Unleaded Aviation Fuel Transition Plan Preparation Guide

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Download: Unleaded Avgas Resources List

In May 2024, HB24-1235, “Reduce Aviation Impact on Communities” was signed into law, which in part incentivizes the transition to unleaded aviation fuels in Colorado. Section VI of that bill (codified in CRS 43-10-108.5 (2)(c)(I)) provides that certain airports located in a densely populated area or that have a significant number of flights over a densely populated residential area must submit additional information to the Division of Aeronautics to be eligible for discretionary grants. Those five airports, as determined by the Division per the bill, are Centennial, Rocky Mountain Metropolitan, Erie Municipal, Boulder Municipal and Longmont/Vance Brand.

Section 6 of HB24-1235 requires that by January 1, 2026, these identified airports must submit to the Division a plan for phasing out the sales of leaded avgas by January 1, 2030 to be eligible for Division grant funding. Industry, through the collaborative EAGLE Initiative, continues work to develop, certify and deploy safe, affordable fleetwide unleaded aircraft fuels. Excellent progress is being made with the development of higher-octane unleaded fuels suitable for use in many aircraft, including those with high compression engines. As of mid-2025, Swift Fuels’ ASTM-compliant UL 94 unleaded avgas is currently available nationwide, and GAMI’s G100UL fuel has limited availability, although they have chosen to not pursue ASTM compliance. Swift Fuels’ ASTM-compliant higher octane 100R is in the final stages of development and is expected to be available in 2026.

While the bill does not specify what the plan needs to include, the Division has prepared the following guidance for plan contents to assist airports in complying with this section of the legislation. All Colorado airports are strongly encouraged to develop an unleaded avgas transition plan.

Plan contents should include:

  • An estimate of the number of based aircraft, including flight school aircraft that could be capable of using   The EAGLE website has a new interactive toolkit that can assist airports with gathering this information.

  • A summary of any incentives the airport plans to offer to assist based aircraft in offsetting the cost of acquiring any necessary supplemental type certificates (STC) needed to transition aircraft to use unleaded avgas.

  • A summary of the airport’s outreach and engagement plan with based tenants to articulate the airport’s plan to transition to unleaded avgas, including any local incentives such as STC acquisition assistance, transitional fuel price subsidy grants through the Division, and promotion of the state income tax credit for STC acquisition that was also included in HB24-1235.

  • A summary of existing fuel storage and dispensing infrastructure that could be reallocated from 100LL to unleaded avgas use, and the airport’s proposed timeframe for such a conversion. Detail whether such fueling equipment would be owned and operated by the airport or a commercial FBO.

  • If no existing fueling infrastructure can be repurposed, detail the new storage and dispensing infrastructure necessary to facilitate the transition to unleaded avgas. Include the following information:
    • Size and location of fuel storage tanks
    • Number and size of fuel trucks
    • Whether the infrastructure would be an airport or FBO-operated
    • Plan for self-serve unleaded avgas, if any
    • High-level costs for the planning, design, construction of storage/dispensing facilities and fuel truck acquisition
    • Expected funding sources (FAA/state/airport/FBO)
    • Expected start and completion dates of unleaded infrastructure development and equipment acquisition
    • Expected date of retail unleaded avgas availability
    • Expected termination date of 100LL sales

  • A defined plan on how frequently this transition plan will be updated and how it will be shared and communicated with airport users and tenants