A B757 CREW; AFTER BEING ISSUED A TA FROM SEA APCH CTL; RECEIVED A CLB RA FROM TCASII.

Narrative

ACFT #1 WAS ON FINAL FOR A VISUAL APCH TO RWY 16L AT SEA. DURING APCH; ATC INFORMED ACFT #1 THAT ACFT #2 WAS ON A VISUAL APCH R BASE FOR RWY 16R WITH ACFT #1 IN SIGHT. ON SHORT FINAL WITH TWR; AT APPROX 1000 FT AGL; ACFT #1 RECEIVED A TCASII ADVISORY (TA). TFC WAS VISUALLY LOOKED FOR OFF THE R SIDE OF ACFT #1; BUT NO VISUAL CONTACT WAS MADE. THEN A TCASII RA OCCURRED. ACFT #1 COMPLIED WITH AND INITIATED AN RA MANEUVER WITH NO TFC IN SIGHT; WHICH WAS A STEEP CLB. ACFT #1 ADVISED TWR THAT IT WAS ON 'THE GO' (WHILE STILL LOOKING FOR TFC). TWR ISSUED A CLRNC OF RWY HDG; CLB TO 2000 FT. ACFT #1 CONTINUED THE RA/GAR MANEUVERS ON RWY HDG WITH A CLB TO APPROX 2250 FT THEN LEVELING AT 2000 FT WHEN THE MANEUVER WAS COMPLETE. DURING THIS RA; ACFT #1 NEVER HAD VISUAL CONTACT WITH THE INDICATED TARGET. ACFT #1 COULD NOT DETERMINE IF THE RA TARGET WAS ACFT #2. ACFT #1 WAS HANDED OFF TO DEP. ACFT #1 REQUESTED AN ILS APCH TO RWY 16R. TWR WAS INFORMED BY ACFT #1 THAT 'THE GAR' WAS INITIATED ON THE PREVIOUS VISUAL APCH BECAUSE OF AN RA. ACFT #1 LANDED UNEVENTFULLY ON RWY 16R.