CHAPTER 2
Ten Steps for Transitioning to Supplying Unleaded Aviation Gasoline Alongside 100LL Through 2030

Step 1. Communicate with Fuel Suppliers and FBOs

As summarized earlier, there are currently four types of unleaded fuels that can be used to varying degrees in gasoline-fueled aircraft, with a fifth under development. Given this, Step 1 in the transition process involves determining which types of unleaded aviation gasolines are available to the airport and gathering relevant data and information regarding those fuels. This information will be required to complete some of the later steps in the process. The fuels available to an airport may vary depending on the region in which the airport is located (particularly in Alaska, where unleaded fuel may not be available for some time), and the best points of initial contact will likely be either the fuel producers themselves (e.g., Swift or GAMI) or the fuel distributors that are currently providing 100LL for fueling operations at the airport. During this process, it is also important to recall that 100LL must continue to be offered along with unleaded aviation gasoline until the final elimination of 100LL.

For airports that own and operate their own fueling facilities, it will likely be airport staff that are best suited to make these initial contacts. This list of pertinent questions includes:

1. What unleaded fuels are commercially available to the airport both now and in the near future, given the ongoing development of unleaded aviation gasoline?
2. Which of the available fuels are required to conform to ASTM International standards and which are Company Specific Products?
3. What volumes of each fuel are available on an ongoing basis?
4. What are the available delivery options for each fuel (e.g., full or partial tanker truck loads, small-volume portable totes, drums, etc.)?
5. What is the pricing structure for each available fuel on a dollar-per-gallon basis, as a function of the monthly or annual average throughput of the fuel at the airport and the type of delivery option?
6. For each available unleaded fuel, what types of gasoline-powered aircraft is it authorized for? Please include differences between fixed-wing and rotorcraft, and between certified, experimental, and amateur-built aircraft.
7. Which unleaded fuels, if any, are covered by FAA Fleet Authorizations, and what aircraft are authorized?
8. If STCs are required for a specific fuel, how can one access the list of aircraft for which STCs are available?
9. If STCs are required, what is the pricing structure for purchasing the STCs?
10. Are there any compatibility issues with any of the available fuels that could create safety concerns if they were mixed with 100LL or any other unleaded fuel (even if that fuel is not supplied at the airport)?

The fuel pricing data obtained under Step 1 will be important for the financial analysis performed under Step 5.

For airports where one or more FBOs operate the fueling facilities, the process will likely need to be a collaborative effort involving both airport staff and FBO employees. In general, the same list of questions presented above will need to be addressed. These include:

1. Are the FBOs willing to consider supplying unleaded aviation gasoline alongside 100LL, at least until the end of 2030?
2. Do the FBOs require that the fuels they provide conform with an applicable ASTM International standard?

To the extent that FBOs are unaware of the U.S. Environmental Protection Agency (EPA) Endangerment Finding or the end of 2030 target for the elimination of 100LL, it is recommended that their employees be directed to the EAGLE website where they can find information regarding the necessity of transitioning to providing only unleaded aviation gasoline (EPA 2025a, EAGLE n.d.). In this case, it may be beneficial to follow up with the FBO once they have gained a better understanding of the issue.

In both cases, it will also be important for airports to determine or ask FBOs for the annual volume of 100LL dispensed at the airport so it can be compared in later steps to the estimated demand for unleaded aviation gasoline. Another key factor requiring data is the proportion of annual aviation gasoline volume dispensed to aircraft that are not based at the airport.

Based on the information received, the airport may be able to make some preliminary decisions regarding which unleaded aviation gasolines should be considered in more detail as candidates in later steps of the transition process. For example, if an airport or FBO requires, either by policy or for liability reasons, that fuels conform to ASTM International standards, then unleaded aviation gasolines classified as Company Specific Products can be eliminated from consideration. Similarly, if the airportʼs objectives include supplying an unleaded fuel suitable for high-performance aircraft, only a 100-octane unleaded fuel may be acceptable. Another example might be eliminating an unleaded fuel that cannot be mixed with other authorized unleaded fuels that are already widely used at other airports in the region.

The result of Step 1 should be the final determination of the unleaded fuel(s) of interest to the airport or a list of candidates for unleaded fuels, as this information is required for several of the subsequent steps. While it is very likely that an airport will choose to dispense only one type of unleaded aviation gasoline, given the current uncertainty in the development of unleaded aviation fuels, this guide and its associated tools were designed to assist airports in evaluating up to four different types of unleaded gasoline. Though this gives airports the ability to consider multiple fuels, it is suggested that they evaluate only the fuels that are both available and of interest to them.

Step 2. Characterize the Airport Fleet for Unleaded Fuel Compatibility

Step 2 in the transition process involves characterizing the fleet of gasoline-fueled aircraft based at the airport. The purposes of Step 2 include:

1. Determining the approximate number of aircraft based at the airport that are authorized to use the unleaded fuel(s) being considered by characterizing the fleet in terms of aircraft type and model, as well as engine make and model.
2. Obtaining an estimate of the annual fuel use of each aircraft.
3. Determining each aircraft operatorʼs general interest in using unleaded fuel.

4. Determining whether each aircraft has already received an STC that allows it to operate on unleaded aviation gasoline, and if so, which one(s).

As discussed later, it is suggested that these objectives be met through a survey of operators of aircraft based at the airport. In order to improve the results of the survey, it is proposed to include all stakeholders at the airport in outreach discussing the planned transition to maximize awareness and understanding. At airports with flight school operations, special attention should be paid to outreach and communications with flight school personnel before conducting the survey. This is important because flight school aircraft may constitute the majority of the fleet based at the airport and are likely to consume larger quantities of fuel than other aircraft.

As noted above, EAGLE has published a guidance document on flight school transitions, which may be useful to airport staff in their outreach to flight schools. Additionally, the fact that the airport is considering a transition to supplying unleaded aviation gasoline along with 100LL should also be communicated to the operators of airport-based aircraft before conducting the actual survey. This can be done through direct meetings with aircraft owners, direct mailings, email campaigns, or other means. Airport staff may also consider offering some sort of incentive to aircraft operators to increase their participation in the survey.

The survey itself is straightforward, and a tool has been developed under ACRP Project 03-73 as a fillable PDF file titled “Individual Aircraft Unleaded Fuel Survey Tool” for use with individual aircraft operators. This survey can also be distributed in printed form if necessary. Additionally, a separate Excel-based tool, “Multiple Aircraft Unleaded Fuel Survey Tool” has been developed for flight schools and other organizations operating multiple gasoline-fueled aircraft to reduce their level of effort in completing the survey. These tools are available on the National Academies Press website (nationalacademies.org/publications) by searching for ACRP Research Report 284: Transitioning to Unleaded Aviation Gasoline: A Guide and Tools.

The surveyed aircraft population should be directed to all gasoline-fueled aircraft, including rotorcraft, historic, experimental, and amateur-built aircraft, which do not have STCs. It is recommended that the survey collect the following information, though some airports may already have access to parts of this data:

• Aircraft owner details, including contact information.
• Aircraft type and N-Number.
• Engine type and model.
• Interest in using unleaded aviation gasoline if it were made available at the airport.
• Unleaded fuel STC status, and if an STC has been acquired, identification of the applicable fuel.
• Estimated annual fuel consumption of the aircraft.

To the extent that airport owners do not participate in the survey, the most important aircraft data (aircraft type, model, and engine type and model) should still be generally available for aircraft covered by Type Certificates (TC), provided N-Number information is available or can be collected for aircraft based at an airport through the FAA Registry website (FAA 2024d). However, airport staff will likely have to determine whether STCs are available for these aircraft by referring to the STC lists available from the fuel manufacturers.

The data collected from the surveys under Step 2 along with data compiled by airport staff from the N-Numbers of non-participating aircraft should be used to develop an aircraft inventory for the airportʼs fleet of gasoline-fueled aircraft. To assist with this, an Excel spreadsheet tool titled “Airport Unleaded Fuel Aircraft Inventory Tool” is provided as a supplement to this publication. This tool, also available on the National Academies Press website, allows airports to create aircraft inventories for up to four different candidate fuels.

Step 3. Estimate Unleaded Fuel Demand and Evaluate Refueling Infrastructure

Step 3 has two objectives: first, to estimate the potential demand for unleaded aviation gasoline(s) at the airport, and second, to evaluate the existing refueling infrastructure to determine whether modifications will be required to provide unleaded aviation gasoline along with 100LL through the end of 2030—the current target date for the elimination of 100LL. In addition to this section of the guide, NATA has developed a white paper addressing various issues related to transitioning to unleaded aviation gasoline, most notably the requirements for converting a refueling system that currently provides 100LL to one that provides unleaded aviation gasoline (NATA 2022). This resource should be read by airport staff involved in the transition.

Estimates of the annual volume of unleaded aviation gasoline demand at the airport from aircraft based at the airport can be derived from the aircraft inventory developed in Step 2 for each unleaded fuel under consideration. The Airport Unleaded Fuel Aircraft Inventory Tool developed for this guide provides multiple ways to calculate this demand. First, an upper bound estimate of the required supply can be determined by summing up the estimated annual fuel consumption of each aircraft authorized for use with each unleaded aviation gasoline being considered. However, this upper bound volume is likely to be an overestimation, as it assumes that all aircraft owners who could use a given unleaded fuel will do so.

The second suggested approach filters the inventory data to include only those aircraft for which an unleaded fuel is authorized and whose operators have expressed interest in using the fuel based on the survey responses. This approach is likely to generate a best-case estimate of unleaded fuel demand, as it assumes that all aircraft operators who express interest will take the necessary steps to use the fuel, including securing any necessary approvals.

The third and final suggested approach is based on the second but applies an additional limitation: Only the aircraft that have already secured STCs (if necessary) are counted toward unleaded fuel demand. This estimate of the volume of unleaded fuel demand could be quite low or even zero, and it likely represents the lower bound of expected unleaded aviation gasoline demand.

As noted earlier, the three volume estimates will define the likely range of potential demand for an unleaded fuel from aircraft based at the airport. This demand must be satisfied by the airport, along with a more central value that will be the closest approximation to at least the initial demand. At this point, the airport staff involved in the transition will need to use these three estimates to determine the volume that best represents the likely demand for each aviation gasoline under consideration. This value will then be used to assess how the airportʼs existing refueling infrastructure may need to be modified to accommodate an unleaded fuel or fuels.

A final consideration in determining the volume value is whether the amount of aviation gasoline supplied to aircraft not based at the airport is significant compared to the total volume supplied by the airport. If it is, the next question is whether any of that volume is expected to transition to unleaded aviation gasoline. If so, the volume value used in the evaluation of refueling infrastructure may need to be adjusted upward.

Once the final unleaded gasoline volume values are established for each gasoline under consideration, they should be compared to the available supply volumes obtained from the fuel supplier in Step 1. If the airportʼs estimated demand volume exceeds the supplierʼs available volume, the choice of the candidate unleaded fuel should be reevaluated.

If sufficient supply is available, the evaluation of the necessary changes to the airportʼs existing refueling infrastructure can begin. This process starts with identifying any unused refueling equipment, including fuel tanks, other fuel storage devices, and fuel trucks that could be

repurposed for supplying unleaded aviation gasoline. Additionally, it should be determined if the expected shift in volume from 100LL to unleaded aviation gasoline would free up infrastructure currently used for 100LL.

If the existing refueling infrastructure is sufficient to accommodate the anticipated volume of unleaded aviation gasoline, the only requirement will be the cleanup and conversion of that equipment from 100LL to unleaded gasoline. The requirements for this conversion process are outlined in the Infrastructure Considerations section of the NATA white paper (NATA 2022) reproduced below:

If existing refueling infrastructure is not available or is insufficient to accommodate the required volume of unleaded aviation gasoline, airport staff must determine the best approach to modifying the airportʼs refueling infrastructure. Depending on the volume of unleaded aviation gasoline needed, these modifications could range from using small portable fuel totes to dedicating one or more fuel trucks to unleaded fuel or constructing new fuel tanks and installing new dispensers.

Once a modification strategy has been identified, it will be necessary to determine the best method for implementation and the estimated cost. At airports where FBOs provide fueling services, their involvement in this determination may be required depending on infrastructure ownership. These cost estimates will be essential for the financial analysis conducted in Step 5.

Step 4. Identify Potential Transition Funding Sources

Step 4 in the transition process focuses on identifying funding sources to cover the cost of transitioning to unleaded aviation gasoline. The primary fixed-cost elements of the transition will likely be associated with the development of new refueling infrastructure, although there may also be significant costs associated with training, insurance, outreach, and administration. The major variable-cost elements of the transition are likely to be the price differential between unleaded aviation gasolines and 100LL as well as the costs of STCs if those are necessary.

The first step in identifying funding sources should involve a discussion with the airport sponsors to determine if they can increase funding to cover some or all of the financial impacts

through changes in the airportʼs operating or capital improvement budget or by providing funding for incentives to cover STC expenses and fuel price differentials.

When considering infrastructure costs, it is important to determine whether some or all of these expenses can be covered through FAA funding. As discussed in Understanding the Transition to Unleaded Aviation Gasoline: A Primer, FAA currently operates two funding programs: the Bipartisan Infrastructure Law (BIL) and the Airport Improvement Program (AIP) (FAA 2022a, 2024a). Airport staff should contact their FAA Regional Airports District Office for the latest information and details on grant funding opportunities for the development of refueling infrastructure for unleaded aviation gasoline.

As of January 2025, Colorado is the only state known to be offering grant funding for infrastructure costs associated with unleaded transitions. However, other states, as well as regional and local governments may provide such funding in the future, and special grants from air quality agencies may also be available [EPA 2023, EPA 2025b, California Air Resources Board (CARB) 2025, Bay Area Air Quality Management District (BAAQMD) 2025]. It is strongly suggested that airport staff explore funding sources beyond the FAA as part of Step 4. Infrastructure costs not covered by grant funding will likely need to be borne by airports, airport sponsors, and FBOs.

Based on the findings of ACRP Project 03-73, grant funding for incentive programs that cover STC costs and offset the price difference between unleaded aviation gasoline and 100LL is less likely to be available, and that which is available is likely to come from airport sponsors. However, this should still be included in the airport staffʼs funding investigation.

Step 5. Perform Financial Analysis of Transition Options

The purpose of Step 5 is to conduct a financial analysis of the unleaded gasoline options under consideration. To facilitate this analysis, an Excel spreadsheet tool titled “Unleaded Fuel Cost Evaluation Tool” is available from the National Academies Press website. The following fixed-cost components of the transition are assumed to be the same for each fuel in the tool:

• Fuel tanks,
• Mobile fuel storage,
• New signage,
• Training,
• Incremental insurance and fixed fuel supplier costs,
• Outreach, and
• Incremental administrative requirements.

Values for these cost estimates were either calculated in Step 4 or will need to be determined specifically for Step 5. Different cost options (new, reused, and leased) can be entered for fuel tanks and mobile fuel storage. Note that any potential grant funding for infrastructure or other aspects of these costs must be subtracted from the toolʼs results to estimate the net cost to the airport. If these cost estimates vary between specific unleaded fuels under consideration, multiple evaluations will need to be conducted using the tool.

Fuel-specific cost inputs, which are treated as variables in the tool depending on the unleaded fuel, include the price of the fuel and the expected revenue (profit) from its sale, price of 100LL and its expected revenue, and the per-aircraft cost of STCs. The impact of fuel price and STC subsidies available through grants can also be considered, but this requires input data on subsidy levels.

Other inputs include the estimated demand volume for unleaded aviation gasoline and the number of aircraft expected to require STCs. This latter value excludes aircraft that had already

purchased STCs at the time of the Step 2 survey. This data was generated in Step 3, and it is important to use the appropriate fuel volume estimate along with the corresponding number of aircraft expected to require STCs in the financial analysis.

The required outputs of the Unleaded Fuel Cost Evaluation Tool for each unleaded fuel under consideration are:

• Total fixed costs of the transition, accounting for any grant funding.
• Total one-time costs for STCs, accounting for any grant funding.
• Annual cost difference between unleaded fuel and 100LL, accounting for any grant funding.

These outputs can then be used to assess the overall financial impact of the transition to each unleaded aviation gasoline under consideration.

Step 6. Decide on the Transition to Unleaded Fuel and Select the Fuel Type

In Step 6, the airport is expected to make two key decisions. The first is when to transition to unleaded aviation gasoline in addition to 100LL. The second, required if multiple fuels were considered, is determining which unleaded aviation gasoline will be supplied. These decisions are expected to follow the airportʼs normal decision-making process in conformance with airportʼs PMCDs, which may involve public meetings, requirements related to publication of notices, and other procedural requirements. The results of the financial analysis along with other factors, such as those listed as “opportunities” in the Primer, will be key elements in the decision-making process. These opportunities include the following and should be considered alongside the understanding that a transition to unleaded aviation gasoline will ultimately have to occur:

• Reducing lead emissions at and around airport facilities, thereby improving the health of both airport users and those who live, work, or go to school in the vicinity of the airport.
• Demonstrating leadership in addressing environmental challenges, such as lead emissions, to both the aviation community and the general public.
• Educating the local aviation community and the public about unleaded aviation gasoline.
• Providing aircraft operators with direct experience in using unleaded aviation gasoline before the current target end date for 100LL of December 31, 2030.

If the airportʼs decision-making process determines that a transition to supplying unleaded aviation gasoline along with 100LL will not proceed, the transition process can be paused until future developments warrant reassessment. This would require updating the work previously completed in Steps 1 through 5 and conducting another round of airport decision-making. If the decision is to proceed, the airport should move on to Steps 7 through 10, discussed later.

Step 7. Implement Transition Plans to Unleaded Fuel

Step 7 marks the transition from the information gathering, analysis, and decision-making activities of Steps 1 through 6 to the implementation of the airportʼs transition to unleaded aviation gasoline alongside 100LL. This step requires the airport to take several key actions considered in the earlier steps of the transition, including:

• Completing the process to secure grant funding for infrastructure and incentive programs.
• Securing an adequate supply and delivery of the selected unleaded gasoline(s) through contracts and other agreements with fuel suppliers and FBOs, as appropriate.
• Moving forward to begin and complete infrastructure construction or conversion projects, including the acquisition of fuel trucks and portable fuel storage, as appropriate.

• Addressing any necessary insurance and/or administrative requirements, including the addition of appropriate signage for unleaded fuel.

Any other issues directly related to the airportʼs facilities or general operations should also be addressed.

Step 8. Develop Safety Procedures

The purpose of Step 8 is for the airport and/or FBOs to develop safety procedures that prevent misfueling caused by supplying an unleaded fuel that is not authorized for an aircraft or by adding an unleaded fuel that is incompatible with another unleaded fuel already present in the aircraft.

This objective can be met through the development of standard operating procedures (SOPs) based on existing misfueling safety practices. Valuable resources on misfueling prevention are available through the NATA Misfueling Prevention program and should be reviewed as part of the development of unleaded aviation gasoline safety practices and SOPs (NATA n.d.).

A key difference between existing misfueling prevention practices and those for unleaded fuel pertains to instances where unleaded fuel approval is based on STCs rather than Fleet Authorization. In such cases, it is essential to confirm that the aircraft requesting unleaded aviation gasoline displays an STC indicating approval for use with the specific fuel. An example SOP developed by Naples Airport is included in Appendix B as an illustration of an unleaded-specific misfueling SOP.

Additionally, although unlikely at present and in the future due to the fact that Swift and GAMI unleaded fuels are not recognized as compatible with each other, the SOP should specify that any aircraft displaying multiple STCs for unleaded fuels must not be refueled until it has been confirmed what type of fuel was last present in the aircraft and the safety of refueling it with the unleaded fuel available from the airport. This procedure would become irrelevant if the compatibility of Swift and GAMI products is confirmed.

Once the development is complete, the new safety procedures for refueling with unleaded aviation gasoline should be incorporated into the airportʼs existing safety protocols and appropriately communicated with all relevant airport stakeholders.

Step 9. Conduct Training, Outreach, and Education

Step 9 of the transition process focuses on conducting training, outreach, and education activities.

Training activities should begin once airport SOPs related to the receipt and supply of unleaded aviation gasoline have been drafted. Training should also include opportunities to solicit feedback from personnel involved in these activities, and the SOPs should be refined as necessary based on that feedback.

Outreach activities should target stakeholders, including flight schools, pilots, airframe and powerplant mechanics, and other directly interested parties, informing them about the details of the airportʼs transition to supplying unleaded aviation gasoline along with the continued supply of 100LL. Making stakeholders aware of any available fuel price and/or STC subsidies would also be a key element of the outreach effort.

Educational activities should target local government agencies, local communities, and other parties with a general interest in considering lead emissions from aircraft operations around the airport. These efforts should address concerns about aircraft lead emissions, broader EPA and

FAA initiatives to mitigate them, and the airportʼs specific local efforts to reduce lead impacts at and around the airport. These efforts may also include additional mitigation measures, such as those outlined in the Primer as well as by the FAA (FAA 2024c).

Step 10. Monitor the Transition, Identify Issues, and Make Adjustments

The final step, Step 10, involves monitoring the implementation of the transition, identifying any issues that arise, and making appropriate adjustments to address them. While these issues will likely be airport-specific, potential challenges may include:

• Unexpectedly high or low demand for unleaded aviation gasoline.
• The need to switch to a different unleaded fuel than originally selected due to future regulations, changes in FAA Fleet Authorizations, or commercial factors.
• The need for additional outreach efforts to stakeholders to overcome unexpected resistance to unleaded fuel use or to address reports of aircraft or engine performance issues with the unleaded aviation gasoline(s) offered at the airport.
• The need for further educational outreach if additional concerns arise from local governments or the community related to lead emissions.
• The need to revise SOPs to enhance safety based on operational feedback.

Additionally, transitioned airports are strongly encouraged to monitor the EAGLE and FAA websites for updates and new requirements related to unleaded aviation gasolines as the process to eliminate the use of 100LL continues. They are also encouraged to share lessons learned with the EAGLE initiative and their FAA Airports District Office or Regional Office to support continuous improvement and assist other airports preparing for transition.