The FAA says it will conduct head-to-head tests of the three unleaded candidate fuels to replace 100LL as it moves toward the full transition to unleaded aviation gasoline by the congressionally mandated deadline of Dec. 30, 2030 (2032 in Alaska). In its long-awaited report on the transition from leaded to unleaded fuel, the agency says it is going to compare GAMI G100UL, Lyondell/Basell UL100E and Swift Fuels 100R under identical conditions to see how they do with detonation, materials compatibility and “fit for purpose” capabilities. The agency will also compare them against three types of 100LL formulations (FBO, minimum specification and high aromatics) to see how they compare with what they will be replacing. The FAA will also independently test the mixing qualities of the unleaded candidate fuels, and this will be done on common aircraft engines. “Engine detonation, materials compatibility and laboratory analytical testing and evaluation will be performed targeting key engines and materials that act as bellwethers for unleaded fuel analysis,” the agency says in the document.
Of course there’s a lot more in the 77-page document that describes the rationale and the process to move to unleaded fuel. For many, it will be an abrupt change because most fuel sellers have only one tank for gasoline. After the FAA has signed off on fuels it deems acceptable for use in the piston fleet, most FBOs and other fuel retailers will have to pick the one they want to use, assuming it fits their customer and infrastructure needs. That announcement will be made, the last of the 100LL will be sold off, and unleaded fuel will be all that’s available. It would appear the intent is to have the testing done by sometime in 2027 with the actual integration of unleaded gas occurring over the next couple of years after that, allowing time for “market experience” to inform any changes in the way the transition is done. Congress gave Alaska an extra two years to get it all done because of the critical importance of piston-powered aircraft in the state.
The agency is apparently prepared for whatever fuels emerge to not work properly in some engines. Lyondell/Basell has been vocal in its position that the chemistry to make a perfect fuel for all applications doesn’t exist and some engines will need paperwork or physical modification (usually ignition timing and fuel system adjustments). But the FAA says options may go beyond that kind of tinkering. “Some examples include installation of electronic ignition or timing controls, installation of anti-detonation injection systems, propulsion technologies including hybrid electric, or even replacement of a spark-ignition piston engine with compression-ignition engines that can take advantage of the widespread availability of Jet A fuel,” the report says.
The purpose of the publication is to gather public comments on the proposals therein. Comments can be emailed to 9-AVS-AIR670-AVGAS@faa.gov and they are being accepted until March 13, 2026.
Full report is below:
The last paragraph is concerning. Am I reading this right?
One of the FAA’s options is engine modification or outright banning of gas engines in favor of Jet A burning diesel?
“FAA says options may go beyond that kind of tinkering. “Some examples include installation of electronic ignition or timing controls, installation of anti-detonation injection systems, propulsion technologies including hybrid electric, or even replacement of a spark-ignition piston engine with compression-ignition engines that can take advantage of the widespread availability of Jet A fuel,” the report says.“
That’s not how I read that. It starts by saying “options”, which means more than one choice to pick. In other words, it sounds like they may say for certain engines/airframes, to use new fuel X, you can either modify it or replace it with a compression-ignition or hybrid electric engine. And from the preceeding sentence, it sounds like these are additional options “beyond that kind of tinkering”, meaning, paperwork and/or timing advance changes.
I read it the same way NordicDave reads it. I’m not panicking about it yet, though. It’s a fool’s errand to try and predict where this is all going – or any kind of timeline.
Yes, if they can’t force the physics to comply with their desire, the only alternative is to use electronic ignition (which by itself does not lower the octane requirement enough) AND ADI. ADI can be used for takeoff but if continuous high power is needed such as on supercharged and turbo normalized engines, The amount of ADI is significant, eating into your payload and volume.
A technically more elegant solution would be direct injection of the spark ignition engine but that is way out of the wheelhouse of our aircraft engine manufacturers, very complex.
Running a super legacy and a warbird on unleaded fuel is meaningless until they reveal that they can operate these engines at the same manifold pressure they can with 100LL.
Figure 6 shows ‘Phase 2’ to be field experience. It does not explain what to do when that experience is negative, it just moves on to distribution.
So the promise that this transition would only happen ‘if a suitable fuel is found”,
Appears to be broken.
KS
“The mission of the FAA is to provide the safest, most efficient aerospace system in the world.” FAA web site
At what point does this transition to unleaded fuel meet this mission statement?
By all means, please submit your safe and efficient ideas as requested.
Well there certainly isn’t any efficiency if TEL stops being produced (legally) at some point, which would ground a whole bunch of big bore piston aircraft. Whether we in the US want to continue using 100LL doesn’t matter much when we don’t have any factories that can produce TEL, so it seems like a better choice to at least have some options available when that eventually happens (and it will eventually happen, whether we’d like it to or not).
The single safest way to transition to unleaded avgas is to eliminate the need for TEL as part of engine design. EPA mandates and Congressional Directives won’t do it.
Of the 10 or so obstacles to using unleaded fuel in air-cooled aircraft engines, slowing the rate-of-burn across the combustion chamber and removing heat from the exhaust valve, guide, and seat are the most critical. Nothing in the FAA’s efforts, or those of PAFI and EAGLE address that.
My personal opinion is that the FAA should acknowledge and reinforce an end date for 100LL as directed. But the burden should be on aircraft and engine manufacturers, not the FAA.
US automobile manufacturers labored through the transition, as did foreign entities, and without direct DOT involvement attempting to find a fuel that worked without lead.
Porsche found a way to deal with unleaded fuel in its air-cooled engines by keeping combustion chambers small and forcing cooling in critical areas. It worked until 1999 when they finally threw in the towel. Now, all are liquid cooled.
Current aircraft engine manufacturers know what needs to be done to make the transition in a safe and efficient manner. But until they are held to account for the unleaded mandate, they won’t.
Glad to see you pointed out that there is no mandate to end the use of lead in aviation fuel. The EAGLE program really has no teeth and will not eliminate leaded fuel as there is no mandate including in its makeup. The FAA and AOPA have created a legal congressional mandate for the requirement of continual use of leaded fuel for aviation engines however.
At Oshkosh this year, my brother asked the president of the AOPA what will happen if no drop in replacement is found for 100 LL Fuel.
He told him that nothing would happen in regards to a fuel replacement for 100 LL and the search for a drop-in replacement will continue basically to eternity as there is no congressional mandate for its elimination.
Eternity is a long time. Lack of a congressional mandate won‘t be relevant if 100LL becomes unavailable due to a lack of TEL to produce it.
To summarize, “what if anything has changed in the last half year or so?”.
Sure seems like issues like O-ring replacement with already approved Viton, or some paint touch up, if needed to be compatible with G100UL, might be a lot easier than “change to compression-ignition engines”. But man, what a bunch of complaining arose over a few issues with some planes with old paint.
I have not seen a lead-free gas at the same price as 100LL. GAMI started filing patents for the fuel in 2009. The specific formulation and process for creating G100UL is proprietary. Another nail in the GA coffin.
You may be too young to remember the changeover from leaded to unleaded mogas, but the same thing happened then. The unleaded fuel was more expensive, partially due to the added processing and different chemicals needed meet the octane requirements of leaded fuel. Some refineries needed to add new processing units – a very expensive proposition. Over time, the whole system adapted, and prices began to fall. The same thing is likely to happen with avgas once the actual changeover occurs.
As for GAMI’s approach to development of G100UL, George Braly is a smart businessman who knows the importance of patent protection for the development of any new product. Going up against large companies like Exxon, Shell, etc. who have huge R&D budgets means that you have to keep your formula under wraps until the patents are in place. That is the whole idea behind the patent concept in the first place. As for his “proprietary” formula and production method, it is available to any company that is willing to produce G100UL for public sale. Sign a licensing agreement (standard procedure for third party vendors) and you are good to go.