KUALA LUMPUR, Malaysia — The last message from the cockpit of the missing Malaysia Airlines flight was routine. "All right, good night," was the signoff transmitted to air traffic controllers five days ago.
Then the Boeing 777 vanished as it cruised over the South China Sea toward Vietnam, and nothing has been seen or heard of the jetliner since.
Those final words were picked up by controllers and relayed Wednesday in Beijing to anguished relatives of some of the 239 people aboard Flight MH370.
The search for the missing plane, which left Kuala Lumpur for Beijing early Saturday, now encompasses 35,800 square miles (92,600 square kilometers) of Southeast Asia and is expanding toward India.
After several days of sometimes confusing and conflicting statements, the Malaysian military officially disclosed why it was searching on both sides of country: A review of military radar records showed what might have been the plane turning back and crossing westward into the Strait of Malacca.
Air force chief Gen. Rodzali Daud said the radar showed an unidentified object at 2:15 a.m. about 200 miles (320 kilometers) northwest of Penang. "I am not saying it's Flight MH370. We are still corroborating this. It was an unidentifiable plot," he said.
Foreign experts and the manufacturers of the radar were studying the images to try to determine whether the blips were in fact the missing plane. For now, authorities said the international search effort would stay focused on the South China Sea and the strait leading toward the Andaman Sea.
Some of the confusion over the statements by Malaysian officials has led to allegations of incompetence, lack of coordination or even a cover-up.
"There's too much information and confusion right now. It is very hard for us to decide whether a given piece of information is accurate," Chinese Foreign Ministry spokesman Qin Gang said in Beijing. "We will not give it up as long as there's still a shred of hope."
Two-thirds of the passengers on the flight were Chinese.
"We have nothing to hide," said Malaysian Defense Minister Hishammuddin Hussein. "There is only confusion if you want to see confusion."
Flight MH370 disappeared from civilian radar screens at 1:30 a.m. Saturday at an altitude of about 35,000 feet above the Gulf of Thailand between Malaysia and southern Vietnam. It sent no distress signals or any indication it was experiencing problems.
The government said it had asked India to join in the search near the Andaman Sea, suggesting the jetliner might have reached those waters after crossing into the Strait of Malacca, some 400 kilometers (250 miles) from the flight's last-known coordinates.
Malaysian officials met in Beijing with several hundred Chinese relatives of passengers to explain the search and investigation, and to relay the last transmission that Malaysian air traffic controllers received before the plane entered Vietnamese airspace, according to a participant in the meeting.
Aviation officials in Vietnam said they never heard from the plane.
Its sudden disappearance led to initial speculation of a catastrophic incident that caused it to disintegrate. Another possibility is that it continued to fly despite a failure of its electrical systems, which could have knocked out communications, including transponders that enable the plane to be identified by commercial radar.
Authorities have not ruled out any possible cause, including mechanical failure, pilot error, sabotage and terrorism, and they are waiting to find any wreckage or debris to determine what went wrong.
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