CPR JET ENCOUNTERS NMAC ON APCH TO BFI.

Narrative

WHILE ON FINAL TO BFI ON THE ILS RWY 13R APCH AROUND THE OM; WE RECEIVED A TCASII ALERT FOR TFC 200-300 FT BELOW US AND JUST OFF OUR L FRONT. WE THEN VISUALLY ACQUIRED A SINGLE ENG AIRPLANE; OPPOSITE DIRECTION; IN LEVEL FLT. IMMEDIATELY THEREAFTER WE RECEIVED AN RA TO CLB; WHICH I DID NOT DO; SINCE I WAS EASILY ABLE TO SEE AND AVOID. THE COPLT THEN INFORMED THE TWR ABOUT THE TFC; AND THEY REPLIED TO THE EFFECT THAT YES; THERE IS TFC OUT THERE. WE THEN PROCEEDED TO A NORMAL LNDG. LOOKING AT THE 10-1A AND 11-1 CHARTS FOR SEATTLE; AS CAN SEE THAT CLASS B AIRSPACE ON FINAL FOR RWY 13R EXTENDS FROM 1800-10000 FT MSL. THEREFORE; OUR TFC WAS PROBABLY OPERATING LEGALLY OUTSIDE THE CLASS B AIRSPACE IN VFR; AND WAS NOT BEING HANDLED BY A RADAR CTLR. THE TFC WAS MOST LIKELY IN THE CLASS D AIRSPACE OF BFI; AND WE GOT THE IMPRESSION THAT HE WAS COMMUNICATING WITH THE TWR; BUT THEY NEVER CALLED THE TFC FOR US UNTIL AFTER THE FACT. IT WOULD BE INTERESTING TO KNOW IF BFI TWR HAS A REPEATER SCOPE. IN THEORY; APCH CTL PROBABLY COULD SPOT A CONFLICT AND HAVE TWR WARN US; BUT THIS ISN'T VERY TIMELY INFO. COMPOUNDING THE PROB IS TERRAIN IN THE AREA OF BFI; WHICH PROBABLY LIMITS DEP PATHS FOR LIGHT ACFT. THIS IS NOT THE FIRST TFC CONFLICT PLTS IN OUR DEPT HAVE HAD GOING INTO BFI. GIVEN THE LARGE AMOUNT OF TFC OPERATING IN THE AREA; BOTH VFR AND IFR; IT SEEMS THAT THIS AREA HAS REAL POTENTIAL FOR A MIDAIR COLLISION. OUR TCASII HELPED PROTECT US IN THIS SIT; BUT IT SEEMS LIKE SOMETHING NEEDS TO BE DONE ABOUT VFR ACFT FLYING OUTBOUND ON OR NEAR THE LOC COURSE. CALLBACK CONVERSATION WITH TRACON SPECIALIST REVEALED THE FOLLOWING: TRACON SPECIALIST REPORTS THAT THE SEATAC RWY 16 FINAL APCH COURSE CROSSES DIRECTLY OVER THE BFI ARPT. THE RWY 16 OM IS LOCATED ON THE BFI ARPT. THE CLASS B AIRSPACE AND ILS APCH WAS DESIGNED TO ACCOMMODATE BFI ARPT TFC PATTERN RESTRS. BFI TFC PATTERN ALT IS 800 FT. BFI TFC IS REQUESTED TO DEP DUE W; UNDER THE CLASS B AREAS; PRIOR TO CLBING. BFI AND SEATAC ATCTS HAVE THE SAME BRITE RADAR DISPLAY. THE TWO TWRS AND THE TRACON HAVE DIRECT ACCESS VOICE LINES TO COORD NON STANDARD OPERATIONAL PROC REQUESTS AND TO INFORM EACH OTHER WHEN ACFT EXECUTE NON STANDARD/NON COORDINATED ACTIONS. EACH FACILITY WILL EXCHANGE OBSERVED AND KNOWN TFC. ACFT INTRUDING CLASS B AIRSPACE ARE COORD WITH EACH OTHER WHEN OBSERVED AND AS TIMELY AS PRACTICABLE. BECAUSE OF THE PROX OF THE TFC PATTERN AND CROSSING TFC; ACFT EXECUTING A RWY 16 APCH WILL BE EXPOSED TO POSSIBLE TCASII ALERTS FROM BFI ACFT OPERATING WITHIN THE TFC PATTERN.