Pilot just screwed-up typing 190o heading rather than 019o on the FMC - Don't you have "fat fingers" too, at times...?
the games a foot watson
It was detected changing course on military radar after the transponder was switched off. Because there was no alert at the time, it was ignored as routine by the military radar operators. Finding the flight recorders is of importance to determine exactly what happened.
The currents in the sea and the plane may of went of course