Whatcha think - Current Status of Unleaded Fuel Candidates

Posted In: Main Forum

Participant

Eric Parks on September 22, 2026 at 8:45 pm #28533

In reply to Scott (#28531)

Scott,

I think the most concern for the engines is the very high output engines that are highly boosted by turbos. So I’m assuming the TSIO-520 and TSIO-540 type engines when they are at full rated power. From what I can tell pretty much all other engines are looking good.

So far as mixing the fuels, yes, they are all supposed to be compatible with 100LL but I’m concerned if I get GAMI G100 UL at one airport and the next airport only has Swift 100R. If mixing the fuels that way is approved then I think it’s a non-issue and the market can decide who is best. From my understanding this is what is being tested now, whether the new fuels can be mixed together.

Participant

Eric Parks on September 22, 2026 at 8:35 pm #28532

In reply to William Beatty (#28528)

William,

I wish I could use MoGas but for my Apache I would need to pump it. So far, I have never seen MoGas available at a pump at an airport that I have flown my Apache into. When I fuel it is typically 30+ gallons at a time so I can’t drag fuel cans out to the airport. The only airport I am aware of in my area that has MoGas available with a pump has too small a runway for me to want to take my Apache into. I have dreamed about having an Experimental that would run off of MoGas in such small amounts that I could haul a couple jerry cans out to fuel it. But at this point I’m stuck with pumping fuel and dreaming about MoGas.

Participant

Scott on September 22, 2026 at 8:27 pm #28531

In reply to Eric Parks (#28507)

Eric, to your first question, I believe that’s the purpose behind the PAFI fleet authorization route. We’d have a drop-in replacement for 100LL across (most of) GA. The FAA’s PAFI page says “The intent of the statement is to authorize qualified candidate unleaded fuels for safe use in applicable aircraft and engines for the U.S. piston-engine general aviation fleet.” I read that as “most aircraft with engines that burn 100LL, with the exception of those that demand special characteristics from fuels.”

My understanding is that PAFI candidate unleaded fuels need to be compatible with 100LL. I believe Steve Ells mentioned this in one of his previous articles on unleaded Avgas.I suppose, but haven’t read one way or another, if there are multiple approved formulations PAFI unleaded fuels, that these would also be required to be mutually compatible? That’s a good question.

From a cost perspective, I have to think that the fleet authorization route is going to be much more cost-effective than model-by-model STCs. As far as the new fuels’ marketability, price seems like it’ll be a huge driver of adoption. If we’re talking a similar price with no downsides; well, that’ll be a much easier path than if the new fuels cost notably more and have potential negatives (say, from a performance or engine longevity standpoint).

One might also wonder how the fleet authorizations will be issued and the potential for a monopoly on the supply side. If an approval is granted to Company X to provide Company X formulated UL, and there are no other options, well, I certainly don’t love that if (when) the use of unleaded fuel is mandated across the fleet.

Keymaster

Kent Dellenbusch on September 22, 2026 at 6:50 pm #28530

In reply to William Beatty (#28528)

You bring up a good point, William. The tank is installed. They must have a heads-up.

Yes – the price. It will be interesting. I think you are kinda spot on.

Kent

Participant

William Beatty on September 22, 2026 at 6:18 pm #28528

If you have a low compression engine running mogas will save you a lot of money. There is a Swift Fuel 100R gas tank now installed at Sebring, Fl KSEF. They are not selling it yet, they are waiting on some approval from some agency. It must be happening soon or they wouldn’t have the tank installed. I’m afraid to hear what it’s going to cost. With local avgas going for around $6.00 a gallon I bet the Swift will be close to $8-9 dollars.

Participant

Eric Parks on September 21, 2026 at 1:42 am #28507

When I bought my little PA-23 Apache with its low compression 150 hp engines I thought this was not much of an issue. All they need is 80 octane. It’ll run on MoGas. So any of these 3 fuels could work just fine for me and the Apache. Now, my Experimental Bearhawk has a 200 hp IO-360 Lycoming and it needs 94 octane but it appears all three should be capable of that as well. So the real issue is getting something the most critical engines can use and then make it widely available.

So I think there are two big questions:

1. Can anyone make a 100 unleaded fuel that all piston engines can run on without modification. If not then what kind of modifications would have to be made and what does that do to aircraft performance?

2. Can we all use one fuel or will there be two or three fuel manufacturers that we would have to choose from. If so, can they be mixed or must they be kept separate?

For the first question I would love to know if having variable ignition timing would help. If so, I would think this would be the single easiest modification and one that may even give better overall fuel burn and/or performance. Other potential mods (water injection?) would be more complex and costly I would think.

The second question could make a huge difference in the real world. If would could have three competitors it would mean companies fighting for market share and perhaps lower prices for pilots but it could also mean not enough for each of the three to have enough volume for efficient production. If the fuels can be mixed then the idea of all three existing together looks more realistic. If I can’t mix different fuels in my tanks then everything gets way more complicated. I think only the FAA can answer that.

Any other big issues? I’m sure there are and I hope they get dealt with soon. In my opinion there has to be a third party (FAA) to check all the claims and counter-claims by each group pushing their own fuel.

The final point here is the many of the newer GA planes getting built are running on Jet-A. I think the big manufacturers could simply pivot to turbine or diesel engines that run on Jet-A and leave the rest of the GA piston fleet to sort it out ourselves. I’m not so sure but what they might actually prefer that we park all our old planes and go away or buy a new ($$$) plane.

Keymaster

Kent Dellenbusch on September 20, 2026 at 6:41 pm #28502

Three high-octane unleaded fuels are at different stages of authorization and deployment:

G100UL: GAMI’s G100UL has broad Supplemental Type Certificate (STC) approval for engines and airplanes (rotorcraft in process).

100R: Swift Fuels’ 100R is approved for approximately 1,200 piston engines and 1,600 airframes via STC. Additionally, Swift Fuels has rejoined FAA’s Piston Aviation Fuels Initiative (PAFI) and continues work toward wider fleet authorization.

UL100: VP Racing Aviation and LyondellBasell’s UL100 is in FAA’s PAFI testing program, with initial portions of the fleet authorization targeted for 2027.

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