One has died (of heart attack), and many more have been injured on a recent Singapore Airlines flight which was unexpectedly dramatically buffeted by severe air turbulence. One of the more tricky types of air turbulence is what is called Clear air turbulence (CAT), which is very difficult to predict. Air turbulence is just a fact of flying and the bane of those with a flying phobia and those who get air sick. But how dangerous is air turbulence, what causes it, and what is there to know or do about it?