Santa Clara County has officially become the first jurisdiction in the United States to adopt G100UL fuel. In November 2024, General Aviation Modifications Inc. (GAMI) hosted a “release party” at Reid-Hillview Airport (KRHV), distributing Supplemental Type Certificates (STCs) and fuel to participants. I participated in the rollout and received an STC for my Baron aircraft. I am aware of numerous pilots in the Bay Area who are now successfully utilizing G100UL fuel at a cost of $6.99 per gallon (as of the time of this writing). The County is currently planning to phase out UL94 fuel.
However, there are challenges. There is a significant push to adopt these new fuels under the pretense of “FAA Approval.” While the fuel has received an STC and meets minimum standards, it does not necessarily conform to industry standards. Unfortunately, the elected officials on the Santa Clara County Board of Supervisors lack the necessary knowledge to distinguish between these two standards and, quite frankly, do not prioritize this distinction. Should any issues arise, they will likely be present at the airport on the same day, but their focus will not be on promoting unleaded fuel. Instead, they will emphasize the potential hazards posed by the airport. However, they will not acknowledge or accept responsibility for their role or the significant consequences of this decision.
It is important to clarify that I support the use of unleaded fuel. It burns cleanly, extending the interval between oil changes, reducing spark plug fouling, and minimizing lead emissions. Nevertheless, I oppose the impulsive decision made by Santa Clara County and California to adopt G100UL fuel before it has been fully tested and proven for widespread adoption.
G100UL fuel is approved by the FAA for both the engine and airframe. It has undergone testing to evaluate its durability, reliability, and compatibility with 100LL fuel. However, it has not been tested for interoperability or compatibility with other unleaded fuels, such as Swift 100R. Swift 100R is currently available at KPAO (Palo Alto) and KSQL (San Carlos). Additionally, as of this writing, 100R is approved for use only in specific models of Cessna 172 with certain engine types. Swift anticipates that 100R will be available fleet-wide in the future. 100R is currently pending ASTM approval. It remains uncertain whether G100UL conforms to ASTM standards, and as of today, it lacks ASTM approval. The reason is that ASTM stipulates that G100UL is a proprietary blend, and its formulation is unknown. Consequently, the refiner is unwilling to disclose it.
G100UL fuel has not been tested for interoperability with other unleaded fuels like Swift 100R, which is currently available at KPAO and KSQL.
A portion of the STC for 100R explicitly prohibits mixing 100R and G100UL in any quantity. GAMI’s STC further specifies that G100UL can only be mixed with 100LL and UL94. The implications of mixing these fuels are significant. Does the engine cease operation? Does it ignite spontaneously? What happens if both STCs are in effect and the pilot desires to switch between fuels? Is it necessary to replace all components that have come into contact with the other fuel (bladders, hoses, etc.)? It is evident that GAMI and Swift are not obligated to conduct interoperability testing, as they are not required to do so.
Presently, the sole responsibility for misfueling rests with the PIC. While it is true that this has always been the case, in the past, it was relatively straightforward to distinguish piston aircraft that utilized 100LL from turbine aircraft that required Jet-A. Although misfuelings did occur (for instance, piston aircraft labeled “turbo” mistakenly refueled by a clueless lineman), the likelihood of such incidents was significantly lower, particularly with Jet-A’s distinctive duckbill nozzle and 100LL’s round nozzle. Notably, neither of these fuels mandates the use of a specific nozzle to facilitate this distinction.
There are two airports in the same county, less than 30nm away from each other, that selling two different fuels that are incompatible with each other.
It is crucial to emphasize that STC approval is contingent upon engine and airframe type, not the aircraft manufacturer. In fact, a third party can create an STC and modify the manufacturer’s type certificate, provided that the modification aligns with data acceptable to the Administrator. Some manufacturers, such as Cirrus, have actively discouraged the use of this fuel in their aircraft.
The National Air Transport Association (NATA), a national industry body representing FBOs, has expressed its opposition to selling this fuel and recommends that it not be carried. Furthermore, NATA suggests that operators maintain a minimum liability insurance of $50 million. Without ASTM approval, there is no assurance regarding the infrastructure (tanks, hoses, pumps, etc.).
The four fuel distributors in the country have declined to distribute this fuel. Consequently, Santa Clara County was compelled to procure it directly from the company responsible for its formulation (Vitol), which has adversely impacted supply and cost. This decision was made after an extended period of waiting for a purchaser to emerge.
To date, only airport sponsors have initiated sales of the fuel, not private vendors. This clearly indicates both liability concerns and political pressure to supply the fuel. The counts in California have mandated that the fuel must be sold when it becomes “commercially available.” Although Santa Clara County was not a plaintiff in that decision, it has fulfilled the legal requirement to supply the fuel by providing UL94.
Has the County conducted a risk assessment? Is it documented? What about the financial risk to the community? By purchasing an unproven fuel with funds from the Airport Enterprise Fund, what assurances does the user community have? Furthermore, if Swift 100R becomes approved for fleet-wide use and becomes the dominant fuel, how will the County, as the sole fuel provider, dispose of the G100UL fuel and protect the community’s investment?
The Board of Supervisors has an obligation to address these concerns, seek answers, and provide guidance to the airport community and the public at large.