BEIJING. More than 40 hours have passed since the missing Malaysian plane carrying 239 people, including more than 150 Chinese, lost contact with air traffic controllers.

Yet the fate of the China-bound Malaysia Airlines plane remains unknown, prompting speculations and worries.  Listed below are the explanations from experts to some of the major mysteries surrounding the missing plane.

How the plane suddenly lost all contact?

Analysts have given three possibilities: 1. The plane might have wrongly flown into a cumulonimbus and lost control. 2. Some accidents happened to the pilots. 3. The air-to-ground communication was cut off because of malfunction. The ground monitors the plane through three ways: the main one is radar surveillance, then voice communication and then the air-ground data link system based on satellite communication technology. Only when the three means are exhausted, can a plane be identified as losing contact. The lack of a call "suggests something very sudden and very violent happened,” William Waldock, who teaches accident investigation at Embry-Riddle Aeronautical University in Prescott, Ariz, was quoted by media as saying. If there was a minor mechanical failure, or even something more serious like the shutdown of both of the plane’s engines, the pilots likely would have had time to radio for help, he said.

Media reports say that the investigation may last for years. The deadly air crash of Air France Flight 447 in 2009 was initially believed to be the result of lightning strike, but the investigation report three years later showed that it was the technical malfunction and human factor that caused the accident.

What happened to the plane at cruising altitude?

The jet’s disappearance was especially mysterious because it apparently happened when the plane was at cruising altitude, not during the more dangerous phases of takeoff or landing.

Just nine percent of fatal accidents happen when a plane is at cruising altitude, according to a statistical summary of commercial jet accidents compiled by Boeing.  Experts speculate that the plane might have suddenly disintegrated in the air or dived vertically in high speed.  After the 9-11 terrorist attacks in 2001, airplanes around the world have all installed bulletproof doors for airline cockpits, which gave enough time for pilots to inform the ground if a plane was hijacked by terrorists, according to civil aviation pilots. Moreover, it is impossible for the plane to vanish from the radar screen if the transponder remains active. Whatever happened to the missing plane, experts think that a conclusion is still too early to tell.

What are the odds for surviving?

There is a saying in the aviation community: you would rather crash into a hill than water.

If a plane has exploded before diving into the sea, the surviving chance would be almost zero, and the fragments of the plane could scatter around in a range over 100 kilometers.  If the plane has lost control before crashing into the sea, which is the usual case, the surviving odds are also very low. A controlled emergency landing in water is extremely rare for commercial passenger airlines and is highly demanding for the pilots’ ability and psychology.

Yin Zhuo, a member of the National Committee of the Chinese People’s Political Consultative Conference and a renowned military expert told media that the surviving hance is rare for a plane to land in the sea. "There are no escape parachutes in civil aviation, and the plane would disintegrate after crashing into the water as a result of the impact force,” he said. "The odds for surviving is not big, but cannot be fully ruled out,” he added.

Below are some successful cases of water landing:

On 15 January, 2009, a U.S. Airways Flight 1549 successfully ditched into the Hudson River between the New York City and New Jersey, after reports of multiple bird strikes. All of the 155 passengers and crew aboard escaped and were rescued.

On April 13, 2013, a jet from Indonesian airline Lion Air crashed into the ocean and snapped into two while attempting to land on the Indonesian resort island of Bali. Luckily all the 101 passengers onboard and the seven crews were safe.

Why so hard to locate and rescue?

The rescue work has continued for hours in the seas between Malaysia and Vietnam where the flight vanished from screens, but still no confirmed sighting of the wreckage was reported.The main wreckage of AF447 missing in 2009 was not found until two years later.

Wang Xiaopeng, a researcher at Chinese Academy of Social Sciences, said that according to official information, the sea area where the accident was presumed to take place is in the waters of the gulf of Thailand. The typical tropical waters there feature strong wind and high seas with tropical circulation beneath, which adds to the difficulty for the search and rescue. But Qian Chuanhai, director of the Typhoon and Marine Meteorological Forecast Center of China Meteorological Administration, said the weather and sea conditions in relevant sea areas would be beneficial to the search and rescue work from Saturday to Tuesday.