Rajan Wilcox
The aviation industry is facing a significant challenge with the impending phase-out of 100LL aviation fuel due to its environmental impact and lead content. This fuel, also known as Avgas or aviation gasoline, has been widely used in aircraft with spark-ignited internal combustion engines. However, concerns about its toxicity and environmental footprint have led to a search for alternatives. While some companies are developing diesel engines and unleaded aviation fuels, the transition away from 100LL is complex due to the specialized needs of aircraft engines and the infrastructure required to support new fuel types. The industry is working towards finding a suitable replacement, with some expecting an unleaded alternative to be approved as early as late 2025.
| Characteristics | Values |
|---|---|
| Replacement of 100LL aviation fuel | Expected in the third quarter of 2025 |
| Replacement fuel | UL100E from LyondellBasell/VP Racing |
| Replacement fuel producer | Piston Aviation Fuels Initiative (PAFI) |
| Replacement fuel status | Passed the first three phases of testing |
| Replacement fuel current testing phase | Full-scale testing, including 10 different engines and eight different airframes |
| Replacement fuel expected approval time | 12 to 18 months from April 2024 |
| 100LL aviation fuel concerns | Contains tetraethyl lead, a toxic additive |
| 100LL aviation fuel alternatives | Automotive fuel and jet fuel |
| 100LL aviation fuel phase-out described as | One of modern GA's most pressing problems |
| 100LL aviation fuel phase-out impact | Affects 30% of aircraft in the general aviation fleet |
| 100LL aviation fuel phase-out challenges | Maintaining availability during the transition and ensuring compatibility |
| 100LL aviation fuel phase-out infrastructure changes | Addition of new tanks or dedicated fuel trucks |
| 100LL aviation fuel phase-out concerns | Misfuelling and insurance |
| 100LL aviation fuel phase-out decision-makers | Aircraft owners and pilots |
| 100LL aviation fuel octane rating | 100, the aviation lean rating |
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What You'll Learn
The environmental impact of leaded aviation fuel
Leaded aviation fuel, or Avgas (aviation gasoline), is a specialised fuel used in aircraft with spark-ignited internal combustion engines. It contains tetraethyl lead (TEL), a toxic additive that boosts octane levels, prevents engine knocking, and aids in lubrication. While lead has been eliminated from automotive gasoline since the 1970s, it remains in Avgas due to the lack of a safe alternative.
Studies have found a direct correlation between the use of leaded aviation fuel and increased blood lead levels in children living near airports. Santa Clara County in California, for example, observed blood lead levels twice as high in children residing within half a mile of the airport compared to those in Flint, Michigan during its water crisis. As airport traffic increased, so did the blood lead levels in children in the area.
The environmental and health impacts of leaded aviation fuel have sparked concerns among government agencies and communities. The Federal Aviation Administration (FAA) and the Environmental Protection Agency (EPA) have acknowledged the issue, with the EPA determining that lead emissions from aircraft engines contribute to air pollution. The Biden-Harris Administration is working towards proposing new standards to protect communities from lead pollution. Additionally, Santa Clara County banned the sale of leaded Avgas at Reid-Hillview Airport, becoming the first airport operator in the country to do so.
The aviation industry is facing pressure to transition to unleaded fuel. While there are challenges in finding a suitable alternative, the FAA and industry have collaborated through the "Eliminate Aviation Gasoline Lead Emissions" (EAGLE) program. The goal is to achieve a lead-free aviation system by 2030, with the FAA approving the use of unleaded fuels like G100UL and UL94. However, the transition must consider the impact on existing aircraft, infrastructure, safety, and economic factors.
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Alternatives to 100LL aviation fuel
The search to find alternatives to 100LL aviation fuel has been going on for over 40 years. This is because 100LL contains tetraethyl lead, a toxic additive used to aid lubrication, increase octane rating, and prevent engine knocking. The lead in 100LL is harmful to the environment and harmful to engines, leaving crud in cylinders and contaminating oil.
One alternative is unleaded 94 Motor octane fuel (UL94). This fuel is manufactured to meet ASTM D7547 and can be used in many common Lycoming engines and a large number of the Cessna piston fleet. It can also be used in any aircraft in Europe or the UK where the engine is certified to use it.
Another alternative is 91UL and 94UL fuel, which Continental considers a transitional step in a long-term strategy to reach a more sustainable aviation solution.
A third alternative is G100UL, which has been produced by Vitol Aviation and has received an STC. Swift Fuels is also going through the approval process for its 100R fuel.
A fourth alternative is diesel engines, which Teledyne Continental Motors (TCM) announced they would develop in 2008 due to concerns about the future availability of 100LL.
A fifth alternative is automotive gasoline, also known as mogas or autogas. This fuel does not contain ethanol and can be used in certified aircraft that have a Supplemental Type Certificate (STC). However, mogas has a higher Reid Vapor Pressure, meaning it boils more readily, and it needs fuel stabilizers if it is stored for more than a few months.
A sixth alternative, UL100E from LyondellBasell/VP Racing, is currently undergoing testing and is expected to receive fleet-wide approval in late 2025.
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The challenges of phasing out 100LL
The aviation industry has been using 100LL fuel for over 70 years. However, the industry is now facing the challenge of phasing out this fuel due to its environmental impact and the potential harm it can cause to human health. The transition to unleaded aviation fuel is not without its challenges, and it has been called "one of modern GA's most pressing problems". Here are some of the key challenges that the industry is facing:
Technical Requirements
Developing an unleaded aviation fuel that meets the technical requirements is a significant challenge. Aviation engines are designed to use fuels with high octane ratings, and the new fuel must be able to replace leaded fuels without compromising performance and engine safety. The technical requirements for such a fuel are high, and there is little room for error.
Aircraft Compatibility
Not all aircraft are compatible with the new unleaded fuels. It is estimated that 70% of 100LL aviation fuel is used by 30% of the aircraft in the general aviation fleet that cannot use any of the existing alternatives. This means that airports and fixed-base operators (FBOs) must maintain a supply of 100LL during the transition to ensure that aircraft engines that require it can still operate.
Infrastructure and Supply Chain
The transition to unleaded fuel will require significant infrastructure changes at airports and FBOs. Companies will need to invest in new tanks or dedicated fuel trucks to store and dispense the new fuel. The supply chain for the new fuel will also need to be established, including fuel producers, distributors, and FBOs.
Misfuelling and Insurance
The introduction of a new fuel type also brings the challenge of misfuelling, which can have serious consequences for aircraft safety. Airports and FBOs will need to implement measures to prevent misfuelling, and insurance companies will need to consider the implications of the new fuel on their policies.
Regulatory and Political Challenges
The transition to unleaded aviation fuel is not just a technical challenge but also a regulatory and political one. The EPA and FAA will need to develop regulations and standards for the new fuel, and there may be resistance or delays in implementing these changes. For example, in December 2023, US Senators from Alaska introduced a resolution seeking to prevent EPA regulation of aircraft engine lead emissions, citing the unique geographic reliance on aviation in the state.
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The process of gaining FAA approval for unleaded fuel
The Federal Aviation Administration (FAA) has set out two pathways for obtaining authorization for the use of a new unleaded fuel. The first is the Fleet Authorization process, which was developed to meet the provisions of Section 565 of the FAA Reauthorization Act of 2018. This process allows eligible aircraft and aircraft engines to operate using qualified unleaded aviation gasoline (avgas) while ensuring safety through the Piston Aviation Fuels Initiative (PAFI). PAFI uses a combination of testing and analysis methods to determine if an unleaded avgas can replace approved leaded avgas. The data obtained through testing is used to support the development of the ASTM production specification for the candidate fuel.
The second pathway is the traditional FAA aircraft type certification/supplemental type certification (STC) process. Under this process, the applicant is responsible for demonstrating that the aircraft and aircraft engines meet all applicable regulations and minimum standards when using the new unleaded fuel. The FAA reviews the compliance data and issues an approval in the form of an STC. Aircraft owners must then take specific actions to implement changes to the aircraft, typically via service bulletins or the installation of an STC. For aircraft with a standard airworthiness certificate, the alteration must be performed by a certified mechanic or authorized entity and comply with the type certificate or STC.
Owners of Special Light Sport Aircraft (SLSA) can implement the authorization after the SLSA aircraft manufacturer issues authorization. Owners of experimental aircraft must individually determine the suitability of each fuel. The STC data is considered proprietary to the applicant, and the FAA does not provide it directly to owners of aircraft with special, restricted, or experimental airworthiness certificates. However, the applicant may choose to provide the necessary information to all interested parties.
Under the STC pathway, there are currently two unleaded fuels: G100UL, developed by General Aviation Modifications, Inc. (GAMI), and 100R, developed by SWIFT Fuels, LLC. In September 2022, the FAA issued an expanded FAA-approved model list STC to GAMI for G100UL, a 100-octane unleaded fuel for general aviation aircraft. In September 2024, the FAA issued Swift Fuels an STC for Cessna 172R/S Skyhawks with Lycoming IO-360-L2A engines to operate on 100R, a high-octane unleaded fuel.
The FAA is currently working with the LyondellBasell/VP Racing team to test and evaluate its high-octane unleaded candidate fuel solution, UL100E, under the PAFI. The FAA expects to issue a fleet authorization for this fuel after the successful completion of full-scale testing.
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The impact of the 100LL phase-out on aircraft owners and pilots
The aviation industry is facing a significant challenge with the impending phase-out of 100LL aviation fuel, which has been the standard choice for pilots and aircraft owners for decades. The impact of this transition on aircraft owners and pilots will be significant and wide-ranging.
Firstly, aircraft owners and pilots will need to make decisions about transitioning to unleaded fuel. This may involve purchasing a Supplemental Type Certificate (STC) to use unleaded automotive fuel or alternative unleaded aviation fuels such as UL94 or G100UL. The STC process adds complexity, especially for homebuilt and experimental aircraft, which make up a significant portion of the general aviation fleet.
Secondly, the availability of 100LL fuel will gradually decrease, affecting flight planning. Pilots will need to consider the availability of unleaded fuel options at their destinations, similar to how electric car owners plan trips around charging stations. This adds a layer of complexity to flight planning, and the consequences of misfuelling or running out of fuel can be severe for aircraft.
Thirdly, the transition to unleaded fuel may impact aircraft performance. While unleaded fuels can bring benefits such as reduced spark plug fouling and longer intervals between maintenance, they may not be suitable for higher-performance aircraft with higher-compression engines. Aircraft owners and pilots will need to carefully consider the compatibility of unleaded fuels with their aircraft's engines and airframes.
Furthermore, the cost of unleaded aviation fuel is a concern. While the industry aims to keep costs comparable to 100LL, the transition to unleaded fuel may result in higher prices, impacting the financial viability of aircraft operations.
Lastly, the phase-out of 100LL will likely have a gradual but significant impact on the aviation industry as a whole. With over 200,000 aircraft in the general aviation fleet and more than 5,000 public-use airports, the transition will affect the freedom to fly, the industry's economic impact, and its ability to provide humanitarian services and disaster relief.
In conclusion, the phase-out of 100LL aviation fuel will have a profound impact on aircraft owners and pilots, requiring them to navigate complex decisions, adapt to changing fuel availability, consider aircraft compatibility, manage potential cost increases, and deal with the industry-wide implications of this transition.
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Frequently asked questions
100LL aviation fuel, or Avgas, is an aviation fuel used in aircraft with spark-ignited internal combustion engines. The 100 in 100LL stands for the lean rating of the fuel, and LL stands for low lead.
100LL aviation fuel is being phased out due to its lead content. There are ongoing efforts to reduce or eliminate the use of lead in aviation gasoline.
A fleet-wide approval for an unleaded fuel alternative is expected in late 2025. However, it is unclear how long it will take for the transition to take place, and 100LL fuel may still be in use for several years.
