The F-117 is Still Flying. But why?

"I would just guess it's for radar signature testing," Richard Aboulafia, an analyst with the Teal Group, said when asked what the F-117 could be doing. "It could conceivably be testing aerodynamics, also. It was one of the earlier generations of planes that shouldn't have been flying but did, thanks to the magic of fly by wire and computers. It could also be fatigue testing for materials that were used on the plane, to see how well those are holding up over time."

Another option is they are test beds of a different kind — retrofitted into unmanned systems, perhaps to check on the capability of optionally-manned systems for stealth aircraft. And of course it's possible they are being kept warm in case of military need, but it's hard to see what gap they would be fitting specifically in the military network.

All of which is to say, as Aboulafia put it, the planes could be used to test "any number of things."