LGT TURNING TO LOC WITH ACFT ON PARALLEL APCH RECEIVES TCASII RA. RESPONDS WITH CLB.

Narrative

APPROX AT MENLO INTXN WE WERE LEVEL AT 4000 FT AND CLRED TO 2500 FT 'RPT ARPT IN SIGHT.' ISSUED TFC AT 2 O'CLOCK; AN LTT; GOING TO 28R. ADDITIONAL TFC 10 O'CLOCK; ALT UNKNOWN; COULD BE SMA LOW. WE RPTED THE LTT 'IN SIGHT.' WE DID NOT RPT ARPT AS HAZE/SMOKE LAYER RESTR OUR VISIBILITY. APCH GAVE US 330 HDG; JOIN 28L LOC. CAPT HAD PREVIOUSLY TUNED ILS DURING APCH BRIEFING AND I TRIED 3-4 TIMES TO IDENT BUT NEVER DID GET A GOOD IDENT ON ILS. WE HAD THE DUMBARTON BRIDGE IN SIGHT THE WHOLE TIME AS WELL AS THE LTT FOR 28R. DURING OUR DSCNT TO 2500 FT AND ABOUT THE TIME WE SHOULD HAVE BEEN JOINING THE LOC; WE GOT AN RA (CAPT SAID A TARGET JUST OFF L OF NOSE; THEN DISAPPEARED; THEN 1 JUST OFF R OF NOSE). HE ADDED PWR; STOPPED TURNING AND CLBED TO FOLLOW TCASII RA. ABOUT 3-5 SECONDS LATER APCH CTL ASKED IF WE WERE JOINING LOC. WE RESPONDED THAT WE WERE FOLLOWING AN RA. APCH ISSUED HDG 240 TO JOIN 28L. WE THEN HAD ARPT IN SIGHT; RPTED IT AND WERE CLRED VISUAL 28L; HANDED OFF TO TWR; AND LANDED WITHOUT FURTHER CONFLICT. THESE 2 APCH PATHS AT SFO ARE VERY CLOSE. A SLIGHT SPD REDUCTION/STAGGERING OF EITHER ONE OF US WOULD CERTAINLY HAVE MADE THE SITUATION MUCH DIFFERENT.