WASHINGTON — A week after one of the most advanced commercial aircraft ever built vanished with 239 people aboard, an international effort involving fleets of ships, planes and satellites appears to be chasing fragmentary data and theories centered on a potentially longer flight far west of the jet's intended destination.
As Saturday dawned in Asia, that search had veered more decisively into new areas: U.S. ships are concentrating on waters west of Malaysia, where the Boeing 777 flight originated, while investigators sought to determine why onboard transponders had apparently been turned off manually.
A federal law enforcement source who has been briefed on the U.S. role in the investigation said periodic signals received by a satellite for several hours after Malaysia Airlines Flight 370 was last identified on advanced radar could indicate it had been deliberately diverted, perhaps by a hijacker or someone intent on landing the plane somewhere else.
"Maybe someone who knew how to do it, to land it safely or at least try to," shut them off, he said. "Or somebody puts a gun to the pilot's head."
It has become clear in the last few days that two in-flight communications systems had been shut down in the cockpit, a scenario confirmed by the source, who spoke confidentially because the investigation is continuing. Both systems would have had to been shut down in the cockpit, by what he called "deliberate acts."
Once they were down, the plane veered west, the source said — confirming radar data reported by authorities.
If the data are accurate, initial search along the intended northeasterly flight path over the Gulf of Thailand may have been in vain.
Several scenarios remain plausible, including a desperate diversion by pilots trying to land a gravely damaged aircraft, or a hijacker commandeering the plane and forcing it to fly somewhere under the cloak of communication darkness.
The source cautioned that U.S. authorities had not pinpointed any "typical incident" indicating terrorism. The FBI and other U.S. law enforcement agencies are relying on information from U.S. intelligence sources, satellite data, the National Transportation Safety Board and information shared from the lead investigators in the Malaysian government.
He said the FBI continued to work the case because three Americans were on board the plane. But he emphasized that as far as he had been told, there was not enough evidence yet to determine how the plane could remain lost for a week.
Malaysian officials, speaking at a news conference Friday, acknowledged that the shutting off of the transponders could indicate there had been a hijacking.
"It could have been done intentionally," said Hishamuddin Hussein, Malaysia's acting transportation minister. "It could have been done under duress. It could have happened as a result of an explosion."
Hussein said the last transmission from the aircraft was at 1:07 a.m. March 8 and indicated that everything was normal. An unidentified blip popped up later on military radar, indicating that something was in Malaysian airspace, but authorities were not yet convinced that it came from Flight 370.
The U.S. Navy confirmed that it had moved the destroyer Kidd from the Gulf of Thailand, which was along the original flight path, to the Strait of Malacca on the west side of Malaysia.
The nature of some of the signals from the plane became more clear Friday. A British satellite telecommunications company, Inmarsat, said the signals registered by its network were "routine" and "automated." But it did not disclose when the communications occurred in relation to the aircraft's disappearance.
Inmarsat said the information was given to SITA, a multinational air transport communications and information technology company, which in turn shared it with Malaysia Airlines.
A SITA spokeswoman would not provide details but said the carrier's communications system, called ACARS, was proprietary. The system is set up so that aircraft and ground stations can send messages regarding flight data, maintenance information or weather reports.
It is connected via radio and satellites and is programmed to send automated messages every hour or so. The system doesn't send an actual location, altitude or direction. It sends information on how the plane is operating.
When Air France Flight 447 went down off the coast of Brazil in 2009, it sent out a series of automated messages about abnormalities in the minutes before the crash.
However, these communication systems can be shut down or interrupted and still be sending out signals, said Tim Farrar, president of the consulting and research firm Telecom, Media & Finance Associates Inc. in Menlo Park, Calif., who is familiar with Inmarsat satellites.
"The airplane's satellite terminal could be on, trying to maintain a connection with a satellite," he said. "Think of it like a heartbeat, trying to keep the link active."
Those signals would not be good enough to construct a highly accurate track on the flight path, he said.
The last known point of radar contact with the jet was midway between Malaysia's east coast and the southern tip of Vietnam.
If the plane did fly west, back over Malaysia and toward the Strait of Malacca, Malaysian military should have been able to pick up radar signals of an aircraft that is anything but stealthy, with a 199-foot wingspan, experts said.
There are now 13 countries scouring the region with ships, spy satellites and submarine-hunting aircraft for any sign of the jetliner.
Serrano reported from Washington and Hennigan from Los Angeles. Times staff writer Barbara Demick in Beijing contributed to this report.Copyright © 2015, Los Angeles Times