In my non-expert uninformed opinion, if the political will would be there UL94 would have replaced 100LL a long time ago. UL94 is basically 100LL but without the lead, so we certainly know how to produce it worldwide at decent cost.<p>- Most planes could switch without any change<p>- Yes, in some cases, changes would be needed, like<p><pre><code> - detuning.
- installing an electronic ignition timing system.
- Installing a new engine, either a newer gasoline engine, a diesel engine, or a turbine engine.
- Scrapping the plane and buying a new one.
</code></pre>
Sure, this would incur cost for some, but c'est la vie. Many such decisions have been made in societies all over the world, often for good reasons.<p>This could still be the solution if the EPA puts their foot down and the PAFI thing mentioned doesn't produce a workable 100UL recipe.