Prior to the KC-46 Pegasus, Boeing had another go at selling the 767 to the USAF as a tanker. The aircraft that they had intended to be the solution at that point was a different configuration to what ultimately made its way in to the inventory. They went as far as building a speculative airframe for the project. However, when the project was aborted (for reasons that are far too complex for a simple blog post), the airframe lay unfinished. It was stored for a while at Paine Field before eventually being scrapped. Here is a shot of it prior to its demise.
The tale of the USAF’s quest for a new refueling tanker has been long and drawn out. People went to jail, awards were made and overturned. None of that matters now. The contract is with Boeing to produce a variant of the 767 as the KC-46 Pegasus. The program has not been smooth. Technical and production issues have caused delays. The in service date has slipped and Boeing has incurred a lot of overruns.
While all of this has been going on, the production process has not stopped. Consequently, while testing still continues, there are production airframes coming off the line. If you go to Boeing Field, there are a bunch of test airframes on the flight line. If you go to Paine Field, there are a bunch more that remain to be finished. It appears that Boeing is building the airframes, sealing them up, not fitting high value items like engines, and parking them wherever there is space. A few years ago, Paine Field was covered in undelivered 787s. Now it is as if time has turned back because the Dreamliner’s predecessor is the type parked all over the place.