EFour spirals rise into the sky, about 48 kilometers from Heathrow Airport, London. These spirals are virtual: they cannot be seen by the passengers, or even by the pilot inside the cockpit. These are routes for airplanes which are going to land or take off from Heathrow, one of the busiest airports in the world.

Heathrow, in West London, is the busiest airport in the world after Charles de Gaulle in Paris and Frankfurt in Germany. About 1,300 pl