Boeing Field is a busy location for UPS.  FedEx run their Seattle operations from SeaTac but UPS has made King County their location of choice.  You get a busy period in the evening with arrivals and departures in a pretty narrow window.  Provided there is evening light, you can get a lot of movements.

I have shot a bunch of their jets over the course of various visits.  Usually I get them arriving and departing from the same location.  I did get some familiar shots this time but I also decided to head to the other end of the field and shoot the departure head on.  They do get airborne pretty quickly and climb quite fast so they rotate a long way off and are well above you by the time they cross the fence.  Not ideal but still a bit of variety for me.