Janice Wood General Aviation News
Drop-in unleaded replacement for 100LL expected to be approved in late 2025 
May 2, 2024
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  • A fleet wide approval for an unleaded fuel for general aviation is expected in the third quarter of 2025.

    That’s the key takeaway from an April 2024 update from representatives of Eliminate Aviation Gasoline Lead Emissions (EAGLE), an industry-government initiative launched in 2022.

    The one remaining fuel in the government’s testing program, known as the Piston Aviation Fuels Initiative (PAFI), is UL100E from LyondellBasell/VP Racing.

    It is the only fuel to get through the first three phases of testing and is now in what the FAA calls “full-scale” testing, which includes 10 different engines and eight different airframes.

    The FAA’s Lirio Liu, EAGLE executive director, reported that on April 10, 2024, UL100E successfully completed a 350-hour engine durability test.

    “Three more tests are scheduled on different engines,” she said, noting the FAA expects the testing to “culminate in a full fleet approval in 12 to 18 months.”

    FAA officials note that UL100E has completed about 5% of its detonation and performance testing, 25% of its durability and performance testing, and 20% of its materials compatibility testing.

    LyondellBasell/VP Racing has produced about 50,000 gallons of UL100E for FAA testing, officials added.

    The other fuel candidate going through the PAFI process, from Phillips 66, did not pass the third phase of testing when “deposits and significant signs of preignition were found,” she said.

    Phillips 66 has paused its testing in PAFI, but is still pursuing an unleaded avgas, she added.

    Meanwhile, the unleaded fuel from General Aviation Modifications Inc. (GAMI), known as G100UL — which received approval through the Supplemental Type Certificate process in September 2022 — is now available for sale.

    More than 1 million gallons of G100UL have been produced by Vitol Aviation.

    Swift Fuels, the other contender in the unleaded avgas race, also has received an STC for its 94UL fuel and is going through the approval process for its 100R.

    Once that is approved, Swift Fuels President Chris D’Acosta said the company will phase out its 94UL fuel.

    He noted that 100R has already completed 400 hours of endurance testing.

    What’s Next

    While fuel testing continues, EAGLE officials are looking to the other three pillars of the initiative: Supply chain infrastructure and deployment; research, development, and innovation; and regulations and policy.

    On the supply chain, which includes fuel producers, distributors and FBOs, EAGLE has already surveyed distributors “to see what the challenges are,” said the FAA’s Ryan Manor.

    Next up will be surveying the producers.

    Top challenges already identified include maintaining the availability of 100LL during the transition, as well as ensuring the compatibility of all the unleaded fuels, he said.

    “This is complex,” he said, noting decisions on the state and local levels — such as attempts to ban 100LL — create additional challenges.

    EAGLE officials noted it is imperative that 100LL remains available “until we have an unleaded alternative.”

    Another challenge to the transition: The market size of avgas.

    Will producers want to get into the business when the demand for 100LL is now about 180 million gallons a year?

    To put that in perspective, the demand for automobile gasoline is 135 billion gallons a year.

    FAA officials reported that 100LL is produced in just seven refineries in the nation run by four companies, noting a refinery in Minnesota stopped producing 100LL in 2023.

    And what about FBOs?

    EAGLE officials report that 3,500 FBOs sell 100LL today and these companies will need to make some decisions about adding the infrastructure for an unleaded fuel — either a new tank or a dedicated fuel truck — as well as dealing with other concerns, such as misfueling and insurance.

    And then there’s the aircraft owners and pilots. Each will have to make a decision when they will transition to unleaded fuel.

    Right now, mogas is available in 180 locations, while 35 sell Swift’s UL94.

    To use mogas, the Swift fuel, or GAMI’s G100UL, aircraft owners must buy an STC.

    To complicate things even further, the STC process only applies to certified aircraft. There will have to be another process for homebuilt and experimental aircraft, which make up about 18% of the more than 222,000 general aviation aircraft in the United States, according to EAGLE officials.

    “Market acceptance will be driven by individual decisions based on many different factors,” they said.

    One of those factors will be whether an aircraft will have to be modified to use the new unleaded fuels.

    “We know that 2/3 of the fleet should not be impacted by the transition to unleaded fuel,” said Lycoming Engines’ Jennifer Miller. “We do expect a portion of the fleet may be impacted by compatibility issues with unleaded fuel.”

    She points to valve recession issues seen with the fleet at the University of North Dakota (UND) after using UL94 for just a few months.

    Lycoming, UND, and Swift Fuels are working to “isolate the cause” of the valve seat recession, with an initial theory being that it is related to the aromatics used in the fuel.

    “The bottom line is that any learning is a gift,” she said. “The sooner we know about a problem, the sooner we can respond.”

    On the regulatory side, the FAA is dealing with having its “new authority” to regulate the composition of fuel, according to the agency’s Ralph Iovinelli.

    “We’re working on the rulemaking now,” he reported. “A lot of details go into informed rulemaking.”

    Once those details are ironed out, a Notice of Proposed Rulemaking (NPRM) will be released and the public will get a chance to comment on it. Once the comments are reviewed, a final rule will be issued.

    While the race to find an unleaded fuel for general aviation was spurred by the Environmental Protection Agency’s October 2023 determination that lead emissions from aircraft could possibly “endanger public health and welfare,” the EPA will play no part in developing or approving the new fuel, FAA officials noted.

    As the update wrapped up, FAA officials noted they are working “as fast as we can” to make all of this happen.

    “There are a lot of activities going on and a lot of questions,” Liu said, “and a lot of aspects still left to do.”

    “As you can see, this is a very complicated process from the refiners to the wing of an aircraft,” added Curt Castagna, co-chairman of EAGLE and president of the National Air Transportation Association, which represents companies that provide a range of services to the general aviation industry, such as FBOs.

    What Does All Of This Mean For You?

    While the industry and regulators go through the necessary steps, what do aircraft owners and pilots need to know?

    Once the LyondellBasell/VP Racing fuel is approved, all you’ll need to use it is a placard and an addendum to your POH.

    If you want to use either mogas, G100UL, or Swift Fuel’s 94UL, you can do it now with an STC.

    For more information: FlyEAGLE.org