As the search for a missing Malaysia Airlines jet entered a sixth day Thursday , investigators remained uncertain about its whereabouts . Here 's a summary of what we know and what we do n't know about Flight 370 , which was carrying 239 people when it disappeared from radar screens over Southeast Asia . THE FLIGHT PATH . What we know : The Boeing 777-200ER took off from Kuala Lumpur , the Malaysian capital , at 12:41 a.m. Saturday ( 12:41 p.m. Friday 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 over the sea between Malaysia and Vietnam . What we do n'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 . But the pilots did n't tell air traffic control that they were doing so . Malaysian officials say they are still trying to determine if a radar blip detected heading west soon after the plane lost contact was in fact the missing jet . If it was , the plane would have been hundreds of miles off its original flight path and headed in the wrong direction . Malaysian officials say they have asked U.S. experts to help them analyze the radar data . We do n't know why the plane would have turned around . While one expert tells CNN the plane 's possible deviation could mean someone deliberately turned the plane around , another expert says power failure could have disrupted the main transponder and its backup , and the plane could have flown for more than an hour . Adding to the puzzle , the Wall Street Journal reported Thursday that the plane may have kept flying for a further four hours after its last reported contact . The newspaper attributed the information to two unidentified people who were citing data automatically transmitted to the ground from the passenger jet 's engines . CNN has so far been unable to confirm the report . '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 a number of painters and calligraphers , as well as employees of an American semiconductor company . According to the airline , the passengers ' 14 nationalities spanned the Asia-Pacific region , Europe and North America . Passengers from China or Taiwan numbered 154 , followed by Malaysians , at 38 . There were three U.S. citizens on the plane . Four passengers had valid booking to travel but did not show up for the flight , according to the airline . `` As such , the issue of off-loading unaccompanied baggage did not arise , '' it added Tuesday in a prepared statement . What we do n't know : Whether any of the passengers had anything to do with the plane 's disappearance . Friends tell of fears as hopes dim for passengers . THE PASSPORT MYSTERY . What we know : Two passengers boarded the plane using stolen passports . Authorities have identified them as Pouri Nourmohammadi , 18 , and Delavar Seyed Mohammad Reza , 29 , both Iranians . Malaysian police believe Nourmohammadi was trying to emigrate to Germany using the stolen Austrian passport . The men entered Malaysia on February 28 using valid Iranian passports , according to Interpol . The use of the stolen passports had raised concern that the people who used them might be involved in the plane 's disappearance . But officials have said they think it is unlikely the Iranian men had links to terrorist groups . Malaysian police said Nourmohammadi 's mother contacted them after her son did n't arrive in Frankfurt as expected . `` The more information we get , the more we 're inclined to conclude that it was not a terrorist incident , '' Ronald Noble , the secretary general of the international police organization Interpol , said Tuesday . What we do n't know : More details about the two men , particularly Reza . Malaysian officials and Interpol also gave slightly different information for Nourmohammadi 's name and age . It was unclear what caused the discrepancy . Would-be immigrants have used fake passports to try to enter Western countries in the past . And Southeast Asia is known as a booming market for stolen passports . THE SECURITY SCREENING . What we know : Interpol says the passports were listed as stolen in its database . But they had not been checked from the time they were entered into the database and the time the plane departed . Noble said it was `` clearly of great concern '' that passengers had been able to board an international flight using passports listed as stolen in the agency 's database . What we do n't know : Whether the passports had been used to travel previously . 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 at the airport in Kuala Lumpur , but have insisted it meets international standards . How does a jet go missing ? THE CREW . What we know : The crew members are Malaysian . The pilot is Capt . Zaharie Ahmad Shah , a 53-year-old veteran with 18,365 flying hours who joined Malaysia Airlines in 1981 . The first officer , Fariq Ab Hamid , has 2,763 flying hours . Fariq , 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 do n'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 did n't report any kind of problems before contact was lost . THE SEARCH . What we know : Dozens of ships and planes from various countries have been scouring the South China Sea near where the plane was last detected . Debris spotted in the area has turned out to be unrelated to the plane . Similarly , an oil slick in the search area was determined to be from fuel oil typically used in cargo ships , not from the plane . Vietnamese searchers found no trace Thursday of `` suspected floating objects '' detected in Chinese satellite imagery near the plane 's last confirmed location . What we do n't know : Whether the search is concentrating on the right place . Authorities initially focused their efforts around the mouth of the Gulf of Thailand , near the plane 's last known position . But they have expanded efforts westward , off the other coast of the Malay Peninsula , and northward into the Andaman Sea , part of the Indian Ocean . On Wednesday , authorities announced that they 'd widened the search area to nearly 27,000 square nautical miles ( 35,000 square miles ) . Jet was 'at safest point ' in flight . THE CAUSE . What we know : Nothing . `` For the aircraft to go missing just like that ... as far as we are concerned , we are equally puzzled as well , '' Azharuddin Abdul Rahman , director general of the Malaysian Civil Aviation Department , said this week . The aircraft model in question , the Boeing 777-200ER , has an excellent safety record . What we do n't know : Until searchers find the plane and its voice and data recorders , it may be difficult to figure out what happened . CNN national security analyst Peter Bergen says the range of possible reasons behind the disappearance can be divided into three categories : mechanical failure , pilot actions and terrorism . But all we have are theories . THE PRECEDENT . What we know : It 's rare , but not unprecedented , for a commercial airliner to disappear in midflight . 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 five days to locate the first piece of debris from that plane -- and nearly two years to find the bulk of Flight 447 's wreckage and most of the bodies in a mountain range deep in the Atlantic Ocean . It took even longer to establish the cause of the disaster . What we do n't know : Whether what happened to the missing Malaysia Airlines plane is similar to what happened to the Air France flight . Investigators attributed the Flight 447 crash to a series of errors by the pilots and their failure to react effectively to technical problems . How traffic control keeps you safe .
The WSJ reports the plane may have flown for four hours after its last known contact . A multinational search over a 35,000-square-mile area is under way at sea . Malaysian officials say they are analyzing radar data from after the plane lost contact . They are trying to determine if a blip on the radar heading west was in fact the plane .