SMA HAS NMAC WITH HELI OVER THE HUDSON RIVER.

Narrative

THE OTHER ACFT INVOLVED WAS A BLACK (OR DARK COLOR) HELI; APPARENTLY TURBINE PWRED. I WAS NBOUND IN THE HUDSON RIVER VFR CORRIDOR AT 800 MSL (HAD SET ALTIMETER TO KENNEDY SETTING) NEAR THE E BANK; IN THE AREA TYPICALLY USED FOR NBOUND FLT TO AVOID CONFLICTS. I HAD APPROX 1 MIN BEFORE ANNOUNCED MY POS AND INTENTIONS ON THE SELF- ANNOUNCE FREQ (123.05) WHEN I WAS OVER THE INTREPID; A COMMON RPTING POINT. AT APPROX THE SAME TIME; OR JUST BEFORE; AN ACFT ANNOUNCED IT WAS PROCEEDING WBOUND OVER MIDTOWN/CENTRAL PARK. AS I APCHED THE MIDTOWN AREA; I SAW THE HELI PROCEEDING WBOUND. IT APPEARED THAT IT WOULD CROSS MY PATH E-W WELL CLR BEFORE I APCHED ITS HUDSON RIVER XING POINT. HOWEVER; ON REACHING THE RIVER; THE HELI SLOWED; APPEARED TO HOVER/TURN AT 180 DEGS FACING E. SUDDENLY; AS I BEGAN TO REACT BY SLOWING; IT ABRUPTLY TURNED S; SE AND PROCEEDED TOWARD ME AT APPROX MY ALT AT A HIGH SPD. IT APCHED FROM MY 1-2 O'CLOCK POS. I BEGAN EVASIVE ACTION BY SLOWING; DIVING AND BANKING/TURNING TO MY L. I LEVELED AT 650 FT MSL. THE HELI ALSO TURNED L TO AVOID COLLISION AND APPEARED TO ASCEND SLIGHTLY. CERTAIN CTLS ON ABRUPT HELI MOVEMENTS IN THIS VFR CORRIDOR MAY HELP AVOID SIMILAR INCIDENTS IN THE FUTURE. A CONTRIBUTING FACTOR MAY HAVE BEEN THE FACT THAT THE SELF- ANNOUNCE FREQ IS OFTEN CLOGGED/DOMINATED BY FBO GND ACTIVITIES; APPARENTLY AT A HELIPORT(S) IN SOUTH MANHATTAN. THIS IMPEDES ACFT ATTEMPTING TO MAKE POS AND INTENTION RPTS. IT IS CONCEIVABLE; ALTHOUGH I DON'T THINK THIS ACTUALLY OCCURRED; THAT THE HELI RPTED HIS INTENTION TO TURN SOUTHWARD; AND HIS XMISSION WAS STEPPED ON BY THE FBO. THE FBO(S) SHOULD OPERATE ON A DIFFERENT FREQ FOR SAFETY REASONS.