NMAC BTWN A CESSNA 152 ON AN EXTENDED FINAL; DUE TO TFC SEQUENCING BY THE TWR; AND A DEPARTING MEDICAL HELI COMING STRAIGHT AT THE C150 FROM DEPARTING THE APCH END OF THE RWY TO WHICH C152 WAS HEADED.

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FLYING IN THE PATTERN; DOING TOUCH AND GOES; WITH A STUDENT WHO IS CLOSE TO SOLOING. TFC GOT HVY WITH AT LEAST 1 ACFT WE HEARD RPT 6 MI OUT; AND HAD BEEN MONITORING ITS PROGRESS. ADDITIONALLY; TFC WAS DEPARTING. TWR SEQUENCED US #3 BEHIND AN ACFT ON SHORT FINAL AND 'A NAVAJO AHEAD AND TO YOUR L.' THE NAVAJO WAS COMING IN FROM THE W; THROUGH STANDIFORD'S (LOUISVILLE'S) AIRSPACE; SO WE HAD BEEN UNAWARE OF ITS PRESENCE UNTIL THIS SEQUENCING. WE HAD STARTED OUR TURN TO BASE; BUT TWR IMMEDIATELY INSTRUCTED US TO WIDEN BACK OUT ONTO DOWNWIND. WE IMMEDIATELY COMPLIED AND ASKED TWR TO CALL OUR BASE AS WE HAD NEGATIVE VISUAL CONTACT WITH THE TFC (NAVAJO) AT THAT POINT. A FEW MOMENTS LATER; TWR CALLED OUR BASE AND WE SAW THE NAVAJO. THE FREQ WAS CONGESTED; WITH NUMEROUS 'STEP-ONS;' AND THE #1 ACFT RPTED GOING AROUND. AT THIS POINT WE WERE ON FINAL; FARTHER FROM THE ARPT THAN USUAL; IN STANDIFORD'S AIRSPACE (WHICH I UNDERSTOOD TO BE OKAY; AS TWR HAD INSTRUCTED US TO GO EXTEND DOWNWIND; ETC). WE HAD HEARD SOME XMISSIONS FROM A HELI (HELI Y) REGARDING DEPARTING FROM THE APCH END OF THE ARPT; BUT DIDN'T HEAR DIRECTION OF FLT. AT THIS POINT; TWR SAID; QUITE SHARPLY; 'HELI Y; DO YOU HAVE THE CESSNA ON FINAL?' MY STUDENT SAW IT A SPLIT SECOND BEFORE I DID; ON A LEVEL COURSE TOWARD US. I SAW IT JUST AS IT BEGAN EVASIVE ACTION; THEN THE PLT REPLIED 'NOW I DO.' AT THAT POINT EVASIVE ACTION BY US WAS UNNECESSARY. CONTRIBUTING FACTORS: HVY TFC; CONGESTED FREQ; WE COULDN'T DETERMINE THE HELI'S INTENTIONS BY LISTENING TO THE FREQ. TWR DID NOT ADVISE US OF THE HELI; EVER; AND HELI WAS PAINTED IN A SHADE SIMILAR TO THE BACKGROUND.