Unleaded avgas has been growing in popularity, especially as a fleet-wide unleaded replacement for 100LL begins to look more like a possibility. Though that time hasn’t come quite yet, Swift Fuels—developer of the already-in-use UL94 unleaded avgas—recently issued a statement commending engine manufacturer Lycoming for doing its part to make unleaded fuel a feasible possibility for GA aircraft.
Lycoming’s contribution? Service Letter 270: a document extending maintenance intervals between oil changes for Lycoming direct drive engines using unleaded fuel. The letter states that using unleaded fuel “decreases the risk of lead fouling of spark plugs and contamination of engine oil with leaded combustion byproducts.” The document also includes a transition procedure for switching to an approved unleaded fuel. Lycoming’s Service Instruction SI-1070V has a current list of Lycoming engines that can run on UL94.
Swift Fuels has also developed UL102, which is currently undergoing testing through the FAA’s Piston Aviation Fuels Initiative (PAFI). The company hopes UL102 will be approved for use in all engines now burning 100LL once PAFI Phase 2 testing is complete in 2018.