There are scant details about what happened to the Boeing 777-200 plane travelling from Kuala Lumpur to Beijing with 239 passengers and crew on board.
“We’re looking at mystery compounded by mystery compounded by mystery,” Chris Yates, who runs a U.K. aviation security consultancy company, told CBC's The Current.
Here are some key questions that remain unanswered.
Where's the plane?
Radio contact with the flight was lost about an hour after takeoff from Kuala Lumpur, which was at 12:21 a.m. on Saturday, March 8. The last contact with air traffic controllers was 120 nautical miles off the east coast of Malaysia, near the northern town of Kota Bharu, located near the Thai border.
About 40 ships and 34 aircraft from 10 countries, including Australia, Vietnam, China and the U.S., are searching the seas off Malaysia and Vietnam for the plane. The search area covers a 50-nautical-mile radius but is reportedly being widened to a 100-nautical-mile radius from its last known position. That widens it from an area half the size of Nova Scotia to double the size of the province.
The search area covers waters east of Malaysia — the Gulf of Thailand and the South China Sea — but also the Strait of Malacca to the west.
Oil slicks and debris initially spotted during the search turned out not to be associated with the flight. Though black boxes can emit radio beacons for radars to pick up, no signals have been detected in the wide search area.
Yates said that it’s “extremely unusual” for a plane to crash without a trace for so many days. In the last such accident, Air France Flight 447, it took about five days to locate the first debris after the plane plunged into the Atlantic Ocean during stormy weather. It took two more years to figure out what actually happened.
Why was there no distress signal?
Air traffic controllers say no distress signal was issued. Several aviation experts say that is not unusual.
In an interview with CBS News, Capt. Chesley Sullenberger, who famously piloted a plane to a safe landing on the Hudson River in New York, noted that pilots are often too busy during a crisis situation to communicate with air controllers. The top priority for pilots is to get the plane under control, and signalling to controllers does little to help them do so.
"The pressure of trying to find out what's going on can keep a crew busy when they're unable to communicate," said Sullenberger.
Andy Kovacs, a Seneca College flight instructor and Air Canada pilot, notes that it is also possible that the aircraft was in a remote location and the crew had difficulty raising air traffic control on the VHF or HF radio. A distress call could've been made but not received.
"If the crew was unable to send a distress call, the event most likely happened very quickly," said Kovacs to CBC News.
Did the plane turn around — and why?
Malaysian military officials say that radar data suggests that the plane might have turned back toward Kuala Lumpur before vanishing. But there’s no indication why they would do so, because no contact was made with air traffic controllers.
Some experts note that it may not be the result of the crew changing the flight direction. In Air France 447’s descent, the plane also changed its direction by more than 180 degrees, but only as an unintentional side effect, according to Bill Palmer, an Airbus 330 captain and author of Understanding Air France 447.
What about the passengers?
Of the 239 people on board the flight, two were Canadian. The majority of the passengers were from China or Taiwan (154) or from Malaysia (38). Others came from India, Australia, France, the United States, Ukraine, Russia and the Netherlands.
Of most interest, however, are the two passengers who boarded with passports stolen from Austrian and Italian citizens. These citizens both reported the documents as stolen in Thailand in 2012 and 2013, respectively, and both were listed in Interpol’s database of suspect passports.
Interpol said it is “too soon to speculate” about connections between the stolen passports and the missing flight, but the incident raised questions about the fact that few countries systematically search Interpol's database containing entries on 40 million stolen passports.
"We have a real case where the world is speculating whether the stolen passport holders were terrorists, while Interpol is asking why only a handful of countries worldwide are taking care to make sure that persons possessing stolen passports are not boarding international flights," said Interpol Secretary General Ronald Noble.
Interpol is checking whether any other passengers used stolen passports.
Could the missing plane be linked to terrorism?
The head of Malaysia's Civil Aviation Authority, Azharuddin Abdul Rahmanthe, called the incident an "unprecedented aviation mystery" and said hijacking could not be ruled out. A police official told Reuters they'd stopped people armed with explosives and carrying fake identity papers from flying out of Kuala Lumpur three times in the past.
However, U.S. government sources who reviewed spy satellite imagery said there were no signs of a mid-air explosion.
Taiwanese authorities revealed Monday that they'd received information about a possible terrorist attack on Beijing's airport four days prior to the departure of the missing flight. "Anything is possible," said Jean Shen, the head of the Taiwanese Civil Aeronautics Administration, but added the two incidents appear to be unrelated and cautioned against jumping to conclusions.
The United States has deployed FBI agents and technical experts to help investigate whether there are any connections to terrorism, but at this time are stressing there is no indication of such ties.
No organizations have claimed responsibility for the attack. And as Yates notes, the use of stolen passports could simply be a case of illegal migration.
It will take a long time before investigators can piece together what happened to the Malaysia Airlines flight. But perhaps not as long as the Air France investigation, which was hindered because the wreckage was submerged deep in the Atlantic Ocean. There, the plane lay several miles underwater. The Gulf of Thailand, by comparison, reaches up to 260 feet in depth.
Airplane black boxes emit a signal that helps search and rescue crews locate the plane, but the signal cuts out after 30 days.