B747 CREW INBOUND TO ONT COMPLETING A 360 DEG TURN ON FINAL BECAUSE OF ALT TOOK EVASIVE ACTION AT 200 FT TO AVOID A HELI XING THE APCH END OF THE RWY.

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WE WERE ON THE ZIGGY 3 ARR AT ONT; CLRED DOWN TO 4000 FT TO INTERCEPT RWY 26L LOC AND CLRED FOR THE APCH; WENT THROUGH GS DSNDING TO 4000 FT; ON LOC DSNDED TO 2800 FT INSIDE PETIS. THIS WAS A TYPICAL SLAM DUNK APCH AT ONT TRYING TO SLOW DOWN AND GO DOWN AT THE SAME TIME. VISIBILITY WAS LOW DUE TO FIRES ON THE HILLS E OF ONT AND THE USUAL SMOG; HAZE IN THE LOS ANGELES BASIN. VISIBILITY WAS AT MOST 4 MI. THE GS CAME OFF OF TOP OF SCALE; IT SHOWED US CONSTANTLY 2 DOTS LOW. FINALLY WE SAW RWY; WE WERE TOO HIGH TO MAKE LNDG. WE ASKED 360 DEG TURN/DSCNT FROM ONT TWR; WE WERE IN FINAL LNDG CONFIGN; FLAPS 25 DEGS GEAR DOWN; AND WEIGHED 545000 LBS (MAX LNDG WT); WITH THE 360 DEG TURN AND DSCNT COMPLETED AND ESTABLISHED ON THE VISUAL APCH TO RWY 26L. AT APPROX 200 FT AGL; WE NOTICED A HELI HAD TAKEN OFF AND WAS XING OUR FLT PATH L TO R AT OUR ALT AND HDG TOWARDS US AT A 45 DEG ANGLE. WE EXECUTED A MAX BANK/PWR/CLBING TURN TO AVOID THE POTENTIAL MIDAIR. (A NORMAL GAR DIDN'T SEEM APPROPRIATE AS OUR WAKE AND THRUST WASH COULD HAVE POTENTIALLY DOWNED THE HELI HAD WE FLOWN RIGHT OVER HIM.) WE RE-ESTABLISHED ON FINAL FOR RWY 26L AND LANDED. THE TWR CTLR APOLOGIZED FOR THE CONFLICT. HE FELT IT WAS HIS DOING. HE ALSO TOLD US THERE HAD BEEN SEVERAL GARS RECENTLY BUT NOBODY HAD MENTIONED THE GS ERROR. A B747 SHOULD NOT HAVE TO MAKE MAX CLBS AND BANK TURNS AT 200 FT AGL UNLESS THEY ARE IN AN AIRSHOW. NONE WAS SCHEDULED FOR THAT DAY; WE CHKED THE NOTAMS AGAIN WHEN WE LANDED.