Some of the possible causes for the plane disappearing include:
— A CATASTROPHIC STRUCTURAL FAILURE. Most aircraft are made of aluminum which is susceptible to corrosion over time, especially in areas of high humidity. But given the plane's long history and impressive safety record, experts suggest that a failure of the airframe, or the plane's Rolls-Royce Trent 800 engines, is unlikely.
More of a threat to the plane's integrity is the constant pressurization and depressurization of the cabin for takeoff and landing. In April 2011, a Southwest Airlines Boeing 737 made an emergency landing shortly after takeoff from Phoenix after the plane's fuselage ruptured, causing a 5-foot tear. The plane, with 118 people on board, landed safely. But such a rupture is less likely in this case. Airlines fly the 777 on longer distances, with many fewer takeoffs and landings, putting less stress on the airframe.
"It's not like this was Southwest Airlines doing 10 flights a day," Hamilton said. "There's nothing to suggest there would be any fatigue issues."
— BAD WEATHER. Planes are designed to fly through most severe storms. However, in June 2009, an Air France flight from Rio de Janeiro to Paris crashed during a bad storm over the Atlantic Ocean. Ice built up on the Airbus A330's airspeed indicators, giving false readings. That, and bad decisions by the pilots, led the plane into a stall causing it to plummet into the sea. All 228 passengers and crew aboard died. The pilots never radioed for help.
In the case of Saturday's Malaysia Airlines flight, all indications show that there were clear skies.
— PILOT DISORIENTATION. Curtis said that the pilots could have taken the plane off autopilot and somehow went off course and didn't realize it until it was too late. The plane could have flown for another five or six hours from its point of last contact, putting it up to 3,000 miles away. This is unlikely given that the plane probably would have been picked up by radar somewhere. But it's too early to eliminate it as a possibility.
— FAILURE OF BOTH ENGINES. In January 2008, a British Airways 777 crashed about 1,000 feet short of the runway at London's Heathrow Airport. As the plane was coming in to land, the engines lost thrust because of ice buildup in the fuel system. There were no fatalities.
Loss of both engines is possible in this case, but Hamilton said the plane could glide for up to 20 minutes, giving pilots plenty of time to make an emergency call. When a US Airways A320 lost both of its engines in January 2009 after taking off from LaGuardia Airport in New York it was at a much lower elevation. But Capt. Chesley B. "Sully" Sullenberger still had plenty of communications with air traffic controllers before ending the six-minute flight in the Hudson River.
— A BOMB. Several planes have been brought down including Pan Am Flight 103 between London and New York in December 1988. There was also an Air India flight in June 1985 between Montreal and London and a plane in September 1989 flown by French airline Union des Transports Aériens which blew up over the Sahara.
— HIJACKING. A traditional hijacking seems unlikely given that a plane's captors typically land at an airport and have some type of demand. But a 9/11-like hijacking is possible, with terrorists forcing the plane into the ocean.
— PILOT SUICIDE. There were two large jet crashes in the late 1990s — a SilkAir flight and an EgyptAir flight— that are believed to have been caused by pilots deliberately crashing the planes. Government crash investigators never formally declared the crashes suicides but both are widely acknowledged by crash experts to have been caused by deliberate pilot actions.
— ACCIDENTAL SHOOT-DOWN. There have been incidents when a country's military unintentionally shot down civilian aircraft. In July 1988, the United States Navy missile cruiser USS Vincennes accidently shot down an Iran Air flight, killing all 290 passengers and crew. In September 1983, a Korean Air Lines flight was shot down by a Russian fighter jet.
AP writer Joan Lowy contributed from Washington.
Scott Mayerowitz can be reached at http://twitter.com/GlobeTrotScott.