The report added that the theory of an unresponsive crew possibly suffering from hypoxia was an operating assumption for the search and 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. Angus Houston, the retired head of the Australian military who is overseeing the country’s search, said in a telephone interview this month that he assumed that the flight had been on autopilot even if a conscious pilot had been at the controls. That is because a Boeing 777 is a very difficult plane to fly manually.

Other officials, who insisted on anonymity because of the diplomatic sensitivity of the issue with Malaysia and China — most of the flight’s passengers were Chinese — 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 that also killed everyone else aboard.

Advocates of the hypoxia theory argue that pilot suicide cases tend to involve pilots who crashed 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 deadly plan over many hours, investigators said.

Depressurization of an aircraft can occur from mechanical failure, an attempted hijacking or many other causes. If a plane undergoes gradual depressurization, pilots do not necessarily notice that they are losing oxygen, and with it, their mental clarity. Masks are supposed to deploy automatically with a loss of air pressure, but they need to be fitted properly for a full flow of oxygen.

At a news conference here on Thursday afternoon, 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,” Mr. Dolan said.