A 100-octane unleaded avgas replacement developed by LyondellBasell and VP Racing—the only fuel currently participating in an FAA fleet approval process—advanced in November when ASTM International published a standard specification to be applied as the FAA completes testing and evaluation of this fuel, the companies announced January 5. Fleetwide FAA approval could follow later this year.
The testing specification (D8631-25) published by ASTM in November completed a pathway for the UL100E blend developed collaboratively by the chemical company and the motor racing fuel provider to potentially earn FAA approval through the Piston Aviation Fuels Initiative, a program created in 2014 to spur development of an unleaded fuel that could replace 100LL across the fleet.
Outside of the ongoing PAFI program, two other unleaded formulations have been brought to market on a limited basis, distributed at select locations, and approved via supplemental type certificate. Swift Fuels announced finalization of an ASTM production specification standard for its 100R blend in 2025, following FAA STC approval of 100R for Cessna 172R and -S models with Lycoming IO-360-L2A engines. Flight schools in the United States and Europe have taken 100R deliveries, and the company is seeking additional STC approvals.
General Aviation Modifications Inc. earned an expansive STC for its G100UL in 2022, though GAMI has, to date, opted not to submit its fuel to ASTM for evaluation. G100UL has so far been distributed at a handful of airports; fuel leaks associated with introducing this new fuel into aircraft and engines that are in many cases decades old prompted the FAA in April 2025 to seek additional information from owners who have good or bad experience using G100UL.
In a January 5 news release, LyondellBasell and VP Racing noted recent completion of PAFI milestones, including material compatibility testing conducted by various aircraft and engine manufacturers, as well as at the FAA William J. Hughes Technical Center for Advanced Aerospace in New Jersey. “Flight testing on a Lancair Super Legacy equipped with a turbocharged TSIO-550 engine and a Harvard Mk IV warbird equipped with a Pratt & Whitney R-1340-AN-1 Wasp radial engine is ongoing,” the release states.
Tests performed at the FAA center to date include endurance and detonation tests on large-block Lycoming and Continental engines, with PAFI tests expected to conclude in September. The FAA will examine the results to determine which aircraft and engine combinations will be eligible for UL100E, the companies said, “and outline any operational and/or engine modifications required for a small portion of the fleet via a Special Airworthiness Information Bulletin.”
AOPA President Darren Pleasance welcomed the announcement as the latest sign of progress toward the aviation community’s shared goal of transitioning to an unleaded fuel that is safe for all piston aircraft to use by 2030.
“This is a meaningful milestone as the aviation industry continues to make progress toward an unleaded future,” Pleasance said. “We congratulate VP Racing and LyondellBasell for the work they’ve done and for contributing to the momentum needed to deliver safe and reliable solutions for general aviation.”
AOPA is a founding member of the Eliminate Aviation Gasoline Lead Emissions (EAGLE) initiative, and additional information about PAFI, and the various fuels working their way toward distribution at scale, can be found at flyeagle.org.