This post will be short as there isn't much supporting info out there.
My database is from the openskynetwork. It is updated monthly. The database only has 4 planes that are associated with Ukraine. After some research on my end (start here), I've concluded that UR-ABA (50815f) is sometimes used as presidential transport for the Government of Ukraine.
If you're a user of my Chrome Extension, you'll know that there is a handy 1-click button that displays things like Russian Oligarchs, or, in this case, Ukraine Gov't & Military.
Tonight while tooling around on the adsbexchange map, I clicked that button and I saw that one of the four Ukrainian planes, namely the UR-ABA plane that does VIP transport, had just landed in Washington, D.C. four hours earlier.
So that is pretty much it. I don't know much else. I expect there to be some kind of news coverage about this tomorrow. I tweeted as many White House Correspondents in the first two rows of the Brady Press Briefing Room that I could find hoping that they either know something or plan to ask Jen Psaki about it.
I will update this post if I learn more tomorrow.