A U.S. official tells CNN that radar showed erratic movements by a plane that the U.S. believes is flight 370 in the early morning hours when it disappeared.
The New York Times is also reporting that the missing airliner experienced significant changes in altitude after it lost contact with ground control.
Military radar signals appear to show the plane climbing to 45,000 feet just after it made a sharp turn to the west and disappeared.
That's above the approved altitude limit.
CNN's Martin Savidge is OutFront in a 777 simulator.