Now, it’s true that one of the benefits of flying at 30,000 feet is a smoother ride. This is at the top of the troposphere, the layer in which most weather occurs. So there’s less turbulence and fewer storms to navigate around. But this is not the main reason that planes fly so high. The bigger reason, of course, is money. As you go up, the density of air decreases. And at 33,000 feet, or 10 kilometers, the density of air is just a third of what it is at sea level. So flying at this altitude, the plane runs into a third of the air molecules it would closer to the ground. That means the plane can fly about 73% faster for the same amount of thrust. And as a result, you get to your destination faster. And since you spend less time in the air, you burn less fuel. Not only that, jet engines are more efficient at altitude. They work by compressing air at the intake, mixing it with fuel and igniting it. the combustion products are ejected very fast from the exhaust nozzle.