3: Ever heard of fly by wire? Most jumbo jets don’t have it.
Even if we assume a hyper unrealistic worst-case scenario wherein someone does get into the plane’s avionics, he’s not going to be capable of taking control of the plane. While a handful of passenger jets have fly by wire, the vast majority still have physical linkages in place for all the relevant controls. What’s left for a hacker to do is toy with navigational controls. Most commercial pilots senior enough to fly the big planes are ex-air force. You don’t think they know how to navigate if a compass goes out?
4: The FBI are taking this very seriously (which is good!)
Even the most whacked out “Cybersecurity Experts” who claim to have access to a flying plane’s aeronautics, full of shit or not, HAVE to be taken seriously. I mean, you can barely tweet a scummy sentence at POTUS without a knock on your door. If they discover that this guy is anything more than full of it, you can bet that the holes which he was allegedly able to exploit will be plugged before your next flight.