A new unleaded aviation fuel candidate, UL100E, developed by LyondellBasell and VP Racing Fuels, is moving closer to fleetwide approval in the United States. This development follows ASTM International's publication of a new standard specification, which addresses remaining technical hurdles and paves the way for FAA review and possible approval later in 2026. UL100E aims to serve as a safe, environmentally friendly alternative to the traditional leaded 100LL avgas, which has been the subject of regulatory efforts to eliminate lead emissions from piston engine aircraft.
In the ongoing FAA Piston Aviation Fuels Initiative, UL100E is currently undergoing comprehensive testing, including compatibility assessments and flight trials using aircraft such as the Lancair Super Legacy equipped with a Continental TSIO-550 engine, and a Harvard Mk IV warbird powered by a Pratt & Whitney R-1340 engine. The FAA will analyze the results to determine which aircraft and engine combinations can operate with UL100E and whether operational modifications are necessary.
If successfully approved, UL100E will fill a market gap, competing with limited alternatives like GAMI’s G100UL and Swift Fuels’ 100R, both of which have partial certifications for particular aircraft types. The push for unleaded fuel gains urgency in California, where local authorities have restricted or banned leaded avgas at airports, heightening industry concern over inconsistent regulations ahead of a national transition.
Industry leaders like Darren Pleasance, President of the Aircraft Owners and Pilots Association, view the ASTM milestone as a significant step toward the goal of introducing a safe, fleetwide unleaded fuel by 2030. He commended the efforts of the involved companies for helping to accelerate the availability of environmentally sustainable options for general aviation.
