Malaysian authorities say the jet carrying 239 people was intentionally diverted from its flight path during an overnight flight from Kuala Lumpur to Beijing on March 8 and flew off-course for several hours. Suspicion has fallen on the pilots, although Malaysian officials have said they are looking into everyone aboard the flight.
Malaysian police confiscated a flight simulator from the pilot's home on Saturday and also visited the home of the co-pilot.
Investigators haven't ruled out hijacking, sabotage, pilot suicide or mass murder, and they are checking the backgrounds of all 227 passengers and 12 crew members, as well as the ground crew, to see if links to terrorists, personal problems or psychological issues could be factors.
'There Is Always Hope'For now, though, Malaysian Defense Minister Hishammuddin Hussein said finding the plane was still the main focus, and he did not rule out finding it intact.
"The fact that there was no distress signal, no ransom notes, no parties claiming responsibility, there is always hope," Hishammuddin said at a news conference.
Although Malaysian authorities requested that all nations with citizens aboard the flight conduct background checks on them, it wasn't clear how thoroughly they were conducting such checks at home.
The father of a Malaysian aviation engineer aboard the plane, Mohamad Khairul Amri Selamat, 29, said police had not approached anyone in the family about his son, though he added that there was no reason to suspect him.
"It is impossible for him to be involved in something like this," said the father, Selamat Omar, 60. "He is a good boy ... We are keeping our hopes high. I am praying hard that the plane didn't crash and that he will be back soon."
Global ResponseSome 26 countries are now involved in the search.
Over the weekend, Malaysian Prime Minister Najib Razak announced that investigators determined that a satellite picked up a faint signal from the aircraft about 7 ½ hours after takeoff. The signal indicated the plane would have been somewhere on a vast arc stretching from Kazakhstan down to the southern reaches of the Indian Ocean.
The northern corridor crosses through countries including China, India and Pakistan – all of which have said they have seen no sign of the plane. China, where two thirds of the passengers were from, is providing several planes and 21 satellites for the search, Premier Li Keqiang said in a statement.
"Factors involved in the incident continue to multiply, the area of search and rescue continues to broaden, and the level of difficulty increases, but as long as there is one thread of hope, we will continue an all-out effort," Li said.
To the south, Indonesia focused on Indian Ocean waters west of Sumatra, air force spokesman Rear Marshall Hadi Tjahjanto said.
Australia agreed to Malaysia's request to take the lead in scouring the southern Indian Ocean with four Orion maritime planes that also would be joined by New Zealand and U.S. planes, Australian Prime Minister Tony Abbott said.
The southern Indian Ocean is the world's third-deepest and one of the most remote stretches of water in the world, with little radar coverage.
Planes will be searching for any signs of the kind of debris that might float to the surface in a crash. Ahmad, the Malaysia Airlines CEO, said the plane had no unusual cargo, though he said it was carrying several tons of mangosteens, a purple tropical fruit.