IIRC, a pilot was interviewed who claimed that there was a fire on the plane, at which point the pilot did his best at maneuvering to deprive it of oxygen, then made a left hand turn toward the nearest airport. He speculated that smoke overwhelmed the interior and the plane was then on autopilot, when it flew for four hours and then into the ocean. This theory does sound plausible to me, but it may or may not be correct.
That theory would be plausible if the fact that the plane did the westerly turn 12 minutes BEFORE the last radio contact with the plane where the co-pilot said “Alright good night” unless the pilots were psychics and saw this supposed fire coming in a premonition this theory does not make sense..now if the turn was made AFTER the last radio contact I might be willing to believe the smoke in the cockpit theory
The nearest suitable airport at the point where they made their left turn was Sultan Mahmud (TGG), on the north coast of the Malaysian Peninsula. It has an 11,417 foot asphalt runway perpendicular to the shore. If there had been a fire on board, they should have made a U-turn and headed there, a distance of 111 statute miles. We also should have heard a mayday.