AN ACR C402 FLC RPTS THAT THEY HAD AN NMAC WITH A HELI DURING LNDG. AS THE C402 STARTED ITS FLARE THE HELI STARTED AN AUTOROTATION TOWARD A GRASS STRIP NEAR TO THEIR RWY CAUSING THE RPTR TO ROLL OUT ALONG THE EDGE OF THE RWY TO AVOID CONTACT.

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I ENTERED THE STANDARD TFC PATTERN IN HANA AT 800 FT. WE MADE MULTI-COM CALLS; STARTING 20 MI OUT ON 122.9. WE SAW A HELI WHICH SEEMED TO BE ABOVE THE TFC PATTERN AND NEVER MADE ANY CALLS. HE DID NOT SEEM TO LAND. WHEN WE TURNED FINAL; HE WAS IN FRONT OF US AND IN LINE WITH THE RWY; AND STILL ON 1000 FT. WE WERE 500 FT. BTWN THE CHKLISTS; CALLOUTS; THE FO CONTINUED TO CHALLENGE THE ROTORCRAFT ON THE RADIO TO MAKE SURE HE WAS NOT LNDG; BUT THERE WAS NO RESPONSE. AS I INITIATED THE FLARE; THE HELI INITIATED A 'AUTO ROTATION.' FROM THIS POINT ON; I HAD TO LAND BECAUSE I WAS NEVER SURE WHAT HIS NEXT MOVE WAS GOING TO BE. THE HELI WAS COMING AT THE NARROW GRASS STRIP NEXT TO THE RWY; AND ENDED UP 500 FT IN FRONT OF THE PLANE RAPIDLY DECELERATING. THE DISTR MADE OUR TOUCHDOWN HARDER THAN USUAL AND AS WE SLOWED DOWN WITH MAX BRAKING; THE HELI MOVED SLIGHTLY R TOWARDS OUR CTRLINE. WE HAD TO GO ALL THE WAY TO THE R OF THIS 100 FT WIDE STRIP IN ANTICIPATION OF HIS MOVES. AS WE PASSED HIM AT 70 FT; WE FINALLY HAD EYE CONTACT. WHEN WE TAXIED OFF THE RWY; THE HELI STARTED MAKING TFC CALLS AND CONTINUED HIS PRACTICE. I THINK I SHOULD HAVE REGARDED THE HELI AS LNDG TFC; IF ONLY FOR THE FACT THAT HE WAS WITHIN 2 MI OF THE RWY. IN HAWAII; RADIO COM _ ESPECIALLY ON 121.9 _ HAS BECOME UNWRITTEN; MANDATORY; BUT I WAS COUNTING ON IT TOO MUCH THAT DAY.