My opinion from early on was that the plane headed toward the north
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Heading SW was a flight into nowhere. Just never made sense IMO.
The only way I could see it going south would be some kind of impossible on board electrical foul-up that locked out all communication, all pilot control, but still left the plane flying. Can't imagine what that would be. The psychotic or suicidal pilot theory just never appealed to me. I just couldn't see someone that narcissistic not wanting at least one person in the world to know what they'd done.
So, the north always seemed a better conclusion to me.