It could very easily have been a plane replacing one like N313P, or similar, outfitted with higher-performance engines.
Perhaps on a test flight to see how it handles. There are plenty of military landing spots up and down the west coast for a plane like that. An empty plane with big engines could go very fast, and maneuver quickly.
That'd be my best guess. If they had used a shell registration and transponder, the flight would still be tracked and then there'd be a flight record they don't want.
It sounds like they had trouble tracking it with primary radar which means there might be something else going on.
It'd be amusing to find out how the people on the other side of this are reacting: Either "hey that was a pretty successful test," or "someone f'd up big time and now we have to clean up this mess."
Or maybe the civilian air radar isn't very good and the operators aren't highly skilled in using it since most traffic uses ADSB now. The article says "disappears from radar" but that could mean "flew out of effective radar range".
It's not the engines that would prove limiting to cruise speed at those altitudes, it's the aerodynamic design of the wing. Airliners are flying at between 78 to 86% of the speed of sound, you can't improve on that in a way that would be dramatically noticeable without a huge redesign.
It could very easily have been a plane replacing one like N313P, or similar, outfitted with higher-performance engines.
Perhaps on a test flight to see how it handles. There are plenty of military landing spots up and down the west coast for a plane like that. An empty plane with big engines could go very fast, and maneuver quickly.
That'd be my best guess. If they had used a shell registration and transponder, the flight would still be tracked and then there'd be a flight record they don't want.
Here's an example of planes that are in this category, and it's not unheard of for a 737 to get souped up engines[1]: https://www.therenditionproject.org.uk/flights/aircraft/inde...
1: Trump put RR engines on his 757, for instance.