SEPANG, Malaysia » Malaysia Airlines Flight 370 experienced significant changes in altitude after it lost contact with ground control, and it altered its course more than once as if still under the command of a pilot, U.S. officials and others familiar with the investigation said Friday.

Radar signals recorded by the Malaysian military appear to show the missing airliner climbing to 45,000 feet, above the approved altitude limit for a Boeing 777-200, soon after it disappeared from civilian radar and made a sharp turn 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, then shows the plane descending unevenly to an altitude of 23,000 feet, below normal cruising levels, as it approached the densely populated island of Penang, one of the country’s largest. There, 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 shows it descending 40,000 feet in the space 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 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 transpired on Flight 370, which disappeared early March 8 carrying 239 people from Kuala Lumpur to Beijing.

Malaysian and international investigators have said in recent days that the plane may have departed from its northerly flight route toward Beijing and headed west across the Malay Peninsula just after it 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 trying to connect with satellites.

But the Malaysian military radar data, which local authorities have declined to provide to the public, add significant new information about the flight immediately after ground controllers lost contact. The combination of altitude changes and at least two significant course corrections could have a variety of explanations, including an intentional diversion by a pilot or a hijacker or uneven flying because of a disabled crew.

The erratic movements of the aircraft after it diverted course and flew over the country also raise questions about why the military did not respond in real time to the flight emergency. Malaysian officials have acknowledged that military radar may have picked up the plane but have said they took no action because it did not appear hostile.

Seven days after the jet’s disappearance, Malaysian authorities have shared few details with U.S. investigators, frustrating senior officials in Washington.

"They’re keeping us at a distance," said one of the officials.

But investigators in Malaysia and the United States recently began receiving additional data about the plane and anticipate receiving more during the weekend, according to a senior U.S. official.

"It’s gotten better and better every day," the official said, referring to information from the plane’s manufacturer, satellites and military radar. "It should provide more clarity to the flight path. It’s not a given, but it’s a hope."

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, and the Malaysian authorities say they are still studying the signals to determine if they came from Flight 370.

But the person who examined the data said it leaves 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, one at Butterworth air force base on the peninsula’s west coast, near Penang, and the other 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 determining a plane’s altitude falls the farther away the plane is. When Flight 370 lost contact with ground control, 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.

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.

Cengiz Turkoglu, a senior lecturer in aeronautical engineering at City University London who specializes in aviation safety, said dramatic changes in altitude can be the result of a deliberate act in the cockpit. ”It is extremely difficult for an aircraft to physically, however heavy it might be, to free fall."

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 maneuver by a pilot or hijacker.

U.S. officials were initially concerned in the first few days after the plane went missing that terrorists had brought it down. But as agents have examined the flight manifest and investigated the two Iranian men who were on the plane traveling with stolen passports, the agents have become convinced that there is not a clear connection to terrorism.

As part of its investigative efforts, the FBI interviewed family members of the Iranian men and used computer programs to determine whether they had ties to known terrorists. Those efforts showed no connections to terrorism, 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 substantially long runway to land a plane of that size, the official said, adding that although the radius the plane could have flown extends into territory in South Asia, "the idea it could cross into Indian airspace and not get picked up made no sense."

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