The comment period for the Draft FAA Transition Plan to Unleaded Aviation Gasoline ends Friday, and the agency has said the public feedback will be a major consideration in putting the final document together. As it stands, the draft sets out four phases to develop and finally distribute unleaded avgas to 49 states by 2030 and Alaska by 2032. The plan is not a rulemaking document, and the dates are goals rather than deadlines. The comments are being sought so the FAA can see if there are factors the agency didn’t consider in figuring out this daunting challenge. Comments can be emailed to 9-AVS-AIR670-AVGAS@faa.gov.
There are three companies developing unleaded high-octane fuels: Lyondell/Basell and VP Racing with their UL100E, GAMI and G100UL, and Swift Fuels’ 100R. All are taking a different path to try to hit the goal of a viable replacement for 100LL. G100UL is already approved, via STC, for use in all certified gasoline aircraft engines and all aircraft except helicopters. Swift’s fuel is STC’d in late-model R- and S-model Cessna 172s and is being used in training aircraft. At last report, Swift was planning to start testing in large-bore engines. The Lyondell/Basell and VP Racing fuel is being tested by the FAA through the Piston Aviation Fuel Initiative (PAFI), and VP Racing issued an update recently.
Lyondell/Basell and VP Racing said in the release that they are starting flight testing of the fuel in a total of nine aircraft after completing detonation and durability testing on Continental IO‑550‑D, TSIO‑520‑VB, TSIO‑550‑K, and Lycoming IO‑390‑C3B6, IO‑540‑K1A5, and IO‑540‑D4A5 engines, which it says power about 77% of piston aircraft. “Across the majority of these platforms, engine operation has been largely transparent, except for a limited number of configurations requiring approximately three degrees of ignition timing retard, resulting in negligible changes in power output and slightly elevated exhaust gas temperatures,” the update said. Pilots report the fuel behaves the same as 100LL “with normal starting characteristics, predictable power response, and no discernible differences in day‑to‑day aircraft operation.”
There will not be a drop in replacement for 100LL. So where does that leave us. It appears that we are at a stalemate. To make some move forward there needs to be another choice forward which seems to include 2 grades of avgas fuel available as we once had but made a huge mistake there. As the realism sets in you can see some movement forward but not from the AOPA or the FAA which is where the effort needs to be made.
By implication, none of these candidate fuels are usable in experimental engines (for which there are no STCs)