There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know.
While the exact nature of this mystery plane in unknown and has since become a subject of intense debate on the internet. Rest assured, our friends at the Mystery Inc have been following its every move.
The latest news is that they are indeed heading AVIC 623rd Institute in Xi'an.