Why do airliners fly so high in the sky?
Why do aircraft fly at high altitude? Is it to save fuel?
Your average jet aircraft cruises between 30,000 and 42,000 ft. This is approximate 5 – 7 miles up in the air. The higher the altitude the less dense the air, or put in a different way, the thinner it is. Therefore there is less resistance (or friction) to stop the aircraft moving through the air. We call this resistance “drag”.
An example is moving your hand through water or golden syrup. It’s much less effort to move your hand through the water, and this is exactly the same principle with an aircraft flying at a higher altitude compared to a lower altitude.
The less resistance that the aircraft encounters, the less power the aircraft needs for a given speed and therefore the less fuel it will burn. This means the aircraft can travel at very fast speeds (about 600 mph or 1000 kmph) whilst burning far less fuel than it would for the same True Air Speed (TAS) at a lower altitude. As fuel accounts for a big percentage of the airlines costs, it is important to keep the fuel burn to a minimum, which in helps turn keeps ticket prices low. This is why aircraft cruise at high altitudes.