The FAA may lay its cards on the table on just how it’s going to have all piston aircraft burning unleaded fuel within the next five years. The agency will issue its Draft FAA Transition Plan to Unleaded Aviation Gasoline in the Federal Register sometime on Jan. 12. The notice that it was happening appeared on Friday, and it says the document will lay out what the agency thinks should happen. “The comprehensive framework outlined in this transition plan encompasses fuel authorizations and comparison testing, market experience, and the national transition to unleaded fuel(s).” We will update as we get more information.
The agency seems to be leaning heavily on public input to help guide this process, which has been underway in one form or another for more than 30 years. It gained urgency about three years ago with a formal “endangerment finding” by the Environmental Protection Agency on the lead emissions from piston aircraft. “The FAA is seeking public comments on the draft FAA Transition Plan to Unleaded Aviation Gasoline to facilitate a structured, safe, timely, coordinated, and orderly transition to unleaded aviation gasoline alternatives while maintaining the operational efficiency of the general aviation fleet,” the Federal Register document says.
The FAA is a partner in the Eliminate Aviation Gasoline Lead Emissions (EAGLE), which is tasked with assessing three candidate fuels for the job. Each of those candidates is following a different path toward acceptance of their fuel. GAMI’s G100UL already has Supplementary Type Certificate approval by the FAA for its use in all certified piston aviation engines, but the company is resisting getting an ASTM International fuel specification. Swift Fuels has also gone the STC route but is also getting an ASTM spec. It has so far only achieved STC approval on late model Cessna 172 R and S models. Lyondell/Basell and VP Racing’s fuel is last in the FAA-run Piston Aviation Fuel Initiative (PAFI) testing regime, but the company has repeatedly warned that some engines will need paperwork or physical modifications to use its fuel. We’ll have details on the FAA plan as soon as they’re released.
Seems the requirement of a drop in fuel for
100 LL is not going to happen. EAGLE will not accomplish its goal and because there is no enforceable law to end lead in aviation fuel but there is a mandated law sponsored by the FAA and the AOPA that guarantees leaded fuel for our future of aviation beyond 2030 nothing is going to change and we can expect to see the same old status quo of leaded fuel in Aviation.
It is sad to see there is no effort to put out a transition Fuel that could be used by 70% of all aircraft. Without the help of an organization like the AOPA to promote an unleaded fuel such as UL 91 alongside 100LL, which is being done in Europe, it looks like we will just be stuck with the current stalemate maybe for eternity.
Oh boy… another FAA plan… I can’t wait. What a joke. What an absolute joke and travesty all at the same time. FAA, just go away, just please go away. You’re worthless…
“…no effort to put out a transition Fuel that could be used by 70% of all aircraft….”
This has been asked and answered multiple times. In short, of the fleet of piston-engine aircraft, ‘only’ 30% need high-octane fuel. But they account for 70% of fuel sales. A “transition” fuel would only account for roughly 30% of total fuel sales.
It doesn’t make economic sense. Splitting the already small avgas market into two smaller pieces would raise the costs for everyone. The ‘transition’ fuel, even though cheaper to make, would cost more because of limited sales. Plus the added expense of adding yet another pump, tank, and/or fuel truck to the airport.
In Europe they are moving on and have UL91 available at many airports and it costs on average 3 dollars less then the 100LL. With the new unleaded 100 that maybe coming to market we are told it would probably be one dollar more expensive than the 100LL currently available.
I don’t know about you, but that is a lot of extra money to buy a more expensive product that I really don’t need just to make people happy that own these aircraft that have to have this high octane product for their aircraft.
I think if UL 91 was available that a lot of aircraft owners whose aircraft required 100 octane fuel would ad water injection on their aircraft to allow them to use the UL91, just to save on fuel costs.
Europe is not the United States. Their fuels are heavily taxed which distorts pricing. Low-octane unleaded fuel being cheaper than 100LL has far more to do with taxes than cheaper production.
Also, general aviation in Europe is a much smaller market and dominated by microlights and other small aircraft running low-compression engines (think Rotax). Much more of the fuel volume is for low compression engines, unlike the U.S.
“I think if UL 91 was available that a lot of aircraft owners whose aircraft required 100 octane fuel would ad water injection on their aircraft to allow them to use the UL91, just to save on fuel costs.”
I know of only one water-injection system. It was announced by Air Plains a decade ago. It covers 3 airframes, carries a 65-lb weight penalty, and cost (back then) $12,000. The price difference between avgas and mogas would have to be much more than a couple of bucks to “save” on fuel costs.
Just want to help with you knowledge on Aviation engines and their compression ratios.
First off normally aspirated Rotax engines have compression ratios of 9 to 1 and 11 to 1 and can use 91 octane fuel. The normal compression ratios of a Continental or Lycoming turbo charged engine is 7.5 to 1 and they normally need at least 100 octane fuel. Most Lycoming or Continental engines that are normally aspirated can use 91 octane fuel and have a compression ratio of 8 1/2 to1 or less.
I think you need to give up your thinking and generalization that compression ratio is somehow the way to determine the requirement of the fuel octane needed for the operation of that particular
engine.
Thanks for the lesson. Though not apparent I’m well aware the compression ratio alone does not determine octane requirements. Which is funny since my father used to test the octane rating of fuel samples using a variable-compression ratio cylinder. In any event, in the 1980s I remember test driving a Jaguar with a V12 engine that had a 11.5:1 compression ratio yet still ran on pump gas.
But none of that changes the fact that the European market is heavily weighted towards low-octane fuel sales with high taxes on avgas. So comparisons to the U.S. market are not valid with regards to the economics of offering a fuel that only satisfies 30% of fuel sales.
What is to prevent engine and airframe manufacturers from issuing service documents that effectively make any new fuel null-and-void? They all sit at the ASTM table, and may even have a say at EAGLE, but unless they find a compelling reason to approve a lead-free fuel lacking meaningful operational history, documented approval will be hard to come by.
Cirrus already did this, specifying no unleaded fuel less than a year ago: https://cirrusaircraft.com/story/update-on-aviation-fuel-landscape/
The transition to unleaded fuel may happen independent of FAA competency (or lack thereof). At least according to this AvWeb (are they still around?) article https://avweb.com/air-shows-events/at-some-point-producing-the-lead-in-leaded-avgas-can-become-too-expensive-to-be-worth-it/
Always interesting when non technical politicians dictate a technical action.
FAA’s own Grant Assurance 40 guidance (Dec 2025) says no fuel yet meets the legal “replacement fuel” test for almost all aircraft, and they even point out a rotorcraft gap. So I’m not sure how anyone can sell a clean Jan 1, 2031 switch.
And even if a fuel is legal to use under an FAA approval, adoption can still get slowed down by manufacturer guidance and warranty warnings. Cirrus has already told SR Series owners it does not approve G100UL, or any unleaded fuel, “at this time.” That sets a serious precedent.
It doesn’t help that the FAA has actively thwarted GAMI’s efforts to introduce G100UL. And Cirrus’ response is surprising considering they were witness to the fuel testing in their airframe. Plus, they employed George Braley to turbocharge their planes when their own engineers couldn’t figure out how to do it, so it’s not like they don’t who he is.
One more thing!
This is a tiny fuel market with big logistics. In 2023 the piston fleet burned about 180 million gallons of 100LL. Cars burn about 376 million gallons of gas a day, so they burn a full year of 100LL in about 11.5 hours. That scale gap is why avgas is a specialty product, and specialty products usually cost more.
I’m for getting the lead out. But here’s the part that doesn’t pencil out. The FAA says airports shouldn’t have to add tankage just to survive the transition, while also warning against mixing 100LL and unleaded. In the real world, a lot of airports will sell both for a while. If you can’t mix, you either add tanks, add trucks, or accept more risk.
Now add the airport layout. A lot of fields have 2 FBOs and a self-serve farm. That’s multiple fuel systems on one airport. If each seller has to build its own unleaded lane, the capital bill gets duplicated, and the per-gallon hit gets worse, especially at low-volume airports that can’t spread costs over many gallons.
And we’re not close yet. Roughly 3,200 airports sell 100LL today, and only about 212 offer unleaded. So this transition is not just paperwork. It’s tanks, trucks, labels, training, quality control, and misfueling prevention. The price spread matters because pilots vote with their wallets. Push it high enough, and people will wait until they’re forced.