INSTRUCTOR PLT OF A GLIDER TRAINING FLT TOOK EVASIVE ACTION TO AVOID A DSNDING TOW ACFT BY RELEASING HIS TOW OF HIS TOW ACFT AND BANKING SHARPLY. NMAC.

Narrative

I WAS INSTRUCTING IN THE REAR COCKPIT WITH AN EXPERIENCED STUDENT IN THE FRONT OF A SCHULTZER SGS2-33 GLIDER BEING TOWED BEHIND A CESSNA L19 TOW PLANE. CLBING THROUGH 1000 FT AGL; I WAS PF WHEN THE STUDENT CALLED OUT 'TFC!' AND POINTED HIGH AND L. IMMEDIATELY ANOTHER L19 TOW PLANE CAME INTO VIEW FROM A 10 O'CLOCK POS IN A STEEP FAST DSCNT AND VERY CLOSE. I RELEASED THE TOW ROPE AND BANKED HARD TO THE R TO AVOID THE IMMINENT COLLISION BTWN THE 2 L19'S. THE DSNDING L19 MADE AN ABRUPT CORRECTION AND PASSED ABOVE AND SLIGHTLY BTWN THE TOW PLANE AND GLIDER. ALL 3 ACFT THEN LANDED NORMALLY. IN THE DISCUSSION THAT FOLLOWED IT WAS DISCOVERED THAT THE TOWING L19 PLT WAS UNAWARE OF THE TFC UNTIL FEELING ITS WAKE. CONTRIBUTING FACTORS WERE THE HIGH-WING BLIND SPOTS OF BOTH THE GLIDER AND TOW PLANE; AND THE INTERSECTING CLB OUT AND LNDG PATTERN ENTRY RTES AND ALTS. AS FOR HUMAN PERFORMANCE CONSIDERATIONS; IN THE FUTURE I WILL GIVE STUDENTS THE AUTH TO ASSUME IMMEDIATE CTL IF REQUIRED BY TIMELINESS (THE FRONT COCKPIT HAS FEWER BLIND AREAS). I WILL ALSO BE MORE VIGILANT IN THIS TFC AREA. BOTH L19 PLTS AGREED THAT A MORE AGGRESSIVE SEE-AND-AVOID ATTITUDE IS APPROPRIATE IN GENERAL AT THIS ARPT.