AN MLG AIRCREW HAD AN NMAC WITH A HELI IN THE TFC PATTERN AT LAX.

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WHILE OPERATING AS FLT X; I WAS CONDUCTING A VISUAL APCH TO LAX RWY 24R USING THE ILS AS A BACKUP. AS WE NEARED THE APCH LIGHTS; WE NOTICED A HELI MOVING FROM R TO L AT OUR ALT. THIS WAS AFTER OUR 500 FT CALL FROM THE RADIO ALT. I COULD SEE THAT WE WOULD PASS UNDER HIM IF I CONTINUED MY DSCNT ON THE ILS; AND IN FACT PASSED DIRECTLY UNDER HIM AT APPROX 250 FT AGL OVER THE APCH LIGHTS. HIS APPROX ALT WAS 400 AGL PUTTING HIM ABOUT 150 ABOVE US. WE NOTIFIED TWR AS WE APCHED HIM AND WAS ASSURED THEY KNEW HE WAS THERE. AFTER LNDG; I CONTACTED THE TWR SUPVR ON DUTY AND WAS TOLD THAT THE HELI RTE FOR XING THE ARPT IS TO FOLLOW SEPULVEDA BOULEVARD AT 1500 FT. THIS HELI PLT HAD FOLLOWED THE CORRECT RTE AND HAD CHKED IN AT 2000 FT BUT WAS NOT EQUIPPED WITH ALT RPTING! THE TWR WAS LED TO BELIEVE HE WAS OVER 1500 FT HIGHER THAN HE ACTUALLY WAS. I DON'T KNOW HOW COMMON THIS IS AMONG HELI PLTS; OR WHY THEY ARE NOT ALSO REQUIRED TO HAVE MODE C TRANSPONDERS IN A TCA; BUT I'M WRITING THIS RPT IN HOPES YOU CAN 'GET THE WORD OUT' TO THESE OPERATORS ABOUT HOW DANGEROUS THIS CAN BE.