WASHINGTON — The main tool available in the search for the missing jet operating as Malaysia Airlines Flight 370 is imprecise and awkward, and unfamiliar to the investigators using it, but it is all they have.
They lack the four ordinary ways of finding an airplane: primary radar, which sends out radio signals and listens for echoes that bounce back from objects in the sky; secondary radar, in which the plane answers an electronic query and sends back a message giving its identification number and altitude; automated transmissions from the plane to a maintenance base; and oral reports by radio from the cockpit crew.
The plane was out of range of ground-based radar by the time it disappeared March 8 shortly after takeoff, and the secondary radar and automated transmission systems were not working and possibly turned off. There was no word from the pilots or crew.
What investigators are left with is an hourly electronic “handshake,” or digital communication, between the airplane and a satellite orbiting 22,250 miles above the Indian Ocean. The satellite is in a geosynchronous orbit, meaning that it appears to hang in a fixed spot above the Earth.
Map of Plane’s Last Contact With Satellite
The missing Malaysia Airlines plane may have been over China or west of Australia when it last made contact with a satellite.
But the handshake is mostly devoid of data, and cannot be used to pinpoint the plane’s last known location. It is the electronic equivalent of catching someone’s eye in the crowd; all it does is establish the angle between the satellite and the plane.
At a news conference on Saturday, Malaysia’s prime minister, Najib Razak, released a map showing the two geographic arcs where the last satellite signal sent from the plane could have come from. One arc extended north from Thailand to Kazakhstan, the other south from Indonesia to the southern Indian Ocean, about 1,000 miles west of Australia.
The satellite handshakes formed a circle all the way around the Earth, but only part of the circle — the two arcs — is relevant to the search because the plane would have run out of fuel beyond the end of each arc. American investigators say the southern arc is of more interest.
Malaysia declared Saturday that the plane had been deliberately diverted, and that the search had become a criminal inquiry. Work by international and Malaysian investigators might have helped the prime minister see the clues from the satellite communications — along with changes in direction made by the plane after communications with the ground ceased — as sinister rather than accidental.
“You look at the facts that you have, and you have to try to make all the pieces fit together,” an American investigator said.