“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 the 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 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.

Increasingly, the search has encompassed seas to the west of the Malaysian peninsula, stretching from the Strait of Malacca to the Bay of Bengal, where the United States and India sent military planes and ships. The move came in tandem with an increasing amount of evidence that the aircraft flew for four hours after it disappeared from air traffic control radar after 1 a.m. last Saturday.

Even with the potential help of the Inmarsat data, the new focus on the open ocean illustrates the difficulty for the multinational search force, which now must scan thousands of miles of the world’s third-largest ocean. The initial search area was in the relatively confined and shallow waters of the South China Sea and Gulf of Thailand, which are among the world’s busiest maritime routes. If the plane ended up in the ocean depths, it will be far harder to find and recover.