G4 CREW RPTS NMAC WITH LIGHT ACFT WHILE ON THE ILS 13 APCH TO BFI.

Narrative

WE WERE BEING VECTORED ONTO THE LOC FOR THE ILS AT BFI RWY 13. WE HAD DSNDED TO 2200 FT MSL AND HAD CAPTURED THE LOC AND WERE USING THE AUTOPLT. WE WERE IN VMC BUT THERE WERE SOME SCATTERED SHOWERS IN THE LCL AREA. WE WERE INFORMED BY APCH CTL THAT WE WERE ON THE LOC AND WERE CLRED FOR THE ILS APCH AND THAT THERE WAS TFC AT OUR 10-11 O'CLOCK POS AND 1 MI; 500 FT BELOW US. I LOOKED AT MY TCAS AND SAW THE TFC CLOSE IN AT 11 O'CLOCK POS AND THE TARGET SHOWED 300 FT BELOW US AND CLBING. WE BEGAN RECEIVING THE 'TFC; TFC' AUDIBLE ALERT BUT WE WERE NOT ABLE TO ESTABLISH VISUAL CONTACT. I DECIDED TO EXECUTE A CLBING EVASIVE MANEUVER BEFORE THE TCAS SYS ADVISED TO CLB AND STATED MY INTENTIONS TO THE FO. AS I BEGAN THE CLB AND STARTED ADVANCING THE THROTTLES; THEN TCAS ALERTED AN RA AND RECOMMENDED A LARGE NOSE-UP CLB AND TRIGGERED A 'CLB; CLB NOW' ALERT. AT THE CLOSEST APCH TO THE TARGET THE TCAS SCREEN SHOWED THE TARGET DIRECTLY UNDER OUR ACFT AND 100 FT BELOW US AND CLBING. WE INFORMED ATC OF OUR MANEUVER AND WERE GIVEN A R TURN TO 250 DEGS. WHEN WE WERE A SAFE DISTANCE FROM THE TARGET WE STARTED A LEVELOFF AND A R TURN. WHILE STARTING THE TURN; WE WERE INFORMED BY ATC OF B737 TFC AT OUR 12 O'CLOCK POS AND TO STOP OUR CLB. BY THIS TIME WE HAD STOPPED OUR CLB AND STARTED OUR DSCNT BACK TO 2200 FT MSL. ATC CONTINUED TO VECTOR US AND WE MADE A NORMAL VECTORED ILS APCH WITH NO FURTHER INCIDENT. WE BRIEFED THE PAX ONCE WE LANDED AND EXPLAINED THE TCAS SYS AND THAT WE PERFORMED AN EVASIVE MANEUVER TO AVOID TFC THAT WAS NOT TALKING TO THE APCH CTLR AND WAS IN A LOCATION THAT HE WAS NOT SUPPOSED TO BE. I TOLD THE PAX THAT IT WAS PROBABLY A SMALL PLANE OUT SIGHTSEEING AND NOT TALKING TO ANYONE. I SPOKE TO A PERSON AT TRACON IN SEATTLE AND TOLD THEM WHAT WE EXPERIENCED. I ASKED WHAT A PLANE WAS DOING ON THE ILS IN PROTECTED AIRSPACE AND SHE SAID THAT THE CTLR SAID THAT HE WAS 'PAINTING' OUR TFC BUT THAT HE WAS NOT WORKING THEM. I ASKED IF ATC TRACKED THE ACFT AND SHE SAID THAT THEY TRACKED IT FOR A WHILE AND THEN LOST THE TARGET. SHE ASKED IF WE GOT A TCAS ALERT ON THE B737 AIRLINER AFTER OUR INITIAL ALERT AND TOLD HER WE DID NOT. SHE SAID NO FURTHER INFO WAS NEEDED AND THANKED ME FOR CALLING. THE FO DID A GREAT JOB OF COMMUNICATING WITH ATC AND CALLING OUT TCAS AND FLT INFO. THIS IS A GOOD EXAMPLE OF A SITUATION THAT WAS RESOLVED SAFELY DUE TO THE USE OF THE TCAS SYS AND GREAT TRAINING.