ACR MLG PASSED ACR WDB ON FINAL WHILE MAINTAINING VISUAL SEPARATION; PROMPTING A COMPLAINT FROM WDB CAPT.

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WHILE MAKING AN INSTRUMENT APCH IN VISUAL CONDITIONS TO LAX; WE EXPERIENCED A SITUATION THAT I CONSIDERED POTENTIALLY UNSAFE. THE WX DURING THE APCH WAS RPTED AS CLR WITH 10 MI VIS. HOWEVER; WE WERE LNDG INTO THE SUN (APPROX XA45) AND THE VIS TOWARD THE ARPT WAS CONSIDERABLY LESS; ONLY ABOUT 5 MI. WE WERE INITIALLY ASSIGNED AND TRACKING THE 25L LOC AND APPROX 15 MI OUT. WE WERE GIVEN A NEW HDG TO INTERCEPT THE 24R LOC AND TRACK IT INBND. SHORTLY AFTER ESTABLISHING OUR TRACK ON THE 24R LOC; WE WERE INFORMED BY LAX APCH CTL THAT MLG Y WOULD OVERTAKE US FROM OUR RIGHT REAR AND BE LNDG ON 24R. WHEN WE INFORMED APCH THAT WE WERE ON THE LOC FOR 24R AT THAT TIME; WE WERE TOLD TO CONTINUE ON THE LOC UNTIL WE HAD THE RWY IN SIGHT AND THEN SIDE STEP TO 24L; AND THAT MLG Y WOULD MAINTAIN VISUAL SEP ON OUR FLT AND LAND ON 24R. ABOUT 10 MI OUT; WE LOOKED OUT THE RIGHT SIDE WINDOWS AND THERE WAS MLG Y AT WHAT APPEARED TO BE LESS THAN 500' LAT SEP; AT EXACTLY OUR ALT (WE WERE ON THE G/S); AND SLOWLY PASSING US. AS I WAS QUITE CONCERNED ABOUT THE CLOSE PROX OF MLG Y; I STARTED EASING TO THE LEFT AND ESTABLISHED THE LOC TRACK AT ONE DOT LEFT DEVIATION. I CONTINUED THIS ONE DOT TRACK UNTIL WE SIGHTED THE RWYS 24 L AND R; AT THE 5.2 ILS DME. AT THIS TIME; WE WERE LINED UP BTWN THE RWYS. WE THEN SHIFTED FURTHER LEFT TO LINE UP WITH 24L FOR OUR LNDG. ALL DURING THIS MANEUVER; MLG Y GRADUALLY PULLED AHEAD UNTIL IT REACHED A POS WHERE I FELT THE PLT WOULD HAVE BEEN UNABLE TO SEE US ANY LONGER AND AT THE SME TIME CONTINUED TO 'CROWD' US OFF THE LOC EVEN THOUGH WE DID NOT HAVE THE RWY IN SIGHT AT THAT TIME. THESE RWYS ARE ABOUT 700' APART (AS BEST AS I CAN MEASURE ON THE CHARTS) AND WHEN WE FINALLY SAW THE RWYS; WE WERE LINED UP EXACTLY BETWEEN THEM AND I SUSPECT THAT MLG Y WAS ON THE LOC WHICH WOULD MAKE THE HORIZ SEP APPROX 350'. THIS BORDERS ON VIOLATING FAR 91.65 (B) AND (C) DEPENDING ON THE DEFINITION OF 'FORMATION FLT.' AFTER LNDG; I SPOKE TO BOTH A LAX APCH CTL SUPVR AND THE CAPT OF MLG Y FLT BY PHONE. THE LAX APCH SUPVR WAS NOT AWARE OF EXACTLY WHAT HAD TRANSPIRED BUT WAS GOING TO SPEAK WITH THE CTLR INVOLVED. THE CAPT OF MLG Y STATED THAT WHEN WE STARTED MOVING TO THE LEFT; HE THOUGHT WE HAD THE RWY IN SIGHT AND SO MOVED TO HIS LEFT TO LINE UP ON THE RWY CENTERLINE. HE ALSO STATED THAT HE HAD US IN SIGHT BEHIND HIM DURING THIS TIME BUT I PERSONALLY DO NOT BELIEVE IT WAS POSSIBLE AT ALL TIMES DURING THE APCH. OBVIOUSLY; BOTH FLTS LANDED SAFELY. THE PROB IS WITH THE POTENTIAL FOR A MIDAIR COLLISION. ALL THAT WOULD BE NEEDED IS FOR SOME DISTR TO MOMENTARILY DIVERT THE CREW'S ATTN; SUCH AS COMS DIFFICULTIES OR MECHANICAL PROBS; AND SUDDENLY THE 350' BECOMES ZERO. I FOUND IT NECESSARY TO ASSIGN 1 MEMBER OF OUR CREW TO KEEP MLG Y IN SIGHT AT ALL TIMES AND TO MAKE A PAX ANNOUNCEMENT TO RELIEVE THE PAX' ANXIETIES; BOTH OF WHICH INTERRUPTED OUR NORMAL CREW DUTIES DURING THIS PORTION OF THE APCH. IF THIS IS IN FACT A 'NORMAL' ATC PROC; I BELIEVE IT SHOULD BE STOPPED. APCHES ON CLOSE; PARALLEL RWYS SHOULD BE STAGGERED TO PROVIDE AT LEAST 1 MI OF LONGITUDINAL SEP. WING TIP TO WING TIP IS NOT SAFE!