLY CAME UP AND RPTED THAT WE WERE ON A VISUAL. IT BECAME APPARENT AT THAT TIME THAT WE WERE ON A CONVERGING PATH WITH AN LTT ACFT ON AN INSTRUMENT APCH. THE LTT BROKE OFF THE APCH; MADE AN S TURN AND UNEVENTFULLY LANDED BEHIND US. APCH CTL AT NO POINT INDICATED THAT THERE WAS MORE THAN 1 ACFT ON THE APCH TO RWY 23; NOR DID WE EVER HEAR ADVISORIES ABOUT AN LTT UNTIL WE SWITCHED TO TWR. AFTER CALLING APCH AT LEAST TWICE AND GETTING NO RESPONSE; AFTER BEING CLRED FOR A VISUAL BEHIND THE FIRST ACFT; WE SWITCHED TO TWR AT THE 90 DEG POS. HAD WE NOT SWITCHED; I DON'T THINK WE WOULD HAVE BEEN ALERTED TO THE SITUATION SINCE APCH WAS NOT TALKING TO US. I BELIEVE THE SITUATION OCCURRED BECAUSE APCH DID NOT INFORM US OF THE ADDITIONAL TFC. HAD WE ORIGINALLY BEEN ADVISED THAT WE WERE #3 TO FOLLOW AN LTT ON A 10 MI FINAL; THERE WOULD NOT HAVE BEEN ANY CONFUSION. IN ADDITION; APCH FAILED TO SWITCH US TO TWR AND DID NOT RESPOND TO AT LEAST 2 CALLS INITIATED BY US DURING A VERY CRITICAL PHASE OF FLT. TO SUMMARIZE; I FEEL THE SITUATION OCCURRED AND WAS COMPLETELY AVOIDABLE HAD THE CTLR BEEN MORE THOROUGH IN THE INFO THAT HE PASSED TO US (THAT WE WERE #3 TO FOLLOW AN LTT--NOT; 'YOUR TFC IS AT 10 MI'). IN ADDITION; IN A HIGH DENSITY ENVIRONMENT; WHEN APCH IS CALLED ON THE RADIO SOME SORT OF RESPONSE FROM THAT CTLR IS ESSENTIAL; EVEN IF IT IS JUST 'STAND BY.'