Industry wide progress on a so-called drop-in replacement for high-octane avgas always seems to go in fits and starts. Lots of noise then a period of silence. Is anyone actually doing something on this, you may ask? The answer is most definitely yes, but the recent news has come more in dribs and drabs than the full-firehose effect we expect around the major airshows.
But let’s start here. The other shoe dropped on the sale of leaded avgas in California. There had been a legal agreement (a consent decree) that depended on the availability of an alternative to 100LL but now the transition is being forced by new legislation signed into law this month that “would prohibit an airport operator or aviation retail establishment, as defined, from selling, distributing, or otherwise making available leaded aviation gasoline to consumers on or after January 1, 2031.” Coincidentally, the End Aviation Gasoline Lead Emissions (EAGLE) program has as its goal a replacement in place by the end of 2030. Reportedly, the California effort was originally slated to take effect earlier but was pushed back with the help of aviation special interest groups.
According to reports, there are still three candidates in the unleaded-avgas derby, so to speak. General Aviation Modifications, Inc. (GAMI) has had its G100UL fuel in development for decades and received a fleetwise STC in 2022 for virtually all fixed-wing aircraft. GAMI has chosen not to participate in either the current EAGLE or its predecessor PAFI programs that are pushing for an ASTM spec for the replacement fuel. GAMI’s path has got it well and truly cross-threaded with the industry groups.
One could argue that GAMI is trying to “go it alone,” but recently Swift Fuels, which, in addition to VP/LyondellBasell, makes up the remaining contestants on the scene, has received an STC for its 100R to be used in Cessna 172R and 172S models. Swift CEO Chris d’Acosta said, “Our 100R unleaded avgas product will be the preferred fuel to eliminate toxic lead from avgas. We are actively working with industry and OEMs on FAA-certifications and ASTM International specifications. Yes, the FAA recently approved a critical part of our engine and airframe (STC) certification program. This follows a similar FAA / ASTM approval pattern we architected for UL94 avgas over 9 years ago.”
Getting the Swift 100R into public use would help the company gain real-world experience with the fuel. Similarly, the demonstration program undertaken by AOPA last year has concluded, according to reporting by the association. AOPA had run a Beech Baron for 200 hours with one engine consuming just 100LL and one consuming only GAMI’s G100UL. “The pilots who have flown the AOPA fuel demo Baron have been unanimous that the unleaded fuel used—GAMI G100UL—acts just like avgas in flight. No special techniques are required for engine starts, full-power takeoffs and climbs, cruises, or descents. If the airplane didn’t have decals and placards proclaiming the presence of unleaded fuel in the left engine, pilots would be hard pressed to notice,” the association said.
Testing did reveal some peculiarities. Apparently an overly rich mixture will leave a dark, ashy deposit on exhaust pipes and spark plugs. In addition, the fuel will apparently stain paint if not carefully cleaned up. In the AOPA report, GAMI founder and developer of the G100UL fuel, George Braly, said “If the fuel is left on the surface and exposed to the UV from sunlight, then that will cause some brown discoloration.”
Finally, there was a very public display of a leaking fuel bladder in the Baron on the side that was using G100UL. According to AOPA, the culprit was more likely old fuel bladders, which were originally made in the 1970s (but later “refurbished”), than a corrosive effect of the fuel.
So where does that leave us? GAMI has approval for fixed-wing aircraft now but has yet to make G100UL widely available. Swift will be seeing 100R flying in certain Cessnas. And VP/LyondellBasell is still in the development phase, which is working toward getting an ASTM spec. With California backing down from making leaded avgas illegal until 2031, some of the pressure might seem to have come off, but the clock is still very much ticking.
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