Comment by walrus01

In a theoretical scenario of the billionaire class of the world having some kind of "advance warning" of the apocalypse, they'd be taking to the air in the hours or several days prior to a total disaster happening. Meaning this would be done while the local governments were ostensibly still functioning, in which case you can't just have your private jet depart without active ADS-B and in-the-clear voice traffic for ground, and air traffic control coordination.

If governments and airspace control have already collapsed, post tense, then of course anything goes.