The reason is that several civilian-owned lightweight propeller aircraft like those produced by Cessna have engines that are still designed to run on leaded gasoline and nothing else, because engine knock (mistimed fuel ignition in the cylinder, and the original reason for leaded gasoline) damages the engine and can cause it to fail mid-flight.
Most commercial and military aircraft used today run on jet fuel instead.
Which is the reason I assumed, but at the same time it doesn't answer the question of why those aircraft were exempted when we were able to ban leaded gas for every car.
Because civilian propeller aircraft are not used in massive numbers like automobiles, therefore there is very little environmental push or financial incentive to convert the 80-year-old designs to new engines or retrofit new engines onto old planes.
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u/TransLunarTrekkie 1d ago
Friendly reminder that leaded gas is banned in the US EXCEPT, for some reason, in aviation use.
Use this information how you will.