FAA refines unleaded fuel transition framework

The release follows a draft plan that was published in January, which was then followed by a 60-day comment period.

The FAA previewed the framework’s release during EAA AirVenture Oshkosh, emphasizing that while the plan provides a foundation for the transition, it is not a prescriptive list of actions that must be taken.

“The goal was really to aggregate information, to be able to provide information, to highlight challenges, and to look at those opportunities that need to be pursued towards achieving that 2030 goal,” said FAA Senior Technical Specialist for Aviation Fuels Paul Wrzesinski. “As part of that, providing the information, what we really wanted to set out to do was to build a solid foundation in terms of knowledge, to provide the same background, sort of the same starting point.”

However, the agency acknowledged the plan is not yet comprehensive because “necessary information” is not yet available, leaving several key questions unanswered:

Which unleaded fuel or fuels will be widely available?

• What are the costs and consequences for aircraft owners transitioning to an unleaded fuel?
• Can competing unleaded fuels be mixed together in aircraft tanks and supply chains?
• Nine organizations, including AOPA, that are part of the Eliminate Aviation Gasoline Lead Emissions (EAGLE) initiative—a government-industry partnership—expressed support for the framework.

Fuel approvals

Three high-octane unleaded fuels have received FAA authorization or are expected to receive it soon.

In 2022, General Aviation Modifications Inc. (GAMI) received a supplemental type certificate (STC) for G100UL, covering all spark-ignition airplane engines and airframes. GAMI is currently working to expand STC approval to helicopters.

On July 14, Swift Fuels received an expanded STC approved model list for 100R that includes more than 1,200 piston engine models and 1,600 aircraft. The next day, Swift’s 100R joined the FAA’s Piston Aviation Fuels Initiative (PAFI), which evaluates unleaded fuels intended for fleetwide authorization.

Unlike an STC, which requires aircraft owners to purchase individual authorization from a fuel developer, an FAA fleet authorization grants approval for the use of unleaded fuel in eligible aircraft without an STC—though owners must still apply any required placards, aircraft documentation changes, and logbook entries.

LyondellBasell and VP Racing are expected to complete full-scale PAFI testing for UL100E this fall.

Both 100R and UL100E are expected to receive fleet authorizations in 2027.

Outside of FAA approvals, all three fuel developers have received or are seeking consensus specifications from ASTM International, a globally recognized organization that establishes uniform quality, safety, and testing benchmarks across various industries, including aviation fuel.

Swift 100R received an ASTM production specification—the final step in the approval process—in September 2025. LyondellBasell and VP Racing’s UL100E received a test specification—the first step in the same process—in November 2025. Meanwhile, GAMI, which currently uses a proprietary specification for G100UL, is now seeking an ASTM production specification for its fuel.

No ’drop-in‘ replacement

For years, pilots, aircraft owners, and AOPA have pushed for a “drop-in” replacement for 100LL, which would allow pilots to use a new fuel with no paperwork or aircraft modifications. But in the transition plan, the FAA has determined that a universal “drop-in” replacement is “not feasible” because none of the candidate fuels—G100UL, 100R, and UL100E—can meet every chemical requirement of the existing 100LL ASTM specification.

As a result, the FAA says virtually every aircraft will require, at minimum, new placards, a handbook or flight manual supplement, and a logbook entry. The agency added that other aircraft (likely those with higher-compression or turbocharged engines) may need additional modifications that are “more in-depth… such as replacement of an engine, installation of new engine pistons, the installation of anti-detonation injection systems, ignition timing changes, or significant changes to operating limitations.”

Transition timeline

The overall transition will proceed in four phases, according to the framework:

• Phase 1: Fuel authorizations and comparisons (ongoing through 2027).
• Phase 2: Gain market experience.
• Phase 3: National transition (targeted completion: 2030).
• Phase 4: Alaska transition (targeted completion: 2032).

The first two phases are expected to overlap as final authorizations and comparison testing are nearing completion.

Despite comments from outgoing FAA Deputy Administrator Chris Rocheleau at AirVenture suggesting that the timeline could extend beyond 2030, the published plan maintains 2030 as the “goal” for completing the national transition, with Alaska following two years later because of unique supply chain challenges. The FAA noted that data gathered in the first phase “is required to develop specific plans for the rest of the transition.”

Fuel testing and mixing fuels

The FAA Technical Center in Atlantic City, New Jersey, is testing the unleaded fuels, evaluating “critical materials properties, detonation characteristics, and critical fit-for-purpose properties.” That data will then be used to develop additional testing, examine engine durability, and test the ability to mix the unleaded fuels within the supply chain.

The agency confirmed that all three unleaded fuels can be safely mixed with 100LL inside of aircraft fuel tanks. Ongoing FAA testing is comparing each unleaded fuel against 100LL, looking at engine detonation, materials compatibility, and laboratory testing using key engines and materials that “act as bellwethers for unleaded fuel analysis.”

The FAA anticipates potential workarounds if fuels are not fully compatible. “If unleaded fuels cannot be mixed,” the plan states, “FAA will work with EAGLE to develop appropriate safety mitigations for the fleet. This would also create a significant barrier to the National Transition, necessitating either duplicate infrastructure to support multiple fuels (depending on the aircraft operator’s preference) or the market forces converging on a single (or multiple compatible) fuel.”

In the plan, the FAA also acknowledged concerns regarding misfueling risks and fuel incompatibility and said that liability is a “critical issue” for fuel producers and FBOs that could also delay the transition.

The FAA plans to publish its findings after each type of testing is complete.

Authorization pathways across aircraft categories

The plan also lays out how fuels are authorized across different aircraft categories.

• Standard airworthiness certificate aircraft:
• Authorized by FAA fleet authorization or STC.
• Any changes required by a fleet authorization, STC, or manufacturer service bulletin must be completed by a certificated mechanic or authorized entity.
• Special airworthiness certificate aircraft (primary, limited, provisional, restricted, and multiple):
• Authorized by FAA fleet authorization or STC. However, an STC may only be available in some cases.
• Any changes required by a fleet authorization, STC, or manufacturer service bulletin must be completed by a certificated mechanic or authorized entity.
• Special airworthiness certificate aircraft (light-sport category aircraft):
• Authorized by FAA fleet authorization. STCs do not apply to light-sport category aircraft, so STC holders must coordinate with the manufacturer.
• Special airworthiness certificate aircraft (experimental, including experimental amateur-built and operating light-sport category aircraft):
• Owners must individually determine fuel compatibility. The FAA noted many experimental aircraft have engines and fuel systems that are common in aircraft with standard airworthiness certificates.
• For fuels authorized under the FAA’s fleet authorization process, owners will have access to useful data.
• For fuels authorized with an STC, owners will need to contact the STC holder for information.

Supply chain and infrastructure

Another area that the FAA identified as requiring study is the transition’s impact on the supply chain and logistics. The plan outlines nine primary risks, including the ability to mix fuels within the supply chain, expanded storage needs for airports and distributors, materials compatibility over long storage periods, and pilot communication gaps regarding fuel availability along planned routes.

“Until all fuels are available, production and distribution scale to regional levels, and a larger portion of aircraft have been altered, stakeholders may not realize a full understanding of the supply chain and logistics barriers or the efficacy of the proposed risk mitigations,” the report said.

Currently, only 212 airports nationwide offer an unleaded avgas alternative. The FAA is encouraging airports and FBOs to invest in additional infrastructure—such as tanks, fuel trucks, skid-mounted systems, fuel trailers, or bowsers—to support both 100LL and unleaded fuel during the transition.

The plan also points out that existing airport equipment, procedures, markings, and training are specific to 100LL. Transitioning will require tanks and trucks to be cleaned and labeled properly, installation of placards and labeling, and retraining personnel.

Impact of public comments

Version 1.0 of the transition plan incorporates significant changes from the 60-day comment period following the January draft. Key additions include dedicated sections on clarifying airworthiness authorization pathways across aircraft categories, expanding on critical concerns including potential modifications, the risks of mixing fuels, transition costs, and regulatory timing.

The FAA plans to publish a public FAQ to clear up confusion and misconceptions in some public comments, along with a standalone summary of the comments received at flyeagle.org.

The FAA says subsequent updates will be published after the remaining phases are complete. The next major revisionis tentatively expected in late 2027, after the first phase is complete.