Najib also said that search efforts in the South China Sea had been ended and that technical experts now believed the aircraft could have ended up anywhere in one of two zones - one as far north as Kazakhstan in Central Asia, the other crossing the southern Indian Ocean.
That conclusion was based on a final signal from the plane picked up on satellite at 8:11 a.m. March 8, nearly seven hours after ground control lost contact with the jet, he said.
While Najib said that investigators had not ruled out alternatives to hijacking, his remarks represented official confirmation that the disappearance of the Boeing 777-200 had not been an accident. He noted that one communications system had been disabled as the plane flew out over the northeast coast of Malaysia and that a second system, a transponder aboard the aircraft, had stopped broadcasting its location, altitude, speed and other information at 1:21 a.m. while the plane was a third of the way across the Gulf of Thailand from Malaysia to Vietnam.
Military radar data subsequently showed that the aircraft actually turned and flew west across northern Malaysia before arcing out over the wide northern end of the Strait of Malacca, headed at cruising altitude for the Indian Ocean.
The 7th Fleet of the U.S. Navy said in a statement Saturday that its search for the missing plane now encompasses the Strait of Malacca and beyond to the Bay of Bengal - an enormous area. But Najib said that representatives of many more governments across the region had been contacted, given how far the plane could have travelled in the several hours it remained airborne after flying out over the Strait of Malacca.
Huang Huikang, China's ambassador to Malaysia, sat impassively in a light gray suit in the front row of the news conference at an airport hotel here on the outskirts of Kuala Lumpur. The disappearance of the jet has mesmerized many in China, partly because nearly two-thirds of the 239 people aboard were Chinese citizens.
The news conference came a day after U.S. officials and others familiar with the investigation said the plane had experienced significant changes in altitude after it lost contact with ground control and altered its course more than once as if still under the command of a pilot.
Radar signals recorded by the Malaysian military appeared to show that the missing airliner climbed to 45,000 feet, above the approved altitude limit for a Boeing 777-200, soon after it disappeared from civilian radar and turned sharply to the west, according to a preliminary assessment by a person familiar with the data.
The radar track, which the Malaysian government has not released but says it has provided to the United States and China, showed the plane then descended unevenly to 23,000 feet, below normal cruising levels, as it approached the densely populated island of Penang. There, officials believe, the plane turned from a southwest-bound course, climbed to a higher altitude and flew northwest over the Strait of Malacca toward the Indian Ocean.
Investigators have also examined data transmitted from the plane's Rolls-Royce engines that showed it descended 40,000 feet in the span of a minute, according to a senior U.S. official briefed on the investigation. But investigators do not believe the readings are accurate because the aircraft would most likely have taken longer to fall such a distance.
"A lot of stock cannot be put in the altitude data" sent from the engines, one official said. "A lot of this doesn't make sense."
The data, while incomplete and difficult to interpret, could still provide critical new clues as investigators try to determine what happened on Flight 370, which disappeared carrying 239 people from Kuala Lumpur to Beijing.
Malaysian and international investigators said in recent days that the plane may have departed from its northerly route toward Beijing and headed west across the Malay Peninsula just after the aircraft disappeared from civilian radar, its pilots stopped communicating with ground controllers and its transponders stopped transmitting data about its speed and location. The plane is also now thought to have continued flying for more than four hours after diverting its course, based on automated pings sent by onboard systems to satellites.
But the Malaysian military radar data, which local authorities have declined to provide to the public, added significant information about the flight immediately after ground controllers lost contact with it.
The erratic movements of the aircraft after it diverted course and flew over Malaysia also raise questions about why the military did not respond to the flight emergency. Malaysian officials acknowledged earlier this week that military radar may have detected the plane but said they took no action because it did not appear hostile.
Because the plane stopped transmitting its position about 40 minutes after takeoff, military radar recorded only an unidentified blip moving through Malaysian airspace. Certain weather conditions, and even flocks of birds, can occasionally cause radar blips that may be mistaken for aircraft.
The person who examined the data said it left little doubt that the airliner flew near or through the southern tip of Thailand, then back across Peninsular Malaysia, near the city of Penang, and out over the sea again. That is in part because the data is based on signals recorded by two radar stations, at the Royal Malaysian Air Force's Butterworth base on the peninsula's west coast, near Penang, and at Kota Bharu, on the northeast coast. Two radars tracking a contact can significantly increase the reliability of the readings.
Still, Ravi Madavaram, an aerospace engineer at the consulting firm Frost & Sullivan based in Kuala Lumpur, said the accuracy of ground-based radars in determining a plane's altitude diminishes the farther away the plane is. When Flight 370 lost contact with ground controllers, it was more than 100 miles from Kota Bharu and 200 miles from Butterworth, distances that he said could degrade accuracy. But the altitudes measured as the plane crossed the peninsula would be more reliable, he said.
A senior aircraft industry executive in the United States said the account of Flight 370's movements that was emerging from the Malaysian military radar information matched what their officials were told.
"Everything we have heard is consistent with the plane flying under the control of someone with at least some flying experience," said the industry executive, who asked not to be identified because of the tense nature of the conversation underway with the Malaysian authorities.
Military radar last recorded the aircraft flying at an altitude of 29,500 feet about 200 miles northwest of Penang and headed toward India's Andaman Islands. The normal cruising altitude of a long-range commercial jetliner is between 30,000 and 40,000 feet.
Cengiz Turkoglu, a senior lecturer in aeronautical engineering at City University London who specializes in aviation safety, said a deliberate act in the cockpit could cause a radical change in altitude.
''It is extremely difficult for an aircraft to physically, however heavy it might be, to free fall," he said.
An Asia-based pilot of a Boeing 777-200, who asked not to be identified because he was not authorized to speak to reporters, said an ascent above the plane's service limit of 43,100 feet, along with a depressurized cabin, could have rendered the passengers and crew unconscious and could be a deliberate manoeuvre by a pilot or a hijacker.
Other experts said that altitude changes would be expected if the pilots became disabled after the plane's autopilot was disengaged. Changes in the weight distribution on the plane as fuel burned off would make the plane descend and climb repeatedly, though changes in course would be harder to explain.
U.S. officials were concerned in the first few days after the plane disappeared that terrorists had brought it down. But as investigators have examined the flight manifest and looked into the two Iranian men who were on the plane traveling with stolen passports, they have become convinced that there is no clear connection to terrorism.
The FBI interviewed family members of the Iranian men and used computer programs to determine whether they had ties to terrorists. Those efforts showed no such connections, leading the investigators to believe the men were smugglers.
Investigators considered but dismissed the possibility that hijackers landed the plane somewhere for later use in a terrorist attack, according to a senior U.S. official briefed on the investigation.
The data, the official said, "leads them to believe that it either ran out of fuel or crashed right before it ran out of fuel."
It would take a long runway to land a plane of that size, the official said. Although the radius the plane could have flown extends into South Asia, the official added, "The idea it could cross into Indian airspace and not get picked up made no sense."
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