ABOVE: many older engines rely on 100LL fuel

Despite promising to issue a full STC (Supplemental Type Certificate) for G100UL unleaded avgas in May, the FAA still hasn’t announced expanded approval for the fuel. The agency also declined to answer queries as to when the approval process will be completed, according to the aviation news portal AvWeb.

A limited number of aeroengines were approved to use G100UL last summer during AirVenture, and it was widely reported that General Aviation Modifications Inc. (GAMI) had completed test work on G100UL and submitted the STC test package to the FAA for approval in February. The test package that was submitted then would expand the number of engines approved for the fuel to practically the entire US GA fleet.

Attempts to replace 100LL started in 2009, when GAMI began work on G100UL. In 2014 the FAA announced its Piston Aviation Fuels Initiative but terminated the project in 2018 after concluding that the two fuels it had examined—one from Swift Fuels and one from Shell—weren’t suitable as drop-in replacements for 100LL. Shell has subsequently stopped public work on a replacement fuel and Swift left the programme.

Image: Keith Wilson