The FAA released a long-awaited draft plan earlier this week that sketches out how the U.S. general aviation fleet could move away from 100-octane low-lead aviation gasoline and transition to unleaded avgas alternatives over the next several years. The document, published for public comment, is intended to provide a national framework for what the agency describes as a “safe and orderly” shift away from the only remaining leaded transportation fuel still in widespread use.
So, what is it, and what does it say?
The Draft Transition Plan to Unleaded Aviation Gasoline is the FAA’s response to congressional direction in the 2024 FAA Reauthorization Act, which charged the administration with eliminating lead emissions from piston-engine aircraft without disrupting flight operations. The plan does not mandate a single replacement fuel or prescribe specific timelines for individual airports. Instead, it lays out a phased process that the FAA says will allow market forces, fuel approvals and operational experience to guide the transition.
Under the draft plan, the FAA’s stated goal remains eliminating the use of leaded avgas nationwide by the end of 2030, with Alaska given until the end of 2032 because of its unique operational and logistical challenges.
The agency is very clear that the document is not a final rule and acknowledges that many of the factors that will shape the transition—including fuel availability, pricing and infrastructure readiness—are largely outside the FAA’s direct control.
Four Phases to a National Transition
The plan uses a four-phase framework. This framework kicks-off with fuel approvals and comes to an end with the full nationwide transition away from 100LL. The FAA describes the approach as deliberately incremental, recognizing both the diversity of the piston fleet and the complexity of the avgas production and distribution system.
Phase 1 focuses on identifying which unleaded avgas options are approved or authorized for use and on comparing their performance and characteristics. Three candidate fuels—GAMI’s G100UL, Swift Fuels’ 100R and LyondellBasell/VP Racing’s UL100E—are at various stages of approval through either the traditional supplemental type certificate (STC) process or the FAA’s newer fleet authorization pathway. Completion of those approvals and then gathering comparative data are of course prerequisites for broader adoption.
In Phase 2, the emphasis shifts to gaining real-world market experience. As more airports and operators begin using approved unleaded avgas, the FAA expects lessons learned in day-to-day operations to inform later stages of the transition. The agency mentions that it expects lab and certification testing to be extensive, but that in-service experience across a wide range of aircraft and operating environments will still be critical for identification of potential issues.
Phase 3 represents the national transition itself, when 100LL would be phased out at airports outside Alaska and replaced by unleaded avgas. The FAA anticipates that this phase will require close coordination among aircraft owners, fuel suppliers, airports and regulators, particularly at facilities that can only support a single avgas grade.
Phase 4 addresses Alaska separately. Because many Alaskan communities rely heavily on piston aircraft for transportation and supply, and because fuel delivery is seasonal and infrastructure limited, the FAA says a longer and more flexible transition period is necessary.
Throughout all four phases, the FAA envisions ongoing outreach, education and development of best practices to support stakeholders as conditions evolve.
Fuel Approvals, Infrastructure and Regulation
The draft plan makes clear that the FAA does not intend to select a single replacement fuel for the fleet. Instead, the agency says the marketplace will determine which unleaded avgas options ultimately replace 100LL, based on availability, cost, compatibility and operator acceptance.
GAMI’s G100UL already has fairly broad STC approval covering most spark-ignition piston aircraft and engines and is available at a small but growing number of airports. Swift Fuels’ 100R has begun limited deployment under STCs and recently cleared an ASTM production specification, while UL100E remains in the FAA’s fleet authorization testing program.
The FAA acknowledges in the plan that the presence of multiple approved fuels introduces operational challenges, including the potential for confusion or misfueling if different unleaded avgas options are not interoperable or cannot be safely mixed. To address that risk, the agency says it may conduct intermixability testing and encourages fuel developers to do the same.
One of the plan’s guiding principles is that airports should not be forced to invest in additional fuel tanks solely to accommodate a prolonged transition period. For that reason, the FAA anticipates that many airports—particularly those limited to a single avgas tank—will continue selling 100LL during the transition and then switch directly to a single unleaded avgas replacement, rather than attempting to offer multiple avgas grades at the same time. The agency frames this flexibility as a temporary condition during the transition period, intended to give aircraft owners, fuel suppliers and airports time to align on a final replacement fuel.
The draft makes clear, however, that this flexibility is not open-ended. Following the Environmental Protection Agency’s endangerment finding on lead emissions from aircraft engines, the FAA says it expects to prescribe fuel standards during Phase 3 that would limit or prohibit lead in aviation gasoline. Once those standards take effect, the manufacture and sale of 100LL would no longer be permitted at mainland U.S. airports, apparently at this stage regardless of an individual airport’s readiness or infrastructure constraints, with the plan identifying the end of 2030 as the target date for completing that transition outside Alaska.
Beyond fuel chemistry and aircraft approvals, the plan also signals a broader shift in how the FAA approaches aviation fuel oversight. Historically, the agency has relied primarily on industry consensus standards, such as those developed by ASTM International, rather than directly regulating fuel composition. This approach will change over the course of the transition; federal regulation will ultimately complete leaded avgas’ phaseout.
Alaska’s Unique Challenges
Alaska has its own piece of the transition plan, thanks to its reliance on piston aircraft and the state’s logistical realities. Many Alaskan airports only receive fuel seasonally, and aircraft alterations are often performed during winter months when there is less flight activity.
The FAA says Congress explicitly recognized these factors by extending Alaska’s transition deadline to 2032. The draft plan envisions Alaska following the same general sequence as the rest of the country but on a longer timeline, with particular attention to issues such as fuel blending, storage limitations and the need to avoid disruptions to essential air services.
The agency also acknowledges that Alaska may need to solutions that won’t be needed, or at least may not be as common, elsewhere. These include considerations around handling residual 100LL during the transition and ensuring that new unleaded avgas can be delivered reliably to remote locations.
Open Questions Remain
The draft plan offers up a high-level framework to guide the transition, but it still leaves plenty of practical and regulatory questions unresolved that are likely to shape how that process is ultimately worked out.
One of the most fundamental uncertainties is timing. Although the plan repeatedly cites the end of 2030 as the goal for completing the transition in the lower 48, it does not specify when the FAA would initiate rulemaking to prohibit leaded avgas, how long compliance periods might last, or how remaining supplies of 100LL would be handled once new fuel standards take effect.
The plan also assumes that one or more unleaded avgas offerings will be widely available by the time Phase 3 begins, but it does not describe how the FAA would respond if production, distribution or pricing fall short of expectations. It remains unclear what level of geographic coverage or market penetration would be considered sufficient to support a nationwide phaseout.
Cost is another concern with limited discussion in the plan. While the FAA acknowledges concerns about increased operating expenses, the plan does not estimate the cost of aircraft alterations, infrastructure changes or long-term fuel pricing. Nor does it outline whether financial assistance, incentives or grant programs might accompany the transition.
Operational questions also remain. The plan allows for multiple approved unleaded avgas options, but does not address whether that diversity is expected to continue on long term or whether the market is likely to consolidate around a smaller number of options. More choices can often be a good thing, but airports with limited infrastructure may need help accomodating competing fuels, for instance.
Enforcement details are also fairly sparse at this stage. Federal fuel standards dictate that leaded avgas will ultimately need to be eliminated, but the draft does not get into things like the mechanics of compliance monitoring, or what penalties might apply once leaded fuel is no longer permitted.
Finally, the plan does not directly deal with the fate of aircraft (or their owners) that may be too impractical or uneconomical to transition. While the FAA’s stated intent is to avoid disrupting fleet operations, it seems highly unlikely that disruption can be avoided altogether. The document leaves details of how those cases might be handled in practice rather fuzzy.
In any event, the document was never intended to answer every question. The draft plan is a framework rather than a final rule and may evolve as additional information becomes available. Public comment is expected to shape future revisions as the agency works to fill in the details behind a transition whose direction is now clear, but whose execution remains to be defined.
So, if you have thoughts, as I’m well aware that many do, I’d encourage you to do your civic duty by offering up your comments to the FAA.
