NMAC IN TFC PATTERN. MULTIPLE HELIS LNDG IN PATTERN WITH FIXED WING ACFT INTRUDING CAUSED RPTR TO EVADE. FIXED WING PLT CLAIMED TO NOT KNOW THE ARPT ALSO HAD HELIS LNDG.

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ENTER THE ARPT FROM THE N (RPTED MY POS 5 MI N; MID FIELD XING FOR A L DOWNWIND LNDG RWY 24 TXWY ZZZ) ALT 4000 FT DSNDING (RPTED: XING MID FIELD FOR A L DOWNWIND LNDG RWY 24 TXWY AT ZZZ) ALT 3000 FT; 2 OTHER HELIS WERE ALSO AT TXWY ZZZ; 1 DOING AUTOS S-SIDE (HELI TFC PATTERN) 1 APCH FROM THE NE TO LAND. A HELI CROSSED OVER INTO THE S (HELI TFC PATTERN) L DSNDING TURN HIGH AND TO THE R REAR OF HELI WORKING THE TFC PATTERN; ROLLED LEVEL 120- 140 KTS INDICATED; NOTED A NAVION DIRECTLY AHEAD AT THE SAME ALT COMING THE OPPOSITE DIRECTION. HE FILLED MY WINDSHIELD (WINGTIP TO WINGTIP) VERY; VERY CLOSE (LESS THAN 1/4 MI). I ROLLED HARD L PULLING COLLECTIVE AT THE SAME TIME. WE MISSED BY 100 FT VERT AND ABOUT 50-100 FT HORIZ. I CALLED ON UNICOM THAT A FIXED WING WAS COMING THROUGH THE HELI TFC PATTERN THE OPPOSITE DIRECTION OF THE FLOW. THE NAVION NOW MADE HIS FIRST RADIO XMISSION ABOUT 'ENTRY UPWIND AT TXWY ZZZ.' DURING MY GND ENCOUNTER WITH THE PLT; HE STATED THAT 'HE'D BEEN FLYING FOR 40 YRS AND NEVER HAD AN ACCIDENT' AND THAT 'HE WAS NOT AWARE THAT TXWY ZZZ HAD BOTH HELI AND FIXED WING TFC PATTERNS.' HE ALSO STATED THAT HE WAS WATCHING ANOTHER ACFT (HELI) LANDED ON THE TXWY NEXT TO THE ACTIVE RWY (240 DEGS). MY ACFT: EMS HELI. HIS ACFT: NAVION; LIGHT TAN COLOR WITH RED/DARK BURNT RED TRIM.