Originally Posted by
QDMQDMQDM 
If the copilot did indeed deliberately fly the aircraft into the Alps, as seems very likely, then that is at first sight completely baffling. If you just want to commit suicide, why on Earth would you want to take 150 innocent people with you? It's just not rational. And that's the thing -- this act was not rational, so therefore we have to look at what could plausibly make someone act in such an irrational manner.
Given the story that is apparently developing concerning who he actually was, maybe the question should be "Why stop at 149 innocent people?"
Certainly those developments seems to answer the question as the states of being rational or irrational.