Lost Jet’s Path Seen as Altered via Computer
WASHINGTON — The first turn to the west that diverted the missing Malaysia Airlines plane from its planned flight path from Kuala Lumpur to Beijing was carried out through a computer system that was most likely programmed by someone in the plane’s cockpit who was knowledgeable about airplane systems, according to senior American officials.
Instead of manually operating the plane’s controls, whoever altered Flight 370’s path typed seven or eight keystrokes into a computer on a knee-high pedestal between the captain and the first officer, according to officials. The Flight Management System, as the computer is known, directs the plane from point to point specified in the flight plan submitted before a flight. It is not clear whether the plane’s path was reprogrammed before or after it took off.
Reconstructing the Plane’s Path
The main communications systems of the Malaysia Airlines plane were turned off about 40 minutes into the flight, forcing investigators to try to piece together the plane’s location from other systems.
Secondary Radar and Text Updates
Air traffic controllers typically know a plane’s location based on what is called secondary radar, which requests information from the plane’s transponder. A plane also uses radio or satellite signals to send regular updates through Acars, the Aircraft Communications Addressing and Reporting System. Both of those systems were turned off
Two Malaysian military radar stations tracked a plane using primary radar, which sends out radio signals and listens for echoes that bounce off objects in the sky. Primary radar does not require a plane to have a working transponder.
If Acars updates are turned off, the plane still sends a “keep-alive” signal, that can be received by satellites. The signal does not indicate location, but it can help to narrow down the plane’s position. A satellite picked up four or five signals from the airliner, about one per hour, after it left the range of military radar.
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