The crash of
AF 447 was due to the co-pilot's inexperience with flying the Airbus A300 without the computer. He was confused by the 'Pull up' audible warning going silent whenever the computer faulted at 40 degree AOT (the computer shut up because it decided the sensor inputs were crazy). So he kept pulling up the joystick up and up thinking the stall ended whenever the audible warning stopped. Whenever he eased the stick forward the computer reawakened and starting bitching again about a stall. Rinse and repeat. And so he belly-flopped right into the ocean.
The other pilot on the right was pushing the joystick forward, but the joystick on the left overrode him, and he didn't realize it. (Boeing uses wheels that are mechanically linked, so pushing one steering wheel forward always pushes the other.)
The official determination was pilot error due to failure to understand how the fly-by-wire A300 behaved whenever the computer kicked offline and went into alternate (mostly manual) flight mode.