NMAC ON LAX ILS COURSE.

Narrative

WHILE INBOUND FROM ARNES; WE WERE ASSIGNED A SPD OF 210 KIAS. WE ASKED TO SLOW DOWN AND WERE GIVEN 180 KIAS OR GREATER TO LIMMA. WE HAD BEEN TOLD TO EXPECT RWY 25L AND SIDE-STEP TO RWY 25R. I DON'T RECALL EXACTLY WHERE WE WERE CLRED FOR THE APCH/SIDE-STEP; BUT IT WAS WELL PRIOR TO LIMMA. WE LOWERED THE GEAR; EXTENDED FLAPS AND GOT A TCASII RA RIGHT AWAY. I HAD JUST STARTED THE SIDE-STEP WHEN I HEARD THE TCASII SAY 'DSND; DSND' AND I INCREASED THE DSCNT RATE. I LINED UP ON RWY 25R AND SHORTLY THEREAFTER TCASII SAID 'CLB; CLB.' DURING THE FIRST RA THERE WAS A RED TARGET BOX SLIGHTLY L OF THE AIRPLANE SYMBOL ON THE EHSI. DURING THE SECOND RA; THE RED TARGET BOX WAS SLIGHTLY L AND SLIGHTLY AHEAD OF THE AIRPLANE SYMBOL. WE EXECUTED A GAR AND ADVISED ATC IT WAS DUE TO A TCASII ALERT. I NEVER SAW THE OTHER AIRPLANE. WE NEVER CALLED VISUAL ON THE FIELD; BUT WERE CLRED FOR A VISUAL MANEUVER. I HAVE A HUNCH THE OTHER AIRPLANE WAS BEING VECTORED BY ANOTHER CTLR. IN ANY EVENT; CTLR OVERLOAD WAS OBVIOUS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE B-767 AND B-757 FOR A MAJOR UNITED STATES ACR. THE RPTR DID NOT SEE THE INTRUDER ACFT BUT THE CAPT AND A JUMPSEAT RIDER DID. THEY ESTIMATED THE MISS TO BE 200-300 FT. RPTR BELIEVES THAT THE INTRUDER WAS GOING TO THE N RWYS AS THE RPTR NEVER HEARD ANY XMISSIONS TO THE INTRUDER. HE LEARNED FROM THE NEWSPAPER THAT 2 B-767S HAD TO GAR THAT EVENING AT LAX BECAUSE OF TCASII ALERTS. THE RPTR BELIEVES THAT THE FIRST ALERT WAS REAL BUT; AS NO ONE SAW AN ACFT; THE SECOND ALERT MAY HAVE BEEN FALSE. IT COULD HAVE BEEN THE SAME INTRUDER NOW AHEAD AND BELOW THE RPTR. SUPPLEMENTAL INFO FROM ACN 296719: I LOOKED OUT L REAR COCKPIT WINDOW AND OBSERVED ANOTHER AIR LINER (THINK IT WAS A 727) ABOUT 200 FT ABOVE AND CONVERGING WITH OUR COURSE AND ALT. AT THE TIME OF THE SECOND TCASII ALERT; I COULD NOT SEE THE 727; NOR ANY OTHER TFC. SOMETHING WENT VERY WRONG IN THE ATC CTL SYS. NO OTHER ACFT SHOULD HAVE BEEN NEAR OUR POS. WE WERE NOT ADVISED OF ANY OTHER TFC AND CERTAINLY DIDN'T EXPECT ANY.