MULTIPLE RWY OP PARALLEL RWYS UNCOORDINATED UNAUTH PENETRATION OF AIRSPACE ACR X HAD LTSS FROM ACR Y ON APCH TO PARALLEL RWY. SYS ERROR.

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EVASIVE ACTION WAS TAKEN IN RESPONSE TO A TCASII RA ADVISORY WHILE BEING VECTORED ON A BASE LEG TO AN ILS AT LAX. ACR X WAS GIVEN A DSCNT TO 2500 FT AND GIVEN VECTORS TO THE ILS 24R IN LOS ANGELES. WE WERE GIVEN A HDG ONLY WITHOUT INSTRUCTIONS TO INTERCEPT THE LOC. THE HDG WAS 190 DEGS AND INTENDED BASE LEG. BOTH PLTS CALLED OUT GOING THROUGH THE LOC AND THE CTLR HAD NOT ISSUED INSTRUCTIONS TO INTERCEPT. ACR X WAS HEADED FOR THE TFC PERFORMING ILS'S FOR RWY 25L ON THE S SIDE OF THE ARPT. BOTH PLTS WERE AWARE OF THIS AND THE PNF COULD NOT GET A BREAK IN THE FREQ TO QUERY THE CTLR. WE GOT A TCASII ADVISORY TO DSND MORE RAPIDLY. AT THE SAME TIME AS THE TCASII ALERT; THE CTLR CAME ON THE FREQ AND SAID HE NEEDED AN IMMEDIATE DSCNT TO 2500 FT AND A TURN BACK TO HDG 280 DEGS TO INTERCEPT RWY 24R LOC. THE CTLR APOLOGIZED FOR FLYING US THROUGH THE LOC; AND THOUGH HE DID NOT ADMIT TO IT; I THINK HE FORGOT ABOUT US OR SIMPLY LOST AWARENESS OF OUR POS. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE RPTR WAS ASKED WHY THE CTLR WAS NOT CONTACTED PRIOR TO GOING THROUGH THE LOC SINCE THE FLC KNEW THEY WERE PROCEEDING INTO TFC ON THE PARALLEL LOC. THE RPTR STATED THE CAPT SAID THIS HAPPENED FREQUENTLY AT LAX. THE RPTR WAS ASKED IF MORE OF AN EFFORT WOULD HAVE BEEN MADE TO CONTACT THE CTLR IF THE ACFT HAD NOT BEEN TCASII EQUIPPED. THE RPTR STATED THE FLC SAW THE TFC ON TCASII AND WAITED UNTIL AN RA WAS RECEIVED. RPTR SAID THAT IF THEY HAD NOT HAD TCASII THEY WOULD HAVE TURNED IN ON THE LOC AND INFORMED THE CTLR. SUPPLEMENTAL INFORMATION FROM ACN 253617: AS THE ACFT ENTERED THE TOP OF THE CLOUD LAYER; THE APCH CTLR IN AN EXCITED VOICE SAID 'ACR Y; CANCEL YOUR APCH.' THIS WAS CONFUSING AS IT GAVE NO INSTRUCTION SUCH AS PULL UP TURN L; ETC. THE TCASII SOUNDED WARNINGS OF STOP DSCNT; CLB; AND MONITOR VERT SPD. THE APCH CTLR THEN SAID WE WERE CLRED TO DSND AND CONTINUE THE ILS APCH WHICH WE DID AND LANDED ON RWY 25L. WE OBTAINED THE TELEPHONE NUMBER FOR APCH CTL. WE WERE TOLD THAT AN ACR X ACFT MANEUVERING FOR RWY 24R HAD OVERSHOT THE COURSE.