AS9120B, ISO 9001:2015, and FAA AC 0056B ACCREDITED

Why do Aircraft release White Smoke Trails?

In the modern world, hundreds of thousands of flights occur every day across the globe as countless aircraft traverse the sky to their respective destinations. If you live near an airport or commonly traveled airspace, there is a good chance that you have had the opportunity to watch various planes travel. While you may not directly ponder it, you will notice that aircraft often travel while leaving long, white smoke trails behind them. Although this is not a common occurrence for most other vehicle types, the trailing of white smoke has become fairly synonymous with aviation. In this blog, we will discuss the reasoning behind this common occurrence, allowing you to be more informed on the purpose of such smoke trails.

Before we explore the reasoning behind white smoke trails, one must first understand the very basics of engine operation. Regardless of whether one has a reciprocating engine or a gas turbine, most non-electric powerplants create propulsion and thrust through the combustion of fuel-and-air mixtures. This combustion process provides ample exhaust gasses that are harnessed for driving a number of crucial systems, but this exhaust must be expelled from the engine after use to reduce pressure and temperatures.

As this exhaust gas exits the engine, it is imparted with a high moisture content that will quickly begin to condense while the aircraft is traveling at such a high altitude. This causes the exhaust gasses released by the engine to become moisture vapor, thus forming the long, white smoke trail that extends out back from the aircraft. As such, onlookers below should not worry about the safety of these trails, as they are not made up of toxic chemicals like some may claim. This is also why aircraft do not release these trails when taking off and landing, only exhibiting them while very high in the atmosphere at an altitude of 20,000 feet or more.

While the trailing white smoke is simply condensed moisture sourcing from imparting exhaust gasses, black smoke trails are a very different story. If one witnesses black smoke trails coming from an engine, it is most likely a result of incomplete combustion. While the engine combustion process is highly controlled and advanced, there can still be instances where fuel is not completely burned. When this happens, the excess fuel will enter the exhaust system of the aircraft, causing the formation of black smoke. In the early days of aviation, witnessing black smoke trails was fairly common, though the occurrence of this has been significantly reduced with the high efficiency of modern combustion processes.

As explained in this piece, white smoke trails are a result of high moisture content in exhaust gasses while traveling at high altitudes, while black smoke trails are a result of incomplete combustion. Neither instances are a result of aircraft intentionally spraying chemicals, that of which is simply a myth. Because of this, there is low harm in either smoke trail, though the latter is definitely a concern for pilots due to it resulting from poor combustion which can detract from performance, efficiency, and more.

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February 19, 2023
December 2, 2022

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