The shift from leaded aviation gasoline (100LL) to high-octane unleaded alternatives represents one of the most significant technical, operational, and regulatory changes in the history of general aviation (GA). The Federal Aviation Administration (FAA) has established a four-phase roadmap to guide the GA piston fleet to a lead-free future. As noted in EAGLE’s previous article The Unleaded Avgas Transition Starts with Safety, Phases 1 and 2 focus on fuel evaluations, comparative testing, and early market experience. The FAA and industry are gathering crucial information from these first two phases to successfully orchestrate an orderly national transition in the lower 48 states (Phase 3), and ultimately, Alaska (Phase 4).
For pilots, aircraft owners, fixed-base operators (FBOs), and airport sponsors, understanding the operational use cases, technical requirements, and lead times required for the final phases is essential. Rather than a sudden calendar deadline, the transition is built around aircraft, airframe and materials compatibility, scalable production, and supply-chain readiness. To help the GA community prepare for what lies ahead, this article provides a plain-language explanation of Phases 3 and 4 of the National Transition Plan.
Phase 3: National Transition (Outside of Alaska)
Phase 3 represents the national rollout, when 100LL avgas is to be replaced by approved unleaded fuels. Moving leaded avgas out of the national supply chain requires close coordination among multiple stakeholders. Fuel sponsors and refiners must scale production to meet the fleet’s projected annual demand of approximately 180 million gallons, aircraft owners and operators must understand and complete necessary aircraft or airframe alterations, and airports or FBOs must manage fuel storage and other impacted infrastructure.
Four Hypothetical Market Scenarios
With a market-driven transition to unleaded fuel, the retail landscape is constrained by critical factors. Will there ultimately be a single fuel that can successfully replace leaded avgas in all piston engine aircraft? Will there be more than one replacement fuel, and will those fuels safely comingle with each other?
Section seven of the FAA’s published Transition Plan for Unleaded Aviation Gasoline maps out four potential scenarios to help stakeholders understand the differences between four distinct market use cases, ranging from the scenario of a single fuel to a fragmented marketplace with multiple incompatible fuels.
By presenting each scenario in an unbiased manner and highlighting the required actions and associated challenges, the agency seeks to provide a greater awareness about the complexity of transition milestones and the importance of close stakeholder collaboration to a successful transition.
Phase 4: The Alaska Transition—Navigating Unique Gaps
Congress recognized that Alaska’s transition to unleaded avgas will require a tailored approach. Approximately 82% of Alaskan communities rely exclusively on piston-engine aircraft for essential mail, groceries, emergency medical transport, and basic necessities. Consequently, a special two-year carve-out provides additional time to address unique constraints in the state.
The Alaskan transition will have to overcome three unique geographical and logistical barriers:
- Seasonal Supply Logistics: Fuel is typically moved into remote Alaskan communities via barge delivery during the short, ice-free window in the summer. This fuel must then be stored in central, single-tank systems for a year or longer, requiring a proactive 24-month planning lead time.
- Seasonal Fleet Operations and Maintenance: Because aircraft are heavily utilized during the summer to maintain community supply links, aircraft alterations and maintenance must be performed during the harsh winter months when flying activity slows. This seasonal constraint requires a highly coordinated, multi-year window for Alaska to conduct its adaptive actions.
- Single-Tank Fuel Blending Limitations: The majority of remote Alaskan airfields operate with a single, central fuel storage tank, making it difficult to deplete residual 100LL without putting critical operations at risk. This may necessitate blending unleaded fuels with 100LL directly in storage tanks, if deemed safe to do so.
Dual-Phase Distribution Strategy for Alaska
To ensure a safe and orderly transition, the National Transition Plan identifies two distinct, regional phases for Alaska:
- Early Transition (18–24 Months Out): Unleaded fuel is prioritized and distributed to larger regional hubs and communities that have the infrastructure capacity and mechanic availability to allow for an early transition.
- Final Rollout (6–18 Months Out): Fuel is delivered to the remaining remote and rural communities, ensuring that no essential transportation needs are compromised before the final transition.
Moving Forward Together: Actionable Steps for Operators
As with earlier phases, a successful national transition relies on proactive collaboration across the general aviation ecosystem. Aircraft owners, operators, and maintainers should treat the Transition Plan as a framework—not as a mandate to change fuels tomorrow. Here is what you can do today to prepare:
- Verify Your Aircraft’s Compatibility: Regularly check your engine and airframe approvals to understand whether your aircraft is eligible under GAMI’s broad Approved Model List (AML) Supplemental Type Certificates (STCs), Swift Fuels’ expanding STCs, or upcoming VP Racing/LyondellBasell’s Fleet Authorizations.
- Engage with Local Airports and FBOs: Encourage your local FBOs and airport sponsors to begin evaluating their fuel infrastructure. Early planning for tank cleanings, placarding, and fuel truck allocations will prevent bottlenecks during future phases.
- Leverage State-Level Incentives: Stay informed on local financial assistance. Some states (e.g. Colorado) provide tax incentives for STC purchases and financial grants to FBOs to subsidize price differentials. Advocate for similar programs in your region.
- Share Your Operational Insights: If you are already operating on unleaded fuel, help shape this data-driven transition. Submit your real-world performance feedback—from routine, problem-free flights to service difficulties—directly to the FAA under SAIB 2025-04 at [email protected].
Stay Informed & Engaged
By focusing on safety over rigid calendar dates, utilizing rigorous comparative testing, and planning for regional logistical variations, the general aviation community can safely execute the transition to unleaded fuel. Access official updates, check your aircraft’s readiness, and download transition resources at flyEAGLE.org.