The search for a missing Malaysian jetliner with 239 people onboard could expand westward into the Indian Ocean based on information that the plane may have flown for at least four hours after it dropped from civilian radar, U.S. officials said Thursday.

A senior U.S. official said the information came from data sent via a satellite communications system by Malaysia Airlines Flight MH370. That data has convinced U.S. officials that the plane’s engines continued to run for at least four hours after all other communication was lost.

If the plane flew on for hours, it raises the likelihood of foul play. U.S. officials said someone in the cockpit could have turned off the transponder and radio before flying on.

“The fact that a modern airplane with a huge amount of redundancy appeared to change course at the same time that the transponder was turned off, that suggests that someone unauthorized took control of that airplane, like an intruder or one of the pilots,” said a U.S. air-crash expert who spoke on the condition of anonymity because the expert is not directly involved in the investigation.

All other communication with the plane ended by 1:30 a.m. Saturday. Around that point, the pilot signed off with Malaysian air-traffic controllers with a casual “All right, good night,” according to news reports. Then the transponder signal that the plane was sending to ground-based radar stations went silent.

New twist in the hunt for missing plane

Other U.S. officials said their information did not reveal what direction the plane flew — or whether it simply circled — during those four hours. That much additional flight time could have put the plane somewhere over the Indian Ocean, far from its Beijing destination, prompting officials to consider whether the search area should be expanded.

Malaysian authorities said they would not release any information until it had been corroborated and verified. “We have nothing to confirm at this moment,” acting Transport Minister Hishammuddin Hussein told a news conference in Kuala Lumpur Friday.

Malaysia’s civil aviation chief Azharuddin Abdul Rahman said satellites did not receive any “distress signal” from the plane, but when asked whether it could have sent “pings”, he said: “What the U.S. team are doing, they are trying their best to get whatever sources they can from the satellite system, to come up with possibilities of where the aircraft should be.”

Malaysian authorities have said they are investigating all passengers and crew aboard, but denied local media reports on Thursday that they searched a home of one of the pilots.

A modern airplane sends information in a steady stream to its owner, the company that built it or the firm that built its engines. In the final minutes before Air France Flight 477 plunged into the Atlantic almost five years ago, it sent 29 automatic error messages to the airline’s home base in France.

The Wall Street Journal first reported that U.S. investigators suspect that the engines on the Malaysia Airlines flight kept running for up to four more hours after the plane reached its last known location. The newspaper later corrected its report to say that this belief was based on satellite data that was designed to report on the status of some onboard systems, not signals from monitoring systems embedded in the plane’s Rolls-Royce engines. The Malaysian government denied the initial report.

In Washington, one senior administration official said the signals came from the Aircraft Communications Addressing and Reporting System (ACARS), with which planes maintain contact with ground stations using radio or satellite signals. The official, who spoke on the condition of anonymity because of the ongoing investigation, said Malaysian authorities shared the flight data with the administration. The fact that the signals did not reveal the plane’s location suggested that it came from the engine.

As the search for the missing Malaysian jetliner continues, The Post's Joel Achenbach explains several possible scenarios for what could have happened and why this case is puzzling experts. (Gillian Brockell and Kate M. Tobey/The Washington Post)

On Thursday, Malaysia Airlines CEO Ahmad Jauhari Yahya strongly denied that the ACARS system continued to function after the plane disappeared from civilian radar at 1:30 a.m. Saturday. The last transmission came 26 minutes after its takeoff from Kuala Lumpur, he said.

“The last transmission was received at 1:07,” Ahmad told reporters. “It said everything is operating normally… As far as the ACARS data, that was the last transmission.”

Several media reports Friday said that the ACARS system was not sending data, but rather “pings” — the result of trying to establish satellite contact. Reuters reported that these pings were transmitted by MH370 once every hour five or six times.

Representatives of both Boeing and Rolls-Royce have been in Kuala Lumpur working with the airline, and neither received data after 1:07 a.m., Ahmad said. A Rolls-Royce spokeswoman refused to comment on the reports.

If the plane continued flying westward, it would have traveled toward the Indian Ocean. In a signal that the United States believed the plane had likely veered off course, the U.S. Navy said Thursday it was shifting one of its ships involved in the hunt, the destroyer USS Kidd, from the Gulf of Thailand to the Malacca Strait on the western side of the Malay Peninsula.

The U.S. military also announced that it would add a P-8A Poseidon aircraft to the search Friday. The plane will join a Navy P-3C Orion surveillance aircraft already patrolling in the area.

India’s defense ministry said Friday a third Coast Guard vessel, the CGS Sagar, is en route from Singapore to join a widening search effort already underway in the Andaman Sea near the Malacca Strait. The ship, when it arrives, will join the INS Kumbhir, an amphibious warfare ship, and INS Saryu, a patrol vessel, along with a host of military aircraft (Navy, Coast Guard and Air Force) searching the waters west of Malaysia.

A senior administration official from the Indian government said Friday that the search team had targeted its efforts in the waters west of Malaysia based on a series of coordinates given to them by the Malaysian government, but he was not sure what data the Malaysians had that lead them to target those specific areas.

On Friday, the Reuters news agency said that military radar-tracking evidence suggested the plane was deliberately flown across the Malay peninsula towards India’s Andaman Islands.

Citing sources familiar with the investigation, it reported that the plane was following a route between navigational waypoints — indicating it was being flown by someone with aviation training — when it was last plotted on military radar off the country’s northwest coast.

Meanwhile, officials on the ground in Port Blair, the capital of the Andaman and Nicobar islands, said they have been in contact with local fishermen in hopes they will report any unusual finds.

“We have conveyed to the local people and the fishermen-watch groups there that if they see something, they should report. But the places where they are looking for the plane near Malacca Straits, we don’t have heavy habitation, a few sparsely populated islands. But we have alerted communities and officers there to report,” said Sudhir Yadav, senior police officer in Port Blair.

Burma, also known as Myanmar, said it would open its airspace to planes looking for the missing airliner and was prepared to join the search if asked, the BBC reported.

In Washington, White House press secretary Jay Carney told reporters that the United States is not in a position to draw any conclusions. He said, “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.”

Search operations in the Indian Ocean, the world’s third-largest ocean with an average depth of nearly 12,800 feet, would present significant challenges.

The United States is “consulting with international partners about the appropriate assets to deploy,” Carney said.

The search for Flight MH370 has at times appeared chaotic and baffling — a mix of rumors, confusion and false leads. The government in Kuala Lumpur acknowledged Thursday that it had made little progress in solving the mystery of the vanished plane.

“We have looked at every lead. In many cases, in fact all the cases, we have not found anything positive,” said Hishammuddin Hussein, Malaysia’s defense minister and acting transport minister.

“This just might be something we have never seen before,” Steven B. Wallace, a former director of the Federal Aviation Administration’s accident investigation office, said in an interview Thursday.

Wallace said progress may be hampered because Malaysia lacks an investigative branch like the U.S. National Transportation Safety Board.

“The pattern here is that the best information is not being immediately presented to the smartest people around who could look at it,” Wallace said. He noted that Malaysian authorities revealed only after several days that their military radar had picked up signs of a plane flying off Malaysia’s western coast after the passenger jet had disappeared much farther east.

Then, China disclosed four days after the disappearance that its satellites had picked up images of what appeared to be debris in the area where the plane vanished. No signs of wreckage were found there.

Simon Denyer and William Wan in Beijing, Karla Adams in London, and William Branigin and Ernesto Londoño in Washington contributed to this report.