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CANBERRA, Australia — Investigators looking into the disappearance of Malaysia Airlines Flight 370 have concluded that the plane was probably not seriously damaged and remained in controlled flight until it ran out of fuel over the southern Indian Ocean.

Their conclusion, reached in the past few weeks, helped prompt the decision to move the search area hundreds of miles to the southwest.

The main evidence for the conclusion lies in a re-examination of Malaysian radar data from the flight and a more detailed analysis of electronic “handshakes” that the aircraft exchanged with an Inmarsat satellite over the Equator, senior officials involved in the investigation said. The altitude data from that tracking now appears to have been inaccurate, officials said.

Malaysian military radar tracked the Boeing 777-200 with 239 people aboard as it performed a U-turn over the Gulf of Thailand on March 8, flew across Peninsular Malaysia and the Strait of Malacca and disappeared at the north end of the Indonesian island of Sumatra. Initial reports on the radar readings suggested that the plane soared to 45,000 feet, above its certified maximum altitude of 43,100 feet, then zoomed down low over the mountains of Peninsular Malaysia before climbing back to 23,000 feet or more over the Strait of Malacca.

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But a comprehensive international review of the data has concluded that the Malaysian radars had not been calibrated with enough precision to draw any conclusions about the altitude.

“The primary radar data pertaining to altitude is regarded as unreliable,” said Angus Houston, the retired head of the Australian military who is now coordinating the search.

Houston said in a telephone interview that it was clearly possible that the plane had been at 23,000 feet at some point during the portion of the flight that was tracked on radar. But he expressed skepticism that anyone could prove that the plane had soared and swooped after its U-turn.

Martin Dolan, the chief commissioner of the Australian Transport Safety Bureau, agreed with Houston.

“There’s nothing reliable about height,” he said in an interview in his office here.

Radar can give reliable readings of an aircraft’s location, speed and direction, but it is reliable on altitude readings only if it is regularly and carefully calibrated to local atmospheric conditions.

Houston and Dolan declined to discuss any details about the Malaysian radar readings, nor would they speculate on why the plane might have been engaged in controlled flight across the Indian Ocean.

Other officials involved in the crash investigation have suggested that either of the plane’s pilots might have commandeered the aircraft in order to commit suicide, or that a smoldering fire in the fuselage might have smothered the pilots and passengers with smoke while allowing the aircraft’s engines to continue to operate.

Some investigators of the crash are convinced that one of the pilots was involved, saying that no credible evidence has appeared for another explanation. But other investigators say that the evidence for pilot involvement is inconclusive and contradictory.

An FBI analysis of a homemade flight simulator taken from the home of the captain, Zaharie Ahmad Shah, found that many simulations had been deleted from it, including some to the Indian Ocean, but investigators said that was hard to interpret as evidence that Zaharie might have plotted a suicidal course. A clinical psychologist advising the inquiry has also been skeptical that anyone would commit suicide by flying for more than six hours with a planeload of people; previous cases linked to pilot suicide have involved pilots who appeared to fly almost straight down soon after takeoff.

Hishammuddin Hussein, Malaysia’s defense minister and acting transport minister, publicly denied British and Australian news reports Monday that the pilot had been identified as the prime suspect.

If the plane did not soar and swoop but maintained a steadier altitude, it would have tended to burn less fuel and so could have gone farther south across the Indian Ocean before its tanks ran dry.

Houston and Dolan each said that the most reliable data came from the electronic handshakes. That data yields a series of six hourly arcs as the aircraft apparently headed south across the Indian Ocean, and a seventh arc based on a partial handshake as the engines appeared to run into difficulty.

“The final arc is very clear,” Dolan said. “Everyone agrees that is where the aircraft ran out of fuel.”

The Australian government initially searched in the northeast corner of the seventh arc, partly because that location was consistent with an aircraft that was limping through the sky fairly slowly because it was damaged, or had burned a great deal of fuel in altitude changes, or both. The initial search was also set off by the detection of undersea sounds that were judged at first to be from the locator beacons of the plane’s black boxes, although investigators later decided that was wrong.

The next phase of the search will be hundreds of miles to the southwest, consistent with an aircraft that flew steadily south at a fairly high cruising speed from the time it disappeared near the northern tip of Sumatra until it ran out of fuel somewhere along the seventh arc, officials said. While the search zone is still being made final, it is likely to be a band from about 25 miles inside the seventh arc to 35 miles outside it, and extending roughly 400 miles along the arc in the southern Indian Ocean.

But the nearly 60-mile width of the band is based on a crucial assumption: that the plane was on autopilot when it ran out of fuel, and that the autopilot was unable to control the plane when the engines stopped. In that case, the plane would have stalled and fallen fairly quickly into the ocean somewhere near where the fuel ran out.

The Australian government is seeking bids for as many as three deep-sea submersibles to scour the ocean floor for the aircraft. Not yet resolved is the path they should take: whether the submersibles should be towed for days nonstop from northeast to southwest along the full length of the band, or back and forth across the width of the band in the areas where the plane is most likely to have crashed.

It takes many hours for the towed submersibles to be turned around at the end of each sweep. So short sweeps of the most likely areas mean that the aircraft might be found sooner, but that the entire search area could take much longer to cover if the plane is not located in the initial weeks.

Private telecommunications analysts have done their own review of the electronic handshakes after Inmarsat published them and also concluded that the most likely location was far southwest of the area initially searched and southwest even of the Australian mainland.

But if a skilled pilot was conscious and still at the controls when the fuel ran out, the plane could have glided more than 100 miles before it hit the water. In that case, an undersea debris field would lie far outside the new search zone, which is to be announced soon.

“We are cautiously optimistic that we will find the aircraft,” Dolan said, adding, “Some are more optimistic, and some are less so.”

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