After not receiving new data from the 777 after its automated reporting system was switched off, the automated satellite pings—the digital equivalent of a handshake—originated at a ground stations and was transmitted up to the orbiting satellite high above the Earth's equator. The satellite relays the ping down to the aircraft below, effectively asking the jet if it is still able to send and receive data. After receiving it, Flight 370 transmitted a return ping back up to Inmarsat, which in turn relayed it to the ground station.
Because the angle and distance of the aircraft relative to the orbiting satellite changed as the jet flew over the Earth's surface, each ping to Flight 370 gave Malaysian officials, the National Transportation Safety Board, the Federal Aviation Administration and the U.K.'s Air Accidents Investigation Branch enough information to plot the 777's speed, altitude and changing path.
