The FAA has approved Swift Fuels 100R unleaded fuel for use in hundreds of engines as the company moves to commercialize the fuel. On March 11, the agency published a hugely expanded approved model list (AML) for the fuel’s supplemental type certificate (STC). The AML expansion was first reported by Aviation Week. The new AML may include engines that were previously approved to use Swift’s 94UL, which is already commercially available at more than 100 airports. The AML covers 88 basic engine types ranging from 65-horsepower Continentals to some big-bore Lycoming 540s. It does not appear to cover any Continental 550s, however.
Swift has previously said it planned to get the 100R STC to cover the engines already approved for 94 UL so it could distribute the new fuel to existing infrastructure as a replacement for the lower octane fuel. It received an ASTM fuel specification for 100R last year. At last report, Swift said it would be testing 100R on engines not covered by the 94 UL STC, including large-bore Continentals. The 100R STC was approved two years ago but only for late-model Cessna 172 R and S fuel-injected models. It has been used to fuel those types of aircraft used by a handful of flight schools as a test bed, and Swift has said that it has been working well. We’ve asked for comment from Swift.
Please stay on it. We EAB types, not subject to STCs and often running a variety of engines, may have trouble discerning if we can use this fuel or not. My RV-7 sports a Mattituck O-360 which is an exact clone of a Lycoming A1A variant but with high-compression 9:1 pistons, for example.
Okay Swift Fuel, please identify the new ASTM Standard Specification for your 100R unleaded aviation fuel for piston engines. Work Item WK91759 is pushing for a new unleaded fuel standard and for a production specification on behalf of 100R, but ASTM does not list either for review. That may be okay for STC approval but will not work for Lycoming or Continental approval.
Paul — Swift Fuels 100R Unleaded Avgas complies with ASTM International D8603 – a production specification approved worldwide. You can buy a copy on the internet at ASTM’s website. https://store.astm.org/d8603-25.html
The item you mentioned WK91759 was an ASTM work file provided by Swift Fuels (used for balloting) which was closed in 2025 immediately after our D8603-25 production spec was approved and issued. ASTM coordinates all these work files among its active members. Post-balloting, various research documents are then archived by ASTM and tied into the production specs as needed for document integrity. If you have further questions, please let us know.
Chris D’Acosta
CEO – Swift Fuels, LLC
ASTM Standard D8603.
Despite the use of “100” in its name, Swift 100R is not the same octane as 100LL Avgas. It is not a drop-in replacement.
Kirk –
Swift Fuels 100R Unleaded Avgas complies with ASTM D8603 and has a minimum MON of 99.6
100LL (leaded) avgas complies with ASTM D910 and has a minimum MON of 99.6
Note: MON means “Motor Octane Number” using ASTM D2700 test method.
Both 100R and 100LL also comply with D909 each with a supercharge rating > 130.
Chris D’Acosta
CEO – Swift Fuels
“Both 100R and 100LL also comply with D909 each with a supercharge rating > 130″
This is the first I’ve ever read of Swift 100R complying with ASTM D909 and having a PN octane rating of over 130.
It’s not even on Swift’s own FAQ page (swiftfuelsavgas.com/faq). Plenty of mentions of 100R complying with ASTM D8603. But not one mention of D909. Why not?
Chris D’Acosta
I want to challenge your statement that Swift Fuel’s 100R meets or exceeds an octane Performance Number rating of 130 or higher in compliance with ASTM D909 test procedure. In fact, I believe you are intentionally misrepresenting the facts your own test results have determined.
In order for 100R to meet a Performance Number rating of 130 or higher, as you claim, the fuel flow would need to exceed the maximum fuel flows (beyond Full Rich setting) current carburetors and/or fuel injection systems are setup to deliver. If my assertion is not correct, how do you explain the exclusion of engines with slightly elevated compression ratios (at or above 9.0 to 1) from the Swift 100R AML?
Chris, we aircraft owners are very nervous about this shift to unleaded high octane avgas. We depend upon people in your position to provide factual, honest, and complete information about your project in order to have any faith at all in this process.
We have listened over the past four years to your repeated claims that 100R would, “…be available by next Spring…” or “….in four or five months…”, only to go through more years of disappointment and growing anxiety. In 2025, members of your audience at Oshkosh spoke up, questioning the inconsistencies in your year to year comments. Chris, it’s time for you and others in leadership positions like yours to come clean with us.
Please expand.
Kirk is correct. Every aviation gasoline has two numbers that describe the detonation properties of a given fuel.
The first number, called Motor Octane Number (MON), describes the basic octane rating based upon the fuel’s chemistry. In all cases under discussion here, that number is 100 (except mention in the article of Swift’s UL97, a different fuel).
The second number, called Performance Number (PN – or sometimes referred to as “Supercharger Number”) represents a specific fuel’s detonation resistance at Full Rich mixture setting under “hot and high” conditions. Our current avgas, 100LL, on average has a PN of 130.
Swift Fuels does not talk about their PN for a very good reason. Buyer beware.
Except the CEO of Swift Fuels has, in this very comment section, explained that their supercharge rating is over 130.
What’s interesting is I haven’t seen that mentioned anywhere else. Even Swift’s own FAQ page makes no mention of complying with ASTM D909 with a PN octane rating of over 130.
And there is the problem, I have spoken till I was blue in the face, hi performance engine fuel requirements are a “MINIMUM “ of 100 octane, why are we developing to the minimum standard instead of something closer to the old 113/130?
Because it is REALLY hard to get to a non-toxic aviation fuel even at the minimum without lead and without other harmful side effects. If it were easy, someone would have done it years ago… It has taken $$ Millions and decades to get to parity with 100LL, and only Swift has done it so far without dissolving paint and fabric and sealants…
I understand and we all want a successful outcome, however since you brought it up what is the cost of this “new” formula compared to current avgas?
While the expense has been huge no one has explained to me how it can’t be done ( other than it’s too expensive and requires some “safe”additive??) which is usually just a hurdle that requires a different approach.
An additional problem as I see it is you need a minimum of 5-10 years of real world testing side by side with current and parallel implementation BEFORE you phase out the current 100LL. Thanks for your reply.
Duane- I’ve been at center of political battles over 100LL at Reid Hillview Airport in CA (where sales of 100LL have been banned since end of 2021) and worked with Swift and GAMI and PAFI. While I admire your concept, lead has special properties that made it good for fuels, and dangerous for people. There is no realistic alternative to get back to 115/130 octane ratings, and Swift’s 100R is a match for 100LL minimum spec. we have been using their UL94 for 5 years and it has worked very well for flight schools and private users. As the sole provider of tetraethyl lead plans to close their plant in the UK, and governments everywhere are trying to ban lead, the industry is out of time by 2030. 100R was estimated to cost about 50 cents more per gallon than 100LL, and rollout is already beginning, and will take years. There have been 5 years of testing, and won’t be another ten of side-by-side. 2030 is a pretty hard deadline.
SOOOO many unanswered questions, not just with Swift, but all the possible alternatives…..
Folks frequently bring un fungibility of the fuels, but seldom speak to compatibility and miscibility—which directly affect the consumer.
Fungibility, in simplest terms, demonstrates that one fuel can “replace” the other–they they function the same from a performance standard. This is definitely good thing, but doesn’t make a fuel the ideal……
Compatibility is critical and somewhat hard or impossible to clearly “guarantee”. Compatibility, honestly, requires testing that is FAR beyond what a fuel supplier can provide and remain financially viable. Compatibility, once again in very simplistic terms, is the property of not causing break-down or degradation (corrosion, sloughing, de-bonding, dissolving, swelling, etc…) of components in the “system”. Think fuel tanks, hoses, seals, o-rings, etc…not just in the engine, but all the support and storage systems for the fuel.
Miscibility gets us to the mixing of fuels. If the fuels are miscible with each other, they can be mixed together and not have any separation or precipitation, etc… They should play well together in their liquid form. Now, how they perform at random mix concentrations could be another thing…..
I maintain the fuel tank at our local airport. We can only have 1 fuel available at a time (small airport, budget doesn’t support having multiple tanks). I have to be sure that the fuel we provide is going to be one that the highest % of planes can use at any time. We operate fully self-serve, so we don’t have personnel available to police fueling. We can’t reasonably control how an individual buys and mixes fuel in their plane. Because of this, we REALLLLY need a fuel that is not only fungible, but compatible and miscible.
I have a Long EZ built back in the 80’s. I am acutely aware of the fact that my fuel tanks are epoxy/glass. I worry how these new fuels will store in MY tanks. I KNOW that 100LL is compatible with my tanks. The others—it looks like I am essentially on my own to find out if my tanks can handle long–or short!–term storage without degrading.
I totally agree we need an unleaded fuel, but I’d be lying if i said I am looking forward to having to change to a new fuel…….
Swift 100R is mixable with UL94, and with 100LL.. It just can’t be mixed with other unleaded 100 fuels. So when 100LL gets outlawed in your area, 100R is going to be the single fuel in the tank.
John,
Your description of “mixable” is not accurate with respect to the important issues.
The REAL issue with respect to “mixability” – – (example to follow) is can any new unleaded fuel – – call it “ABC” – – be mixed with 100LL in any random or arbitrary fraction – – and then legally (and then also safely) be flown in the high performance fleet. Examples: A Malibu or a Mirage or a Navajo or 10:1 CR normally aspirated Lycoming – – and many tens of thousands of other high performance aircraft. (Note: That fleet of high performance piston aircraft typically consume about 70% of all the 100LL used each year.
The answer is the only unleaded fuel approved by the FAA that is legal to use in that manner is G100UL Avgas.
Please ask any follow questions you may have. I will try to check back and respond when I have a few spare clock cycles!
George Braly
GAMI
gwbraly@gami.com if you have questions you do not want to post here on Russ’s excellent forum.
I did not see the IO360 A1B6 200HP Lycoming engine in that list. So a quick search shows that NO Angle Valve high compression 8.7 to 1 or higher, Lycoming engines made the list. Darn. These engines can detonate on 100LL and were already subject to a service instruction to reduce timing from 25 to 20 degrees advance. Conclusion: The fuel has proven to be good for engines with low compression and low specific output. The jury is out on fuel’s performance in the very popular higher performance engines.
NOTED: Rotax engines are not on the list
Even if your engine is on the list, aren’t there still airframe implications? Can you use this fuel in your airplane along with 100LL without modifications, or do you have to “convert” it to this fuel exclusively?