But had the plane gone northwest to Central Asia, it would have crossed over countries with busy airspace. Some experts believe it more likely would have gone south, although Malaysian authorities are not ruling out the northern corridor and are eager for radar data that might confirm or rule out that.
U.S., Australian and Indonesian planes and ships are searching waters to the south of Indonesia's Sumatra Island all the way down to the southern reaches of the Indian Ocean, the world's third-deepest and one of the most remote stretches of water.
The area being covered by the Australians is massive — 600,000 square kilometers (232,000 square miles) — and will take weeks to search thoroughly, said John Young, manager of Australian Maritime Safety Authority's emergency response division.
"This search will be difficult. The sheer size of the search area poses a huge challenge," Young said. "A needle in a haystack remains a good analogy."
Associated Press writers Ian Mader, Jim Gomez and Eileen Ng in Kuala Lumpur, and Kristen Gelineau in Sydney, Australia, contributed to this report.
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