The aircraft climbed to 39,000 feet, just short of the Boeing 777-200ER's 41,000-foot safe operating limit, and maintained that altitude for about 20 minutes over the Malaysian Peninsula before beginning to descend.
In addition to this newly revealed development, investigators have determined that the missing jet was equipped with four emergency locator transmitters, or ELTs, which are designed to transmit a plane's location to an emergency satellite when triggered by a crash or by contact with water.
The ELTs were at the plane's front door, its rear door, in the fuselage and in the cockpit, said the source, who was puzzled over why they appear either not to have activated or, if they did activate, why they were not picked up by the satellite.