C182 PLT HAD AN NMAC WITH A HELI OVER PTW.

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CHAIN OF EVENTS: CTAF RADIO CALLS. 'POTTSTOWN LIMERICK TFC SKYLANE X 3 MI S OF GOOGL PRACTICE LOC RWY 28 POTTSTOWN LIMERICK.' 'POTTSTOWN LIMERICK SKYLANE X HOLDING OVER GOOGL 4.7 MI E OF RWY 28 POTTSTOWN LIMERICK.' 'POTTSTOWN LIMERICK SKYLANE X INBOUND ON PRACTICE LOC RWY 28 4.7 MI FROM RWY 28 POTTSTOWN LIMERICK SKYLANE X. OTHER CTAF RADIO TFC: MOONEY RPTS 3 MI N ENTERING R DOWNWIND; CHEROKEE RPTS 3 MI TO THE W ENTERING DOWNWIND RWY 28; DIAMOND IN THE PATTERN; HELI 5 MI NW 1400 FT. 'POTTSTOWN LIMERICK SKYLANE X 3 MI FINAL RWY 28 WILL BREAK OFF APCH AND PROCEED TO THE S.' CTAF RADIO TFC MONITORED AND MOONEY; CHEROKEE ON BASE WITH DIAMOND ON DOWNWIND. NO OTHER CALLS FROM HELI. 'POTTSTOWN LIMERICK SKYLANE X 3 MI S 1200 FT WILL ENTER XWIND FOR DOWNWIND R TFC RWY 28 POTTSTOWN LIMERICK.' MOONEY AND CHEROKEE LANDED AND DIAMOND ON FINAL FOR RWY 28. NO CALLS FROM HELI. POTTSTOWN LIMERICK SKYLANE X XWIND RWY 28 ENTERING DOWNWIND RWY 28 POTTSTOWN LIMERICK.' POTTSTOWN LIMERICK SKYLANE X DOWNWIND RWY 28 POTTSTOWN LIMERICK. AT THIS POINT A BLUE AND WHITE SiKORSKY HELI APPEARED 8 O'CLOCK POS LEVEL (SKYLANE AT PATTERN ALT 1200 FT) AND PULLED UP OVER AND NEARLY HITTING SKYLANE (UNDERBODY OF HELI NOTICED IN OVERHEAD GLASS PANELS) WITH VERT AND HORIZ SEPARATION ESTIMATED AT 100 FT. SOME WAKE TURB DUE TO ROTOR DOWNWASH. SKYLANE CONTINUES ON DOWNWIND. HELI LANDS STRAIGHT AHEAD ON RAMP. 'HELI THIS IS THE SKYLANE ON DOWNWIND DIDN'T YOU SEE ME.' HELI: '(SIC) I HAD YOU IN SIGHT? ' ANOTHER RADIO CALL (NOT SURE WHO): 'HE CAN (EXPLETIVE DELETED) TALK.' 'POTTSTOWN LIMERICK SKYLANE X R BASE RWY 28.' 'POTTSTOWN LIMERICK SKYLANE FINAL RWY 28.' CONTRIBUTING FACTORS: 6 ACFT APCHING AN UNCTLED ARPT. HELI FAILED TO MAKE REQUIRED RADIO CALLS AND FLY STANDARD TFC PATTERN. HUMAN PERFORMANCE CONSIDERATIONS: SKYLANE X AFTER NOTICING THAT THERE WERE NO CTAF RADIO CALLS FROM HELI OTHER THAN 'HELI 5 MI NW 1400 FT' SHOULD HAVE ASKED FOR POS OF HELI. HELI SHOULD RPT POS ON CTAF AND FLY STANDARD TFC PATTERN.