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
Also airplanes live longer and the rich dudes who own them tend to be conservative.
They may also be brain dead from lead exposure.
There was also an argument for valve seat protection afforded by lead gas, but they should eat the cost of engine rebuilds and be forced to comply. Especially as many of those planes are for hobby anyway.
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.
The aviation industry is second only to nuclear in regulatory conservatism. They grind through change slowly, methodically, and expensively.
Every engine manufacturer went through a lengthy certification process to get their engines approved to run on avgas. If you want to burn a slightly different kind of fuel, you either need to go through that entire process again, or you have to convince the FAA that there is so little difference in the new fuel that it will perform identically in every engine that has ever been certified on the old fuel.
They finally achieved that second one earlier this year, after decades of work.
This makes the most sense by far. I think it has a lot to do with we just don’t put the money towards research and development we did in the 40’s and 50’s. Sure we still R&D but no one is dreaming up completely new ideas from the ground up and getting funding.
The most promising short-term approach is switching from spark ignition to compression ignition: Jet fuel is very comparable to diesel fuel, and doesn't have the same problems with lead that avgas has. It has a higher energy density, providing lower fuel burn and longer range. And it is significantly cheaper than 100LL, let alone 100UL.
Europe has a significant number of diesel-engined general aviation aircraft burning Jet-A. Several manufacturers have received supplementary type certificates to swap out gasoline engines for diesel in many of the most popular GA aircraft.
Longer term, electric and hydrogen are being researched, but it will be a long time before they are viable options in the GA fleet.