Missing Malaysia Airlines Flight 370: What we know and don't know

Three days ago, a Malaysian passenger jet with more than 200 people on board vanished in the skies over Southeast Asia.

On Monday, investigators appeared to be no closer to explaining how a large plane could seemingly disappear into thin air.

A large-scale search involving boats and planes from a range of countries continues at sea. Relatives of the people on board keep up their painful wait for news. Officials have warned them to prepare for the worst.

And theories abound about what may have taken place.

Until clearer information comes to light, here's a summary of what we know and what we don't know about Malaysia Airlines Flight 370.

Flight 370: Areas being searched

THE FLIGHT PATH

What we know: The Boeing 777-200 took off from Kuala Lumpur, the Malaysian capital, at 12:41 a.m. Saturday (Friday afternoon ET). It was scheduled to arrive in Beijing at 6:30 a.m. the same day, after a roughly 2,700-mile (4,350-kilometer) journey. But around 1:30 a.m., air traffic controllers in Subang, outside Kuala Lumpur, lost contact with the plane as it was flying over the sea between Malaysia and Vietnam.

What we don't know: What happened next. The pilots did not indicate any problem to the tower, and no distress signal was issued. Malaysian military officials cite radar data as suggesting the plane might have changed course and turned back toward Kuala Lumpur before it vanished. But the pilots didn't tell air traffic control that they were doing so. And at this point, we don't know why the plane would have turned around.

'We have to find the aircraft'

THE PASSENGERS

What we know: There were 239 people on board: 227 passengers and 12 crew members. Five of the passengers were younger than 5 years old. Those on board included respected painters and calligraphers, as well as employees of an American semiconductor company.

According to the airline, there were passengers of more than a dozen nationalities, spanning the Asia-Pacific region, Europe and North America. The most heavily represented were people from China or Taiwan at 154, and Malaysia at 38. There were three U.S. citizens on the plane. Five passengers ended up not boarding the aircraft. Their bags were removed and were not on board the jet when it disappeared, authorities said.

What we don't know: The real identity of some of the passengers. Two people who boarded the plane under the guise of an Italian and an Austrian citizen were using stolen passports, officials say. Authorities say they are investigating the possibility that others on the plane were traveling under fake passports.

Friends tell of fears as hopes dim for passengers

THE PASSPORT MYSTERY

What we know: The tickets for the two people using the stolen Italian and Austrian passports were both bought Thursday in Thailand, according to ticketing records. Both tickets were one-way and had itineraries continuing on from Beijing to Amsterdam. One ticket's final destination was Frankfurt, Germany; the other's Copenhagen, Denmark. The original owners of the passports were not on the missing plane, authorities say. Both had their passports stolen in Thailand -- the Austrian's was taken last year and the Italian's in 2012.

What we don't know: Who the people using the stolen passports are, and whether they have any connection to the plane's disappearance. The director general of the Malaysian civil aviation department, Azharuddin Abdul Rahman, said Monday that the men who traveled on the stolen passports "are not Asian-looking men," citing security footage from the airport. But authorities have so far declined to disclose any other details from the investigation into their identities.

The stolen passports have raised fears that foul play could be behind the plane's disappearance. Officials say they are not discounting any possibilities at this point, including a hijacking -- but they haven't found any link to terrorism. Another possible explanation for the stolen passports is that illegal immigrants were using them to try to enter Europe. There are previous cases of illegal immigrants using fake passports to try to enter Western countries. And Southeast Asia is known to be a booming market for stolen passports.

THE SECURITY SCREENING

What we know: Interpol says the stolen passports were in its database. But no checks were made on them between the time they were entered into the database and the departure of the missing plane. Interpol Secretary General Ronald K. Noble said it was "clearly of great concern" that passengers were able to board an international flight with passports listed in the agency's database of stolen passports.

What we don't know: Whether the passports had been used to travel previously. Because no checks were ever made on the stolen documents, Interpol says it's "unable to determine on how many other occasions these passports were used to board flights or cross borders." Malaysian authorities are investigating the security process that allowed the passengers to board the flight, but officials insist the airport that the plane departed from complies with international standards.

How does a jet go missing?

THE CREW

What we know: All the crew members on board the plane were Malaysian. The pilot of the missing plane is Capt. Zaharie Ahmad Shah, a 53-year-old with 18,365 flying hours. He joined Malaysia Airlines in 1981. The first officer, Fariq Ab Hamid, has 2,763 flying hours. Hamid, 27, started at the airline in 2007. He had been flying another jet and was transitioning to the Boeing 777-200 after having completed training in a flight simulator.

What we don't know: What went on in the cockpit around the time the plane lost contact with air traffic controllers. The passenger jet was in what is considered the safest part of a flight, the cruise portion, when it disappeared. The weather conditions were reported to be good. Aviation experts say it's particularly puzzling that the pilots didn't report any kind of problems before contact was lost.

THE SEARCH

What we know: Thirty-four planes, 40 ships and search crews from 10 countries are scouring a large area of the South China Sea near where the plane was last detected. Pieces of debris spotted in the area have so far turned out not to be from the plane. "We have not found anything that appear to be objects from the aircraft, let alone the aircraft," Rahman, the of the Malaysian civil aviation department, said Monday. Similarly, oil from a slick discovered in the area was determined to be fuel oil typically used in cargo ships, not from the plane.

What we don't know: Whether the search is concentrating on the right place. Authorities began focusing on a stretch of sea around the mouth of the Gulf of Thailand, near the plane's last known position. But they have since expanded search efforts farther west, off the other coast of the Malaysian Peninsula and north into the Andaman Sea, part of the Indian Ocean. And the more time passes, the more ocean currents will move things around, complicating the investigators' task.

Jet was 'at safest point' in flight

THE CAUSE

What we know: Quite frankly, nothing. "For the aircraft to go missing just like that ... as far as we are concerned, we are equally puzzled as well," Rahman said Monday. The aircraft model in question, the Boeing 777-200, is considered to have an excellent safety record.

What we don't know: Until searchers are able to find the plane and its voice and data recorders, it will be extremely difficult to figure out what happened. CNN's national security analyst Peter Bergen says the range of possible reasons behind the disappearance can be divided into three main categories: mechanical failure, pilot actions or terrorism. But until more information becomes available, all we have are theories.

THE PRECEDENT

What we know: It's rare for a big commercial airliner to disappear in midflight. But it's not unprecedented. In June 2009, Air France Flight 447 was en route from Rio de Janeiro to Paris when communications ended suddenly from the Airbus A330, another state-of-the-art aircraft, with 228 people on board. It took four searches over the course of nearly two years to locate the bulk of Flight 447's wreckage and the majority of the bodies in a mountain range deep under the Atlantic Ocean. It took even longer to establish the cause of the disaster.

What we don't know: Whether the actual fate of the missing Malaysia Airlines plane is in any way similar to that of the Air France flight. Investigators attributed the Flight 447 crash to a series of errors by the pilots and a failure to react effectively to technical problems. If there are no survivors from the Malaysian plane, it will rank as the deadliest airline disaster since November 12, 2001, when American Airlines Flight 587 crashed into a New York neighborhood, killing all 260 people on board and five more on the ground.

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