The new report on the crash of Air France flight 447 concludes that pilot error was responsible for the crash– or more accurately, that the pilot’s mental model of how so safe a plane would react to a challenging situation failed. As Popular Mechanics explains,

We now understand that, indeed, AF447 passed into clouds associated with a large system of thunderstorms, its speed sensors became iced over, and the autopilot disengaged. In the ensuing confusion, the pilots lost control of the airplane because they reacted incorrectly to the loss of instrumentation and then seemed unable to comprehend the nature of the problems they had caused. Neither weather nor malfunction doomed AF447, nor a complex chain of error, but a simple but persistent mistake on the part of one of the pilots.

As Jalopnik puts it, the pilot misunderstood how a plane designed to be flown automatically would respond to problems:

[O]ne of the two junior officers in charge of an Air France flight that crashed in June 2009 was of the belief that he couldn’t crash the plane and thus made poor decisions because of misunderstanding the complex systems designed to protect the aircraft.

Jalopnik argues that this system, and ones like adaptive cruise control, work 90% of the time, but have an under appreciated ability to fail catastrophically:

works extremely well when it is fully in control, but when it loses a key piece of information and requires an input from a human — just like in the tragic Air France flight — things can go terribly wrong.

It’s a textbook example of Yale sociologist Charles Perrow’s idea of everyday catastrophes, and his argument that safety systems can reduce the rate of accidents but make the ones that happen catastrophic.

The Popular Mechanics article is a chilling reconstruction of the last minutes of the flight, and how the pilots managed to stall the plane.