TWR CTLR ALLOWED MLT TO DEPART; OPPOSITE DIRECTION TO AN ARRIVING SMA RESULTING IN LESS THAN STANDARD SEPARATON AND A NMAC.

Narrative

DURING AN ILS APCH TO RWY 6 AT TTN; NEAR MISS OCCURRED WITH AN ACFT DEPARTING THE ACTIVE RWY 24. WX AT THE TIME WAS 4000 SCATTERED; VIS 15 MI; WIND 270 DEGS AT 10 KTS. THE FLT WAS A STUDENT TRAINERS FLT ON AN IFR FLT PLAN. PHILADELPHIA APCH CLRD US FOR THE ILS 6 AND HANDED US OVER TO TRENTON TWR. TWR CLRD US FOR THE ILS 6 CIRCLE TO LAND 24 WITH A LEFT DOWNWIND. THE STUDENT'S ILS WAS ERRATIC AND A LOT OF CONVERSATION BTWN STUDENT AND INSTR OCCURRED. AT APPROX 700' MSL TWR INSTRUCTED US TO MAKE AN IMMEDIATE LEFT TURN (REPEATED SEVERAL TIMES). WE COMPLIED WITH THE FIRST CALL AND AN MLT PASSED OVERHEAD AND TO RIGHT BY 300'. AS WE ENTERED RIGHT DOWNWIND FOR 24 WE WERE GOING TO BREAK OFF THE ILS AND CIRCLE FOR 24. I STATED AT THE PUBLISHED CIRCLING MINIMUMS OF 680' MSL (467' AGL). HE CLRD US FOR THE ILS CIRCLE TO LAND 24 (WHICH WAS NOT A PRACTICE APCH.) THE TWR ADVISED US THAT THAT IS NEVER THE CASE AND WE MADE LEFT TFC FOR 24 (WHICH WAS NOT THE CLRNC). I BELIEVE THE SITUATION COULD HAVE BEEN AVOIDED IF THE INSTR (MYSELF) WAS PAYING MORE ATTN OUTSIDE THE COCKPIT AND THE CTLR SHOULD HAVE NEVER CLRD THE MLT FOR TKOF ON 24 UNTIL OUR ACFT BROKE OFF THE LOC OR HE ADVISED US ABOUT THE OTHER ACFT DEPARTING RWY 24.