Frequently Asked Questions

EAGLE and its members are working to facilitate a national transition to unleaded fuels that is safe and smart. It is working to ensure availability of fuels that meet the safety needs of the general aviation fleet. For more information, please refer to the comprehensive article by the National Air Transport Association (NATA) Unleaded Avgas Conversion Considerations for Aviation Fuel Providers and EAGLE’s Guidance on Transitioning a Flight School to Unleaded Avgas.

One challenge is a limited fuel storage and dispensing infrastructure at airports. FAA encourages airports and/or FBOs to take enabling actions, such as installing an additional tank or leveraging a spare tank to store/dispense unleaded fuel while maintaining 100LL through the transition period. Given the relatively low avgas demand, the costs to add an additional tank may be prohibitive.

Another challenge is the lack of understanding of the pathways to authorize fuels. Industry stakeholders need an understanding that any new fuels must meet the needs of aircraft owners and are compatible with production, distribution and dispensing systems. To learn more about these pathways, visit flyEAGLE.org.

A small percentage of the current aircraft fleet may require modifications either to their operating limitations or the hardware to allow safe use of unleaded fuels. This is being addressed via the Research, Development, and Innovation and the Unleaded Fuel Evaluation and Authorization pillars of EAGLE. To learn more, please reference UAT ARC Final Report – Part I Body, various parts of Section III and FAA UAT ARC Final Report Part II Appendicies.

The EAGLE initiative is a comprehensive public-private partnership consisting of aviation and petroleum industry and U.S. government stakeholders, working toward the transition to lead-free aviation fuels for piston-engine aircraft by the end of 2030, without compromising safety or economic health of the general aviation industry

The EAGLE initiative will be modeled after CAAFI (Commercial Aviation Alternative Fuels Initiative) and will be led by an Executive Director selected jointly by industry and government. Work on the EAGLE initiative will be organized in four pillars, each led by an industry expert or government leader.

Many aircraft in the current general aviation fleet need 100-octane fuel in order to avoid engine detonation and catastrophic engine failure. Lead has long been used as an additive to boost fuel octane, allowing these aircraft to fly safely. Finding a suitable unleaded substitute has long been a goal of the general aviation industry and the FAA. While the mission has been challenging, there has been recent progress. As important, the unleaded transition must be safe and smart, and airports and communities must provide a supply of 100 low-lead (100LL) for all aircraft to fly safely during this transition.

While levels of airborne lead in the United States have declined 99% since 1980, there is still more work to be done to lower risks of lead exposure to communities adjacent to general aviation airports. Accordingly, the general aviation industry and the FAA are working hard to eliminate all lead in aviation fuel as soon and safely as possible, through the Eliminate Aviation Gasoline Lead Emissions (EAGLE) initiative.

The EAGLE framework encompasses four pillars designed to foster the necessary evaluation, authorization, regulatory, innovation, and infrastructure solution sets to enable the commercial viability of unleaded aviation gasoline needed to facilitate the transition. The initiative supports the White Houses’s sustainable transportation and broader environmental priorities and is part of the ongoing effort to build a sustainable aviation system.  

• EAGLE, or the Eliminate Aviation Gasoline Lead Emissions initiative, has set the goal of 2030 or sooner for the elimination of lead emissions from general aviation. The full transition to an unleaded aviation gasoline will require good planning, processes, execution, accountability, and active stakeholder participation (including industry and government).
• While the goal to eliminate all general aviation aircraft lead emissions is 2030 or sooner, airports, Fixed Base Operators (FBO), and airport users are encouraged to implement constructive mitigation measures today to reduce lead emissions and plan to facilitate a safe transition.
• In the near term, airport communities can offer unleaded fuel types while maintaining 100 low-lead (100LL) to ensure safe operations of those aircraft that must still use it during the transition. A key enabling step for airports may include installing additional fuel infrastructure, e.g., an additional tank, fuel truck, or leveraging an available tank. Airports are also encouraged to include transitioning to unleaded fuels as part of their airport planning initiatives (e.g., master plans).

Individual fuel suppliers, distributors, and airports consider multiple factors when determining if a fuel is commercially viable, such as:

Aviation gasoline production equates to approximately 0.14% of motor gasoline consumption and is currently only produced in 7 of the nation’s 125 refineries. The limited amount of production, coupled with the highly safety-critical nature of the fuel’s intended market constrains the distribution of this fuel to a system of barge, rail, and truck, which represents the most economical means of transportation.

The transition to unleaded fuel, poses unique challenges. The safety-critical nature of aircraft operations necessitates specialized handling of aviation fuels to ensure their cleanliness, dryness, and adherence to specifications throughout the distribution system. While the production and distribution of new unleaded aviation gasoline could differ from the current system, the reliance on the product arriving clean, dry, and on specification will remain. This, coupled with the continuing small volume of product compared to other transportation fuels, will likely result in the continued reliance on specialized handling and the use of barge, truck, and rail for shipment.

All currently approved unleaded fuels and those in development are safely mixable with 100LL.

Pilots and operators should always check the fuel’s specification or approval documents (i.e.- Supplemental Type Certificate, Pilots Operating Handbook, Owner’s Manual, Airplane Flight Manual etc.) with their airframe and/or engine OEM to confirm which combinations are permitted, as well as any limitations on blending with other fuels.

The ability to combine these fuels safely is critical for aircraft owners, pilots, the aviation industry, and the FAA. The FAA and industry are evaluating options to ensure safety for these fuels.

Owner/operators of Experimental Amateur-Built aircraft are responsible for reviewing available data and determining suitability for their individual aircraft.

• For those interested in using fuel(s) approved via the STC process, we recommend contacting the STC holder directly. These fuel developers own relevant data and plan to make it available to interested parties upon request.
• Guidance and data packages for the fuel being evaluated under the FAA’s Fleet Authorization via PAFI program will be provided to the owners of E-AB aircraft by the FAA.

Please stay engaged with EAGLE and our partners for updates and resources. For more information, please see The Two FAA Pathways to Approve the Use of Unleaded Aviation Fuel.

As directed by Congress in the FAA Reauthorization Act of 2024, FAA is currently developing a transition plan to safely enable the transition of the piston-engine general aviation aircraft fleet to unleaded avgas by 2030. This includes consideration of early deployment of new unleaded fuels at airports that choose to bring an unleaded fuel in addition to 100LL as well as a national transition in which a viable unleaded avgas replaces 100LL within the current infrastructure.

Airports considering an early adoption of unleaded fuel(s) are encouraged to contact their fuel supplier to discuss infrastructure options. Some candidate fuel providers are working with airports to offer temporary or portable storage tanks during the transition period. Additionally, interested stakeholders might find the following information from the FAA Airports Office helpful:

• Airports are encouraged to support transition-enabling infrastructure:
• Infrastructure Investment and Jobs Act (IIJA) Airport Infrastructure Grant (AIG) allocated funds can be used on sponsor-owned revenue-producing aeronautical support facilities, such as fuel farms. For additional info. see IIJA page and FAQs (note: FAQs are in the process of being updated as of Fall 2025 and will be shared with a wider audience once available).
• The FAA is authorized to provide funding for aircraft fueling systems, e.g. for fuel tanks and trucks.
• Airports are also encouraged to include transition to unleaded fuels in airport planning initiatives and to identify it in Airport’s Capital Improvement Plans.

All unleaded fuels in both STC type certification and PAFI programs have performed well across all the engines tested, showing positive results such as reduced engine wear and cleaner operation, particularly in Continental engines. It is not practical nor possible to conduct testing on each make and model of piston-engine across the entire U.S. aircraft fleet. Therefore, FAA certification and authorization testing uses an “envelope” approach to ensure safety and compatibility across a wide range of engines. by identifying key performance and design characteristics that impact safe operation and specific engine which represent the corners of the envelope.

Based on a specific unleaded fuel performance and composition, the primary focus areas for testing to ensure safety of the fleet are detonation, materials compatibility, and engine durability.

• Fleet Authorization Pathway – Information about the PAFI test program, including specific engines identified for testing of detonation, performance and durability, as well as the current status of testing is available from the EAGLE website: www.flyeagle.org
• STC Pathway – The FAA type certification process is conducted between an applicant and FAA; all project details are proprietary, so please contact those companies for any additional information such as testing of specific make and model engines.

The FAA approves the use of fuel under one of the two approval pathways, either under the Fleet Authorization via the Piston Aviation Fuels Initiative (PAFI) testing program, or under the traditional STC/TC pathway. Once the FAA approves the use of a new fuel, it is up to the open market to deploy the fuel in terms of production, distribution, airport/FBO availability, and owner/operator use. Ultimately, the open market will determine the commercial viability of new unleaded fuel or fuels that replace 100LL.

We are currently in phase one of the four-phase transition plan, focusing on fuel approvals and authorizations, as well as deployment to and use of new unleaded fuel(s) by early adopters. Broader availability is expected as we move into phase two, currently targeted for mid to late 2027, when we anticipate increased access and opportunities. We remain committed to data-driven decisions and will continue to provide updates as more information becomes available.

We are actively monitoring fuel supply and working with stakeholders, including TEL producer Innospec, to ensure continued availability until a safe, acceptable alternative is in place. At this time, there is no legislative ban on 100LL in 2030; the date is a goal, not a cutoff. Ongoing data collection and coordination will inform future actions and necessary rulemaking, ensuring the fleet is supported and a smooth transition is achieved.

Congress recognized the importance of 100LL aviation gasoline remaining available during the transition phase until a suitable unleaded replacement is approved and widely available across U.S. airports. In 2025, FAA implemented a new grant assurance requiring continued availability of 100LL aviation gasoline at federally funded airports through at least Dec. 31, 2030 (December 31, 2032 in Alaska), or until an FAA-approved unleaded alternative becomes widely available. See the FAA Questions/Answers on Grant Assurance 40, Access to Leaded Aviation Gasoline.

No. Congress has reiterated a need for an orderly transition, and the FAA’s role in EAGLE remains unchanged. The program was just reauthorized in 2024, which, via section 827 directs the FAA to continue to partner with industry and other Federal government stakeholders in carrying out the mission of the industry-government initiative, EAGLE, and take such actions as may be necessary to facilitate safe and orderly transition to the unleaded fuel by the end of 2030 (2032 for Alaska).

Airport owners/operators, service providers (FBOs) and other stakeholders are free to deploy UL94 as soon as they choose. Airports can pursue support through federal and state grant funding, such as through the Airport Improvement Program (AIP), to install infrastructure for unleaded fuels like UL94. Some states and localities also offer incentives to offset fuel and STC costs, encouraging earlier adoption. FBOs and airports are working together, where FBOs have invested in the necessary infrastructure to implement unleaded fuels. These efforts help facilitate a smooth transition to unleaded fuel now, paving the way for UL100 deployment when it becomes available.

FAA guidance allows for both industry consensus specifications and independent specifications for the purpose of type certification; an ASTM specification is not required for FAA certification under the TC/STC approval pathway. An ASTM standard is however required for fuel pursuing FAA fleet authorization utilizing the PAFI testing, as per the 2018 FAA Reauthorization.

Although not required for FAA safety certification or authorization, ASTM fuel specification is the industry standard for independent peer review and understanding of a new fuel. As such, ASTM specification is widely relied upon by aircraft and engine manufacturers, fuel refiners and distributors, airports, and FBOs for risk assessment, warranty support, and market acceptance.

Fuels without an ASTM specification are not excluded from consideration as a potentially viable replacement for 100LL by FAA or government regulation; however, the developer of such a fuel will need to address additional considerations required by industry stakeholders to support business risk decisions for deployment and use.

Avgas (aviation gasoline) is an aviation fuel with spark-ignited internal combustion engines. In aviation, Avgas is distinguished from conventional gasoline (petrol) used in motor vehicles, termed mogas (motor gasoline). Unlike motor gasoline, formulated since the 1970s to allow platinum-content catalytic converters for pollution reduction, the most commonly used grades of avgas still contain tetraethyllead (TEL), a toxic substance used to prevent engine knocking (premature detonation). Ongoing experiments aim to reduce or eliminate the use of TEL in aviation gasoline.

A “drop-in” fuel does not affect the airworthiness and performance of the existing aircraft and engines and typically does not require new aviation fuel-related operating limitations. An extensive qualification test program that encompasses fuel property evaluation and engine and aircraft testing would be required to determine if a new fuel is a drop-in.

The segment of the existing fleet of engines and aircraft for which a new fuel is not a drop-in is called the “non-transparent fleet.” FAA approval of new operating limitations and changes such as new or modified hardware, adjustments, or new operating procedures/limitations will be required for aircraft and engines in the non-transparent fleet.

Original Equipment Manufacturer (OEM) Service Bulletins are communication vehicles used by engine and aircraft type certificate (TC) holders to advise owners/operators of approved aviation fuels. New aviation fuels added to a TC are approved under traditional certification procedures and airworthiness standards, after which the OEM service bulletin is updated with the newly added fuel.

A Special Airworthiness Information Bulletin is an information tool that alerts, educates, and makes recommendations from the FAA to the aviation community. SAIBs contain non-regulatory information and guidance that are not mandatory and do not meet the criteria for a mandatory FAA Airworthiness Directive (AD).

The segment of the existing fleet of engines and aircraft for which a new fuel is a drop-in is called the “transparent fleet.” Changes such as new or modified hardware, adjustments, or new operating procedures/limitations are not required for the aircraft and engines in the transparent fleet. Still, FAA approval may be required to enable operation under the existing operating limitations.