To turn off the transponder, someone in the cockpit would have to turn a knob with multiple selections to the "off" position while pressing down at the same time, said John Goglia, a former member of the U.S. National Transportation Safety Board. That's something a pilot would know, but it could also be learned by someone who researched the plane on the Internet, he said.
The Aircraft Communications Addressing and Reporting System has two aspects, Goglia said. The information part of the system was shut down, but not the transmission part. In most planes, the information section can be shut down by hitting cockpit switches in sequence in order to get to a computer screen where an option must be selected using a keypad, said Goglia, an expert on aircraft maintenance.
That's also something a pilot would know how to do, but that could also be discovered through research, he said.
But to turn off the other transmission portion of the ACARS, it would be necessary to go to an electronics bay beneath the cockpit. That's something a pilot wouldn't normally know how to do, Goglia said. The Malaysia plane's ACARS transmitter continued to send out blips that were recorded by satellite once an hour for four to five hours after the transponder was turned off. The blips don't contain any messages or data, but the satellite can tell in a very broad way what region the blips are coming from.
Malaysia's prime minister said the last confirmed signal between the plane and a satellite came at 8:11 a.m. — 7 hours and 31 minutes after takeoff. This was more than five hours later than the previous time given by Malaysian authorities as the possible last contact.
Airline officials have said the plane had enough fuel to fly for up to about eight hours.
"The investigations team is making further calculations which will indicate how far the aircraft may have flown after this last point of contact," Najib said.
He said authorities had determined that the plane's last communication with a satellite was in one of two possible arcs, or "corridors" — a northern one from northern Thailand through to the border of the Central Asian countries Kazakhstan and Turkmenistan, and a southern one from Indonesia to the southern Indian Ocean.
The northern route might theoretically have taken the plane through China, India, Pakistan, Afghanistan — which hosts U.S. military bases — and Central Asia, and it is unclear how it might have gone undetected. The region is also home to extremist Islamist groups, unstable governments and remote, sparsely populated areas.
Flying south would have put the plane over the Indian Ocean, with an average depth of 3,890 meters (12,762 feet) and thousands of kilometers (miles) from the nearest land mass.
Goglia said that if Malaysian military radar tracked the plane turning west, it then followed a standard route across the peninsula until it was several hundred miles (kilometers) offshore and beyond military radar range. Airliners generally keep to such highways in the sky to avoid colliding with other planes, but the routes are not straight lines, he said. That means it's likely someone was still guiding the plane, Goglia said.
Britain-based aviation security consultant Chris Yates thought it was highly unlikely the plane would have taken the northern route across land in Asia.
"In theory, any country that sees a strange blip is going to get fighter planes up to have a look," he said. "And if those fighter planes can't make head or tail of what it is, they will shoot it down."
Najib said search efforts in the South China Sea, where the plane first lost contact, had ended.
Indian officials said navy ships supported by long-range surveillance planes and helicopters scoured Andaman Sea islands for a third day Saturday without any success in finding evidence of the missing jet.
Two-thirds of the plane's passengers were Chinese, and China's government has been under pressure to give relatives firm news of the aircraft's fate.
In a stinging commentary on Saturday, the Chinese government's Xinhua News Agency said the Malaysian information was "painfully belated," resulting in wasted efforts and straining the nerves of relatives.