Based on data collated by the British company Inmarsat's satellite network, the plane was on one of two possible arcs - one stretching north from Thailand to Kazakhstan and crossing more than 10 countries, and one to the south over Indonesia and out across the southern Indian ocean. Experts have said the aircraft could have been on the ground when it sent its satellite signals.
Boeing 777s need a runway at least 1525m long, limiting the number of possible sites within the 2200 nautical mile-radius it is believed the plane could have flown from its last known position.
Sources in Kuala Lumpur told the Independent that full diplomatic permissions were being sought in order to rule out the theory that the plane could have flown to areas of Afghanistan and Pakistan that are not under government control.
Large areas of the southern half of Afghanistan are ruled by the Afghan Taliban, while some areas of North-West Pakistan, near the Afghan border, are controlled by the Pakistan Taliban.
A spokesman for Malaysia Airlines said: "These are matters for the jurisdiction of those regions and Malaysia's armed forces and department of civil aviation. In regard to Pakistan and Afghanistan, we cannot explore those theories without permission. We hope to have that soon."
For a commercial plane to pass undetected through these regions, which are highly militarised with robust air defence networks, many run by the US military, would require a combination of extremely sophisticated navigation, brazen audacity and security failure by those monitoring international airspace.
However, with so little known about the fate of the plane, and the investigation growing in scale every day, it is yet another line of inquiry that remains impossible to rule out. Pakistani civil aviation officials said they had checked their radar recordings and found no sign of the missing jet.
The
Wall Street Journal
said Pakistan was one of five Asian nations which said their radar systems hadn't detected any sign of the Malaysia Airlines aircraft. Indonesia, Burma, Thailand and India said there was no sign the plane had flown over their territories.
"Such a large object could not have gone undetected," one Indian military official in Port Blair in the Andaman Islands told the newspaper.
Malaysian officials said they had requested help from a dozen Asian countries and had asked them to provide radar data. They have also asked for assistance from Vietnam, Thailand, Indonesia, Australia and France, which administers a handful of islands deep in the southern Indian Ocean.
"The search area has been significantly expanded, and the search area has changed. We are now looking at large tracts of land, crossing 11 countries as well as deep and remote oceans," said Malaysia's Transport Minister Hishammuddin Hussein.
Khalid Abu Bakar, Malaysia's police chief, said investigators researching the backgrounds of the people who boarded Flight MH370 had found no passengers with aviation expertise. Reuters reported police had said their inquiries had found no links between Shah and any militant group.
Flight MH370: The mystery deepens
Where could it land?
All official airports are monitored, but that does not make a landing impossible. There are unofficial ones, not least airstrips created and then abandoned during World War II and the Vietnam War.
What was the plan?
That is one of the many baffling aspects of the disappearance. If the person or people responsible wanted to destroy the aircraft, it could simply have been downed at once or flown into a target. So presumably there was a more audacious plan.
What points to terrorism?
Southeast Asia is home to a number of al-Qaeda-linked groups, particularly in Indonesia - home to both Jemaah Islamiyah and Jamaah Ansharut Tauhid. There were 30 attacks there in 2012 alone. The last position of the plane puts it on a flight path that links the region to Europe and takes it towards the Middle East. Then there is the East Turkestan Islamic Movement, an umbrella group wanting a homeland for ethnic Uighurs in China's Xinjiang region.
What would make terrorism unlikely?
Intelligence officials cite a lack of "chatter" among monitored extremists. Then there's the level of organisation involved in commandeering a plane and flying it undetected. This, experts claim, would involve "something beyond the mission planning for 9/11". There is also the question of why no one credible has so far demonstrated responsibility. A former FBI assistant director, James Kallstrom, thinks the terrorists want the plane to use as a weapon "for some dastardly deed down the road".
Could it have been piracy?
The Straits of Malacca are one of the world's great piracy hot spots. A US official has warned that MH370's disappearance may itself be an "act of piracy". The plane could be resold for tens of millions of dollars and the passengers ransomed.
How can a plane vanish - are there radar blackspots?
Many travellers have been astonished that there is no global system tracking all aircraft at all times. Over oceans, coverage is very patchy - and over populated areas, if a pilot chooses to disable communications equipment, even a 250-tonne plane can be elusive.
Who could have been responsible?
One or more of the passengers; one or more of the crew; or even, as the aviation security expert Philip Baum has speculated, one or more stowaways.
What are the key questions the investigators need to address?
If the pilots were acting under duress, why did they not activate an emergency distress signal? Why were the crew not challenged about the disabled Acars system? And were any mobile phone calls made or SMS messages sent by passengers? If the answer to the last question is "no", then one conclusion may be that the aircraft was well out to sea. Independent
