NMAC BTWN AN SMA TWIN AND A MIL HELI IN PROX OF CLASS D AIRSPACE.

Narrative

OPERATING AN OH58 HELI; SUPPORTING LCL LAW ENFORCEMENT IN COUNTER NARCOTICS OPS; USING THE DOD-FAA APPROVED CALL SIGN. CREW WAS MAINTAINING SURVEILLANCE ON AN AREA APPROX 6 NM SE OF NEW ORLEANS LAKEFRONT ARPT (NEW). OBSERVATION PATTERN BEING USED HAD THE ACFT ENTERING AND EXITING THE CLASS D AIRSPACE REPEATEDLY. AIR CREW HAD ESTABLISHED 2- WAY COM WITH TWR PRIOR TO DEPARTING NEW AND STATED INTENTIONS TO OPERATE IN THIS AREA. HAVING JUST COMPLETED SUPPORT OPS; AIR CREW WAS BEGINNING TO REPOSITION E OF SEARCH AREA. ACFT WAS POSITIONED IN THE MIDDLE ON THE N LEG OF DIAGRAM. THE PIC IN THE L SEAT OBSERVED A LIGHT TWIN ENG FIXED WING AIRPLANE AT 12 O'CLOCK AND APPROX 500 FT HORIZ AND JUST ABOVE HELI FLT PATH. THE PIC TOOK CTL OF THE ACFT AND INITIATED AN IMMEDIATE DSCNT. THE HELI DSNDED; AVOIDING THE FIXED WING. THE RAPID RATE OF DSCNT CAUSED THE MAIN ROTOR TO OVERSPD; OUT OF LIMITS. THE PIC INITIATED AN IMMEDIATE PRECAUTIONARY LNDG TO A MIL HELIPORT (6LA0). THE INITIAL ALT OF THE HELI WAS APPROX 1500 FT MSL. THE CONDITIONS WERE VFR WITH HAZE. THE AIRPLANE HAD ITS LNDG LIGHTS ON. THE HELI HAD ANTI- COLLISION LIGHTS AND POS LIGHTS ON. THE AIRPLANE WAS HEADING W INTO THE SUN. I BELIEVE BOTH ACFT WERE IN A POS THEY WERE ALLOWED TO BE IN AT THAT TIME. I EXPECTED TFC INFO FROM TWR DUE TO BEING EITHER JUST INSIDE OR OUTSIDE THE CLASS D. IF THE TWR ALLOWED THE FIXED WING TO BE ON A BASE TO RWY 36 AT NEW; TFC RPTS SHOULD HAVE BEEN MADE REGARDING OUR HELI. HOWEVER; THE RESPONSIBILITY OF MAINTAINING SEPARATION LIES EQUALLY UPON THE PIC OF EACH ACFT. THE PROB OF BOTH PIC'S FAILURE TO OBSERVE THE OTHER; COMPOUNDED BY THE HAZE; SUN; AND POSSIBLE EXPECTATIONS OF ATC BEYOND THE REQUIREMENTS; LED TO THE EVENT.