It's not something that is easy. We are looking at so many vessels and aircraft, so many countries to coordinate, and a vast area for us to search. But we will never give up. This we owe to the families of those on board. —Malaysian Defense Minister Hishammuddin Hussein
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.
In June 2013, Boeing issued a safety alert to Boeing 777 operators, telling them to inspect for corrosion and cracks in the crown fuselage around a satellite antenna. The alert says one airline found a 16-inch crack in one plane, then checked other 777s and found more cracking.
"Cracks in the fuselage skin that are not found and repaired can propagate to the point where the fuselage skin structure cannot sustain limit load," Boeing said. "When the fuselage skin cannot sustain limit load, this can result in possible rapid decompression and loss of structural integrity."
The FAA issued a safety order Wednesday that is effective April 9, directing operators to make repairs outlined in Boeing's safety alert.
Asked about the safety alert as it relates to the Malaysia Airlines disappearance, former U.S. National Transportation Safety Board member and aircraft maintenance expert John Goglia said he thought it was "pretty far down on the probability list."
"It could lead to depressurization of the airplane," Goglia said, "but it wouldn't turn off the transponder and it wouldn't prevent the pilots from calling" by radio.
Aeronautical engineer Chuck Eastlake, a former professor at Embry-Riddle Aeronautical University in Daytona Beach, Fla., added that it's unlikely a rapid depressurization of the plane would cause it to disintegrate in the air.
Two U.S. Federal Aviation Administration technical experts and a regional representative are in Kuala Lumpur as part of an NTSB team supporting the investigation. Experts in air traffic control and radar are providing technical help, the board said.
Hishammuddin described the multinational search as unprecedented. Some 43 ships and 39 aircraft from at least eight nations were scouring an area to the east and west of Peninsular Malaysia.
"It's not something that is easy. We are looking at so many vessels and aircraft, so many countries to coordinate, and a vast area for us to search," he told a news conference. "But we will never give up. This we owe to the families of those on board."
Confusion over whether the plane had been seen flying west prompted speculation that different arms of the government might have different opinions about its location, or even that authorities were holding back information.
Earlier in the week, Malaysia's head of civil aviation, Azharuddin Abdul Rahman, was asked why the Strait of Malacca was being searched and replied, "There are things I can tell you, and things I can't," suggesting that the government wasn't being completely transparent.
If all those on board are confirmed dead, it would be the deadliest commercial air accident in 10 years.
Choi Tat Sang, a 74-year-old Malaysian, said his family is still holding out hope that the plane and all on board are safe. His 45-year-old daughter-in-law, Goh Sock Lay, was the chief flight attendant. Her 14-year-old daughter, an only child, has been crying every day since the plane's disappearance.
"We are heartbroken. We are continuing to pray for her safety and for everyone on the flight," he said.
Associated Press writers Jim Gomez in Kuala Lumpur, Isolda Morillo in Beijing, Niniek Karmini in Jakarta, Indonesia, Joan Lowy in Washington, and Rod McGuirk in Canberra, Australia, contributed to this report.