Air France Flight 447 was en route from Rio de Janiero to Paris on May 31, 2009, for an overnight trip, when it vanished. There was no warning before the flight crashed into the Atlantic Ocean in the early morning hours of June 1, 2009 -- nearly four hours after take-off. The 2009 crash, which killed all 228 passengers and crew on board, is considered one of the worst -- and most mysterious -- aviation disasters in modern history. One theory is that the co-pilots were not properly trained and depended too heavily on the plane's automated system.