In China, it's common for men who have had enough with their society to snap and go on rampages stabbing, hacking, or hammering elementary schoolers to death, it's an entire phenomenon there.
https://en.wikipedia.org/wiki/School_attacks_in_ChinaThe reason I bring this up is that given this mindset, and the footage showing the plane dropped suddenly with no seeming attempts to recover, I wouldn't put it past a suicidal Chinese pilot to decide to take a whole plane full of people with him.
