A woman and a girl look at a Malaysia Airlines plane on the tarmac of Kuala Lumpur International Airport in Malaysia on March 13, 2014.
Communications satellites picked up faint electronic pulses from Malaysia Airlines Flight 370 after it went missing on Saturday, but the signals gave no information about where the stray jet was heading and little else about its fate, two sources close to the investigation said on Thursday.
The "pings" indicated that the aircraft's maintenance troubleshooting systems were switched on and ready to communicate with satellites as needed. But no data links were opened because the companies involved had not subscribed to that level of service from the satellite operator, the sources said.
The system transmits such pings about once an hour, the sources said, but it remains unclear how many signals the plane sent after air traffic control lost track of it.
Boeing Co, which made the missing 777 airliner, and Rolls-Royce, which supplied its Trent engines, declined to comment.
Earlier Malaysian officials denied reports that the aircraft had continued to send technical data and said there was no evidence that it flew for hours after losing contact with air traffic controllers early Saturday after taking off from Kuala Lumpur en route to Beijing.
The Wall Street Journal had reported that U.S. aviation investigators and national security officials believed the Boeing 777 flew for a total of five hours, based on data automatically downloaded and sent to the ground from its engines as part of a standard monitoring program.
Sources familiar with the investigation reiterated that neither Boeing nor Rolls-Royce had received any engine maintenance data from the jet after the point at which its pilots last made contact. Only one engine maintenance update was received during the normal phase of flight, they said, speaking on condition of anonymity.
That said, the latest evidence of an electronic whisper from the plane, extending an electronic handshake to satellites but containing no data, suggests the aircraft was at least capable of communicating, though nothing else is known about its situation or whereabouts.
There is still no evidence that demonstrates the plane's disappearance was related to foul play, U.S. security sources stressed, though the officials said they still have not ruled out the possibility of terrorism.
Reuters reported on Monday that the aircraft had made no automatic contact with the ground after vanishing with 239 people on board.
Modern aircraft can communicate with airline operations bases and sometimes with the headquarters of its manufacturers automatically in order to send maintenance alerts known as ACARS messages. It was this system that sent out the regular ping, which may have lasted for several hours, the sources said.
Airlines can also subscribe to an expanded service that collects more data about the performance of the aircraft and sends it back to maintenance control rooms at the airline and Boeing.
But Malaysia Airlines had not signed up for Boeing's Airplane Health Management system, people familiar with the matter told Reuters this week.
© Thomson Reuters 2014