Narrative:

I called boeing ground requesting a northwest departure and was told to taxi to 13R, alpha 9. During taxi, ground called me back and asked me, due to congestion on 13R, to taxi to 13L for the northwest departure. At 13L, after runup, I called boeing tower on 118.3 and informed the tower I was ready for departure nwbnd from 13L. I was cleared for immediate takeoff, no delay, due to touch and go traffic, and was instructed to make a left downwind departure. I am a 150 hour VFR pilot and have always flown from boeing field. Many times I have requested a northwest departure and have never been instructed to use the short runway or to depart northwest from the east side of the field. I took off and on upwind confirmed with the tower that I was to make a left downwind rather than a right downwind. The tower told me to make a left hand turn and watch for traffic in the pattern and for traffic coming in from mercer island. On downwind the controller again advised me of traffic coming into the pattern from mercer island. I acknowledged 'xyz looking'. I received no more instructions from the tower but did remain on the 118.3 frequency. When I was just over the kingdome I turned toward winslow, aware that I was out of the air traffic area, but unaware that there was IFR traffic on the approach to 13R. I continued to monitor the tower frequency for traffic avoidance. My altitude at this time was approximately 1100', well below the TCA and 500' below the cloud ceiling. I saw the air carrier jet pass behind and above me. I would judge the jet to have been about 400' above me and 200' behind. I thought I saw it bank slightly to its left. Within 30 seconds the tower called me and asked me to identify, and then informed me that I had crossed the path of IFR traffic on the ILS. The tower then asked me to call them when I returned to the field. As I approached winslow, I realized the ceiling was lowering and switched to 120.6 to request a return to the field. I landed 13R and was again instructed by ground to call the tower upon my arrival. My questions to the tower during that phone call are the same ones I have now: why was I cleared for a northwest departure from the east side of the field? Why was I not informed of the traffic on the approach to 13R? The tower had called other small aircraft traffic to me, and knew I was still on frequency when asking me to identify after the incident. During the entire episode I was aware of my location, altitude, and the airspace regulations affecting my flight. The control zone was not in effect, I was out of the air traffic area, and my altitude was below the TCA and within VFR requirements. I was relying both on my visual abilities and the traffic control system to fly safely.

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Original NASA ASRS Text

Title: SMA AND LGT HAVE NMAC IN APCH LANE TO BFI.

Narrative: I CALLED BOEING GND REQUESTING A NW DEP AND WAS TOLD TO TAXI TO 13R, ALPHA 9. DURING TAXI, GND CALLED ME BACK AND ASKED ME, DUE TO CONGESTION ON 13R, TO TAXI TO 13L FOR THE NW DEP. AT 13L, AFTER RUNUP, I CALLED BOEING TWR ON 118.3 AND INFORMED THE TWR I WAS READY FOR DEP NWBND FROM 13L. I WAS CLRED FOR IMMEDIATE TKOF, NO DELAY, DUE TO TOUCH AND GO TFC, AND WAS INSTRUCTED TO MAKE A LEFT DOWNWIND DEP. I AM A 150 HR VFR PLT AND HAVE ALWAYS FLOWN FROM BOEING FIELD. MANY TIMES I HAVE REQUESTED A NW DEP AND HAVE NEVER BEEN INSTRUCTED TO USE THE SHORT RWY OR TO DEPART NW FROM THE E SIDE OF THE FIELD. I TOOK OFF AND ON UPWIND CONFIRMED WITH THE TWR THAT I WAS TO MAKE A LEFT DOWNWIND RATHER THAN A RIGHT DOWNWIND. THE TWR TOLD ME TO MAKE A LEFT HAND TURN AND WATCH FOR TFC IN THE PATTERN AND FOR TFC COMING IN FROM MERCER ISLAND. ON DOWNWIND THE CTLR AGAIN ADVISED ME OF TFC COMING INTO THE PATTERN FROM MERCER ISLAND. I ACKNOWLEDGED 'XYZ LOOKING'. I RECEIVED NO MORE INSTRUCTIONS FROM THE TWR BUT DID REMAIN ON THE 118.3 FREQ. WHEN I WAS JUST OVER THE KINGDOME I TURNED TOWARD WINSLOW, AWARE THAT I WAS OUT OF THE ATA, BUT UNAWARE THAT THERE WAS IFR TFC ON THE APCH TO 13R. I CONTINUED TO MONITOR THE TWR FREQ FOR TFC AVOIDANCE. MY ALT AT THIS TIME WAS APPROX 1100', WELL BELOW THE TCA AND 500' BELOW THE CLOUD CEILING. I SAW THE ACR JET PASS BEHIND AND ABOVE ME. I WOULD JUDGE THE JET TO HAVE BEEN ABOUT 400' ABOVE ME AND 200' BEHIND. I THOUGHT I SAW IT BANK SLIGHTLY TO ITS LEFT. WITHIN 30 SECONDS THE TWR CALLED ME AND ASKED ME TO IDENT, AND THEN INFORMED ME THAT I HAD CROSSED THE PATH OF IFR TFC ON THE ILS. THE TWR THEN ASKED ME TO CALL THEM WHEN I RETURNED TO THE FIELD. AS I APCHED WINSLOW, I REALIZED THE CEILING WAS LOWERING AND SWITCHED TO 120.6 TO REQUEST A RETURN TO THE FIELD. I LANDED 13R AND WAS AGAIN INSTRUCTED BY GND TO CALL THE TWR UPON MY ARRIVAL. MY QUESTIONS TO THE TWR DURING THAT PHONE CALL ARE THE SAME ONES I HAVE NOW: WHY WAS I CLRED FOR A NW DEP FROM THE E SIDE OF THE FIELD? WHY WAS I NOT INFORMED OF THE TFC ON THE APCH TO 13R? THE TWR HAD CALLED OTHER SMA TFC TO ME, AND KNEW I WAS STILL ON FREQ WHEN ASKING ME TO IDENT AFTER THE INCIDENT. DURING THE ENTIRE EPISODE I WAS AWARE OF MY LOCATION, ALT, AND THE AIRSPACE REGS AFFECTING MY FLT. THE CTL ZONE WAS NOT IN EFFECT, I WAS OUT OF THE ATA, AND MY ALT WAS BELOW THE TCA AND WITHIN VFR REQUIREMENTS. I WAS RELYING BOTH ON MY VISUAL ABILITIES AND THE TFC CTL SYSTEM TO FLY SAFELY.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.