THE search for Flight MH370 has now been expanded deep into the northern and southern hemispheres, stretching from Australia to Kazakhstan.
Australian vessels are scouring the southern Indian Ocean and China has offered 21 of its satellites to help Malaysia in the unprecedented hunt.
With no wreckage found in one of the most puzzling aviation mysteries of all time, passengers' relatives have been left in an agonising limbo.
Investigators say the Boeing 777 was deliberately diverted during its overnight flight and flew off-course for hours. They haven't ruled out hijacking, sabotage, or pilot suicide, and are checking the backgrounds of the 227 passengers and 12 crew members - as well as the ground crew - for personal problems, psychological issues or links to terrorists.
Malaysian Defence Minister Hishammuddin Hussein said on Monday that finding the plane was still the main focus, and he did not rule out that it might be discovered 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.
French investigators have arrived in Kuala Lumpur to lend expertise from the two-year search for an Air France jet that crashed in the Atlantic Ocean in 2009.
They said they were able to rely on distress signals in their search. But that vital tool is missing in the Malaysia Airlines case because the flight's communications were deliberately silenced ahead of its disappearance, investigators say.
"It's very different from the Air France case. The Malaysian situation is much more difficult," said Jean Paul Troadec, a special adviser to France's aviation accident investigation bureau.
Malaysia's government sent diplomatic cables to all countries in the search area, seeking more planes and ships, and asking for any radar data that might help.
The search initially focused on seas on either side of Peninsular Malaysia, in the South China Sea and the Strait of Malacca.
It was vastly expanded after Malaysian Prime Minister Najib Razak said over the weekend that investigators determined that a satellite picked up a faint signal from the aircraft about 7 1/2 hours after takeoff. The signal indicated the plane would have been somewhere on a vast arc stretching from Kazakhstan in Central Asia to the southern reaches of the Indian Ocean.
Hishammuddin said on Monday that searches in both the northern and southern stretches of the arc had begun, and that countries from Australia in the south, China in the north and Kazakhstan to the west had joined the hunt.
Had the plane gone northwest to Central Asia, it would have crossed over countries with busy airspace. Some experts believe it more likely would have gone south, although Malaysian authorities are not ruling out the northern corridor and are eager for radar data that might confirm or rule out that route.
Australia agreed to Malaysia's request to take the lead in searching the southern Indian Ocean with four Orion maritime planes that would be joined by New Zealand and US aircraft, Australian Prime Minister Tony Abbott said.
Indonesia focused on Indian Ocean waters west of Sumatra, air force spokesman Rear Marshall Hadi Tjahjanto said.
The vast scope of the search, now involving 26 countries, was underlined when a US destroyer that already has helped cover 38,850 square kilometres of water dropped out.
The navy concluded that long-range aircraft were more efficient in looking for the plane or its debris than the USS Kidd and its helicopters, so effective Tuesday the ship was leaving the Indian Ocean search area, said Navy Cmdr William Marks, spokesman for the 7th Fleet.
Navy P-3 and P-8 surveillance aircraft remain available, and can cover 38,850 square kilometres in a nine-hour flight.
