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normal Jet A-1 fuel. But investigators, considering the flight’s path over the Arctic Circle, wondered: could the fuel have frozen in flight, caused the crash, then thawed before they could find a trace of it? The British Airways flight had followed a path through territory at the border of China and Mongolia where the recorded ambient air temperature that midwinter day was –85 degrees Fahrenheit. As the plane crossed the Ural Mountains and Scandinavia, the recorded temperature fell to –105 degrees. These were not considered exceptional temperatures for polar flight. Although the freezing point for Jet A-1 fuel is –53 degrees, the dangers were thought to have been resolved. Aircraft taking Arctic routes are designed to protect the fuel against extreme cold, and the pilots monitor the fuel temperature constantly. Cross-polar routes for commercial aircraft opened in February 2001, and thousands of planes have traveled them without incident since. In fact, on the British Airways flight, the lowest fuel temperature recorded was –29 degrees, well above the fuel’s freezing point. Furthermore, the plane was over mild-weathered London, not the Urals, when the engines lost power.

Nonetheless, investigators remained concerned that the plane’s flight path had played a role. They proposed an elaborate theory. Jet fuel normally has a minor amount of water moisture in it, less than two drops per gallon. During cold-air flights, the moisture routinely freezes and floats in the fuel as a suspension of tiny ice crystals. This had never been considered a significant problem. But maybe on a long, very smooth polar flight—as this one was—the fuel flow becomes so slow that the crystals have time to sediment and perhaps accumulate somewhere in the fuel tank. Then, during a brief burst of acceleration, such as on the final approach, the sudden increase in fuel flow might release the accumulation, causing blockage of the fuel lines.

The investigators had no hard evidence for this idea. It seemed a bit like finding a man suffocated in bed and arguing that all the oxygen molecules had randomly jumped to the other end of the room, leaving him to die in his sleep—possible, but preposterously unlikely. Nonetheless, the investigators tested what would happen if they injected water directly into the fuel system under freezing conditions. The crystals that formed, they found, could indeed clog the lines.

Almost eight months after the crash, this was all they had for an explanation. Everyone was anxious to do something before a similar accident occurred. Just in case the explanation was right, the investigators figured out some midflight maneuvers to fix the problem. When an engine loses power, a pilot’s instinct is to increase the thrust—to rev the engine. But if ice crystals have accumulated, increasing the fuel flow only throws more crystals into the fuel lines. So the investigators determined that pilots should do the opposite and idle the engine momentarily. This reduces fuel flow and permits time for heat exchangers in the piping to melt the ice—it takes only seconds—allowing the engines to recover. At least that was the investigators’ best guess.

So in September 2008, the Federal Aviation Administration in the United States issued a detailed advisory with new procedures pilots should follow to keep ice from accumulating on polar flights and also to recover flight control if icing nonetheless caused engine failure. Pilots across the world were somehow supposed to learn about these findings and smoothly incorporate them into their flight practices within thirty days. The remarkable thing about this episode—and the reason the story is worth telling—is that the pilots did so.

How this happened—it involved a checklist, of course—is instructive. But first think about what happens in most lines of professional work when a major failure occurs. To begin with, we rarely investigate our failures. Not in medicine, not in teaching, not in the legal profession, not in the financial world, not in virtually any other kind of work where the mistakes do not