Flight MH370: 13 Things You Need To Know

As the search for Flight MH370 continues, we answer 13 questions about the disappearance and what could have happened.

When did the plane disappear?

Flight MH370 vanished from radars early on Saturday, an hour into a flight from Kuala Lumpur to Beijing. When it last made contact, the jet was cruising at 35,000 feet over the South China Sea. There are reports that the plane tried to turn around but this would give rise to the question: why didn't the pilot communicate this decision to air traffic control? Meanwhile, at an undisclosed time a relative reportedly managed to call one of the passengers. Investigators have repeatedly tried to call the same number without success.

:: Sky News will be showing a 12-minute special report on the story so far of the missing flight MH370 at 2.30pm.

Who was on board?

The plane's manifest contained 12 crew from Malaysia and 227 passengers from 14 different countries: 153 Chinese, 38 Malaysians, seven Indonesians, six Australians, five Indians, four French, three Americans, two each from Iran (both travelling on fake passports), New Zealand, Ukraine and Canada, and 1 each from Russia, Taiwan and Netherlands. Among the passengers was a 19-strong group of prominent artists returning from an exhibition in Malaysia. It is also known that five children - aged two to four - were on board. The oldest person on the plane was 79.

What are the main theories?

Mechanical error remains the most likely explanation. Poor conditions and strong turbulence always have to be considered, but weather conditions were good in this instance. Four areas of investigation are focused on the possibility of human involvement: hijacking, sabotage, psychological problems or personal problems with passengers or crew.

Could there have been a mechanical error?

Inquiries into Air France flight 447 that dived into the Atlantic Ocean in 2009 en route from Brazil to Paris, killing 228 people, blamed both technical and human error. However, in the event of engine failure, a plane such as the Boeing 777-200 could glide for 80-90 miles (128-145km), giving the pilot time to issue a distress signal. The descent would also have been traced by radars. The lack of any Mayday makes an explosion a possibility.

Could the plane have broken up in the air?

The apparent lack of wreckage from MH370 does point to a high-altitude disaster. In such an event the debris would be spread far and wide, making it difficult to find. A smaller field would indicate the plane probably fell intact, breaking up on impact with the water. In the event of a sudden loss of pressure due to a window blowing out the crew would dive the plane in order to lose altitude - but this would not cause the plane to disintegrate.

The plane's safety record?

Sudden, accidental, structural failures are considered extremely unlikely in today's passenger aircraft. This is especially so with the Boeing 777-200, which has one of the best safety records of any jet. One of the missing plane's wingtips was clipped in an incident while taxiing in 2012 but it was repaired and certified as safe.

Could it have been a terrorist attack or hijacking?

In the event of a hijacker trying to enter the cockpit, a pilot can send a secret distress code - something that wasn't done on Flight MH370. The profiles of all 239 passengers are being checked against databases worldwide but the terrorism theory was weakened on Tuesday when Malaysian police confirmed it had identified the two passengers who were travelling on fake passports. Both were said to be seeking asylum in Europe. In the 1988 Lockerbie bombing, claims of responsibility came soon after the disaster - but no one has come forward to claim the Malaysia incident as their attack.

Human error?

The 53-year-old pilot was very experienced, having amassed more than 18,000 flying hours since being employed by the airline in 1981. However, in Indonesia in 2007, Adam Air flight 574 disappeared with 102 passengers during a domestic flight, where the authorities found the pilots lost control after becoming preoccupied with malfunctioning navigational equipment. Former Navy pilot Dr Simon Mitchell told Sky News: "We've expended billions of dollars on developing very sophisticated aids to make the life of the pilot safer and more straightforward, but there are still opportunities whereby mistakes can be made."

Why was there no distress signal?

One explanation is that the plane fell into a communications black spot. Former Boeing 777 instructor and United Airlines captain Ross Aimer explained: "These are very sophisticated (items of) equipment that should have been working under any conditions - in the water, in the jungle, after a fire, after an explosion - and none of them have talked to the outside world yet. There are spots in the world, however, that are called blind spots, where you cannot communicate for some reason. Unfortunately, that area near Vietnam, over the Gulf of Thailand, those are some of the black spots."

Where is the search taking place?

Nine aircraft and 24 ships are currently taking part in the search in the seas off Vietnam and Malaysia. Search teams from Australia, China, Thailand, Indonesia, Singapore, Vietnam, Philippines, New Zealand and the US are assisting. Officials said on Tuesday that the search was being conducted on both sides of Vietnam's Ca Mau peninsula. The search area has been expanded from 50 nautical miles from where the plane disappeared - over waters between Malaysia and Vietnam - to 100 nautical miles (115 miles; 185km). This expansion was a result of a new report from the Malaysian military, who say they tracked the plane in the Strait of Malacca - a long distance from where it last made contact - in the hours following its disappearance.

Why has no wreckage been found?

Whatever caused the apparent crash, there would be some debris - but it could take a while to find. It took two years to find the main wreckage of Air France flight 447 in 2009. In 2007, in the case of the Adam Air flight, it was a week before an Indonesian naval vessel detected metal on the ocean floor. It was a further two weeks before the US Navy picked up signals from the flight data and cockpit recorders and seven months for the recorder to be recovered. If the plane had crashed on land, chances are the wreckage would have been found by now. At sea, much of the plane would have sunk, but some debris should remain on the surface. Worryingly, the longer the search takes the harder it becomes as the wind and tide spread any debris further from the initial crash zone.

Could the 'black box' provide answers?

As well as wreckage, search teams are looking for the aircraft's emergency locator transmitter (ELT) - though these do not always work if a plane hits water. However, attached to the plane's black box is a device known as a pinger. This can emit radio signals deep under water for up to 30 days - or 40 days in warm water.

Has a plane ever simply vanished?

Since the start of the jet age in the 1950s, nearly every major aircraft that disappeared was found - eventually - and the rare exceptions did not involve passengers. In September 1990, a Boeing 727 plunged into the North Atlantic after running out of fuel. The accident was attributed to poor pilot planning and the wreck was never recovered. Another Boeing 727 transporting diesel to diamond mines in Africa took off without clearance and with its transponder turned off. It is believed to have crashed in the Atlantic Ocean.

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