FAA Grants Fleetwide Unleaded Avgas STC

GAMI's G100UL is the first FAA-approved unleaded gasoline for all spark-ignition engines and airframes.


As we were quite literally pushing the button to send our October 2022 issue off to the printer, news unexpectedly arrived that many of us had been waiting for: The FAA granted General Aviation Modifications, Inc. (GAMI) its long-sought airframe and engine supplemental type certificate (STC) for the company’s G100UL unleaded aviation gasoline. Although GAMI previously had earned an STC for a number of common, relatively low-power airframe/engine combinations, the September 1, 2022, announcement meant that every aircraft certificated by the FAA and powered by a spark-ignition engine now can use an unleaded gasoline.

The AOPA’s press release about the news quoted GAMI co-founder George Braly as saying, “This is a big day for the industry. It means that for a lot of our general aviation communities, and especially for a high fraction on the West Coast, relief is on the way. And it means that our industry will be able to go into the future and prosper, and provide the essential infrastructure for this country for everything from Angel Flights to critical training of our future airline pilots.”

For its part, AOPA had a similar reaction. “I’m proud of GAMI, the industry team, and the FAA for persevering over the long term and getting a fuel that the FAA has recognized as a viable alternative to low lead,” AOPA President Mark Baker said. “It’s vital that we find solutions to what has been plaguing general aviation since the seventies. It’s certainly the biggest issue I have dealt with in my time at AOPA. “This is a big deal,” Baker added, “but there is a lot of work yet to be done.”

Tim Roehl, President and Co-founder of GAMI, added, “It’s a great day for GA!  Not only can we look forward to a lead-free fuel future, the benefits of the G100UL will improve the maintainability and reliability of our engines, enhancing dispatchability and safety!”

Comparing G100UL To The Existing 100LL Avgas

According to the company, GAMI’s G100UL has many advantages over today’s 100LL, in addition to being lead-free. Among them are:

  • In addition to having “no lead (TEL),” the fuel has equivalent octane performance and can work in even the most demanding high-compression-ratio and turbocharged engines.
  • GAMI’s G100UL has no “organometallic additives” or “scavenging agents” and consequently burns exceedingly clean, similar to today’s unleaded auto fuels. This results in exceptionally clean combustion chambers, free of deposits and materially improving such maintenance headaches like frequent oil and spark plug changes required with today’s leaded fuel.
  • It is fully “miscible” or “fungible” with 100LL in any proportion without loss of properties and approved as such in the wing of an airplane.
  • Being petroleum-based, G100UL can be produced at a large number of refineries or specialty chemical production facilities, improving the logistics of delivering this aviation gasoline through the existing infrastructure.
  • GAMI’s G100UL has been tested for its material compatibility and found to be acceptable for use with a wide range of materials. No changes are required of the aircraft or engine other than the application of placards.
  • Operationally, the G100UL is virtually identical to 100LL and actually has a bit more energy (BTUs/gal), providing increased aircraft range.


Of course, FAA approval is just one of the hurdles that must be overcome before you can burn unleaded fuel in your spark-ignition airplane engine. Manufacturing, distribution, purchasing the STCs and a host of other issues remain to be resolved, probably including a few no one has thought of yet. Among them is how and when a given airport will begin to sell G100UL, and what the STC will cost.

According to GAMI, the G100UL STC will be priced “in a manner similar to the pricing for other fuel STCs that have been available for low octane gasolines.” The price will be based on engines and horsepower, similar to how mogas STCs from the Experimental Aircraft Association and Petersen Aviation are priced now. The company has said it envisions an immediate, online ability to purchase the appropriate STC once the fuel becomes available at retail.

Distribution is another major issue. The company has partnered with the Avfuel Corporation “to over-see the logistics of productions and distribution. Avfuel is a global supplier of aviation fuels and services, and currently sells 100LL to more than 650 FBOs,” according to GAMI.

As for when G100UL will be available at your local airport, “GAMI and Avfuel anticipate that the availability of G100UL will expand nationally over a period of a few years, at a pace determined by eventual depletion of 100LL stocks, the number and location of new producers and blenders, and any mandates by the Federal and local governments.” According to GAMI, initial rollout most likely will occur “with one of the large flight training schools.”


Among other documentation, GAMI has made available its FAA-approved Airplane Flight Manual Supplement. Some of the operational details include:

Color: “The native color of G100UL avgas tends to be yellow to dark amber. Mixed 50/50 with 100LL, it will typically have a green tint.”

Limitations: “Operating procedures, including power settings, fuel flows, operating temperatures, operating limitations, etc., as listed in the aircraft POH, FMS, or placards remain unchanged while operating on G100UL avgas.”

Performance: “Performance will be essentially unchanged by the use of G100UL avgas, alone, or in any combination with other fuels approved for your airframe and engine.”

Weight/Balance: “The weight of the unusable fuel will increase by ~4% when G100UL is used in place of 100LL. This slight increase in empty weight is considered negligible and does not require the empty weight or c.g. to be re-calculated.” Also, “When using Grade G100UL avgas, use 6.25 lbs/gal for weight and balance calculations. For Grade 100LL, use 6.0 lbs/gal for weight and balance calculations. For mixtures of G100UL avgas and other fuels, either use 6.25 lbs/gal or calculate the weight of the combined fuel types, as indicated by their respective weights/gallon.”

This flight manual supplement and other materials, including copies of the G100UL STCs, are available free for the download from www.gami.com, GAMI’s web site. 


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