On the evening of May 31, 2009, 216 passengers and 12 crew members boarded an Air France Airbus 330 at Antonio Carlos Jobim International Airport in Rio de Janeiro, Brazil. The flight, Air France 447, departed at 7.29pm local time for a scheduled 11-hour flight to Paris. It never arrived. At 7 o’clock the next morning, when the aircraft failed to appear on the radar screens of air traffic controllers in Europe, Air France began to worry, and contacted civil aviation authorities. By 11am, they concluded that their worst fears had been confirmed. AF447 had gone missing somewhere over the vast emptiness of the South Atlantic.

How, in the age of satellite navigation and instantaneous global communication, could a state-of-the art airliner simply vanish? It was a mystery that lasted for two years. Not until earlier this year, when autonomous submersibles located the airliner’s black boxes under more than two miles of water, were the last pieces of the puzzle put together. What doomed the 228 men, women and children aboard Air France 447 was neither weather nor technological failure, but simple human error. Under pressure, human beings can lose their ability to think clearly and to properly execute their training—a well-known failing that has proven all too difficult to eliminate.

Over at Popular Mechanics I’ve got a long piece offering a detailed blow-by-blow account of how one of the co-pilots of the Air France jetliner managed, in the course of just five minutes, to take a perfectly operational airplane from an altitude of nearly seven miles down to impact with the ocean. Here, I’d like to offer a nutshell summary of what happened, and what our understanding implies for the future of air safety.

Air France 447 was operating with three pilots: a captain, who was the most senior crewmember, and two co-pilots. At any given time, two of them were required to be in the cockpit, seated at the pair of seats equipped with controls. Four hours into the flight, the captain went to take a nap, leaving the flying of the plane to the more junior of the co-pilots, Pierre-Cédric Bonin. Sitting beside him was the other co-pilot, David Robert.

The crisis began mere minutes later, when the plane flew into clouds roiling up from a large tropical thunderstorm, and the moisture condensed and froze on the plane’s external air-speed sensors. In response, the autopilot disengaged. For a few minutes, the pilots had no way of knowing how fast they were going, and had to fly the plane by hand—something, crucially, that Bonin had no experience doing at cruise altitude.

The proper thing for Bonin to have done would have been to keep the plane flying level, and to have Robert refer to a relevant checklist to sort out their airspeed problems. Instead, neither man consulted a checklist, and Bonin pulled back on the controls, causing the airplane to climb and lose airspeed. Soon, he had put the plane into an aerodynamic stall, which means that the wings had lost their ability to generate lift. Even with engines at full power, the Airbus began to plummet toward the ocean.

As the severity of their predicament became more and more apparent, the pilots were unable to reason through the cause of their situation. Despite numerous boldfaced clues to the nature of their problem—including a stall-warning alarm that blared 75 times–they were simply baffled. As Robert put it, after the captain had hurried back to the cockpit, “We’ve totally lost control of the plane. We don’t understand at all… We’ve tried everything.”

Psychologists who study performance under pressure are well aware of the phenomenon of “brain freeze,” the inability of the human mind to engage in complex reasoning in the grip of intense fear. It appears that arousal of the amygdala causes a partial shutdown of the frontal cortex, so that it becomes possible to engage only in instinctive or well-learned behaviour.

In the case of Air France 447, it appears that Bonin, in his panic, completely forgot one of the most basic tenets of flight training: when at risk of a stall, never pull back on the controls. Instead, he held back the controls, in a kind of panicked death-grip, all the way down to the ocean. Ironically, if he had simply taken his hands away, the plane would have regained speed and started flying again.

Compounding the problem was a peculiar feature of the Airbus’s cockpit layout. Unlike a Boeing jet, in which one pilot’s movement of the control yoke moves the other pilot’s yoke as well, an Airbus features “asynchronous” controls, meaning that moving one control doesn’t cause the other to move as well. Bonin’s colleagues probably never knew that he had the controls all the way back—perhaps because they never imagined that any certified airline pilot could engage in such a misguided response.

Perhaps the most tragic moment of the entire transcript occurs in the final moments, when Bonin at last tells the others that he has had the controls back the entire time. “No, no, no,” says the captain. But by then it is already too late.

What can we learn from AF447? Above all, the tragedy reinforces an unfortunate truth about air travel that many passengers do not appreciate: that the most dangerous component of a modern commercial jetliner is the brain of the pilot at its controls. The majority of fatal airline accidents (vanishingly rare though they may be) are due to pilot error.

One way that airline manufacturers have tried to work around this problem is to increase the amount of automation, so that planes can largely fly themselves. But this tendency has had an ironic effect: the more pilots rely on automation, the less practiced they are at flying a plane by hand when an emergency requires it.

As a pilot myself, I love taking the controls of an airplane and through it finding a perfect freedom of movement in the sky. I would never want a computer to take that away from me. But the practical reality of moving passengers in perfect safety from point A to point B requires a different perspective. As technology improves, and flight control systems become more sophisticated, the relative inadequacy of we two-legged mammals will only become more apparent. Ultimately, the idea of a relying on a human being in the cockpit may come to seem a sentimentality too expensive to afford.

UPDATE: I’ve added another post, explaining what the flight’s final minutes probably felt like from the passengers’ perspective, here.