At issue are estimates of how far the plane may have traveled after it ran out of fuel, notably whether it followed a tight or broad spiral down as it fell or glided toward the ocean, officials said.
“We’re really doing further work to test our assumption about the end of flight, which defines our search area,” said Martin Dolan, the chief commissioner of the Australian Transport Safety Bureau. “It’s really testing to make sure we haven’t missed anything, and that our assumptions remain valid.”
The failure to find any wreckage in the area also raises the possibility that the plane began descending earlier, or perhaps changed course in an attempt at an emergency landing at sea, though investigators have discounted these outcomes as inconsistent with other evidence.
There is still hope that the plane will be found in the search zone, an expanse of 46,000 square miles, about the size of England. But ocean survey vessels have scoured about 90 percent of the area and are expected to finish the rest in August. Unless new information emerges, that is when the governments of Australia, Malaysia and China plan to abandon the search, leaving one of the greatest mysteries in the history of modern aviation unsolved.
Flight 370 disappeared on March 8, 2014, while flying to Beijing from Kuala Lumpur, the Malaysian capital, carrying 239 passengers and crew members from 15 nations. An analysis of radar and satellite communications data determined that the Boeing 777-200 made several turns and then flew south for five hours with little deviation. But investigators never pinpointed where the plane ran out of fuel.
Instead, they identified a 400-mile arc from which the plane most likely sent its last satellite signal. Survey vessels have been going back and forth at walking speed across that swath of the southern Indian Ocean for two years, using sonar devices towed over the seafloor to scan the Stygian depths more than two miles below the waves.
Investigators are now asking whether they have been looking in the right place. They are reconsidering an assumption that when the plane’s engines ran dry, the aircraft spiraled into the sea without traveling a horizontal distance of more than 10 nautical miles — a relatively tight spiral.
Analysts at Boeing and elsewhere have been re-examining their models of how the aircraft operating under autopilot might have responded to an initial loss of power on one side of the aircraft, and, up to 15 minutes later, on both sides. The simulations assume the right engine ran out of fuel first, because over its years of service that engine on the aircraft had tended to burn slightly more fuel than the left engine, according to records from Rolls-Royce, the engines’ manufacturer.
The three countries bankrolling the search for the missing Boeing 777-200 agreed in April last year not to expand the search area unless new information provided clear clues that the plane was somewhere else.
So far, no evidence has emerged that would justify an expanded search, Mr. Dolan said.
While the search for Flight 370 is already the largest and most costly in aviation history, relatives of passengers on the plane have called for it to be extended, as have many scientists, pilots, hobbyists and others mesmerized by the mystery of its disappearance.
“There is no reason we should give up the search — at least they have to give us an answer,” said Steve Wang, a technology company salesman in Beijing who has served as an unofficial spokesman for the families and whose 57-year-old mother was on the plane. “Everything about MH370 remains a mystery — what happened, and how?”
The search zone was calculated using the last automatic signal sent by the aircraft’s engines to a satellite right before it disappeared. The signal indicated that the satellite system had been reset, suggesting a power failure, possibly caused by the engine’s running out of fuel.
Though the signal did not include location data, analysis of the time it took the transmission to travel to and from the satellite led investigators to focus on the 400-mile arc.
But Duncan Steel, a scientist on a panel of experts that has advised the Australian government, said the arc might have been drawn too far south. Investigators have assumed the plane was at cruising altitude when it sent its last signal, he said, but if the plane had started descending earlier as it ran low on fuel, it would have covered less distance before it hit the ocean.
Investigators said on May 12 that two pieces of debris recovered in March from South Africa and from Rodrigues Island, part of Mauritius, were “almost certainly” from the missing plane. But neither part — a piece of the interior panel in the main cabin and a piece of engine covering — provided significant information about the aircraft’s final location.
Australia’s minister of infrastructure and transport, Darren Chester, announced on May 26 that two more pieces of debris had been found in Mauritius and another in Mozambique that would also be examined for possible links to the missing aircraft.
The Australian government said on Friday that four more pieces of debris, three found on Madagascar and one on a southern Australian island, would be checked to determine whether they came from the missing plane.
Three other pieces linked to the plane were discovered on African beaches last year and early this year. One was identified as clearly belonging to the right wing, while another was identified as “almost certainly” coming from the right wing and a third as “almost certainly” coming from the right side of the tail.
The accumulation of parts from the aircraft’s right side has led some to suggest that the plane may have changed course before it crashed, possibly under the control of a conscious pilot.
In theory, a pilot could have attempted an emergency landing by turning the plane and trying to land it just behind an ocean swell, before the next swell arrived.
One of the many risks of such a maneuver would be a wave’s snagging and tearing off a wing, leaving wing debris that might end up floating far away while the rest of the aircraft landed more softly and sank.
Peter Marosszeky, a longtime aircraft engineer who advised Boeing on the development of the 777 aircraft and is now the managing director of Aerospace Developments, a Sydney consulting firm, said some wing parts were made from lightweight composite materials that would float easily.
If a conscious pilot were still at the controls, it also would have been possible in theory for the plane to glide and travel much farther after it ran out of fuel.
But Mr. Dolan said considerable data from the rest of the flight, including signs that the plane maintained its speed, altitude and heading hour after hour as it traveled south across the Indian Ocean, made it very unlikely that a conscious pilot was at the controls.
By Keith Bradsher
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