“It’s something of the scope I’ve never seen before,” Cmdr. William Marks, the spokesman for the United States Navy Seventh Fleet, which sent two guided-missile destroyers to join the search, said in a telephone interview. Of the size of the Indian Ocean, he added: “Essentially, it’s like looking for a person somewhere between New York and California. It’s that big.”

Malaysian officials on Sunday briefed representatives from 22 countries that could help search along the two corridors where satellite data indicate the plane may have wound up, having flown up to six hours after its disappearance beyond the range of military radar in western Malaysia. Mr. Hishammuddin said Malaysia would also ask China, France, the United States and other countries to provide satellite data.

But establishing what happened to the plane also depends on reconstructing events in the cockpit in the early morning of March 8, when the jet was passing over the Gulf of Thailand between northern Malaysia and southern Vietnam. At that time, its communications links were severed, and it changed direction, flying across the Malay Peninsula and out over the Strait of Malacca.

Given the complexity of that feat, experts and American government officials say, experienced aviators, possibly one or both of the pilots, were probably involved, either willingly or under coercion.

The plane took off at 12:41 a.m. on March 8 carrying 239 people headed for Beijing and reached a cruising altitude of 35,000 feet at 1:01 a.m. Six minutes later, at 1:07 a.m., the Malaysian authorities say, the plane sent its last Acars message, which reported nothing amiss.

Investigators have not said how they concluded the system was disabled or when they believe that took place. It does not send a message when it is turned off. But Mr. Najib said it shut down just before the jet reached the east coast of Peninsular Malaysia, which independent radar tracking recorded at 1:08 a.m.