[stevenwoo]

Based on past decisions, it's going to take some revolutionary technology that is cheaper than avgas fuel/engines. Isn't the USA is the largest and last major country that uses leaded fuel for small planes. We'll do almost anything to save small plane owners the cost of upgrading.

[bdamm]

Mainly because avgas is not a meaningful contributor to climate change or environmental lead. It's a pittance when compared to anything else; commercial aviation all sources, DoD, road transport for GhG and piping, paint, and industrial sources for lead.

[stevenwoo]

I should have been clear I was not comparing greenhouse emissions of avgas to replacement but that contributing more lead in any amount to the environment is pretty terrible since we all pay for the effects, even considering whataboutism of all other human lead pollution. The forever persistence of lead and ready bioavailability makes it special.

[sokoloff]

Leaded avgas is used worldwide wherever high-compression or turbo-charged spark ignition aviation engines operate.

There is an unleaded fuel program (several candidate fuels in testing) and I believe one has a chance to be a drop-in replacement. It’s not yet certified and so we keep using 100LL (worldwide, not just in the US).