Investigators focus on pilots as hunt for plane widens from Indian Ocean to Central Asia

Malaysian authorities Sunday were investigating the pilots of the missing jetliner after it was established that whoever flew off with the Boeing 777 had intimate knowledge of the cockpit and knew how to avoid detection when navigating around Asia.

Satellite data suggested the plane flew for at least 7 ½ hours — more than six hours after the last radio contact — and that it could have reached as far northwest as Kazakhstan or deep into the southern Indian Ocean, making the hunt by 12 nations involving more than 100 planes and ships one of the largest in aviation history. Given that the northern route would take the plane over several countries, experts thought a southern path over one of the most remote stretches of water much more likely.

In the first detailed findings on what happened to the plane, Prime Minister Najib Razak said Saturday someone severed communications with the ground and deliberately diverted Flight 370 back over the Malay Peninsula after it departed Kuala Lumpur for Beijing early on March 8.

The revelations raised questions over possible lapses by Malaysian authorities, including why the air force wasn't aware that a jetliner was flying over the country. It also triggered speculation over who on the plane was involved — and what motive they might have for flying away with a plane carrying a 12-person crew and 227 passengers.

If the pilots were involved in the disappearance, where they working together or alone, or with one or more of the passengers or crew? Did they fly the plane under duress or of their own volition? Did one or more of the passengers manage to break into the cockpit, or use threat of violence to gain entry and then pilot the plane?

Malaysian authorities have not ruled out any possibility, and the answers to those questions will have to wait until the flight data recorders are recovered, assuming the plane is ever found.

Police are investigating all those on board, especially the pilots and anyone else on the manifest with possible aviation experience. That could include past contact with each other, physiological, mental or financial issues or ties to extremist organizations.

Malaysian officials and aviation experts said that whoever disabled the plane's communication systems and then flew the jet must have had a high degree of technical knowledge and flying experience, putting the pilots at the top of the possible suspects list.

"In view of this latest development, the Malaysian authorities have refocused their investigation into the crew and passengers on board," Najib told reporters, reading from a written statement but not taking any questions.

Police on Saturday went to the Kuala Lumpur homes of both the pilot Zaharie Ahmad Shah, 53, and co-pilot Fariq Abdul Hamid, 27. They have released no details on their investigation so far.

Zaharie, who joined Malaysia Airlines in 1981 and had more than 18,000 hours of flying experience, was known as an avid aviation enthusiast who had set up an elaborate flight simulator at home. Earlier this week, the head of Malaysia Airlines said this was not unusual.

Fariq was contemplating marriage after having just graduated to the cockpit of a Boeing 777. He has drawn scrutiny after the revelation that he and another pilot invited two female passengers to sit in the cockpit during a flight in 2011.

The flight departed Kuala Lumpur at 12:40 a.m. heading toward Beijing. Investigators now have a high degree of certainty that one of the plane's communications systems — the Aircraft and Communications Addressing and Reporting System (ACARS) — was partially disabled before the aircraft reached the east coast of Malaysia, Najib said. Shortly afterward, someone on board switched off the aircraft's transponder, which communicates with civilian air traffic controllers.

To turn off the transponder, someone in the cockpit would have to turn a knob with multiple selections to the "off" position while pressing down at the same time, said John Goglia, a former member of the U.S. National Transportation Safety Board. That's something a pilot would know, but it could also be learned by someone who researched the plane on the Internet, he said.

The ACARS system has two aspects, Goglia said. The information part of the system was shut down, but not the transmission part. In most planes, the information section can be shut down by hitting cockpit switches in sequence in order to get to a computer screen where an option must be selected using a keypad, said Goglia, an expert on aircraft maintenance.

That's also something a pilot would know how to do, but that could also be discovered through research, he said.

But to turn off the other transmission portion of the ACARS, it would be necessary to go to an electronics bay beneath the cockpit. That's something a pilot wouldn't normally know how to do, Goglia said. The Malaysia plane's ACARS transmitter continued to send out blips that were recorded by satellite after the transponder was turned off. The blips don't contain any messages or data, but the satellite can tell in a very broad way what region the blips are coming from.

Najib confirmed that Malaysian air force defense radar picked up traces of the plane turning back westward, crossing over Peninsular Malaysia into the northern stretches of the Strait of Malacca. Authorities previously had said this radar data could not be verified.

The air force has yet to explain why it didn't spot the plane flying over the country, and respond. The search was initially focused on the Gulf of Thailand and the South China Sea, where the plane severed its communication links. That search has now ended.

"One that thing that does bother me greatly is the fact that unidentified aircraft could navigate back over Malaysia and out to sea without a physical or material response to that fact," said Britain-based aviation security consultant Chris Yates. "They were not watching."

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Associated Press writers Ian Mader, Eileen Ng and Jim Gomez contributed to this report.