Swift 100R unleaded STC expands as distribution ramps up

The July 14 announcement detailed a significant expansion of the STCs first awarded in 2024 for two Cessna 172 Skyhawk models with Lycoming IO-360-L2A engines that enabled Swift's 100-octane unleaded blend to enter flight school service. A production specification for 100R was published by ASTM International in 2025, essentially an independent confirmation that a specific fuel formulation meets industry consensus standards. While ASTM does not approve any particular fuel for use in any particular aircraft, the production specification offers standardization reassurance to regulators including the FAA and its international counterparts that do approve fuels for aircraft use, as well as to fuel retailers and distributors who transport, store, and sell the fuel.

The 100R STC expansion to include aircraft that burn 56 percent of all avgas sold in the United States, by the company's calculation, is being followed by a rapid increase in distribution, the company reported in the July 14 press release: "In the coming weeks, many airfields, flight schools and private users whose aircraft have utilized Swift’s UL94 unleaded avgas for many years will begin their transition to utilize 100R unleaded avgas while other airfields have chosen to start fresh now with 100R. These airfields are located across 29 different states (e.g. California, Colorado, Utah, Minnesota, Arizona, Florida, Wisconsin and many more)."

Swift included a Google map of its current distribution network in the release.

Swift is one of three companies seeking to make 100-octane unleaded fuel available to all aircraft and allow 100LL to be phased out by 2030. General Aviation Modifications Inc. earned an expansive STC in 2022 that covers all piston airplanes, but has struggled to ramp up distribution beyond a handful of airports. Unlike Swift's 100R, G100UL has not been submitted to ASTM International for evaluation by manufacturers and engineers, which increases reluctance among distributors to introduce a new fuel. G100UL has also suffered from public reports of fuel leaks and stains associated with its use, including AOPA's 200-hour test of G100UL in a Beechcraft Baron that concluded in 2024. (A&P/IA Jeff Simon examined the issue in 2025 and noted that aromatics including those contained in G100UL may degrade older hoses and other fuel system components.)

The third leading unleaded contender, UL100E, formulated in a collaboration between LyondellBasell and VP Racing, has for years been the only fuel still participating in the FAA Piston Aviation Fuels Initiative as a candidate for fleetwide approval. ASTM published a testing specification for UL100E in November 2025, allowing further testing of the formulation, to be followed, presumably, by a production specification. (The difference between the two specifications is similar to the difference between an experimental airworthiness certificate granted to a prototype aircraft, and a type certificate that allows the aircraft to be mass-produced, though, again, ASTM does not approve aircraft or fuels.)

Swift's ASTM production specification, combined with the expanded STC, gives 100R a potential leg up on distribution because 100R can, according to the company, be mixed with avgas in aircraft tanks, in any proportion, and retailers and distributors value the standardization that the ASTM specification represents.

Mixing fuels in the supply chain is more complicated than that. Swift's older UL94 blend must be stored separately because an airport mixing 100LL and UL94 in storage would lower the octane rating of the resulting blend below the requirements of certain high-compression engines. An FAQ posted by the company previously stated, incorrectly, that airports will not need to install a separate tank for 100R. D'Acosta responded to an AOPA inquiry on this point July 16 and advised that this is not correct, and the information has been removed.

Swift's STC requires placarding the aircraft, and it remains to be seen how airports will accommodate the new fuel at scale, because aircraft without the STC would not legally be allowed to use 100R. Swift offers to advise airport owners and management about the best practices for installing tanks, or preparing existing tanks, to store 100R.

The company noted in the latest release that it has produced and sold 5.8 million gallons of unleaded aviation fuel since UL94 was introduced in 2015. CEO Chris D'Acosta said in an email exchange that more than 200,000 gallons of 100R are included in that total, and most of the 100-octane unleaded blend has been sold to U.S. flight schools and overseas customers. He noted the company's "forever STC" (the price of which was reduced to $100 in 2020 and can be updated to cover both of Swift's unleaded blends at no additional charge) enables current and future users to benefit from the advantages of 100R over UL94, including the higher octane; more complete combustion thanks to added oxygenate; and a proprietary additive designed to limit valve seat recession, intake coking, and wear, "all proven by our testing since 2018!"

In October 2023, the University of North Dakota announced its flight school was terminating a test of Swift UL94 and returning the fleet to 100LL, citing "significant" exhaust valve/seat recession. A&P/IA Mike Busch, in a monthly opinion column for the February 2024 issue of AOPA Pilot, raised questions about UND's decision and methodology, noting the recession observed could be related to the hardness of the original parts: "Bottom line: We really shouldn’t expect any problem running unleaded avgas in any engine with hardened exhaust valve seats—this includes all Lycoming engines and any Continental engine with cylinders manufactured in 2019 or later," Busch wrote. "There’s also plenty of anecdotal evidence that low-compression Continentals—such as the ubiquitous O-470-R/S engines in legacy Cessna 182s—do just fine on unleaded fuel despite their older-style unhardened seat inserts."

Testing of 100R in high-compression engines is ongoing, Swift Fuels noted in the July 14 release. The company is working with manufacturers and the FAA "to accelerate the approval of more aircraft and engines spanning the entire global piston fleet. This is a tedious process, and our work is targeted in tranches of similar high-performance engines… our goal is to complete our 100R engine certification work by end of 2027 or early into 2028."

Additional information is available in the Swift Fuels press release and FAQ.