Why Some Airplanes Still Use Leaded Fuel

Contrary to popular belief, leaded fuel is still around. The U.S. Environmental Protection Agency (EPA) phased it out in the mid-1990s — but it allowed for certain exceptions. New cars, trucks and other automobiles are now prohibited from using leaded fuel, but the EPA allows airplanes and a few other alternative types of vehicles to use leaded fuel. Why do some airplanes still use leaded fuel exactly?

All About Avgas and Why Some Airplanes Still Use It

Leaded aviation fuel is known as avgas. According to the U.S. Federal Aviation Administration (FAA), it’s the only type of transportation fuel that contains lead.

One of the main reasons some airplanes still use leaded fuel is simply because their engines don’t support unleaded fuel. Older airplanes feature older engines, and some of these engines can only run on leaded fuel like avgas. If leaded aviation fuel was banned, the airplanes would essentially be grounded — at least until their engines have been swapped out or modified to run on unleaded fuel.

Leaded gas has a higher octane rating than unleaded gas. Octane rating is a measurement of a fuel’s antiknock properties. The higher the octane rating, the greater the resistance to combustion without igniting or detonating. Leaded fuel has a high octane rating. Therefore, it can burn at higher temperatures inside of an engine’s combustion chamber.

Leaded vs Unleaded

While some airplanes still use leaded fuel, unleaded fuel is far more common. Almost all commercial airliners, for instance, now use unleaded fuel. Many small airplanes also run on unleaded fuel.

Commercial airliners and other modern airplanes typically run on a type of kerosene-based unleaded fuel. It may have a lower octane rating than leaded fuel, but it’s less likely to foul the spark plugs. Spark plug fouling is a phenomenon in which a spark plug accumulates contaminants such as oil or carbon to the point where it becomes less effective. And unleaded fuel, of course, is better for the environment.

The Continued Push for All-Unleaded Aviation Fuel

There’s still a collective effort to phase out all leaded aviation fuel in favor of unleaded aviation fuel. In February 2022, the FAA announced a partnership with some of the aviation and petroleum industries’ biggest stakeholders. Known as the Eliminate Aviation Gasoline Lead Emissions (EAGLE), the new initiation seeks to phase out leaded aviation fuel completely by the end of 2030.

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