Why do commercial flights fly just below the stratosphere?

Contents

• The five layers of the atmosphere
  • The Troposphere
  • The Stratosphere
  • The Mesosphere
  • The Thermosphere
  • The Exosphere
• In which layer of the atmosphere do aeroplanes fly?
  • Pilots need to know the atmosphere inside out
• You may be interested in…
  • The Kármán Line, the border with outer space
  • How do clouds form?
  • Icing: Ice formation on aircraft
  • What is a METAR and what is it used for?
  • Why do aircraft take off against the wind?
  • The Earth’s Atmosphere

The troposphere, the lowest layer of the earth’s atmosphere, extends up to an average altitude of 12 km, up to 6 km at the poles and up to 20 km in the tropics.

It is home to humans and all of the Earth’s biodiversity. Of course, it is also the layer in which birds fly.

The troposphere is the layer in which all meteorological phenomena originate and is also the layer used by aviation.

The stratosphere extends from about 12 to 50 kilometres above sea level. Unlike the troposphere, the higher the altitude, the higher the temperature in this layer.

But the most important thing about the stratosphere is that it contains the ozone layer, also known as the ozonosphere. This layer contains 90% of all ozone gas in the atmosphere and is capable of neutralising up to 99% of high-frequency ultraviolet rays.

Finally, the stratosphere is where some military aircraft flights pass through, and also where the International Space Station is located.

Now that you are clear about the particularities of each of the layers of the Earth’s atmosphere, you may be wondering in which layer do aeroplanes fly. Although we’ve already given you some background, we’ll expand on the subject below.

The layer in which aircraft fly is the troposphere, the layer closest to the Earth, although within this layer, each type of aircraft uses a different altitude depending on its needs.

For example, school flights, as well as private flights in general, always remain in the troposphere. This is because it is necessary to maintain visual references with the terrain, and piston engines need oxygen to operate.

Commercial aircraft, on the other hand, use the upper reaches of the troposphere. This allows them to take advantage of the low air density to achieve higher speeds and lower fuel consumption. In addition, this altitude is free of intense weather phenomena and birds.

Finally, military flights use the area between the troposphere and the stratosphere, known as the tropopause. In this layer, the density is even lower, so their jet engines are at their most efficient.

It's a common situation for travelers. You fasten your seat belt, listen to the pre-flight safety demonstration (we hope), and prepare yourself for takeoff. After a few moments, the pilot comes on the overhead, "Ladies and gentlemen, we are now at our cruising altitude of 36,000 feet."

It's time to kick back and wait for that refreshment cart to come around. But how many of us have stopped to wonder why planes go this high up in the first place? According to USA Today, the common cruising altitude for most commercial airplanes is between 33,000 and 42,000 feet, or between about six and nearly eight miles above sea level. Typically, aircraft fly around 35,000 or 36,000 feet in the air.

To put that in perspective, the peak of Mount Everest measures 29,029 feet. But this is why we have pressurized cabins: so you don't feel as if you're literally trying to breathe on top of Mount Everest.

The area is called the lower stratosphere, which is just above the troposphere, the lowest part of the atmosphere, according to the UCAR Center for Science Education. Flying in this area has many benefits that make flying one of the leading ways for travelers to get from one place to another.

Fuel Efficiency

The biggest reason for this altitude lies in fuel efficiency. The thin air creates less drag on the aircraft, which means the plane can use less fuel in order to maintain speed. Less wind resistance, more power, less effort, so to speak. Spending less on fuel is also great for airlines, for obvious reasons. Keep in mind though, that a plane's engines also need oxygen in order to work, according to Traveller, since they need this molecule to create combustion, which also creates energy. So, flying too high can also cause problems. Plus, the higher a plane goes, the more fuel it has to burn in order to get there so there are some drawbacks with certain altitudes as well.

Avoiding Traffic and Hazards

Yes, there is "traffic" up in the air. Flying higher means planes can avoid birds (usually), drones, and light aircraft and helicopters, which fly at lower altitudes. According to Your Mileage May Vary, the direction in which your plane is traveling can also affect what altitude it will climb to. Planes flying eastward (including northeast and southeast) will fly at odd altitudes (i.e. 35,000 feet) and all other directions will fly at even altitudes. Routes going in the same direction are also often planned so that planes are 1,000 feet above or below each other to avoid a collision.

Weather

Have you ever wondered why the view outside your plane window can be sunny one moment and rainy the next upon descending into your destination airport? That has everything to do with the altitude. Most planes are flying above the troposphere, where weather events usually happen, according to Traveller.

Turbulence

Of course, turbulence still happens on airplanes, but you may be surprised to know that it happens a great deal less because of the high altitude of many commercial flights. According to The Points Guy, when planes run into air pockets and fierce winds, air traffic controllers can sometimes suggest different altitudes to avoid it. According to USA Today, flying higher can actually minimize turbulence.

Emergencies

A higher altitude can also give pilots one precious commodity when they're up in the air: time. According to Traveller, should something happen that would warrant an emergency landing, the high altitude gives pilots much longer to fix the situation or find a safe place to land than if they were on a light aircraft cruising at 10,000 feet.

Different Planes, Different Altitudes

Not all planes are made to cruise at the same altitude. According to Thrillist, a plane's altitude is determined by its current weight and the atmospheric conditions at the time of flight. A flight's direction (as mentioned above), the amount of turbulence (based on reports by other pilots in the air), and flight duration are also factors.

Who Makes The Call?

Despite pilots being in control of the plane, they aren't the ones who decide on its altitude. Air dispatchers, instead, are in charge of planning and deciding a plane's route, including altitude, as well as tracking where an aircraft is in the air. According to an interview with Richard Taylor of the CAA in Traveller, there are laws in place that dictate aircraft must not fly "below 1,000 feet over a built-up area, or 500 feet over any person, vehicle or structure."

Why do commercial airplanes fly above the troposphere?

Why do planes not stay longer flying in the troposphere?

Why don t commercial airlines fly over the poles?