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.
100LL has been used since 1974? And with 10 ppm lead is not a problem; even with environmentalists saying it is a problem. The airport to watch is Van Nuys, CA, with as much small aircraft traffic as large airline airports like LAX or Atlanta, or Chicago O’Hare. If lead shows up next to the principal departure runways at Van Nuys, then a problem is looming. If not, then no problem exists with unleaded avgas. So, Van Nuys airport is the canary in the coal mine and I believe the FAA is monitoring lead levels at Van Nuys Airport. With the rest of the small aircraft fleet spread over the entire US, no problem can exist except at the most busy general aviation airports; Van Nuys in particular. Which also means the no lead avgas is simply not needed. And since the current push on small aircraft is electric motors with batteries and alternators, the fleet of general aviation aircraft using internal combustion engines and leaded gas will likely shrink over time. Strongly suggesting the environmentalists are beating a dead horse. Just not enough lead in 250,000 small aircraft with internal combustion engines to warrant no lead avgas gas. And in fact, no lead avgas causes exhaust valves to seize over time without the lead for cooling. This person found out for himself in his 1964 Cessna 172 during the 1980s using unleaded avgas and burning two exhaust valves 200 flying hours apart. Unleaded avgas does not provide the cooling needed for aircraft internal combustion exhaust valves.
There is no point fighting the switch to unleaded - it is going to happen!
What I want to know is why no journalists mention GAMI any more. Since this is the only unleaded 100 fuel that can be used in every piston engine fixed wing aircraft made - it would seem to be relevant to mention/compare and contrast, whenever something from another firm is mentioned.
But - maybe advertising dollars are on the line and a concerted effort is being made to kill the little upstart company’s product before it can gain a foothold. Is Avweb controlled in this way?