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.
Britain-based aviation security consultant Chris Yates thought it was highly unlikely the plane would have taken the northern route across land in Asia.
