MULTIPLE APCH AND RWY CHANGES PROVES DIFFICULT FOR 'GLASS COCKPIT' FMS ACR PLT.

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THIS IS A RPT FILED MORE AS A COMPLAINT ABOUT LAX (SOCAL) APCH PROCS. INCIDENTS LIKE OURS ARE NOT UNCOMMON AND I'M SURE MANY SIMILAR COMPLAINTS AND RPTS HAVE BEEN FILED OVER THE YRS. THIS INVOLVES THE PROB OF MULTIPLE CHANGES ON THE ARR AND APCH INTO LAX AND WHEN FLYING THE B757 WITH A SLOW FMC; IT BECOMES; AT TIMES; UNSAFE WITH A LOT OF HEADS DOWN WORK TO PROGRAM THE FMS; CHANGE FREQS; BRIEF NEW PROCS; ETC. WE HAD BEGUN OUR DSCNT AND WERE CLRED TO FLY TO CIVET; CIVET 4 STAR TO RWY 25L. THE FOLLOWING CHANGES THEN OCCURRED AS WE CONTINUED OUR DSCNT; COUPLED WITH FREQ CHANGES; ALT RESTRS AND SOME SPD RESTRS. SHORTLY AFTER THE INITIAL CLRNC WE WERE RECLRED THE REDEYE 2; RWY 6L. AS WE CONTINUED AND REPROGRAMMED AND REBRIEFED WE WERE THEN CLRED BACK TO THE CIVET 4 RWY 25L; ONCE AGAIN REPROGRAM; REBRIEF. SOON AGAIN YET ANOTHER CHANGE TO THE MITTS 1; RWY 24R. THIS WAS FOLLOWED SOON BY DIRECT SMO VOR; RWY 7L; WHICH THEN CHANGED TO RWY 6R AND THEN UNBELIEVABLY CHANGED AGAIN TO RWY 6L. IF YOU ARE AWARE OF THE DIFFICULTY IN REPROGRAMMING THE B757 FMC; CHANGING FREQS; REBRIEFING THE APCH AND RWY; MAKING ALT RESTRS; SPD RESTRS; AND ALSO RADIO CALLS; AS WELL AS THE NECESSARY CHKLISTS; YOU'LL GET THE PICTURE OF WHAT A MESS THIS WAS. PLEASE DON'T FOLLOW THIS UP WITH A LETTER OR BULLETIN ABOUT ANTICIPATING THESE CHANGES FOR WE WERE PREPARED AND WE WERE SUCCESSFUL IN COMPLETING EACH CHANGE. HOWEVER; WE WERE TASK SATURATED. HAD THERE BEEN WX OR A POSSIBLE ACFT PROB INVOLVING COM PROCS AND/OR OTHER CONSIDERATIONS; A VERY UNSAFE SIT WOULD HAVE EXISTED.