Malaysia Airlines
If no survivors are found, Malaysia Airlines Flight 370 will be the deadliest air disaster since 2001Wikimedia Commons

Two days ago, Malaysia Airlines flight 370 with 239 people on board went missing over the sea between Vietnam and Malaysia. Investigators worldwide are trying to piece together exactly what happened, as well as find the whereabouts of the missing Boeing 777-200 jet.

The flight took off from Kuala Lumpur, the Malaysian capital, at 12.41am last Saturday. It was scheduled to arrive in Beijing at 6.30am the same day, after a 2,300 mile (3,700 km) journey. At around 1.30am, air traffic controllers in Subang lost contact with the plane.

Various theories have been suggested for the fate of the missing aircraft, from terrorism to structural failure. Azharuddin Abdul Rahman, Malaysia's civil aviation chief, has stated the fate of the jet "remains a mystery", yet hijacking has not be ruled out as a cause. If all passengers on board the flight perished, it will be the deadliest airline disaster since 2001, when American Airlines Flight 587 crashed into a suburb of New York.

IBTimes examines what remains a mystery about Malaysia Airlines flight 370:

The flight path

What happened after the air traffic controllers lost contact with the plane in Subang is unknown. The pilots did not indicate any warning the plane was in trouble and no distress signal was issued. However, Malaysian military officials have suggested radar data indicates the plane may have changed course, or turned back. The pilots did not tell air traffic control they were doing so and no reason for this has been given.

Malaysia Airlines missing flight
A female relative of a passenger onboard Malaysia Airlines flight MH370 cries as she talks on her mobile phone at the Beijing Capital International AirportReuters

The real identity of some of the passengers

There were 239 people on board, which consisted of 227 passengers and 12 crew members. Passengers spanned from across the world, including the Asia-Pacific, Europe and North America.

However, two people who boarded the plane under the disguise of an Italian and an Austrian were using stolen passports. Malaysian daily, the Star, has reported one of the passengers was not of Malaysian origin. Inspector General of Police Tan Sri Khalid Abu Bakar, said: "I can confirm that he is not a Malaysian, but cannot divulge which country he is from yet." According to CNN, the two passengers appeared to have purchased their tickets together, using Thai currency through South China Airlines.

If security screening at Kuala Lumpur was sufficient

Interpol has said it is "unable to determine on how many other occasions these passports were used to board flights or cross borders" because no checks were ever made on the stolen documents. Officials have stated the plane departed with international standards of safety, yet concerns have been expressed over the fake documents.

The location of the plane

Vietnamese officials released an image of what they believed to be debris from the plane. It also announced parts of the plane's tail may have been found, yet these theories have not been confirmed. Alleged oil slicks in the water off Vietnam's southern coast have sparked theories of a wreckage location, but no official information has been released. Sky News have confirmed the yellow object floating in the sea is not a life raft. They have also suggested the oil slicks are not from the missing aircraft.

What became of the flight crew

Nobody knows what happened on the flight deck of the plane just before it vanished. It was in the cruise portion of the flight, considered to be the safest part of flight. Weather conditions were reported to be good and the pilots did not report any technical failures before contact was lost. Capt. Zaharie Ahmad Shah, 53, has 18,365 flying hours, while first officer Fariq Ab Hamid has 2,763 flying hours and started at the airline in 2007.

If Flight 370 is similar to Air France Flight 447

In 2009, an Airbus A330-203 disappeared off the coast of Brazil without sending a distress signal. It lost contact with air traffic control at 38,000 ft, while the Malaysia Airlines flight lost contact at 35,000 ft. However, problems with the pitot tubes (equipment to measure air speed) were cited as a possible cause for the crash of Flight 447, as well as pilot error and adverse weather conditions over the Atlantic. According to ABC news: "The occurrence of the failure in the context of flight in cruise completely surprised the crew of flight AF 447. Despite these persistent symptoms, the crew never understood that they were stalling and consequently never applied a recovery manoeuver."

If terrorism was involved

Searchers have been unable to find the voice and data recorders for the flight. Other than mechanical failure and pilot actions, terrorism has been cited as a possible cause. The storming of a cockpit or a detonated device could limit the time the pilots had to issue a distress signal and the fake passports have led some to suggest there was criminal activity involved. No solid evidence has been found. According to the Mirror, no groups have claimed responsibility for the disappearance. Al-Qaeda, as well as its affiliates associated with its fundamentalist jihad, normally claim responsibility shortly after acts of terrorism.