Taken from the lycoming website.
The fact we face is that because automobiles no longer burn
leaded fuel, aviation fuel has become the largest source of
airborne lead emissions. By EPA reports, 45% of airborne
lead emissions is attributed to TEL enhanced avgas. The U.S.
Environmental Protection Agency has been petitioned by
environmental concerns and will need to act in accordance
with the U.S. Clean Air Act. It has begun a process that
will most likely lead to the elimination of leaded aviation
gasoline within this decade.
“The 20% of aircraft burning Avgas mandatorily burn most of the current supply so there would be relatively little reduction in demand if the other 80% start going to the trouble of sourcing auto fuel or whatever.”
Avgas 91UL is Avgas. Biggest users in the UK are the flying clubs / schools and my guess is that 99% of the school fleet will get approved for Avgas 91UL. Even some of the IO540 variants will get approved if the “Total plan” comes off.
Rod1