Have you ever wondered why airplanes fly at 35,000 feet? Probably not, but the answer is quite interesting! Let us break it down for you…

One of the main reasons is that the air thins out the higher the plane rises, allowing it to travel quicker and easier. As such, the plane uses up less fuel, which saves the airline a lot more money.

The best altitude for the airplane to fly at is between 35,000 and 42,000 feet. If it goes below, there’s more air resistance, and if it goes too high, there’s not enough oxygen for the engines to operate properly. To determine the best altitude, planes have to fly higher or lower depending on the weight of the plane—if it’s lighter, it should fly higher, if heavier, then lower.

Peter Terry, a commercial airline pilot who has been flying for 30 years says, “Each individual aircraft has an optimum altitude (for minimum cost or minimum fuel burn) which will be based on its individual weight…Concorde flew at much higher altitudes – 50,000/60,000 feet – where there were no other aircraft and so were able to cruise climb [that is keep climbing].”

A captain for Air Canada, Doug Morris, says that it’s better if the plane flies higher “because the thinner air imposes less drag”.

Moreover, there are aviation laws known as the lowest safe altitude (LSALT), which is standard around the world. Richard Taylor, who works for the British Civil Aviation Authority (CAA), says the LSALT “applies much more to light aircraft than airliners, but it is illegal to fly below 1,000 feet when over a built-up area, or 500 feet over any person, vehicle or structure…That is as much for environmental reasons such as noise as it is for safety”.

In terms of the maximum, there are no laws that say an airline has to fly above a certain height. However, as we mentioned earlier, the oxygen levels are much lower at higher altitudes, which engines have a hard time operating at. Interestingly enough, the world record was set by Alexandr Fedotov in 1997, who flew a military Soviet MiG-25M up to 123,520 feet!

The Weather Above 35,000 Feet

When an airplane flies high in the sky, it can bypass pretty much all bad weather—something all of us who are grounded don’t always have the pleasure of bypassing.

The atmospheric layer called the troposphere is where most of the Earth’s weather phenomenon happen such as rain and wind, and it’s also where clouds are located. The troposphere extends right up to about 36,000 feet, and above that is the stratosphere—the layer that airplanes fly in to bypass turbulence we all love so much ;).

And the cold? The higher up you are, the colder it gets (I’m sure you’ve noticed how that tiny hole in the window always has frost around it?). The average temperature in the stratosphere is about -60°F (-51°C)—warmer than Antartica!

Rule Out Other Air Traffic

Another reason why planes fly at such a high altitude is to avoid other air traffic such as helicopters, Tricycle Gears, Taildraggers, Seaplanes, Sports Aircrafts, as well as birds and insects. And even though there are thousands of commercial airplanes flying all at once in the sky (there are about 5,000 in the U.S. alone), very rarely do we ever see a nearby airplane, thanks to all the traffic control centers.

(This article first appeared on TravellerAU.)