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FLYING involves coping with quite a few uncomfortable realities – among them the horrid taste of in-flight tea. Central to these, of course, is just how one manages to defy gravity in a pressurised aluminium cylinder brimful of highly flammable kerosene.

Brian Clegg answers many of the more pressing questions people have about commercial aviation. What is a contrail, for instance? Why did volcanic ash ground so many flights in Europe in 2010? And what is it that keeps us airborne?

He also rehearses a few experiments passengers can toy with (and some they cannot, unless they want to get arrested) – such as cloud spotting and estimating your distance from other planes. He also explains why airline tea is so appalling: water boils at too low a temperature in the cabin’s low pressure to make a decent brew. For that knowledge alone I, for one, was grateful.