Boeing's new chase plane
It looks as if Boeing commercial airplanes is leasing a T-38 from Thornton Aircraft to help with flight testing of the 787 and 747-8F. The plane is a 1963 Northrop T-38A Talon, registered N638TC. The plane arrived as "Boeing 63 Tango" on Monday, 15 February to Boeing Field and went to the Boeing 3-350 Bldg (the former B-29 Hangar). Boeing owns a T-38A as well as two CT-33's (one of which is getting heavy maintenance done at the moment). My theory to why this T-38 is in town is because Boeing's own T-38 could be down for maintenance or is an additional chase plane for flight testing.
Today, N638TC accompanied BOE001 (787 No. 1) for high speed flutter tests over Eastern Washington.
I don't how long the plane will be with Boeing, so make sure you take a picture of it while you can.