Relatives of Chinese passengers aboard missing Malaysia Airlines Flight MH370 watch a TV news program about the missing flight. Photo / AP
Simon Calder of The Independent answers some of the top questions about Malaysia Airlines Flight MH370.
What happened to Malaysia Airlines MH370?
At 41 minutes past midnight on Saturday morning, a Boeing 777 jet took off from Kuala Lumpur International Airport, destination Beijing Capital Airport. On board were 12 crew and 227 passengers, at least two of whom were travelling under assumed identities with stolen passports. The aircraft flew routinely for about two hours, heading north-north-east. It crossed the Malaysian peninsula and setting out across the South China Sea towards to the southern tip of Vietnam. Soon afterwards, contact with the aircraft was lost. No emergency calls were made. That is more or less all that the grieving families of the passengers, and the travelling public, know.
Does that mean some people know more?
Probably. The sudden expansion of the search area to the Malaysian mainland and the Strait of Malacca, on the "wrong" coast, suggests that sophisticated military surveillance equipment detected more about MH370 than the civil authorities knew. While the US (or Chinese) military would not be keen to share the information for fear of revealing secrets about their surveillance activities, they appear to have given some advice from the shadows to the search teams.
What could explain the absence of any emergency call?
A wide range of circumstances, including a catastrophic event - caused, for example, by a mid-air collision or an accidental or deliberate explosion. Both pilots may have been incapacitated - again, through misfortune or malice. Or it may simply have been that an on-board emergency occurred and all their efforts were focused on saving the aircraft rather than communicating with the outside world. That is what happened aboard Air France 447, the Rio-to-Paris flight that crashed into the Atlantic after a high-altitude stall.
Could the same high-altitude stall have befallen MH370?
Possibly, but what is the odd is the absence of debris from the aircraft in the sea. With the Air France crash, flotsam was found relatively quickly, even though the crash site was more remote. Nor has there been any trace of a kerosene slick, which you would expect to see; jet fuel floats, and would be expected to leak in a high-speed impact with water.
It is one of many possibilities. Over Lockerbie in 1988, Pan Am 103 was blown up by a bomb checked in by a passenger who did not board. Since then, passengers and their bags are supposed to be reconciled. If passengers do not board, their luggage is routinely removed. But baggage is often flown independently of the owners, as anyone who has lost a case in transit will know. There is also a possibility, however remote, that ground staff could have been involved.
Image 1 of 43: Christchurch man Paul Weeks was among the 239 passengers on the Malaysia Airlines flight MH370 which went missing over the Gulf of Thailand.
Several people checked in bags but didn't board the flight. Isn't that suspicious?
No, it's wrong. The airline say four passengers were no-shows. They didn't get as far as check-in.
Have questions been raised about the Boeing 777's safety - in particular the danger that ice might obstruct fuel to the Rolls-Royce engines, as happened with a BA flight at Heathrow?
The BA 777 that crash-landed at Heathrow, with no loss of life, experienced fuel starvation because of ice crystals forming. It was on the final approach at the time. In contrast, MH370 was at 35,000 feet, a height at which it would have been able to glide for more than 100 miles, during which "Mayday" calls could be made. Even if all power from the engines is lost, a special device provides emergency power for the pilots.
What other theories have been put forward?
Just about everything short of alien abduction. A surprisingly popular theory is that the aircraft was downed by a missile from North Korea, even though the rogue state is 2,000 miles away from the area in which the aircraft was lost.
What steps do airlines take to check passengers' documents against a list of lost or stolen passports?
Typically, none. The US authorities take a keen interest in every individual flying to or through American airspace, and demand advance information that is checked against "watch lists" to detect suspicious passengers. But while Interpol collates information on stolen travel documents, it is not routinely shared with airlines.