Unleaded Avgas Faces Potential Pitfalls In The Fuel Supply Chain

The National Air Transportation Association (NATA) says the first FAA-approved 100-octane unleaded aviation gasoline is unavailable at the pump because its proprietary formulation is not based on an industry consensus specification, but the first shipment from a 1-million-gal. supply refined by Vitol Corp. was expected from Baton Rouge, Louisiana, late in April after it passed laboratory testing.

G100UL, one of three high-octane unleaded avgas candidates being advanced to replace 100 Low Lead (100LL), has FAA supplemental type certification (STC) approval for use in all piston-engine fixed-wing aircraft, but lacks a product specification from ASTM International—something industry has historically relied on when introducing new fuels, NATA says in a white paper, “Factors Affecting the Commercial Sale of Emerging Unleaded Aviation Fuels,” that it released in early April.

NATA, which represents the interests of aviation businesses including fixed-base operators (FBO) and their partner fuel distributors, released the paper days before G100UL developer George Braly told BCA at the Sun ‘n Fun Aerospace Expo in April that about 1-million-gal. of the new unleaded fuel was stored in Baton Rouge, Louisiana, awaiting final laboratory testing. Once found to conform with his company’s STC, the fuel can be shipped to any FBO or airport that wants to sell it, Braly said.

Standards

General Aviation Modifications Inc. (GAMI), Braly’s company, first started work on the 100-octane unleaded avgas in 2009 but has not sought an ASTM product specification. Vitol Aviation, a Swiss-based multinational energy company, refined the first batch, confirmed Robert Emmett, Vitol’s project coordinator and head of compliance.

Formerly known as the American Society for Testing and Materials, ASTM is a standards organization that develops product specifications through a consensus process involving industry technical experts.

Whereas STC approval by the FAA certifies that a fuel complies with the agency’s airworthiness requirements for safe operation in an aircraft, ASTM evaluates a fuel for its compatibility with materials throughout the supply chain upstream of the aircraft, “including those used in hoses, filters, gaskets and other wetted components among railcars, transport trucks, fuel farms, mobile refuelers, and other dispensing equipment,” NATA says.

The FAA granted approved model list STCs allowing the use of G100UL in all spark-ignition piston engines and airframes in September 2022.

Since 2015, Swift Fuels of West Lafayette, Indiana, has produced UL94, a 94+ MON (motor octane number) unleaded avgas for lower-compression, lower-octane-demanding engines. UL94 was vetted through the ASTM process and meets the ASTM D7547 specification. Swift is also seeking FAA STC approval of 100R, a 100-octane unleaded avgas, as well as an ASTM fuel specification.

A third high-octane unleaded fuel—UL100E, developed by LyondellBasell and VP Racing—is undergoing testing through the FAA-led Piston Engine Aviation Fuels Initiative (PAFI). The companies have said they are also applying for an ASTM specification.

When asked if he would consider licensing GAMI’s patents and other intellectual property for G100UL, Braly said at Sun ‘n Fun that he would consider it. “For a whole lot less than they’re spending on PAFI, the government of the U.S. could negotiate an agreement,” he said. “Let’s make a deal.”

Compatibility For Mixing

The NATA white paper advises that in addition to materials compatibility with the fueling infrastructure, FAA approval does not address the fungibility or compatibility of mixing different unleaded fuels in aircraft, airport storage tanks or refueling trucks, exposing aviation businesses it represents, including FBOs and fuel distributors, to potential liability. The association recommends against offering an unleaded avgas unless it has an ASTM or other industry-consensus specification, confirmation of its materials compatibility with the fueling infrastructure and FAA verification of its compatibility with other FAA-approved unleaded avgas formulations.

“G100UL has an FAA STC approval based on a proprietary fuel specification known only to the FAA and GAMI; however, no industry consensus standard or ASTM International product specification has been set for G100UL at this time,” the NATA paper states.

“Because the FAA does not indemnify any entity in the supply chain for damages caused by fuel-related issues, fuel distributors and FBOs will similarly lack assurances that the unleaded fuel they are selling will not expose them to liability. At present, G100UL is not commercially available for distribution and sale in the U.S. largely due to the fact it does not have an ASTM International product specification.”

At GAMI’s Sun ‘n Fun press conference, Braly also said the G100UL stored in Baton Rouge is about the amount of fuel that piston-engine aircraft in California burn in a month. Sale of 100LL is prohibited at some airports in California, so there is a pressing need there for a 100-octane unleaded avgas, he said.

When Vitol can offer G100UL for sale, the fuel will be considered commercially available, he advised. That is an important distinction because a 2014 consent decree reached between parties in the California Superior Court in Alameda County requires FBOs in the state to sell high-octane unleaded fuel when it becomes “commercially available.”

FBOs that continue to sell 100LL once G100UL is available could be held in contempt of court and face fines, Braly said.

The NATA white paper also references the consent judgement in California. It reports that the plaintiff in that legal action—the Oakland-based Center for Environmental Health (CEH)—recently demanded that fuel distributors offer G100UL for sale by March 1. The CEH did not respond to a BCA inquiry seeking more information.

“NATA’s understanding is that most distributors and FBOs do not believe that G100UL is ‘commercially available’ as defined in the settlement and have provided a detailed response to CEH explaining their reasoning,” the paper states.

“NATA shares the position of these distributors and FBOs. The FAA’s approval of G100UL for use in a broad portion of fixed-wing (but not yet rotor-wing) aircraft engines and types is a positive step, but by itself should not be interpreted to force distributors and FBOs to offer G100UL as a sole replacement for 100LL at present.”

“All of the engines used in both normal category and transport category rotorcraft are already covered in the Engine [approved model list] STC,” Braly said in a email. “The ‘rotorcraft airframes’ are not yet covered.  However, that process is very far along and that approval is anticipated fairly soon.

“Robinson Helicopter did independent flight testing and wrote a report finding G100UL Avgas to be transparent to the use of 100LL in the Robinson helicopters.  That report has been provided to the FAA as part of the GAMI/G100UL data package in support of the rotorcraft airframes being added to the G100UL AML listings for aircraft.”