But the "pings" indicated its maintenance troubleshooting systems were switched on and ready to communicate with satellites, showing the aircraft, with 239 people on board, was at least capable of communicating after losing touch with air traffic controllers.
The system transmits such pings about once an hour, according to the sources, who said five or six were heard. However, the pings alone are not proof that the plane was in the air or on the ground, the sources said.
An international search for the 777, which left Kuala Lumpur early Saturday bound for Beijing, involves at least a dozen countries. Ships and aircraft are now combing a vast area that has been widened to cover the Gulf of Thailand, the Andaman Sea and on both sides of the Malay Peninsula.
The United States, which has sent ships and planes, said the search area may soon expand into the Indian Ocean, consistent with the theory that the plane may have detoured to the west about an hour after take-off from the Malaysian capital.
"It's my understanding that based on some new information that's not necessarily conclusive - but new information - an additional search area may be opened in the Indian Ocean," White House spokesman Jay Carney told reporters in Washington.
India's defense ministry has already ordered the deployment of ships, aircraft and helicopters from the remote Andaman and Nicobar Islands, 740 miles east of Chennai, at the juncture of the Bay of Bengal and Andaman Sea.
The Indian armed forces will hold a meeting on Thursday to decide how to coordinate their search efforts with other countries that are participating, a senior command officer said.
An Indian P8I Poseidon surveillance plane was sent to the Andaman islands on Thursday, ready to join the search once cleared, the head of India's Andaman and Nicobar air force command, Air Marshal P.K Roy, said on Thursday.
The U.S. Navy was sending an advanced P-8A Poseidon to help search the Strait of Malacca, separating the Malay Peninsula from the Indonesian Island of Sumatra. It had already deployed a Navy P-3 Orion aircraft to those waters.
U.S. defense officials later told Reuters that the U.S. Navy guided-missile destroyer, USS Kidd, was en route to Strait of Malacca, answering a request from the Malaysian government. The Kidd had been searching the areas south of the Gulf of Thailand, along with the destroyer USS Pinckney.
LITTLE FRESH LIGHT
The new information about signals heard by satellites shed little light on the mystery of what happened to the plane, whether it was a technical failure, a hijacking or another kind of incident on board.
While the troubleshooting systems were functioning, no data links were opened, the sources said, because the companies involved had not subscribed to that level of service from the satellite operator, the sources said.
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.
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.
Malaysian authorities have said the last civilian contact occurred as the Boeing 777-200ER flew north into the Gulf of Thailand. They said military radar sightings indicated the plane may have turned sharply to the west and crossed the Malay Peninsula toward the Andaman Sea.
It is one of the most baffling mysteries in the history of modern aviation - there has been no trace of the plane since nor any sign of wreckage despite a search by the navies and military aircraft of over a dozen countries across Southeast Asia.
"It's extraordinary that with all the (satellite and telecommunication) technology that we've got that an aircraft can disappear like this," Tony Tyler, the head of the International Air Transport Association that links over 90 percent of the world's airlines, told reporters in London.