General Aviation Modifications Inc. (GAMI) has submitted the paperwork to obtain an ASTM specification for its G100UL unleaded avgas to help the widespread adoption of GAMI 100UL avgas, which already has an FAA approved specification. Founder George Braly confirmed he attended a meeting of ASTM in Chicago six weeks ago to ask for formation of a task force to review the fuel and that request was accepted. “That’s the first step,” he said. A webpage was also created where GAMI can upload technical data on the fuel for review by task force committee members who will decide whether or not to issue an ASTM specification based on that FAA approved data and testing.
Lyondell/Basell and Swift Fuels have already been issued ASTM specs for their E100 and 100R fuels respectively, and GAMI’s lack of that documentation emerged as a major impediment to industry acceptance of its fuel.
GAMI has resisted going through the ASTM process after the company withdrew an application launched in 2010 when Braly said the process took so long that the FAA urged him to instead seek an GSS specification under the FAA STC approval process. That, says Braly, carries more weight than an ASTM spec but the fuel’s lack of an “industry standard” has become a roadblock for advancing G100UL through the marketplace.
Braly said that the FAA has already made a specific finding that the FAA specification is the equivalent of an ASTM or other industry consensus specification. “I think the environment is different than it was” in 2010-2013 when the previous application was being considered by ASTM, he said.
In 2022, the approved model list for GAMI’s STC on G100UL was issued to cover all certified aircraft engines and all airframes, except helicopters, which are pending. GAMI is submitting the results of the testing and FAA approvals done by the FAA to ASTM as support for its fuel specification. If ASTM accepts the FAA data and approvals, Braly said he hoped to have the ASTM fuel specification within a year.
In 2024, GAMI partnered with fuel refiner Vitol to make about a million gallons of G100UL for distribution to two airports in California and one in Mississippi and another in Texas. Questions were raised about materials compatibility when several aircraft operators in California reported leaking and staining by fuel on their aircraft. Braly says that in every case he’s examined (with one exception), the aircraft had also previously been leaking 100LL as evidenced by blue stains on aircraft surfaces. The sole exception involved a lower access panel that had previously been repaired. Braly said the leaks were maintenance related.
He also said that he’s been flying a Cirrus SR22 for 16 years with G100UL avgas and there have been no issues. That Cirrus SR22’s fuel tanks have been inspected on site and in person by both the FAA and Cirrus engineers and have a clean bill of health.
A stain that formed on the wing of a Beech Baron operated by AOPA was determined to have been caused by a leaking fuel bladder and subsequent dissolving of glue used to keep the wing rivets from ablating the bladder inside the wing. The staining issue and other questions raised about the fuel’s effects on seals, O-rings, and fuel system lubricants have prompted the FAA to compare the materials compatibility of all three fuels as part of its transition process to unleaded fuel. Braly said the FAA has maintained an extensive database of all of the field reports of any issues and found no safety of flight issues to date.
The neverevereverneverever ending story.
We will all be smelling funny (or not at all) by the time this is solved.
Go Braly go. I really would like to see his effort succeed.
I agree. I noted the concerns in my reply. But did not highlight the strong points. The GAMI fuel is in fact better than 100LL with regard to octane, detonation resistance and cleanliness. Widespread adoption would allow even better aircraft performance. That alone makes the fuel the strongest contender.
Imagine reducing the ignition timing from 25 degrees to 20 degrees, erasing 5HP on my already underpowered 200HP 177RG? just to use 100LL without detonation? Now imagine another reduction in timing to 17 degrees BTDC to utilize Swift’s offering? Dropping another 7 to 10HP. Such a change is outside of certification and safety limits.
The ignition timing is part of the engine certification. If you retard the timing you are derating and decertifying the engine. Retarding the timing has many other detrimental effects: poor combustion, higher emissions, more combustion deposits and coking, higher EGTs more ring sticking, more valve sticking, more plug fouling, reduced range, lower ceiling, to name a few.
I am all for using a no lead replacement fuel that compares with 100LL in terms of octane rating AND causes no increased valve seat recession.
Lessons from the automotive industry have shown that we need different engine technologies to burn unleaded fuel.
m-Toluidine (the aromatic amine GAMI uses in G100UL to raise octane) is the most likely culprit.
At the 2–3 % concentration present in the bulk fuel it is reasonably compatible with most seals and gaskets. The problem appears when the fuel evaporates and leaves the amine behind. Concentrated m-toluidine is far more aggressive.
For widespread adoption, any fuel-system components that still use non-compatible elastomers will eventually need to be resealed with materials known to hold up (Viton, fluorosilicone, etc.). That part is straightforward—we already know which materials work.
The harder issue is wet wings. In our flight department we operated Extra 300Ls and other aircraft whose integral tanks are built with a variety of composites, epoxies, and sealants. Manufacturers change these formulations over time; our oldest Extra 300L had visibly different internal wing sealants than the newest Extra NG even though the wing design was the same. Long-term testing of every possible combination is simply not practical.
So the open question remains: which of the various wetted materials will eventually soften, lose adhesion, or fail—producing leaks or, in the worst case, a structural concern?
We need independent testing of the fuels instead of relying on the claims from the manufacturers.
Cirrus Aircraft came out against GAMI fuel and prevented owners from using this fuel. This is a large fleet of GA aircraft. The reason is GAMI is corrosive to composite airplane structures. It causes damages to the small number of Cirrus that participated in the test. The damages are serious enough that the Cirrus Aircraft company saying GAMI fuel cannot be used. I wish for a non-leaded fuel but more testing is needed.
Braley running G100UL in his Cirrus for 16 YEARS seems to contradict Cirrus’ claim. I wonder what the REAL reason is?
As Chris said above, aircraft manufacturers change their ways of building fuel tanks over time. It is possible that both issues with Cirrus planes can be true. The 16 year old SR22 that GAMI used as a test bed might be compatible with G100UL, but newer planes with different materials of construction may no longer tolerate the fuel.
Ironically, the new fuel candidates seem to have different issues. G100UL has no ENGINE related problems but has fuel SYSTEM issues, while the ether-based fuels (Swift and Lyondell) have few SYSTEM issues but significant ENGINE issues (high performance engines). Either way, none of them seem to be a true “drop in” replacement.
These problems should convince us to have independent testing of these non-leaded fuel instead of relying on the claims from the fuel manfacturers their fuels is safe. A university with a large fleet of Cessna tested a unleaded fuel, non GAMI, and the test fleet suffered engine valve issues. Those who quickly claimed these fuel are 100% safe suffered from the common fanboyism.
I would like an independent testing rather than believing GAMI data. So far, Cirrus reaction was based on independent testing of GAMI fuel. Less fanboyism, more independent testing.
Do watch the materials testing videos, then decide. The videos tell of a harsh reality. The octane boosting aromatic amines in G100 are extremely unlikely to pass the required materials testing requirements.
The reason no OEM will touch any of these fuels, whether GAMI, VP or SWIFT is it requires modifying the TC on the airframe and engine. And that resets GARA liability leaving OEMs open to be sued for 18 years from that date. SO unless GARA liability is addressed, they will continue to be against the fuels. And for reference my aircraft was based in Watonsville for 2 years with G100 in the tanks, and there were no adverse effects.
Cirrus with their ban of GAMI G100LL FUEL IN THEIR Cirrus Aircraft comes across as non-credible given Baly’s 16-year usage of G100UL in his own Cirrus.
People can claim anything. This is why independent testing removes all the biases. George Baily has his own bias and surely he never disclosed any of the issues until Cirrus found out from their testing in a very short time.
If you care to look at an independent testing of UL aviation fuel, checkout this link:
https://www.youtube.com/watch?v=qgn_-vORcR8
I don’t know how George Baily tested his fuel but the author of the Youtube video uncovered a lot of serious problems with the fuel without much problems.
All of my independent testing videos (and AirVenture talks) are available at the following link:
Unleaded Avgas Materials Testing
Thank you for your very detailed work!!! Excellent.
It would be interesting to run your 100LL testing in reverse: Find a batch of 100LL with as much aromatics as you can find and see how long it takes to yield results comparable to what you got on G100UL. My understanding is that 100LL has no direct limit on aromatics — other elements of the D910 spec only produce a practical limit. So some batches have more aromatics, others have less. And since many of these materials are subject to more or less continuous exposure to avgas, it would be interesting to know how much longer they would last if exposed to a “worst case scenario” 100LL formulation. If we are in a world where older materials are just inherently going to fail eventually even with 100LL, that would be quite a finding.
Hi Daniel, It is true that ASTM D910 does not put a hard limit on aromatics. However, the limit of aromatics are inherently limited by other constraints in the specification like freezing point, the distillation curve, net heat of combustion, and vapor pressure. This likely limits aromatics to around 25% (which is quite uncommon). When the FAA did a national survey in 2014 (See slides 13-14), aromatics were averaging far less than 15%, Not sure if you watched all of my videos, but in video 9, I explored various levels of aromatics in 100LL for o rings, bladders, and mil-6000 hose. I ended up adding toluene to 100LL in order to mimic higher aromatic fuels. The term aromatic is sort of key here, because while xylene, toluene, and benzene are aromatics, there is another strong solvent at play with G100UL, that is an aromatic amine called m-toluidine. It’s quite powerful. My assertion is that there is enough history with 100LL that we know what impacts it has on our aircraft, so I elected to not go down that path further especially since the best comparison is the average fuel (not extremes). It’s difficult to randomly find high aromatic spec fuels without ordering it or getting the certificate when it shows up an FBO. I also doubt high aromatic 100LL will yield the same spectacular results with paint as I’ve seen with G100UL.
Understand that being at the upper limit is quite unlikely. It was more a question of leaning into the stress test notion. I saw an EAA webinar from Mike Busch about a crash in Australia linked to deterioration of nitrile o-rings. So it was more thinking about what risks we are currently running since our fuel systems sit exposed to 100LL 24/7 for effectively the entire chronological age of the aircraft.
So if G100UL causes spectacular degradation in short periods, that’s eye opening as we saw in your results.
But if 100LL causes the same thing over some period of years, that’s a case for changing the materials out over time because there’s no established service limit for any of these materials.
this from an actual Cirrus/g100L GAMI USER:
An actual user
Reply to
Pat
2 hours ago
‘The reason no OEM will touch any of these fuels, whether GAMI, VP or SWIFT is it requires modifying the TC on the airframe and engine. And that resets GARA liability leaving OEMs open to be sued for 18 years from that date. So,unless GARA liability is addressed, they will continue to be against the fuels. And for reference my aircraft was based in Watsonville for 2 years with G100 in the tanks, and there were no adverse effects.’
I understand that Bailey has a horse in this race, and I am all for independent testing in the future, but I also think that we can over analyze this project and never find a perfect solution.
I am very glad to hear that you noticed no issues. Also, I very much like the performance benefits of the G100 fuel. My best guess is that many aircraft will need fuel system re-work prior to G100 utilization.
Just for the record,
I’d rather have a 100% solution which forces people who haven’t been maintaining their aircraft to actually maintain them – then do a bunch of nerfing to the entire fleet then prolong those lack of maintenance timebombs. They’ll leak and blame whatever formulation comes along on the change.
I understand your point and you are correct, there are many older aircraft, mine among them. However if a change in fuel type results in a new leak, do we really blame that on poor maintenance? My plane does not leak, not even a little.
I honestly want the GAMI fuel to succeed, it outperforms 100LL, what’s not to love about that? That single fact makes the fuel the strongest contender. I question whether it will pass materials compatibility testing. I’d try it in my simple plane, if it were available here. But I can fix any issues that might crop up. The next guy can’t.
Except Braley did NOT JUST CONCOCT SOME HYDROCARBON ELIXER AND make a bunch of claims about it. He has reams of TEST PROCEDURES AND RESULTS.
Unfortunately, my point stands, yesterday’s Cirrus and today’s Cirrus do not utilize the exact same elastomers, epoxies, seals, glues and fibers. Manufacturers of these products come and go, environmental rules change the formulations, and profit among products all change the game.
Actually, it doesn’t prove your point because I’ve owned 5 Cirrus, including 2 Generetion 1 with 20+ year old tanks and 3 G6s. None of them leaked on G100. So there is that.
That is good news! Love to hear it. The compatibility testing results may still be G100’s Achilles heel. From my end, I am willing to go the G100 direction. I want more performance, not less.
Here is the Cirrus service Advisory from 2025:
February 6, 2025Cirrus is dedicated to advancing personal aviation and proactively addressing the evolving landscape of sustainability regulations, particularly the shift toward unleaded aviation fuels. We continue to actively support industry efforts and the FAA-Industry EAGLE program, including through the PAFI and STC certification program pathways, to develop, evaluate, and advance new fuels while supporting a safe industry transition to a future unleaded fuel environment.
As of January 2025, EAGLE is actively evaluating three potentially feasible alternatives/replacements for 100LL: GAMI G100UL, LyondellBasell/VP Racing UL100E, and Swift 100R. GAMI G100UL is the first unleaded, 100-octane aviation fuel to be offered to aircraft owners and operators directly, and the fuel began distribution to aircraft owners in November 2024. It is currently offered at 3 airports: KRHW (Reid-Hillview Airport of Santa Clara County, California), KWVI (Watsonville Municipal Airport, California), and KTUP (Tupelo Regional Airport, Mississippi).
Cirrus has been engaged in a comprehensive testing and evaluation program of the GAMI G100UL fuel for over a decade and has been monitoring field experience with GAMI G100UL since November 2024. While some aspects of the initial Cirrus testing of the GAMI G100UL fuel were encouraging, Cirrus has identified specific concerns regarding material compatibility. Lab testing in coordination with FAA representatives and on-aircraft field observations revealed seal degradation when in contact with GAMI G100UL fuel that has resulted in damage to airframe components and could create airworthiness concerns. We are actively engaged with a Cirrus owner who began using GAMI G100UL in November 2024 and has since observed paint degradation, seal degradation, and fuel leakage. Cirrus is working with the FAA and the aircraft owner to conduct further investigation and testing. There have also been reports of non-Cirrus aircraft owners observing similar paint and seal degradation and fuel leaks since using GAMI G100UL which have been posted in various online forums.
While Cirrus is committed to a safe and timely transition to unleaded aviation fuel, at this time Cirrus does not approve the use of GAMI G100UL fuel, or any unleaded fuel, in any Cirrus SR Series airplanes. Additionally, Cirrus currently does not warrant or represent in any way an operator’s use of the GAMI G100UL fuel in SR Series airplanes. The continued safe operation of all Cirrus aircraft around the world remains our top priority.
Cirrus is committed to working directly with industry associations and all stakeholders, including AOPA, GAMA, the FAA, and the EAGLE program, to support the transition to unleaded aviation fuels. Cirrus is dedicated to supporting all major fuel companies in their pursuit to bring alternative high-octane fuels to market with the continued goal of ensuring the operational safety of both the powerplant and airframe fuel systems. As fuels progress through the development and certification process and are offered to aircraft owners, we are committed to conducting materials compatibility, on-aircraft fuel performance testing, field observation, and testing of real-world usage of these fuels. We look forward to ensuring a safe and smooth transition to unleaded fuel for all Cirrus SR Series owners and support AOPA’s efforts to gather feedback regarding unleaded aviation fuel usage via their online survey.
Please refer to Cirrus Service Advisory SA24-14R1 for further information.
Here is the YouTube Video made by Juan Brown in 2025 regarding GAMI G100UL:
My Experience with GAMI G100UL on a 1967 Mooney