The Leaded Avgas Endgame, the GAMI G One Hundred UL Approval That Changed the Equation, and What Every Piston Pilot Needs to Know Before the Next Fill-Up

A certified, 100-octane, unleaded replacement for 100LL avgas now exists and is approved by the FAA. The question is no longer whether the industry will transition away from leaded aviation gasoline - the regulatory, legal, and scientific pressure has settled that - but how fast the infrastructure will follow.

Why Lead Is Still in Your Avgas

Tetraethyl lead has been part of aviation gasoline since the 1930s. It was banned from automotive fuel in the 1970s, but aircraft were a different story. Piston aircraft engines - particularly high-performance and turbocharged models - depend on high-octane fuel to prevent detonation.

The physics matter here. When a fuel-air mixture ignites abnormally, the result in a car engine might be an audible knock. In an aircraft engine operating at high power settings, with tight tolerances and no option to pull over, detonation can destroy a cylinder in seconds. Octane rating prevents this. Tetraethyl lead is an extremely effective octane booster, which is why it survived in aviation long after it disappeared everywhere else.

The piston fleet compounds the problem. It spans everything from a low-compression Piper Cherokee flat-four to a turbocharged Continental TSIO-550 producing more than 300 horsepower. A single drop-in replacement has to work across all of it, or the distribution system fractures into multiple grades.

The FAA’s Decade-Long Search for a Replacement

The FAA launched the Piston Aviation Fuels Initiative (PAFI) in 2014 with one stated goal: a single drop-in replacement for 100LL that required no engine modifications and worked across the certificated piston fleet. More than a decade later, two unleaded fuels have emerged from that process.

Swift Fuels 94UL is the first. Unleaded, available at select airports, and suited to lower-compression engines. Pilots flying Cessna 152s, Cherokees, Grummans, Champions, and many other trainers may already be approved to use it - the answer is in the pilot’s operating handbook. For a significant share of the training fleet, 94UL is a real, available option right now.

But 94 octane is not enough for high-performance engines. Turbocharged Cirrus SR22s, Beechcraft Bonanzas, Piper Malibus, and other high-compression aircraft need 100 octane. Closing that gap has been the core challenge of the entire transition effort.

What the GAMI G100UL Approval Actually Means

In August 2022, the FAA issued a Supplemental Type Certificate to General Aviation Modifications Inc. (GAMI) for their G100UL fuel. This was a landmark: for the first time, a certified, 100-octane, unleaded aviation gasoline was approved for the certificated piston fleet.

G100UL uses proprietary chemistry to achieve 100-octane performance without tetraethyl lead. GAMI’s data submission to the FAA covered cold starts, high-altitude cruise, and hot-day, high-power-setting operation. The FAA reviewed it and approved it.

GAMI built its reputation on precision fuel injection systems - their injectors have been a standard upgrade for pilots seeking balanced fuel flow from Continental and Lycoming engines. That background means the company knows aircraft engines exceptionally well. What an STC approval does not provide, however, is a supply chain.

Why G100UL Isn’t at Your Airport Yet

An approved fuel and an available fuel are two different things. Scaling G100UL from an STC to widespread airport availability requires refineries willing to produce the product, a distribution network to move it, FBOs willing to invest in storage infrastructure, and enough pilots buying it to make the economics work.

As of fall 2025, G100UL is available at a growing but still limited number of airports, concentrated in Texas, parts of the Southeast, and a handful of locations in the West. The FAA’s PAFI page and GAMI’s website maintain current availability lists. Cross-country planning with G100UL currently requires checking fuel stop availability in a way that pilots have never had to do with avgas.

The infrastructure hurdle is real. For an FBO to carry a second grade of avgas, they need separate underground storage - which typically means excavation, new tanks, new plumbing, separate pumps, regulatory permits, updated insurance, and trained staff. A full fuel system installation at a small airport can run well over $100,000. For a rural FBO at a non-towered field serving a few dozen local aircraft, that is a significant investment against thin margins, and operators won’t make it until demand justifies it and until they’re confident the product won’t be superseded in a few years.

The FAA has attempted to address this through guidance and Airport Improvement Program funding, but the AIP was not designed for fuel transitions. The need is real at hundreds of airports simultaneously, and the process is slow.

The Regulatory Timeline Behind the Transition

The legal pressure behind this shift is not speculative. In 2023, the Environmental Protection Agency issued a formal endangerment finding on lead emissions from piston aircraft. Under the Clean Air Act, an endangerment finding is not a position paper - it is a legal determination that obligates the EPA to propose regulations. Legal challenges can slow rulemaking, and the process moves in years rather than months, but the finding is on the books.

Communities near busy general aviation airports have raised lead exposure concerns for more than a decade. Studies of neighborhoods adjacent to high-traffic GA airports have documented elevated blood lead levels in children. Several states have seen local government pushback; at least one jurisdiction attempted to restrict leaded fuel sales before the effort ran into federal preemption issues. The FAA controls airspace, and fuel regulations are federal, but the community pressure is sustained and well-documented.

How Europe Made the Switch - and What It Tells Us

European aviation moved toward unleaded light aircraft fuel before the United States addressed it formally. Aviation UL 91, a 91-octane unleaded fuel, is widely available across European airports and in use across a large share of the European piston fleet.

The European experience confirms that transitioning away from leaded avgas is operationally achievable. The important caveat is that Europe’s piston fleet trends toward lower-compression engines, so a 91-octane product covers more of the European fleet than it would in the United States. The specific American challenge - the high-compression, high-performance end of the fleet - is precisely the gap G100UL was designed to close.

What Piston Pilots Should Do Right Now

Check your aircraft first. If you fly a lower-compression engine, the approved fuel types section of your pilot’s operating handbook will tell you whether Swift 94UL is already approved. If your home airport carries it, you can begin using it today.

If you fly a high-compression or turbocharged engine, check GAMI’s G100UL STC coverage list. Coverage has been expanding steadily as GAMI works through the fleet. For many aircraft, no additional paperwork is required beyond confirming your model is listed. If you fly something with a modified engine, a non-standard installation, or a vintage design with unusual tolerances, verify directly with GAMI before assuming coverage applies.

Talk to your FBO. Ask whether they have a timeline for adding unleaded options. They may not have a clear answer, but the question signals demand. FBOs respond to market signals. If the same question comes from ten pilots in a month, it moves the business case.

Owners of classic or vintage aircraft - particularly designs built before the 1960s - should verify compatibility around older valve seat materials and fuel system components. The broad position from engine manufacturers including Lycoming and Continental Aerospace Technologies is that the vast majority of their certificated engines are compatible with G100UL, confirmed in the STC documentation. But older, non-standard, or heavily modified installations warrant individual verification.

Key Takeaways

• The science is settled and the legal direction is established. The EPA’s 2023 endangerment finding obligates federal action on aircraft lead emissions, and that process is underway.
• A certified 100-octane unleaded replacement exists. GAMI’s G100UL received FAA STC approval in August 2022 and is approved for a growing list of certificated piston aircraft with no engine modifications required.
• Swift Fuels 94UL is available now for lower-compression engines at select airports and may already be approved for your aircraft.
• The infrastructure gap is the primary obstacle. G100UL availability is currently limited to select airports in Texas, the Southeast, and parts of the West - cross-country planning must account for fuel stop availability.
• The transition will arrive at your airport on its own schedule. Airports near communities with active environmental concerns will move faster; rural fields serving older fleets may move slower. Understanding your aircraft’s options now is better than discovering them at the pump.