PA-30 Twin Comanche
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 16; Flight Crew Total 613; Flight Crew Type 365
Situational Awareness
Airspace Violation All Types; Conflict NMAC
Flight Crew Took Evasive Action
Human Factors; Airspace Structure
[I was] flying southbound just southwest of Boeing Field's Delta airspace when southbound highwing plane passed just beneath me. I did not see it until just as it passed under my left wing. I waited to see it pass out on the other side but did not see it. I was concerned that it may be maneuvering rather than in straight and level flight and took evasive action via a turn to my left back to a northbound direction while looking for the traffic. I never did see it again; but I may have inadvertently entered Boeing Field's Delta airspace without communication during my turn to avoid the traffic. Attitude estimated at 2;400 MSL but may be a couple of hundred feet either side of that as well. I was looking for traffic forward and to my side; but not approaching from my rear quarter. It was approaching me from my rear quarter and I should have been very visible to the other aircraft inasmuch as I was in front of it. I do not know how to prevent this type of encounter.
A PA-30 pilot experienced an NMAC with a same direction high wing aircraft that passed 200 FT below the Piper.