B757 PIC RPT ON A POTENTIAL CONFLICT WHILE ON THE ILS APCH TO RWY 25L AT LAX. AN ACR COMMUTER OVERSHOT THE EXTENDED LINE OF RWY 25R AND CREATED A TRYING EXPERIENCE FOR HIM. PIC DEALT WITH THE DECISION MAKING PROCESS FOR AVOIDANCE AND THE PROBS THAT INFLUENCED THAT PROCESS.

Narrative

FLT BOS-LAX. WHILE ON FINAL APCH TO RWY 25L THE APCH CTLR ADVISED US OF A BRASILIA ON AN INTERCEPT HEADING FOR RWY 25R AT OUR 2-3 O'CLOCK POS. THE FO FINALLY SPOTTED THE ACFT AND TO HIS SHOCK; ADVISED ME THAT IT LOOKED AS IF HE WAS GOING TO OVERSHOOT HIS RWY 25R CTRLINE. THE FO KEPT AN EYE ON HIM AND ADVISED ME TO ALTER OUR TRACK L. THE TWR CTLR THEN ADVISED ME OF HELI TFC TO THE L ALSO. NOT KNOWING THE EXACT POS OF THE BRASILIA; IT MADE A CHOICE TO GAR DIFFICULT. I MOVED SLIGHTLY L UPON ADVICE OF THE FO; ALSO INCREASING OUR SPD TO PUT DISTANCE BTWN BOTH ACFT. THE BRASILIA KEPT PACE; THEN WE RECEIVED AN RA TO DSND. MY CONCERN BESIDES THE HELI WAS; IF A GAR WAS INITIATED; WOULD OUR WAKE TURB (B757) PLACE THE BRASILIA IN JEOPARDY? IF I HAD KNOWN WHAT THE CTLR WAS TRYING TO DO EARLY ON I WOULD HAVE ABANDONED THE APCH. I QUESTION THE WISDOM OF BOTH THE CTLR AND THE ACCEPTANCE BY THE BRASILIA PLT. I DO NOT LIKE BEING PLACED IN A SIT WHERE LITTLE OR NO OPTIONS EXIST. BOTH ACFT LANDED WITHOUT INCIDENT.