The FAA has amended Swift Fuels’ existing engine STC for 100R unleaded avgas, broadening the list of covered engines effective earlier this month. The STC was first issued in September 2024, but now points to updated fuel specifications dated Feb. 19, 2026, along with a revised approved model list identifying eligible engines. Installing an engine modified under the STC still requires a separate airframe STC.
The fuel’s initial engine approval covered the Lycoming IO-360-L2A, but the amended AML now includes a much broader mix of Continental, Lycoming, Franklin and other engines.
Intermixing 100R with other approved avgas grades is allowed only under Swift Fuels’ published instructions. Swift Fuels states that 100R is fully intermixable with 100LL at any ratio in approved engines and aircraft, provided all STC limitations and service instructions are followed.
The amendment comes as the FAA continues developing its broader transition plan for unleaded avgas. In material the agency released in 2025 and early 2026, the FAA outlined a phased approach aimed at ending use of 100LL by the end of 2030 outside Alaska, with Alaska given until the end of 2032.
The FAA has made it clear that it does not plan to select a single replacement fuel. Instead, the agency has said the transition will depend on fuel approvals, market experience, infrastructure and operator acceptance, with 100R among the fuels now moving through that process.