Asked by: Katie Barker, Leamington Spa
There are lots of benefits to flying at an altitude of 11km. The air is thinner, producing less aerodynamic drag and thus reducing fuel consumption. It is also cold, around -55°C, which boosts the efficiency of the jet engines.
Plus, this part of the atmosphere – known as the stratosphere – is less turbulent, making for a smoother flight.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.