How can air traffic controllers lose sight of a modern Boeing 777 while it flies thousands of kilometers? In the age of satellite communications and GPS, it shouldn't be hard to track an airliner's location over the ocean. But Malaysia Airlines Flight 370 (MH370) has pointed up holes in the technology and spurred discussions about improving it. At present, commercial airliners are still mostly located in the sky using radar. While a plane is over or near land, "secondary" radar sends out coded pings and a plane's transponder answers with its own identifying signal. Contact with MH370 was lost in the early hours of 8 March over the Gulf of Thailand when its transponder mysteriously stopped operating. Seconds later, its transponder mysteriously stopped operating. It was still visible to conventional, uncoded radar as it turned west over Thai and Indonesian territory, but over the Indian Ocean it was out of range.
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