Correction: A report by Australian officials on the disappearance of Malaysia Airlines Flight 370 over the Indian Ocean in March said the most likely scenario was that the plane’s crew had become incapacitated and listed as a possible cause hypoxia. This New York Times article misstated the conclusions of the report.
CANBERRA, Australia — A missing Malaysia Airlines jet appears to have been on autopilot as it flew south across the Indian Ocean until running out of fuel, Australian officials said Thursday in announcing a new deep-sea search for the aircraft.
A report issued by the Australian Transport Safety Bureau, outlining how the new search zone for Flight 370 had been chosen, said the most likely scenario was that the crew was suffering from hypoxia or was unresponsive for another reason as the jet headed south across the Indian Ocean on March 8.
Hypoxia occurs when a plane loses air pressure and the pilots, lacking adequate oxygen, become confused and incapable of performing even basic manual tasks.
Pilots are trained to put on oxygen masks immediately if an aircraft suffers depressurization. Their masks have an hour’s air supply, compared with only a few minutes for the passengers.
The plane, which left Kuala Lumpur, Malaysia, bound for Beijing with 239 people aboard, made its turn south toward the Indian Ocean about an hour after it stopped responding to air traffic controllers.
The crew stopped communicating while the aircraft was over the Gulf of Thailand. Authorities believe the plane then did a U-turn, crossed the Malaysian Peninsula and then headed northwest across the Strait of Malacca before turning south.
It is believed to have crashed somewhere in the southern Indian Ocean off the western coast of Australia, which has been coordinating the search.
Evidence for an unresponsive crew as the plane flew south includes the loss of radio communications, a long period with no maneuvering of the aircraft, a steadily maintained cruise altitude and eventual fuel exhaustion and descent, the report said.
The report added that this was an operating assumption for the search and that it was not meant to infringe on Malaysia’s authority as the government responsible for conclusively identifying a cause for the loss of the plane.
There is no consensus among investigators, even within the Australian government, on the hypoxia or unresponsive-crew theory. Other officials, who insisted on anonymity because of the diplomatic sensitivity of the issue, said some investigators still leaned toward the possibility that one of the pilots deliberately flew the plane to the southern Indian Ocean in a suicide mission.
Advocates of the hypoxia theory argue that pilot suicide cases tend to involve pilots who crash their planes suddenly, not after hours of flight. A clinical psychologist advising the investigation has been very skeptical of the suicide theory, saying it would be highly unusual for a suicidal person to proceed with such a plan over many hours, investigators said.
Depressurization of an aircraft can occur from mechanical failure, an attempted hijacking or many other causes. The Australian report did not speculate on why the crew might have succumbed to hypoxia or otherwise become unresponsive.
At a news conference in Canberra on Thursday, Martin Dolan, the chief commissioner of the Australian Transport Safety Bureau, said someone on the plane had put it on autopilot, but he declined to speculate as to who might have done so and why.
“If the autopilot is operational, it’s because it has been switched on,” Dolan said.