It would be reasonable to wager that the majority of air passengers have never questioned why the traditional cruising altitude is 35,000 feet.

The number has entered household lexicon as the catch-all height at which we fly from A to B. But do all planes soar this high – and if so why?

The higher the better

One of the central reasons behind aircraft altitude is that, as the air gets thinner with every foot climbed, planes can travel more easily and therefore move faster and burn less fuel, saving airlines (and in theory, you) money.

The “sweet spot” of flying is regarded as between 35,000 and 42,000 feet – too high and the oxygen becomes too sparse to fuel the engines, too low and the air resistance is greater. This optimum height is linked to the usual weight of a commercial jet – that is, heavier planes fly lower, and lighter higher.