The Malaysian Airlines flight that disappeared on Saturday with 239 people on board is one in a series of aviation incidents that have puzzled investigators over the years.
Perhaps one of the best-known disappearances involves Amelia Earhart, the first woman to fly solo across the Atlantic Ocean. In a 1937 attempt to circumnavigate the globe, Earhart lost contact with her ground crew while she was over the Pacific Ocean. No trace of her plane was ever found.
A more recent crash that has caused lingering concerns is that of TWA Flight 800, which blew up over Long Island, New York, in 1996. An official investigation concluded that a short circuit in the fuel tank caused the crash that killed 230 people. But some investigators said there is evidence that the jet was destroyed by an external explosion.
Questions linger concerning Egypt Air Flight 990 which crashed into the Atlantic in 1999. The plane left New York for Cairo, carrying 217 people. U.S. investigators questioned whether one of the pilots' last words indicated a suicide mission.
And a final report on the 2009 crash of an Air France jet indicates there was confusion in the cockpit after ice crystals affected the plane's sensors and its autopilot disconnected. Two hundred and 28 people were killed when the plane went down during a flight from Rio de Janeiro to Paris.