I was driving over to Seattle a while back and, as I crossed the I-90 floating bridge, I saw a Learjet maneuvering at low level around the hill ahead of me. I decided to see what was going on since I suspected this might be an FAA jet flying a variety of approaches. Sure enough, it was one of their Lear 60s. I have seen them on a number of occasions before at different airports. Tracking them on something like FlightRadar24, it is easy to work out what they are since they fly a tone of patterns around an airport normally dealing with simple arrivals and departures.
Boeing Field is not such an airport as it has a lot of training activity but the Lear is a bit faster than the average piston single. I didn’t know how long it had been there so it could have gone before I arrived but they still had a few circuits to do before they were finished. These involved a different sequence of approaches from offset positions from which they could take their measurements and then break off to do it again. It is interesting to see a business jet being thrown around like this in a way that would not keep the average customer happy!