Six months ago, Rocky Mountain Metropolitan Airport Director Paul Anslow didn’t want to talk about leaded fuel. He said he had "zero control" over the airport's use of it. Today, the airport is racing to become the first in Colorado to completely phase the fuel out.
Key things here:
The gas used in the small planes with piston-driven propellers has lead in it. Yeah, the same stuff that was banned from automotive fuel because it causes brain damage in kids.
The FAA has a plan to make going lead-free a requirement by 2031...but right now there isn't anything stopping airport owners (often local governments) from making the switch happen faster. Only thing which might stop this is that the Republican version of the FAA reauthorization bill contains a requirement that airports keep on selling leaded fuel forever, so it's also important to stop that from becoming law.
Old airplane engine designs were created assuming leaded fuel, and the slight reduction in horsepower associated with pre-2022 unleaded fuels was a problem for them. So the phaseout is just getting started, with it happening in only a handful of airports to date
And IIRC, the lead contributed to long term reliability of the engine too, something you definitely want to have in a single-engine plane. You don't want to switch fuels and end up with Cessna's falling out of the sky.
Another issue is that so many small airplanes use engines designed in the 40s and 50s. Sure there have been some updates over the years but the basics havent changed because of the testing requirements from the FAA on new engine designs. Aviation need to become faster at bringing affordable updates to aircraft that dont also limit capability
That definitely made it a lot harder to end the use of lead. Those old engines account for about 1/3 of the small planes in use, and made it a lot harder to develop an unleaded aviation gas suitable for all planes. (There is a widely available one which can be used in the other 2/3 already)
That's why you should see if your local government can force a phase-out sooner where you live. So far as I am aware, only a couple airports in California and the one in Colorado have done so.