Lead isn't actually a requirement for piston-engine aircraft. It's just that most piston engines available with: 1) world-wide certification 2) world-wide

Lead isn't actually a requirement for piston-engine aircraft. It's just that most piston engines available with: 1) world-wide certification 2) world-wide base of trained mechanics 3) already widely deployed (you can't just "swap" engines on a plane design) Are piston engines whose original design happened ages ago when leaded gasoline was the cheapest fuel with necessary performance (and that includes not just octane rating, but also things like evaporation rate at given atmospheric pressure - you don't want your fuel tank to explode due to gasoline vapors). Several newer designs in Europe have been playing around with Diesel engines again, because thanks to being heavier fraction it doesn't have as much evaporation problem of gasoline, and also diesels are by design very tolerant of fuel types. Most importantly, a plane with an aviation diesel engine can just as well use non-ethanol-added diesel from car gas station, or any of the Jet-A1 compatible fuels available on airfields (pretty sure everything that isn't accidental leftover of SR-71 blackbird operation will work just fine).