International investigators arrived in Malaysia to help in the hunt for the jet missing for more than a week with 239 passengers and crew on board. (Reuters)

International investigators arrived in Malaysia to help in the hunt for the jet missing for more than a week with 239 passengers and crew on board. (Reuters)

The search for Malaysia’s missing airliner pushed on Monday across a vast spread of the Indian Ocean into the waters off western Australia as officials here contradicted earlier information that pointed to a planned takeover in the cockpit.

The government had previously said that a key satellite communications system had been disabled sometime before the cockpit made final radio contact with air-traffic control — and before Malaysia Airlines Flight MH370 disappeared from civilian radar contact on March 8 with 239 passengers and crew members on board.

That sequence of events suggested that something suspicious was underway before that final radio call was made, and that one or both pilots were either involved in a plot to commandeer the Boeing 777 or were acting under duress.

But authorities acknowledged Monday that they do not know exactly when that data system went dark, making it harder to pinpoint when the suspected act of hijacking or sabotage was initiated.

The new disclosure does not change the criminal nature of the investigation. It still appears likely that someone was trying to cover his tracks as the plane was deliberately flown off-course.

1 of 84 Full Screen Autoplay Close Skip Ad × ‘Deliberate action’ cited in Malaysia Airlines flight’s disappearance View Photos In the most comprehensive account to date of the missing Malaysia Airlines Flight 370’s fate, Malaysian Prime Minister Najib Razak on Saturday said that the plane was steered off course after its communications systems were intentionally disabled and that it could have flown for seven additional hours. Caption In the most comprehensive account to date of the missing Malaysia Airlines Flight 370’s fate, Malaysian Prime Minister Najib Razak on Saturday said that the plane was steered off course after its communications systems were intentionally disabled and that it could have flown for seven additional hours. March 15, 2014 Crew members look outside windows from a Malaysian air force CN235 aircraft during a search-and-rescue operation to find the missing Malaysia Airlines Flight 370 over the Strait of Malacca. Prime Minister Najib Razak said on Saturday that Malaysia was ending its search for the vanished jetliner in the South China Sea after investigations indicated the missing plane likely turned far to the west. Mohd Rasfan/AFP/Getty Images Buy Photo Wait 1 second to continue.

The New York Times reported Monday night, citing senior U.S. officials, that the first turn to the west that diverted the plane from its planned flight path was carried out through a computer system that was most likely programmed by someone in the plane’s cockpit who was knowledgeable about airplane systems. If true, this would reinforce investigators’ belief that foul play was involved and increase their focus on the plane’s captain and first officer, the report said.

And on Tuesday, China’s ambassador to Malaysia said background checks on Chinese nationals onboard the flight revealed no evidence showing they were involved in terrorism, The Associated Press reports.

The search has been plagued by a series of contradictory statements from Malaysian authorities that have frustrated countries in the region and caused anguish for relatives of those on board.

Chinese Premier Li Keqiang asked Malaysia to provide more detailed and timely data about the flight, which had departed Kuala Lumpur and was bound for Beijing, the Chinese news agency Xinhua said.

Australia committed several more planes to a search off Perth, the west coast city whose offshore waters run to 13,000 feet deep. Malaysian Prime Minister Najib Razak asked the Australians to coordinate the activity.

In a statement, Australian Prime Minister Tony Abbott said, “Australia is preparing to work with assets from a number of other countries, including surveillance aircraft from New Zealand and the United States.”

With the focus switching to Australian waters, the U.S. Navy said its ship that had been looking for wreckage in the Andaman Sea would pull out of the search.

View Graphic New data has provided an arc of possible locations for Malaysian Flight MH370.

Narrowing search area

Malaysian Defense Minister Hishammuddin Hussein said Monday that it was important to narrow the focus of the hunt.

“The area is huge,” he said, “and what we’ve been doing is to try to narrow this.”

Malaysian officials have asked countries throughout the region to search their radar records for clues as to where the airliner could have flown. Aviation officials in Pakistan say they have no evidence that the plane entered the country’s airspace. Indian defense officials and air-traffic controllers have scoffed at the theory that a plane could have flown across that country undetected. However, security analysts said that radar does not cover all 1.2 million square miles of that country.

Malaysian officials said that they were reviewing psychological tests of crew members and that they had asked Chinese authorities to examine the histories of the 154 Chinese passengers.

U.S. aviation expert Ron Carr said that whether the plane is found may depend on how it struck the water. He said that if it came in as though it were landing, it would float for a while and then sink, creating a large underwater target for sonar detectors. If it came down hard and broke into pieces, plenty of debris would be floating.

“The third option is the aircraft went under water at a steep angle,” said Carr, who was an Air Force and airline pilot for 39 years before becoming a professor at Embry-Riddle Aeronautical University in Arizona. “It would accordion down into a smaller size that would make discovery more difficult. A ship or an aircraft would have to be in the right place, at the right time, looking in the right spot to see any floating debris, if there was any floating debris left to see.”

Unlike in the most recent airliner to crash in the ocean, Air France Flight 447 in 2009, Carr said, there is no clue as to where to search.

“As time goes by, I would say it would become more and more difficult to find the [Boeing] 777, and at some point the cost of the search will reach a point that it will be abandoned and the possibility of it never being found obviously goes way up,” he said.

Evidence points to a plan

Malaysia Airlines chief executive Ahmad Jauhari Yahya said the automatic communications system made what proved to be a final transmission at 1:07 a.m. on March 8, relaying routine information about the plane’s performance. The next transmission, from the Aircraft Communications Addressing and Reporting System (ACARS), was due 30 minutes later but never arrived, he said.

“The last ACARS transmission was 1:07. It was supposed to transmit 30 minutes from that, but that transmission did not come through,” he said. “When was it switched off? Any time between then and 30 minutes later.”

At 1:19 a.m., the co-pilot of Flight MH370, Fariq Abdul Hamid, said, “All right, good night,” to air-traffic controllers in Kuala Lumpur, two minutes before the plane disappeared from civilian radar, authorities said.

The recording of that final radio contact is being analyzed to see if it could indicate whether everything was normal in the cockpit at the time. On Sunday, Hishammuddin had told reporters that the ACARS system was shut down before the “good night” communication, suggesting that the person at the controlswas either hiding information or being forced to cover up the irregular situation. Malaysian authorities revealed Monday that it was the co-pilot who said good night to air traffic control.

Indications that something malign was occurring before the final radio call had led many people to suspect that the co-pilot or the plane’s captain, Zaharie Ahmad Shah, might have been behind the plane’s disappearance. Zaharie had flown for the airline for 30 years and had not shown any sign of personal trouble recently, friends said.

Hishammuddin said Zaharie and Fariq’s homes were visited on March 9 and then searched over the past weekend. Police are examining a flight simulator from Zaharie’s home, he said. But he has warned against jumping to conclusions, saying that the pilot and co-pilot had not asked to fly together that day.

Evidence has steadily mounted that the plane’s diversion — by passengers or crew members — was meticulously planned.

The plane’s transponder, a device that identifies and locates the airliner for civilian air-traffic control, was turned off just as it was leaving Malaysian airspace and entering that of Vietnam. At that point, the plane appeared to turn back toward the Malay Peninsula, flying on for as many as seven hours without being spotted.

Steven B. Wallace, a former head of investigations at the Federal Aviation Administration, said he is confident that the mystery will be solved. But “I’m slightly less confident than I was on the day this investigation began,” he said. “This is the modern jet transport era, and this is a state-of-the-art aircraft. Jet airliners have never disappeared. We’ve never seen anything like this.”

Halsey reported from Washington. Chico Harlan in Kuala Lumpur, Tim Craig in Islamabad, Annie Gowen in New Delhi and Ernesto Londoño in Washington contributed to this report.