Updates

This is the first in a three-part series explaining how the next generation of unleaded aviation fuels may be authorized for use in specific engines and aircraft. This installment examines the Type Certificate (TC) and Supplemental Type Certificate (STC) processes, which enable eligible aircraft and engines to operate using qualified unleaded aviation gasoline (avgas) under the FAA’s traditional certification procedures. The second part will review the Fleet Authorization process, developed through the Piston Aviation Fuels Initiative (PAFI), which allows eligible aircraft and engines to operate safely using unleaded avgas. The final installment will discuss the importance of industry consensus standards, such as those from ASTM International, in ensuring the safe, consistent production, distribution, and use of aviation fuels. For more information on
these topics, visit: https://flyEAGLE.org.  

Q: Why should pilots and aircraft owners be invested in the unleaded avgas approval process?
Pilots and aircraft owners play a critical role in the transition to unleaded fuels. Staying informed ensures they can adopt new fuels safely and efficiently while maintaining compliance with the required approvals or authorizations.

While the approval processes may seem technical, they directly affect daily operations, safety, maintenance, and long-term aircraft reliability. By understanding these impacts, owners can confidently navigate the transition and make informed decisions for their aircraft and missions.

Q: What is an STC, and how is it used to authorize unleaded aviation fuel for specific aircraft and engines?
A Supplemental Type Certificate (STC) is an FAA-issued approval that authorizes the use of specific fuel, fluids, parts, and/or equipment in a designated list of aircraft and engines. It is one of two pathways fuel developers can use to bring their products to market.

Through the STC process, fuel developers are solely responsible for testing the compatibility, safety, and performance of a new fuel with specific aircraft and engine models. Once the FAA reviews and approves the data, an STC is issued, authorizing the use of the fuel. The STC database can be searched to identify aircraft models approved for a specific modification or installation.

The applicant can sell the STC to customers, enabling them to modify their individual aircraft for the use of the fuel specified in the STC. This modification typically includes updating the fuel placard and may require additional adjustments depending on the STC. For aircraft with a standard airworthiness certificate, the alteration must be performed by a certificated mechanic or authorized entity in compliance with the STC.

STC data is considered proprietary to the applicant. Therefore, the FAA does not provide STC data directly to owners of aircraft with special, restricted, or experimental airworthiness certificates. However, the applicant may choose to share the necessary information with interested parties. Owners of Special Light Sport Aircraft (SLSA) can implement the authorization after the SLSA manufacturer issues approval. Experimental aircraft owners must individually determine appropriate unleaded fuels, either by conducting their own compatibility assessments or consulting the STC holder for relevant data.

Q: What is the Approved Model List (AML)?
The AML is a list of aircraft models approved for a specific modification or installation, typically under a Supplemental Type Certificate (STC). Aircraft owners must take specific actions to implement changes to their aircraft, typically through Service Bulletins or the installation of an STC. For aircraft with a standard airworthiness certificate, the alteration must be performed by a certificated mechanic or authorized entity in compliance with the TC/STC.

Q: How does the STC process differ from the FAA fleet authorization process?
Under the FAA’s traditional STC/AML process, an applicant is responsible for demonstrating that the aircraft and engines meet all applicable regulations and minimum standards under the normal certification process when using the new unleaded fuel. The FAA reviews the compliance data provided by the applicant and, upon approval, issues an STC.

Under the Piston Aviation Fuels Initiative (PAFI), the FAA uses a combination of testing and analysis methods developed in collaboration with industry to determine if an unleaded avgas qualifies as a replacement for approved leaded avgas. The data obtained through testing supports the development of the ASTM production specification for the candidate fuel.

The FAA will identify the makes and models of type-certificated and non-type-certificated piston aircraft and engines that can safely operate with the qualified unleaded avgas, compiling them in the Eligible Fleet Authorization Summary Report (EFASR), which will also include experimental aircraft.

Additionally, the FAA will issue a Special Airworthiness Information Bulletin (SAIB) and provide detailed instructions to implement the necessary alterations for using the fuel. The candidate fuel is then qualified as a replacement fuel under the fleet authorization process for the eligible portion of the fleet.

Q: Why is it important for pilots and aircraft owners to read and understand an unleaded fuel STC?
It’s crucial for pilots and aircraft owners to read and fully understand an STC, as it outlines the specific modifications, limitations, and operational requirements necessary to safely integrate the approved fuel or equipment into their aircraft. Strict adherence to the STC ensures compliance with FAA regulations while maintaining the safety, reliability, and airworthiness of the aircraft. Currently two fuels, G100UL from General Aviation Modifications, Inc. (GAMI) and Swift Fuels’ 100R have approved AML-STCs.

By understanding both pathways, pilots and owners can better plan for the transition to unleaded fuels. Whether through individual STCs or fleet-wide approvals, these processes are designed to ensure safety and reliability.

Part 2 of this three-part series will delve into the FAA Fleet Authorization process and its benefits for the general aviation community.

Eliminate Aviation Gasoline Lead Emissions (EAGLE) is a comprehensive government-industry initiative consisting of the aviation and petroleum industries and U.S. government stakeholders, and a wide range of other constituents and interested parties, all working toward the transition to lead-free aviation fuels for piston-engine aircraft by the end of 2030 without compromising the safety or economic health of the general aviation industry. To learn more, visit: https://flyEAGLE.org

For more information on the transition to unleaded aviation fuel, visit: https://flyEAGLE.org

The growing availability of unleaded aviation fuel represents a crucial step toward eliminating lead emissions from aircraft. However, it also introduces new misfueling risks that occur when the wrong type, grade, or mix of fuel is delivered to an aircraft. With multiple fuel options now available, pilots, aircraft owners and line service personnel must be more vigilant than ever to ensure fueling safety.

Misfueling can lead to catastrophic engine failure, which is why clear communication between pilots and line service personnel is essential.

Pilots should confirm the limitations of the engine and airframe. And, when placing full-service fuel orders, confirm every detail of the order—including type, grade, and volume—with line service personnel, or be aware of these factors when conducting self-service fueling.  Aircraft must also have proper logbook documentation and placards installed.

It is important to note that while the new unleaded fuels are designed to mix with 100LL, it remains uncertain whether they can be safely mixed with each other. Until more information is available, unleaded fuels must not be combined. Again, each engine and/or aircraft may have specific limitations that aircraft owners need to be aware of when fueling their aircraft.

Resources such as the Energy Institute’s Misfuelling Resources, AOPA’s Safety Brief, the National Air Transportation Association’s (NATA) Misfueling Prevention Program, and the EAGLE’s Guidance on Transitioning a Flight School to Unleaded Avgas offer valuable guidance during this transition. As unleaded fuels become more widely available, diligence and adherence to proper protocols will be essential to maintaining safety and protecting your aircraft.

Eliminate Aviation Gasoline Lead Emissions (EAGLE) is a comprehensive government-industry initiative consisting of the aviation and petroleum industries and U.S. government stakeholders, and a wide range of other constituents and interested parties, all working toward the transition to lead-free aviation fuels for piston-engine aircraft by the end of 2030 without compromising the safety or economic health of the general aviation industry. To learn more, visit: https://flyEAGLE.org

The aviation community has long recognized the need to eliminate lead emissions from piston-engine aircraft, a goal set to be achieved by the end of 2030 through the leadership of the Eliminate Aviation Gasoline Lead Emissions (EAGLE) initiative. This ambitious endeavor brings together government and industry partners committed to finding a safe and reliable unleaded aviation fuel that is viable throughout the aviation supply chain.

As the general aviation community works toward this goal, the role of aircraft owners cannot be overstated. They are, after all, the ultimate end-users of any new fuel, and their buy-in will be critical to its success.

This transition is about more than meeting regulatory requirements—it’s about ensuring that aircraft owners feel confident in the safety and reliability and availability of the new fuel. The solution must be robust enough to meet the diverse needs of the piston-engine fleet, ranging from the World War II era planes to modern helicopters.

Currently, there are three promising unleaded fuel candidates. Their developers are pursuing either the Fleet Authorization (FA) under the Piston Aviation Fuels Initiative (PAFI) or the traditional Supplemental Type Certification (STC) process via an approved model list (AML). Both pathways ensure that engines and aircraft can safely operate on the new fuel, however, regardless of the path to approval to use in the aircraft, consumer acceptance will hinge on more than FAA approval.

Fuel developers must not only prove their products’ safety and compatibility with the existing fleet but also demonstrate to key industry stakeholders that their product is reliable. Aircraft owners need assurance that switching to a new fuel won’t void manufacturer warranties. They also need to be confident that it won’t cause damage to paint, electronics, engine components or fuel systems. The aviation supply chain will need assurances as well. This next fuel must be produced, distributed, stored, possibly comingled with other fuels, pumped, and consumed without causing damage or requiring significant equipment modifications. Industry stakeholders understand that any new fuels must meet the needs of aircraft owners and be compatible with production, distribution and dispensing systems.

EAGLE has worked diligently over the past 18 months to keep stakeholders informed, providing updates on the progress of key unleaded fuel developers. General Aviation Modifications Inc.’s (GAMI) G100UL and Swift Fuels’ 100R are advancing through the STC process. GAMI has already secured a broad Approved Model List (AML) STC for its fuel in 2022 for piston engines and airplanes. Recently, the FAA granted Swift Fuels its first STC for the use of its 100R in Cessna 172 R & S model aircraft powered by Lycoming IO-360-L2A engines, with many additional engines and airframes being evaluated for approval in the weeks ahead. LyondellBasell/VP Racing’s UL100E is progressing through the PAFI pathway, having completed about 25 percent of critical materials compatibility and full-scale engine detonation and performance testing. Both Swift Fuels and LyondellBasell/VP Racing have also begun working through ASTM International on the development of an industry consensus production specification for their respective fuels.

The recent updates from EAGLE provide optimism. To learn more visit: flyEAGLE.org (See Stakeholder Meetings). Progress is being made, and general aviation’s path to acceptance of unleaded fuel continues.

Congress and the FAA’s commitment to this initiative is underscored by the 2024 FAA Reauthorization, which supports the continued availability of 100-octane low-lead (100LL) avgas until the end of 2030, or when a certified unleaded alternative is available at airports. (Alaska, a state heavily reliant on piston-engine aircraft, has been given a slightly extended timeline protecting continued availability of 100LL through the end of 2032). However, the collaborative industry/government EAGLE goal is clear: the elimination of leaded aviation fuel by the end of 2030.

General aviation is moving to ensure a safe, reliable transition to unleaded avgas without jeopardizing the operational safety of the piston-engine fleet. Aircraft owners must stay informed and engaged as this transition unfolds. It is important that they educate themselves on any restrictions that may accompany an STC and comply with any OEM directives that may be issued. They are the key players in this process, and their comfort with these new fuels will drive this monumental shift.

It is not enough for the FAA to approve these new fuels. The industry—from aircraft owners to fuel distributors to FBOs that dispense fuel and aircraft manufacturers that provide continued operational support—must accept them. Safety, reliability, and commercial viability must guide this transition, ensuring that by the end of 2030, piston-engine aircraft can take to the skies with unleaded fuel that is dependable. The future of general aviation depends on it.

Eliminate Aviation Gasoline Lead Emissions (EAGLE) is a government-industry initiative consisting of the aviation and petroleum industries and U.S. government stakeholders, and a wide range of other constituents and interested parties, all working toward the transition to lead-free aviation fuels for piston-engine aircraft by the end of 2030 without compromising the safety or economic health of the general aviation industry. To learn more, visit: https://flyEAGLE.org