Chris Iz: The problem there is that you could swap the two premises around and still have had the plane hitting the mountain. For example, assume that the waypoint was where he thought it was, and assume that the radar operator was drunk. In that event, there would have been no accident if he had relied on the AINS, but there would have been if the radar operator's double-vision had him with Erebus dead ahead, the operator therefore recommending an urgent turn to the left.