David Coiley, a vice president of Inmarsat, a British satellite telecommunications provider, said the missing plane had been equipped with a signaling system from the company that sends out a “keep-alive message” to establish that the plane’s communications system is still switched on.

The plane sent out a series of such messages after civilian radar lost contact, he said. Those messages later stopped, but he declined to specify precisely when or how many messages had been received. Mr. Coiley said Inmarsat was sharing the information with the airline and investigators.



“It does allow us to determine where the airplane is relative to the satellite,” he said of the signal, which he likened to the “noises you might hear when a cellphone sits next to a radio or a television speaker.” He said: “It does allow us to narrow down the position of the aircraft” — at moment when the signal was sent.

Such equipment automatically checks in to satellites, much as a mobile phone would check in to a network after passing through a mountain tunnel, he said. Because the pings go over a measurable distance at a specific angle to one of the company’s satellites, the information can be used to help calculate the trajectory of an aircraft and narrow down its approximate location — though not necessarily its resting point.

“Communications systems are part of the mandatory requirement for operating any flight, and we are comfortable that it would have been operating accordingly,” Mr. Coiley said.

http://www.nytimes.com/2014/03/15/wo...light-370.html