Merlin SW4 pilot has an airborne conflict vicinity of bfi.

Attributes
ACN	707077
Time
Date	200608
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : sea.vortac
State Reference	WA
Altitude	msl single value : 2500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : bfi.tower
Operator	common carrier : air carrier
Make Model Name	Merlin IV A
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	arrival : vfr
Flight Plan	None
Aircraft 2
Controlling Facilities	tower : bfi.tower
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent : intermediate altitude
Person 1
Affiliation	company : air carrier
Function	flight crew : captain
Qualification	pilot : atp pilot : cfi pilot : commercial pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 200 flight time total : 4100 flight time type : 1400
ASRS Report	707077
Events
Anomaly	conflict : airborne critical non adherence : far
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Miss Distance	horizontal : 500 vertical : 500
Supplementary
Problem Areas	Flight Crew Human Performance Airspace Structure
Primary Problem	Flight Crew Human Performance

Narrative:

The event took place during a flight between seatac and boeing field. After departing to the west from seatac; the seatac tower advised that I was clear of class B airspace and frequency change was approved. I immediately switched over to boeing field tower frequency. After leveling off at 2500 ft; I spotted an aircraft at 11 O'clock position. The other aircraft was approximately 500 ft higher and on the same course. Since the other aircraft was slower and had the right-of-way; I decided to pass them from the right as described in the FARS. During this time I established radio contact with boeing field tower and stated my position and intentions. The other aircraft was monitoring the same frequency. As soon as they heard that I was in the same vicinity as them; they altered their course 90 degrees to the right; which caused the 2 airplanes to come in close proximity. Evasive action was taken by both airplanes; they started to climb and I started a descent. I believe this incident could have been avoided if I had requested radar services for that short 7 min flight or if the flight was conducted under IFR. In the future; I intend on using the radar services if available -- no matter what the circumstances.

Original NASA ASRS Text

Title: MERLIN SW4 PLT HAS AN AIRBORNE CONFLICT VICINITY OF BFI.

Narrative: THE EVENT TOOK PLACE DURING A FLT BTWN SEATAC AND BOEING FIELD. AFTER DEPARTING TO THE W FROM SEATAC; THE SEATAC TWR ADVISED THAT I WAS CLR OF CLASS B AIRSPACE AND FREQ CHANGE WAS APPROVED. I IMMEDIATELY SWITCHED OVER TO BOEING FIELD TWR FREQ. AFTER LEVELING OFF AT 2500 FT; I SPOTTED AN ACFT AT 11 O'CLOCK POS. THE OTHER ACFT WAS APPROX 500 FT HIGHER AND ON THE SAME COURSE. SINCE THE OTHER ACFT WAS SLOWER AND HAD THE RIGHT-OF-WAY; I DECIDED TO PASS THEM FROM THE R AS DESCRIBED IN THE FARS. DURING THIS TIME I ESTABLISHED RADIO CONTACT WITH BOEING FIELD TWR AND STATED MY POS AND INTENTIONS. THE OTHER ACFT WAS MONITORING THE SAME FREQ. AS SOON AS THEY HEARD THAT I WAS IN THE SAME VICINITY AS THEM; THEY ALTERED THEIR COURSE 90 DEGS TO THE R; WHICH CAUSED THE 2 AIRPLANES TO COME IN CLOSE PROX. EVASIVE ACTION WAS TAKEN BY BOTH AIRPLANES; THEY STARTED TO CLB AND I STARTED A DSCNT. I BELIEVE THIS INCIDENT COULD HAVE BEEN AVOIDED IF I HAD REQUESTED RADAR SVCS FOR THAT SHORT 7 MIN FLT OR IF THE FLT WAS CONDUCTED UNDER IFR. IN THE FUTURE; I INTEND ON USING THE RADAR SVCS IF AVAILABLE -- NO MATTER WHAT THE CIRCUMSTANCES.

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.