The FAA released its final Transition Plan to Unleaded Aviation Gasoline on Thursday, outlining a four-phase process intended to move the U.S. piston fleet away from 100LL.
The 72-page document responds to an unleaded avgas requirement in the 2024 FAA Reauthorization Act and retains the goal of eliminating leaded avgas use by the end of 2030 outside Alaska. The state would receive an additional two years due to its unique set of fuel-distribution and operational challenges.
This final plan comes months after the FAA released a draft version of the plan in January. Despite an active comment period on the draft version, formal comments on that version of the plan have yet to be released to the public.
The FAA did say in the final plan that the 60-day comment period prompted revisions addressing Phase 1 progress, possible aircraft modifications, fuel mixing, regulatory timing and cost. The agency also committed to regular updates during Phase 1, a revised transition plan in late 2027, a public FAQ and a separate document summarizing substantive comments and explaining how the FAA handled them.
Unleaded Avgas Testing Comes Before Full Transition
Phase 1 of the final plan covers fuel approvals and direct comparisons among the three high-octane candidates: GAMI G100UL, Swift Fuels 100R and LyondellBasell/VP Racing UL100.
The FAA projects that work will be completed in spring 2027. Phase 2 would expand market use and gather operational experience, and is projected to conclude by mid-to-late 2028.
“The transition to unleaded fuel is a positive step forward for general aviation community and people who live and work near general aviation airports,” FAA Administrator Bryan Bedford said in the agency’s announcement. “Our move to safely integrate unleaded fuels is a collaborative effort that involves everyone from aircraft manufacturers and fuel suppliers to airports and the pilots in the cockpit.”
The FAA has not established firm start dates or detailed schedules for Phase 3, the national transition outside Alaska, or Phase 4, the Alaska transition. Phase 3 is intended, however, to complete the changeover outside Alaska by the end of 2030, while Phase 4 carries an end-of-2032 goal.
The agency expects to define those schedules, milestones and regulatory actions for both phases in an updated plan after Phase 1 is completed, tentatively in late 2027.
The FAA plans to compare the three candidate fuels under common test conditions. The program will examine detonation performance, engine operation, material compatibility, fuel composition and other properties. Testing will also address the effect of mixing each unleaded avgas with 100LL and combining different unleaded fuels.
Each developer supports mixing its product with 100LL inside an aircraft tank, according to the plan. None currently supports mixing its unleaded fuel with a competing unleaded avgas.
Aircraft Will Require Individual Action
The plan makes clear that FAA approval of a fuel does not automatically authorize every individual aircraft to use it without further action. At a minimum, each aircraft will need a new fuel placard, revised operating information and a logbook entry. A certificated mechanic or repair station generally must complete those changes for aircraft holding standard airworthiness certificates. Some airplanes may require additional work involving ignition timing, fuel-system materials, pistons or other engine hardware.
The authorization route will depend on the fuel. G100UL and 100R have received supplemental type certificate approvals of differing scope, while UL100 is pursuing fleet authorization through the FAA’s Piston Aviation Fuels Initiative. Swift has also entered PAFI to seek fleet authorization for 100R.
The FAA expects the marketplace to determine which fuel or fuels replace 100LL, although the plan acknowledges that incompatible products could divide the country into regional fuel markets and increase the risk of misfueling.
“The transition plan assumes right now that the market is going to decide, and that’s probably not realistic,” AOPA acting Co-President Katie Pribyl said during an AirVenture forum, according to AOPA. “We want the FAA to have a role in that beyond just approving fuels. They’re doing the testing. We believe that they’re in the best position to help the industry come to that decision on what that fuel is going to be.”
Phase 2 would give aircraft owners, flight schools, airports and fuel suppliers time to gain operating and distribution experience before the national changeover. The plan calls for 100LL to remain available during that period. Federally obligated airports that offered the fuel in 2022 generally must continue doing so until statutory replacement criteria are satisfied or the applicable transition deadline is reached.
Airports that cannot store two grades of avgas may need temporary unleaded avgas tanks, fuel trucks or other equipment before becoming early adopters. The FAA says airports and FBOs should not be required to install additional permanent tanks solely to support the transition. At locations that can offer only one grade, the eventual switch from 100LL may need to occur on a coordinated date rather than through a gradual phase-in.
Cost, Compatibility and Supply Remain Open Questions
The plan identifies cost, liability and schedule as the unleaded avgas transition’s principal risks. Aircraft owners could face expenses for STCs, mechanic labor or hardware changes, while airports may need changes to storage and dispensing equipment. Fuel producers must also develop enough capacity to replace roughly 180 million gallons of annual 100LL demand.
“A successful transition must preserve the reliability, safety, and accessibility that pilots, aircraft owners, service providers, airports, and communities depend upon every day,” EAGLE industry members said in a statement included in the plan. “The plan acknowledges challenges going forward with such issues as fuel compatibility and commingling, storage and distribution infrastructure, liability concerns, regulatory clarity, and possible aircraft and engine modifications.”
Alaska presents a more unique challenge for rolling the plan out. Much of the state’s avgas arrives through seasonal bulk deliveries, and many remote locations utilize just one storage tank. The FAA recommends beginning coordination for Alaska’s full annual unleaded avgas volume about 24 months before the December 2032 deadline. Phase 4’s actual milestones will depend on fuel selection, aircraft alterations, storage limitations and experience gained during the national transition.
The FAA expects to begin rulemaking during Phase 2 to establish unleaded avgas standards and provide the full regulatory framework for ending leaded-fuel sales. Many of the details that will determine the unleaded avgas transition’s effect on aircraft owners remain unresolved, including fuel prices, required aircraft modifications, compatibility among competing fuels and replacement-fuel availability away from an aircraft’s home airport.
FAA Deputy Administrator Chris Rocheleau described the 2030 unleaded avgas mandate as “aggressive” during a Meet the FAA Administrator forum last week at AirVenture.
“I can tell you with confidence we’re not going to set an arbitrary date that says, ‘well, this is what it says,’ without making sure that whatever we’re going to put in those aircraft is safe,” Rocheleau said.
This early reporting represents a first-pass look at the new unleaded avgas transition plan, and there is still more to be learned. AVweb will continue reviewing the plan in order to provide a deeper analysis for pilots, aircraft owners, airports and fuel suppliers soon.
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