Global Express (BD700)
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 100; Flight Crew Total 21000; Flight Crew Type 4000
Situational Awareness
Conflict NMAC
Flight Crew Took Evasive Action
Aircraft; Human Factors; Procedure
On takeoff; as we were cleaning the airplane up; PF looking out the Heads Up Display (HUD) and ahead; PNF cleaning up flaps; the [small aircraft] appeared to drift into our departure path. We had been given notice of the closely matching tail number and that he had just departed. We had him in sight as he departed; but our speed rapidly caught up to them after takeoff.After we departed; he had drifted into our departure path and at 500 feet; we needed to turn 30 degrees to our right to avoid a collision. We passed within 100 feet (our wingspan) and at his altitude.Tower was trying hard to get him to move; but their mic had broken at just that time and while they were replacing the mic another controller was also broadcasting for the [small aircraft] to move back left. We were hearing those transmissions. Tower sometimes splits controllers between the two parallel runways so we weren't hearing transmissions to the [small aircraft] until this occurred.As we went into our turn; the [small aircraft] started their turn to the left.In [all my] years of flying; this is as close as I've come to a collision. I was just cleaning up the airplane as PNF and when I looked up and out; the windshield was 3/4 full of another airplane's wing.
BD700 Captain reported an NMAC with a small aircraft on departure at BFI.