Malaysia Airlines flight MH370 has been missing since Saturday, March 8, and every new piece of information seems to shroud the flight's disappearance in more mystery.
Malaysian investigators now say deliberate action was taken to turn off communications systems and steer the aircraft far off course. "Pings" sent from the plane to a commercial satellite hours after MH370 disappeared suggest either a northern or southern route of flight, creating a search area that stretches from Kazakhstan into western China or from Indonesia into the southern Indian Ocean.
The mystery has spawned dozens of theories from experts and armchair analysts alike, all with varying degrees of credibility. Going on the information made public so far, there are only a few theories that fit — though none satisfactorily. Here are the remaining likely possibilities for flight MH370. [5 Real Hazards of Air Travel]
1. Pilot suicide
MH370's transponder and its Aircraft Communications Addressing and Reporting System (ACARS) were both turned off shortly after the plane took off at 12:41 a.m. local time. There was a 14-minute gap between the last transmission of the ACARS and the last signal from the transponder, suggesting these systems were not destroyed by a sudden emergency.
Furthermore a voice, thought to be the plane's co-pilot Fariq Abdul Hamid, spoke to air traffic control in Malaysia after the ACARS turned off and just before the transponder turned off. The final message from the lost plane was a calm, "All right, good night." (Update at 7:59 a.m. ET on March 18: This timing is now in question, as Malaysian authorities now say they are unsure exactly when the ACARS switched off, but it was between 1:07 a.m. and 1:37 a.m.)
The plane then turned from its Beijing-bound route. A military satellite detected it west of the Malaysian peninsula at 2:15 a.m. local time.
"Based on the details surfaced so far, it seems to have been a very well-planned and performed operation," said David Cenciotti, a former Italian Air Force pilot and journalist, who blogs at TheAviationist.com.
The expertise required to conduct these maneuvers has investigators looking into the pilot and co-pilot, Capt. Zaharie Ahmad Shah, 53, and 1st Officer Fariq Ab Hamid, 27.
Theoretically, one of these men could have decided to commit suicide by airplane. Pilot suicide would be highly unusual, but not unprecedented. For example, U.S. investigators concluded that a 1999 crash near Nantucket, which killed all 217 people onboard EgyptAir Flight 990, was the result of the co-pilot deliberately flying the plane into the sea (Egyptian investigators dispute that finding).
Similarly, SilkAir Flight 185, which crashed in Sumatra in 1997, may have been a pilot suicide. There were no mechanical failures to explain why the plane went into a vertical dive, the U.S. National Transportation Safety Board concluded. The plane's trajectory could be explained by the captain's deliberate action, however. [Understanding the 10 Most Destructive Human Behaviors]
Something similar could have happened to Flight 370. But the explanation seems strange: Other pilots who have committed suicide-by-plane have aimed the nose at the ground and ended it quickly. MH370 flew for hours after contact was lost.
"Why would you take 200 other people with you, a logical individual would want to know?" said Gregory "Sid" McGuirk, a professor of air traffic control at Embry-Riddle Aeronautical University.
2. Pilot conspiracy
Another theory holds that the pilots, or one of them, deliberately rerouted the plane for other reasons. This theory banks on the technical knowledge needed to change the plane's flight path, as well as suspicious circumstances around the flight's timing. [The 10 Craziest Conspiracy Theories]
Turning off the transponder and ACARS in the cockpit is as easy as flipping a switch and turning off a breaker, McGuirk told Live Science. The transponder, however, reportedly went off just as the plane was being handed off from Malaysian air traffic control to Vietnamese air traffic control.
Radar only has a radius of 150 to 200 miles (240 to 320 kilometers), McGuirk said. Over the continental United States, radar overlaps so there are no gaps. Over the ocean, however, there can be no ground-based antennas. Some countries, including India, also have gaps in their radar coverage, McGuirk said.
"If that's the case, then somebody knew exactly where the radar coverage gap was and decided to act at that moment," McGuirk said. "That's kind of far-fetched."