Clear-air turbulence is so named because it comes literally out of the blue. It occurs when bodies of air moving at wildly different speeds meet: as the winds shear against each other, vortices and chaotic movements are produced. While much studied, particularly in the high troposphere where long-haul aircraft operate, it remains almost impossible to detect or to predict. For this reason, it is much more dangerous than the predictable forms of turbulence that occur on the edges of storms and large weather systems, because pilots are unable to prepare, or route around it. And incidences of
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