C182 PLT AND TV NEWS HELI HAD NMAC.

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I WOULD LIKE TO RPT A NEAR MISS THAT OCCURRED AT UMP ON SEP/XA/98 AT APPROX AB00. MY ACFT IS A CESSNA 182S. THE OTHER ACFT WAS A HELI WITH XXX PRINTED IN LARGE LETTERS ON SIDE. I WAS PRACTICING LNDGS AND STAYING IN THE TFC PATTERN WHEN I WAS NEARLY STRUCK BY THE HELI. THE NEAR MISS OCCURRED ON THE DOWNWIND LEG OF THE TFC PATTERN WHILE I WAS ENRTE FOR LNDG ON RWY 33. I HAD JUST LOWERED THE FIRST NOTCH OF FLAPS AND WAS ABEAM OF THE NUMBERS ON RWY 33 WHEN I SAW A HELI COMING UP FROM UNDER THE L SIDE OF MY ACFT. THE HELI WAS BANKED 45-90 DEGS TURNING AWAY FROM MY ACFT AND RISING AT A HIGH RATE OF SPD. I IMMEDIATELY AND ABRUPTLY TURNED TO THE R AT A BANK ANGLE THAT EXCEEDED 60 DEGS. WE MISSED BY AN ESTIMATED 50 FT! THE HELI CONTINUED THE EXTREME BANK ANGLE TURNING TO THE L THEN AT THE SAME ALT THAT I WAS FLYING -- 1600 FT INDICATED ALT. AS I REGAINED CTL OF THE ACFT; THE HELI ANNOUNCED THAT HE HAD TURNED TO AVOID TFC. I ANNOUNCED THAT I WAS CONTINUING IN THE DOWNWIND LEG OF THE FLT PATTERN FOR LNDG ON RWY 33. SPD OF BOTH ACFT WAS APPROX 100 KTS. ALT OF NEAR MISS WAS 1600 FT INDICATED ALT (PATTERN ALT). MY ACFT HAD LNDG LIGHTS AND STROBE LIGHTS OPERATING. MY ACFT HAD XPONDER TUNED TO 1200 AND IN ALT POS SQUAWKING. RADIO COM ON FREQ 123.00; UNICOM AND CTAF; BEFORE AND AFTER THE NEAR MISS WERE AS FOLLOWS: 1) METRO TFC SKYLANE YYY TAKING ACTIVE RWY 33; WILL BE STAYING IN PATTERN; ANY TFC PLEASE ADVISE; METRO. 2) METRO TFC SKYLANE YYY DEPARTING RWY 33; WILL BE STAYING IN PATTERN; METRO. 3) METRO TFC SKYLANE YYY TURNING XWIND RWY 33; METRO. 4) METRO TFC SKYLANE YYY TURNING DOWNWIND RWY 33; METRO. 5) THE HELI ANNOUNCED THAT HE WAS TAKING OFF. NEAR MISS OCCURRED: 6) THE HELI ANNOUNCED THAT HE HAD TURNED TO AVOID TFC. 7) METRO TFC; SKYLANE YYY CONTINUING DOWNWIND LEG; RWY 33; METRO. WX CONDITIONS AT TIME OF NEAR MISS: 3-5 MI VISIBILITY AND BROKEN CLOUDS AT 2500 FT CEILING.