As ships and aircraft search thousands of square miles for a missing Malaysian Airlines jetliner, officials are trying to understand how the Boeing 777 could have apparently dropped out of the sky without warning or distress signal.
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The mysterious lack of contact and the fact that the plane disappeared from radar midflight is so rare that it brings to mind only one other plane disaster in recent years, the doomed 2009 Air France flight 447.
The Air France flight, an Airbus A330, from Rio de Janeiro to Paris crashed in the Atlantic midway through the flight without sending a distress signal. All 228 aboard were killed.
It took three years for investigators to piece together what led to the crash, with two years spent just trying to find the black box data recorders on board. In 2012 the French government's official accident investigators, the BEA, released their final report, which found that the flight crashed due to a combination of technical failures and pilot error.
The BEA found that a speed sensor on board the plane, called a pitot tube, stopped functioning after becoming clogged with ice at high-altitude while the plane was flying through a thunderstorm.
As a result, the auto-pilot disengaged and shifted the controls back to the pilots. As they flew in heavy turbulence the Air France pilots failed to properly diagnose the severity of the problem because the pitot tube, a critical piece of equipment to the aircraft, was sending inaccurate data to the cockpit, the report said.
"Despite these persistent symptoms, the crew never understood that they were stalling and consequently never applied a recovery maneuver," the 2012 report said.
When the auto-pilot was disengaged, a co-pilot pulled the nose of the plane, which led to aerodynamic stall. From the first stall warning at 2:10 a.m. to when the plane crashed four minutes later, the pilots never sent a distress signal as they frantically tried to save the plane.
According to the black box recordings, the pilots appeared unaware they were going to crash until the final seconds before hitting the water.
"Our investigation is a no-blame investigation. It is just a safety investigation," Jean-Paul Troadec, the director of BEA, told ABC News in a 2012 interview. "What appears in the crew behavior is that most probably, a different crew would have done the same action. So, we cannot blame this crew. What we can say is that most probably this crew and most crews were not prepared to face such an event."
ABC News' Matt Hosford, Lauren Effron and Nikki Batiste contributed to this report.