FLC OF A B757 DSND IN RESPONSE TO A TCASII RA. ATC ADVISED OF A B737 AS CAUSING THE TCASII RA; WHO WAS JUST BEHIND THEM AND ON A VISUAL APCH TO THE OTHER PARALLEL RWY THAN THAT WHICH THEY WERE ASSIGNED. THE RPTING CAPT COMPLAINED THAT ACFT SHOULD NOT BE ALLOWED TO BECOME TOO CLOSE UNLESS IN FORMATION FLT.

Narrative

RECEIVING A TCASII RA; REACTING TO ITS COMMAND; AND THEN SEEING THE B737 300 FT ABOVE AND SLIGHTLY BEHIND YOU IS AN EXPERIENCE ONE WOULD HOPE NEVER HAPPENS. AN EVENT LIKE THIS OCCURRING WHILE UNDER TERMINAL AREA RADAR CTL; IN CLR SKIES; SHOULD NEVER HAPPEN. MY FLT WAS FLYING ON A LONG EXTENDED STRAIGHT-IN ILS APCH TO RWY 25L. ATC ADVISED US TO LOOK FOR A B747 IN OUR 1-2 O'CLOCK POS MANEUVERING FOR ONE OF THE 'N COMPLEX' RWYS 24L/R. AFTER THE CTLR'S SECOND INQUIRY IF WE SAW THE B747; I ACKNOWLEDGED THE ACFT IN SIGHT. ABOUT A HALF MIN LATER; WE RECEIVED AND COMPLIED WITH A TCASII DSND RA. UPON OUR NOTIFYING THE CTLR ABOUT OUR RA; HE RESPONDED THE CONFLICTING TARGET WAS A B737; BEHIND US. HE STATED THE PLTS HAVE US VISUALLY IN SIGHT AND WERE FLYING A VISUAL APCH TO RWY 25R (500-700 FT LATERAL OFFSET). THE CTLR CLAIMED HE PREVIOUSLY ADVISED US OF THIS B737 ACFT; BUT WE NEVER HEARD OR ACKNOWLEDGED THE ADVISORY. THE SIT STARTLED ME. MY CONCENTRATION BECAME FOCUSED ON THE OTHER PLANE'S PROX. THE OTHER PLANE FLEW ABOVE US; BELOW US; BEHIND AND AHEAD OF US UNTIL LNDG. I HAD DIFFICULTY MAINTAINING ATTN TO MY ACFT'S PERFORMANCE DURING THE CRITICAL STAGES OF SHORT APCH AND LNDG. I HAVE EXPERIENCED MANY SIDE-BY-SIDE; WINGTIP-TO-WINGTIP APCHS TO CLOSELY SPACED PARALLEL RWYS UNDER THE CONCEPT OF 'VISUAL APCH.' NONE OF THESE WERE VERY COMFORTABLE TO FLY. SEVERAL TIMES; I NEVER SAW THE OTHER PLANE DUE TO IT BEING SLIGHTLY BEHIND MY VIEWING CAPABILITY. MOST OF THE PLT'S EFFORT IS ON AVOIDING A COLLISION; WHEN WE SHOULD BE CONCENTRATING ON FLYING A SAFE; STABILIZED APCH TO LNDG. THE SEPARATION OF PARALLEL RWYS AT LAX; SFO; AND SNA ARPTS IS LESS THAN 700 FT. INFLT MANEUVERING CAN BRING ACFT SEPARATION MUCH CLOSER. WHEN WILL THE MINOR SLIP IN JUDGEMENT OCCUR; OR THE UNEXPECTED TURB ARISE; OR THE MECHANICAL MISHAP HAPPEN TO CAUSE THE UNTHINKABLE COLLISION AND LOSS OF LIFE? FLYING DANGEROUSLY CLOSE TO ANOTHER ACFT IS NOT CONDONED AS NORMAL OPERATING PROCS. DO WE NOT HAVE SEPARATION STANDARDS THAT TRIGGER A NEAR MISS RPT WHEN NOT MET? IF AN AIR TFC CTLR TELLS ONE PLT TO FOLLOW ANOTHER PLANE VISUALLY; DOES THIS MEAN THE SEPARATION STANDARDS DO NOT APPLY? WHAT ASSURANCE DOES THE LEADING PLT HAVE THAT THE FOLLOWING GUY WILL NOT COLLIDE INTO HIM BY MISTAKE? AFTER ALL; I HAVE AT TIMES SEEN THE 'WRONG' PLANE I WAS LOOKING FOR.