Unleaded Avgas operator reverting back to leaded fuel

The University of North Dakota (UND) – which operates one of the largest flight training fleets in the US – has reported valve seat recession issues in some Lycoming engine powerplants installed in its training aircraft following its switchover from leaded to unleaded Avgas.

UND undertook the change from leaded Avgas (100LL) to Swift Fuels’ unleaded Avgas (UL94) in June 2023 and by October last year had logged some 46,000 flying hours (FH) using the new fuel before discovering the engine issues and reverting back to 100LL.

Now, following extensive analysis, engine manufacturer Lycoming has released a statement citing that “under certain conditions, use of UL94 may impact valve seat recession.” Lycoming says the analysis indicates that aromatic chemical concentrations in UL94 may cause the erosion of the valve seats under some flight conditions. The ‘aromatics’ in question include benzene, toluene and xylene which are used to boost octane in fuel and when used in elevated concentrations may result in “slower flame speed, radiant heat from particulates, and particulate abrasiveness to valve seats that may contribute to valve seat recession.”

Lycoming says it’s working with the Federal Aviation Administration (FAA) to study the effects of aromatics on engines and notes that aromatics concentrations are not specified by the regulations governing unleaded Avgas.

If aromatics turn out to be a problem for engines, Lycoming says it will work with the fuel industry to address aromatics levels and give guidance to operators on appropriate leaning techniques to prevent engine damage.

The engine manufacturer added that it remains committed to the FAA Eliminate Aviation Gasoline Lead Emissions (EAGLE), a regulator/industry initiative to identify and deploy a high-octane unleaded replacement for 100LL for piston-engine aircraft by the end of 2030.

Image accredited to UND. 

Author: FTN Editor

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