DA20 FLC HAS NMAC AT HWV.

Narrative

FIRSTLY; A STUDENT AND I WERE WORKING ON PILOTAGE SKILLS AND ATTEMPTING TO FIND OUR WAY TO HWV; ON LONG ISLAND; WHILE UNDER THE FLOOR OF CLASS C ISP AT 1200 FT; AND NEARLY WANDERED INTO THE SURFACE AREA SURROUNDING ISP AFTER WE CONFUSED SOME RADIO TWRS MARKED ON THE SECTIONAL FOR TWRS THAT WERE ACTUALLY FARTHER E. A LOOK AT OUR GPS TOLD US A 130 DEG HDG WOULD TAKE US TO HWV; WHICH WAS UNEXPECTED AND; THEREFORE; A BIT UNNERVING. NEVERTHELESS; WE QUICKLY SPOTTED HWV NOW THAT WE WERE LOOKING IN THE RIGHT DIRECTION; CALLED IN FOR TA'S AT ABOUT 5 MI NW AND STARTED SETTING UP FOR A L DOWNWIND ENTRY FOR RWY 6; WHEN IT WAS ANNOUNCED THERE WOULD BE A SWITCH TO L TFC FOR RWY 15. NO PROB; MY STUDENT QUICKLY MADE THE NECESSARY ADJUSTMENTS; AND WE WENT IN FOR A TOUCH-AND-GO. AS WE WERE TAKING OFF AND APCHING 300 FT; I SAW A HELI AT 500 FT DIRECTLY IN FRONT OF US (MAYBE 1/4 MI). I WAS NOT SURE EXACTLY WHAT TO DO AS THIS WAS MY FIRST TIME TO HWV. WE HAD NO MORE RWY IN FRONT OF US TO LAND; I DIDN'T WANT TO GO BELOW THE HELI; FEARING ITS VORTICES; BUT THAT WAS MY ONLY OPTION AT THE MOMENT. I THEN LOOKED R AND SAW NO OBSTACLES; MADE A STEEP TURN -- NOT MY FAVORITE THING TO DO LESS THAN 200 FT ABOVE THE TREES; BUT AT LEAST IT WOULD TAKE ME ON A COURSE BEHIND THE HELI AND NOT BACK INTO TFC THAT WAS ON THE L DOWNWIND. AND I DON'T THINK I ACTUALLY HAD TO TURN TOO FAR OFF COURSE BEFORE IT WAS CLR THE HELI WAS NO LONGER A FACTOR. I THEN MADE A RADIO CALL TO WARN THE OTHER ACFT IN THE PATTERN ABOUT THE HELI. THINKING BACK ON IT; I SHOULD HAVE MENTIONED THAT IT WAS TRANSITIONING TO THE N; TO WARN ANYONE IN THE L DOWNWIND; BUT I DIDN'T. ANYWAY; IT SEEMS CLR THAT THE HELI HEARD RWY 6 WAS IN USE AND FLEW AT 500 FT PARALLEL TO AND S OF THE RWY (A SAFE MOVE AS TFC WAS FLYING L TURNS AT 1000 FT). HOWEVER; IT MUST NOT HAVE BEEN MONITORING CTAF; AND DID NOT HEAR ABOUT THE CHANGE TO RWY 15; WHICH THEN PUT IT RIGHT OVER THE DEP END OF THE RWY. HOPE THIS IS HELPFUL.