The most dangerous parts of a flight are takeoff and landing. In fact, just 9 percent of fatal accidents happen when a plane is at cruising altitude, according to Boeing.

So the disappearance of a Malaysia Airlines Boeing 777 well into its flight Saturday morning has led aviation experts to assume that whatever happened was quick and left the pilots no time to place a distress call.

"Either you had a catastrophic event that tore the airplane apart, or you had a criminal act," said Scott Hamilton, managing director of aviation consultancy Leeham Co. "It was so quick, and they didn't radio."


Capt. John Cox, who spent 25 years flying for US Airways and is CEO of Safety Operating Systems, said the problem had to be big enough to stop the plane's transponder from broadcasting its location.




Some of the possible causes for the crash include:

-- A catastrophic structural failure of the airframe or its Rolls-Royce Trent 800 engines. Most aircraft are made of aluminum, which is susceptible to corrosion over time, especially in areas of high humidity. But given the plane's impressive safety record, experts suggest this is unlikely.

-- Bad weather. Planes are designed to fly though 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. But in the case of Saturday's Malaysia Airlines flight, all indications show that there were clear skies.

-- Failure of both engines. However, Hamilton said the plane could glide for up to 20 minutes, giving pilots plenty of time to make an emergency call.

-- A bomb. Several planes have been brought down by an explosion, including Pan Am Flight 103 between London and New York in December 1988.

-- Hijacking. A hijacking seems unlikely given that they typically include landing at an airport and 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 that investigators suspect were caused by pilots deliberately crashing the planes.

-- Accidental downing by some country's military. In July 1988, the Navy missile cruiser USS Vincennes accidently shot down an Iran Air flight, killing all 290 aboard. In September 1983, a Korean Air Lines flight was shot down by a Russian fighter jet.

-- Associated Press