Narrative:

I was on a daytime VFR flight from bfi to fhr. I departed bfi on runway 31L; climbing 'straight out' to the northwest (heading 310 degrees). The floor of class B airspace over most of bfi is 1100 ft MSL. North of the airport it is 1800 ft MSL. Field elevation is 18 ft MSL. Aircraft are supposed to avoid flying over or near the baseball and football stadiums north of the field; just east of the straight-out departure path. Between the low class B floor; the ballparks; the overlapping airspace of 3 twred airports (sea; bfi; and rnt); higher terrain and a few sets of tall towers north and northwest of downtown seattle (741 ft; 1015 ft; 1049 ft; and 1071 ft MSL); and float plane traffic on lake union and lake washington; this tends to be very congested airspace. Aircraft might be on any of several radio frequencys (sea tower; 2 bfi tower frequencys; seattle approach or departure) or no radio contact. I climbed to 1000 ft MSL to stay below the class B airspace; and maintained runway heading (310 degrees) to avoid flying unnecessarily close to the ball park on my right and to stay clear of any traffic inbound to the bfi downwind (should be on my left for runway 31L; on my right for runway 31R). At about 3 NM north of bfi; approaching the south end of elliot bay; I requested and was granted a frequency change to contact sea departure for flight following. I had pre-programmed that frequency on 1 radio. I looked at the radios and the communication panel to verify that I was switching to the right frequency on the right radio. This took a few seconds. As I looked back up and outside; my back seat passenger (a retired professional pilot sitting directly behind me on the left side of the aircraft) tapped me on the head; leaned over my shoulder; and pointed ahead and to the left and down (he was not on the intercom). I saw what appeared to be a beech king air coming almost directly at me; moving quickly from my 10-11 O'clock position; wing up in a right turn. Climbing away from that aircraft might cause me to violate the class B airspace. A right turn away from that aircraft might put me too close to the ball park. A climbing right turn; my best course of evasive action; might do both. That caused me to hesitate momentarily; then make a moderate course and altitude correction. Had it not been for the airspace restrs; I would have made a much more significant and more immediate correction. The other aircraft passed within 100 ft of my left wing; about 20 ft below me; and continued its turn behind me. I did not hear the other aircraft on the radio (they might have been on a different frequency; as described above). Based on the other aircraft's constant bank angle and altitude and their lack of any evasive action to miss me; I doubt that they ever saw me.

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Original NASA ASRS Text

Title: PLT OF PA28 EXPERIENCES NMAC WHILE DEPARTING BFI.

Narrative: I WAS ON A DAYTIME VFR FLT FROM BFI TO FHR. I DEPARTED BFI ON RWY 31L; CLBING 'STRAIGHT OUT' TO THE NW (HDG 310 DEGS). THE FLOOR OF CLASS B AIRSPACE OVER MOST OF BFI IS 1100 FT MSL. N OF THE ARPT IT IS 1800 FT MSL. FIELD ELEVATION IS 18 FT MSL. ACFT ARE SUPPOSED TO AVOID FLYING OVER OR NEAR THE BASEBALL AND FOOTBALL STADIUMS N OF THE FIELD; JUST E OF THE STRAIGHT-OUT DEP PATH. BTWN THE LOW CLASS B FLOOR; THE BALLPARKS; THE OVERLAPPING AIRSPACE OF 3 TWRED ARPTS (SEA; BFI; AND RNT); HIGHER TERRAIN AND A FEW SETS OF TALL TWRS N AND NW OF DOWNTOWN SEATTLE (741 FT; 1015 FT; 1049 FT; AND 1071 FT MSL); AND FLOAT PLANE TFC ON LAKE UNION AND LAKE WASHINGTON; THIS TENDS TO BE VERY CONGESTED AIRSPACE. ACFT MIGHT BE ON ANY OF SEVERAL RADIO FREQS (SEA TWR; 2 BFI TWR FREQS; SEATTLE APCH OR DEP) OR NO RADIO CONTACT. I CLBED TO 1000 FT MSL TO STAY BELOW THE CLASS B AIRSPACE; AND MAINTAINED RWY HDG (310 DEGS) TO AVOID FLYING UNNECESSARILY CLOSE TO THE BALL PARK ON MY R AND TO STAY CLR OF ANY TFC INBOUND TO THE BFI DOWNWIND (SHOULD BE ON MY L FOR RWY 31L; ON MY R FOR RWY 31R). AT ABOUT 3 NM N OF BFI; APCHING THE S END OF ELLIOT BAY; I REQUESTED AND WAS GRANTED A FREQ CHANGE TO CONTACT SEA DEP FOR FLT FOLLOWING. I HAD PRE-PROGRAMMED THAT FREQ ON 1 RADIO. I LOOKED AT THE RADIOS AND THE COM PANEL TO VERIFY THAT I WAS SWITCHING TO THE RIGHT FREQ ON THE RIGHT RADIO. THIS TOOK A FEW SECONDS. AS I LOOKED BACK UP AND OUTSIDE; MY BACK SEAT PAX (A RETIRED PROFESSIONAL PLT SITTING DIRECTLY BEHIND ME ON THE L SIDE OF THE ACFT) TAPPED ME ON THE HEAD; LEANED OVER MY SHOULDER; AND POINTED AHEAD AND TO THE L AND DOWN (HE WAS NOT ON THE INTERCOM). I SAW WHAT APPEARED TO BE A BEECH KING AIR COMING ALMOST DIRECTLY AT ME; MOVING QUICKLY FROM MY 10-11 O'CLOCK POS; WING UP IN A R TURN. CLBING AWAY FROM THAT ACFT MIGHT CAUSE ME TO VIOLATE THE CLASS B AIRSPACE. A R TURN AWAY FROM THAT ACFT MIGHT PUT ME TOO CLOSE TO THE BALL PARK. A CLBING R TURN; MY BEST COURSE OF EVASIVE ACTION; MIGHT DO BOTH. THAT CAUSED ME TO HESITATE MOMENTARILY; THEN MAKE A MODERATE COURSE AND ALT CORRECTION. HAD IT NOT BEEN FOR THE AIRSPACE RESTRS; I WOULD HAVE MADE A MUCH MORE SIGNIFICANT AND MORE IMMEDIATE CORRECTION. THE OTHER ACFT PASSED WITHIN 100 FT OF MY L WING; ABOUT 20 FT BELOW ME; AND CONTINUED ITS TURN BEHIND ME. I DID NOT HEAR THE OTHER ACFT ON THE RADIO (THEY MIGHT HAVE BEEN ON A DIFFERENT FREQ; AS DESCRIBED ABOVE). BASED ON THE OTHER ACFT'S CONSTANT BANK ANGLE AND ALT AND THEIR LACK OF ANY EVASIVE ACTION TO MISS ME; I DOUBT THAT THEY EVER SAW ME.

Data retrieved from NASA's ASRS site as of January 2009 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.