Why Do Airplanes Leave White Trails Behind Them?

For those who are curious, here’s the explanation from pages 143–144 of my book Havada Bir Ömür.

These white trails, known as contrails, can give the impression that an aircraft is flying while emitting smoke. Although they have inspired imaginative and mysterious stories, even conspiracy theories, they are actually no different from the vapor we see when we breathe in cold weather.

Aircraft fly at high altitudes to consume less fuel and to avoid being affected by atmospheric conditions. Just like cars, fuel consumption in aircraft produces exhaust gases. When airplanes fly at altitudes of around 10,000 meters in temperatures ranging from −30 to −56 degrees Celsius, the cold air entering the engines heats up and turns into water vapor. As this vapor exits the engine into the extremely cold air, the water droplets freeze and turn into ice crystals.

This creates the white, cloud-like trail that appears behind the aircraft. Over time, it evaporates and disappears.

On average, engine exhaust gases consist of about 70% carbon dioxide, 29% water vapor, and 1% other gases.

In aviation terminology, these trails are called contrails, a shortened form of the words condensation and trail.

When aircraft descend to lower altitudes, the outside air is warmer, so these white trails do not form. Studies show that contrails appear in only about 10% of flights.

These trails can also indicate changing weather conditions and approaching storms.

Contrails are sometimes confused with so-called chemtrails, which have led to various conspiracy theories. Claims that aircraft deliberately release chemicals to influence the world or humanity according to secret plans have never been proven. However, scientists note that contrails can have a harmful effect by contributing to increased atmospheric temperatures.