whhheeeEEEEEEEEEEEEEEE! The scream of jet engines rises to a crescendo on the runways of the world. Every second, somewhere or other, a plane touches down, with a puff of smoke from scorched tyre rubber, or rises in the air, leaving a smear of black fumes dissolving in its wake. From space, the earth might look to a fanciful eye like a huge carousel, with planes instead of horses spinning round its circumference, up and down, up and down. Whhheeeeeeeeeee!