They believe the plane’s sharp turn 40 minutes into the flight and the disabling of the communications system suggest an experienced pilot was in control. But the lack of any motive — and the disappearance of the plane — has left authorities increasingly mystified during a search that has lasted more than 11 days. As Malaysia appealed to countries in the two major search areas to share surveillance data, vital information emerged from Thai air force radars on Tuesday that revealed clues about the aircraft’s wayward path.