Seven theories about missing Malaysia Airlines Flight 370

Countless theories have surfaced about the disappearance of Malaysia Airlines Flight 370. Even the most logical hypotheses about what happened to the Boeing 777 have holes. Here is a look at some of the leading, plausible theories — and their flaws.

1 MALICIOUS PILOT ACTION: Investigators are looking at the histories of Capt. Zaharie Ahmad Shah, 53, who has been flying for Malaysia Airlines since 1981, and co-pilot Fariq Abdul Hamid, 27, who just started flying a 777. Zaharie had built his own flight simulator at home, unusual but not out of the norm. Many aviation enthusiasts have similar setups; one Los Angeles flight attendant recreated a Pan Am first-class cabin in his garage. Investigators are now trying to restore files deleted from that simulator. Why suspect the pilots? The plane's transponder stopped signaling its location to air-traffic controllers and other planes at the perfect moment: the handoff from Malaysia's controllers to those in Vietnam. In the final radio contact from the plane, the co-pilot told Malaysian controllers "All right, good night." Vietnamese controllers were never contacted and the transponder shut off. The plane abruptly turned and then kept flying for up to seven hours. The idea of pilots using a plane to commit suicide and mass murder is scary, taboo within the industry, but not unprecedented. A SilkAir crash in 1997 and an EgyptAir crash in 1999 are both believed to have been the result of deliberate actions by pilots.

2 TERRORIST HIJACKING: This theory was prominent early on after it was discovered that two Iranians on board — one 18, the other 28 — were traveling on stolen passports. Investigators haven't found anything linking either to terror groups; it is believed they were trying to illegally immigrate to Europe. Ever since 9/11, it's been much harder for an unauthorized person to enter the flight deck. Also, no credible group has taken credit for the disappearance and intelligence agencies say they haven't noticed any chatter in terrorist circles regarding the jet.

3 SUDDEN CATASTROPHE: Aviation experts initially suspected this. Perhaps a bomb onboard, or some type of failure with the engines or airframe — but debris would have been found in the spot where the transponder went off. If there was a sudden breakup, pieces of the plane would have been radar-visible.

4 DECOMPRESSION: A slow or sudden decompression, causing a loss of oxygen, could have killed everyone on board. If oxygen levels dropped, a loud, automated warning would have alerted the pilots to put on their oxygen masks and immediately descend below 10,000 feet, where there is enough oxygen to breathe without aid. If the plane depressurized and killed its occupants, which happened on professional golfer Payne Stewart's business jet in 1999, that would explain the silence from crew and passengers. But aviation experts say in that case, the plane should have kept flying automatically toward Beijing and been visible on radar.

5 HIDDEN PLANE: This theory suggests that it's possible that somebody landed the plane at a remote airport and is hiding it from the world. Maybe they want to hold the passengers hostage, although nobody has taken responsibility or demanded a ransom. Maybe there was something of value in the cargo hold — and this was the world's most elaborate robbery. Maybe terrorists have the plane and plan to load it with jet fuel and explosives and use it as a missile in the future. Those scenarios all have holes. A very skilled pilot would have to land the plane at a small airport that normally doesn't accommodate large aircraft. And they would have to dodge several nations' radar systems, though some have suggested that it flew in another jet's "shadow.''