Comment by flareback

Devils Advocate: They need to evaluate very carefully the switch. If an engine was designed to run on 100LL then there's a switch to G100UL then care must be taken to ensure it won't mess up the engine. We're not talking about a land based engine (like a car) where if the engine stops you just coast over to the side of the road and call a tow truck. You're talking about an emergency landing which means possible damage to people and property other than the pilot and plane. Many of the general aviation planes out there were built in the 60's and 70's so the FAA needs to be sure it won't cause problems.