What are the white streaks that planes leave behind?

When you peer at the sky on a bright day, you can often see criss-crossing white lines left behind by aircraft. But have you ever wondered how they are formed and why? We looked into the phenomenon.

1. Contrails are formed when vapor from the engines freezes.

The trails left behind by planes are officially called contrails, short for concentration trails. They form a bit similarly to how the breath you exhale can condense into vapor on a cold day.

In short, contrails are formed when the water vapor in the exhaust from the plane’s engines condenses into water droplets, which then freeze into ice particles composing a line-shaped cloud.

The impurities in the jet exhaust form some of the particles on which water droplet grow, before freezing.

2. Contrails commonly occur at high altitudes

The most important factors for contrail formation are temperature and humidity.

Most typically, the trails are formed by jet planes that fly at the right altitude, around 25,000 to 40,000 feet, where the air is cold enough. The trails form most often at a temperature below minus 40 degrees Celsius.


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Post this on Facebook and you’ll be surrounded with 40yr old Karen’s saying that it’s big pharma and the government puts chemtrails to infect the population. Which we know is not true

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Welcome to the community!

This is very informative! Although I already knew what these were, I (and I’m sure a lot of people) did learn something from here :)

Thanks for sharing!

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Hello and welcome to the community, I hope you enjoy it here,

Please don’t copy and paste a websites page and not give credit, you copied some of the article below.


As mentioned by a user above, you need to be at TrustLevel 2 to post #real-world-aviation topics. Go and check the links he provided to learn more. And as mentioned by another user, once you’re allowed to post in #real-world-aviation, please don’t just copy/paste an article, especially when you’re not providing a source.