That change was based on analysis of satellite data. But officials said a reexamination and refinement of that analysis indicated the aircraft was traveling faster than previously estimated, resulting in increased fuel use and reducing the possible distance it could have flown before going down. Just as a car loses gas efficiency when driving at high speeds, a plane will get less out of a tank of fuel when it flies faster.
Martin Dolan, chief commissioner of the Australian Transport Safety Bureau, said a wide range of scenarios went into the calculation.
"We're looking at the data from the so-called pinging of the satellite, the polling of the satellites, and that gives a distance from a satellite to the aircraft to within a reasonable approximation," he said. He said that information was coupled with various projections of aircraft performance and the plane's distance from the satellites at given times.
In Beijing, some relatives of the 153 Chinese passengers on the plane said the shift in the search area added to their confusion and frustration.
"What on earth is the Malaysian government doing?" said Wang Chunjiang, whose brother was a passenger. "Is there anything more that they are hiding from us?"
Investigators continued puzzling over what might have happened aboard the plane. A U.S. official, speaking on condition of anonymity because the official was not authorized to speak amid an ongoing investigation, said the FBI's searches of computer hard drives belonging to pilot and co-pilot, including a flight simulator with deleted files, have yielded "no significant information" about what happened to the plane or what role, if any, the crew might have played in its disappearance.
If investigators can determine the plane went down in the newly targeted zone, recovery of its flight data and cockpit voice recorders could be complicated.
"There are a number of ridges, escarpments and fracture zones that run through this area, so it's a fairly complex area," said Rochelle Wigley, director of the Indian Ocean Mapping Project at the University of New Hampshire. Wigley said determining the ocean floor topography within the search zone depends on its exact coordinates. While investigators appear to be focusing on an area where much of the sea floor is about 6,600 feet (2,000 meters) below the surface, depths may reach a maximum of about 19,700 feet (6,000 meters) at its easternmost edge, she said.
Wong reported from Kuala Lumpur. Associated Press writers Scott McDonald and Eileen Ng in Kuala Lumpur; Kristen Gelineau in Sydney; Rod McGuirk in Canberra, Australia; Nick Perry in Wellington, New Zealand; and Eric Tucker and Matthew Pennington in Washington contributed.