ACR LGT ACFT ON APCH HAD NMAC WITH AN LTT ALSO ON APCH TO ADJACENT PARALLEL RWY. INTRUDER ACFT OVERSHOT CTRLINE AND RPTR WAS LIMITED IN MANEUVERING L DUE TO HELI TFC.

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ESTABLISHED ON LOC AND GS FOR RWY 25L AT 1500 FT AGL; APPROX 10 NM E OF LAX. AFTER CLRED FOR APCH; APCH CTL ADVISED US THAT A BRASILIA ACFT WAS JOINING THE LOC FOR RWY 25R AND THAT THE BRASILIA WAS AT OUR R SIDE AND ABOVE IN A TURN AND DSNDING. AS I TURNED AND LOOKED I SAW THE BRASILIA DSNDING TOWARDS US AT OUR 3 O'CLOCK POS; DIRECTLY ABEAM. THE BRASILIA STARTED A TURN TO THE R TO INTERCEPT THE LOC BUT OVERSHOT FINAL AND CONTINUED TO DSND AND OVERSHOOT INTO OUR POS. THE BRASILIA WAS IN A DSNDING TURN WITH HIS BELLY TOWARD US. IN MY OPINION HE COULD NOT SEE US SINCE I COULD NOT SEE HIS COCKPIT WINDOWS. HE WAS APPROX 200-300 FT AWAY. I INFORMED THE CAPT THAT THE BRASILIA WAS DSNDING INTO US AND WE WOULD NEED TO DEV L OF COURSE. I RADIOED APCH CTL OF THE SIT AND OUR NEED TO DEV L OF COURSE TO AVOID THE BRASILIA. DURING THIS TIME; APCH HAS ALSO ADVISED US OF A HELI BELOW AND OFF OUR L. WE DID NOT HAVE THE HELI IN SIGHT. OUR TCASII WAS ACTIVE AT THIS POINT COMMANDING A DSCNT AT 2000 FPM TO AVOID THE BRASILIA. (WE DEVIATED SLIGHTLY L AND DOWN TO AVOID A COLLISION.) THE BRASILIA LEVELED OFF AND BEGAN HIS APCH DIRECTLY OFF OUR WINGTIP AND SLIGHTLY BEHIND. THE BRASILIA MAINTAINED THIS POS THROUGHOUT THE APCH TO LNDG. WE CONSIDERED A GAR DURING THIS EVENT BUT WERE CONCERNED ABOUT OUR WAKE TURB AND THE BRASILIA AND HELI. WE (AND THE BRASILIA) LANDED WITHOUT FURTHER INCIDENT. IN HINDSIGHT; I QUESTION THE TIMING OF THE APCH CTLR WHO PUT THE BRASILIA ON A BASE HDG AND AN INTERCEPT WITH ANOTHER ACFT ON FINAL (US) WHEN THE ROLLOUT AND APCH WOULD BE DIRECTLY ABEAM AND IN POSSIBLE CONFLICT. ESPECIALLY WITH SUCH CLOSE RWYS (RWY 25L/R) A STAGGERED APCH WOULD SEEM WISER. THE BRASILIA ALSO APPEARED TO MAKE NO EFFORT AT ESTABLISHING ANY LATERAL SEPARATION.