Near the end of February 2025, the FAA/industry coalition Eliminate Aviation Gasoline Lead Emissions (EAGLE) issued Part 2 of its series entitled “Clearing the Air: How Unleaded Aviation Fuel Is Gaining Approval.” This part focused on the FAA Fleet Authorization process. It is on the EAGLE website at flyeagle.org/updates.
EAGLE’s Part 1 covered the STC process, with Part 3 to come next month to discuss the “critical role” of industry consensus standards, the process of fuel approval via an ASTM spec and FAA approval. We note right here that while EAGLE has been ostensibly neutral when it talks about the routes to FAA approval of an avgas—STC, PAFI (Piston Engine Fuel Initiative) fleet authorization and ASTM/FAA routes—we feel that it has failed in its duty to be neutral. Part 2 is consistent with its past behavior actively or passively denigrating the STC approval route. This is not surprising as EAGLE was organized to only support the ASTM and Fleet Authorization route and not the more rigorous FAA STC fuel approval method—even though it is an FAA organization.
Fleet Authorization
Explaining the Fleet Authorization process in the new Part 2, EAGLE correctly said that the FAA collaborates with industry partners to “conduct comprehensive testing of candidate fuels.” What it neglected to say was that this “comprehensive testing” is less rigorous than that which was performed to approve the currently STC’d drop-in 100LL replacement, G100UL, which distribution EAGLE has been, in our opinion, trying to block, while being funded with taxpayer money. The “EAGLE” fuel developer gets a free ride, unlike the STC process. EAGLE has never released information on its, or PAFI’s, finances for this testing.
EAGLE also didn’t mention that of the original four or more candidate fuels for fleet authorization in the PAFI/EAGLE program, there is only one left. It is from Lyondell/Bassell and VP Racing (Lyondell/VP)—and that fuel is not a drop-in replacement for 100LL. More on that later.
EAGLE explains that the “Fleet Authorization process will result in the FAA, through PAFI, authorizing a qualified unleaded fuel for use in aircraft and aircraft engines. The makes and models of type certificated and non-type certificated piston aircraft and aircraft engines that can safely operate with the qualified unleaded avgas will be compiled and published by the FAA in a document called the Eligible Fleet Authorization Summary Report (EFASR).
“Once the EFSAR is published, the FAA will issue a Special Airworthiness Information Bulletin (SAIB) which will ‘identify the qualified fuel, specify the aircraft and engines eligible to use the qualified fuel, and provide references and other information to accomplish the alteration necessary to enable the use of the fuel.’” Based on available reports from EAGLE, a Fleet Authorization fuel is not going to be a drop-in replacement for 100LL—so one wonders why EAGLE and the taxpayers are even pursuing it. It’s also a huge red flag and an indication that owners should be paying close attention to what emerges from the Fleet Authorization process as it could devalue their aircraft because it may have a seriously adverse effect on the performance of some high-performance aircraft to the point that they cannot meet the performance standards under which they were certificated. They could, in fact, be stranded after 100LL goes away. EAGLE doesn’t mention these very real issues.
Part 2 goes on to say, “PAFI is required by the FAA to make fleetwide authorization decisions…” There is a fundamental problem with that statement. Under FAR Part 1.1, a major alteration to an engine is defined as a change which might appreciably affect performance or powerplant operation. In FAR Part 21.93 Classification of Changes in Type Design, paragraph (a) defines major changes as anything that has any appreciable effect on operational characteristics.
That leads to FAR Part 21.113, which requires that any person—such as Lyondell/VP—who seeks to make a major change to a Type Design must do so via STC. The way we read the clear language of the FARs, the FAA does not have the authority to issue a Fleetwide Authorization for a new avgas—Lyondell/VP must go through the STC process. In our opinion, failure to do so will be an invitation for a lawsuit under the Administrative Procedures Act. Nevertheless, we’ll continue our review of EAGLE’s Part 2.
Testing
In comparing the Fleet Authorization and STC processes, EAGLE says that it collaborates with industry partners to conduct comprehensive testing of a candidate fuel including compatibility with various aircraft materials, engines, operating environments and supply chain components. That’s accurate, but it’s also nearly identical to the testing required under an STC. However, in describing the STC testing, EAGLE doesn’t call it “comprehensive,” it calls it “required.” In our opinion such editorializing is false and misleading.
In Part 2, EAGLE ignored the FAA-approved language in the STC setting the spec for G100UL in which the testing was described: “This specification incorporates and requires the use of additional or alternative laboratory test methods which are more modern and more precise as compared to several of the laboratory test methods traditionally used over the past 75 years for industry standard fuel specifications, such as ASTM International D910.” (Italics ours.)
The FAA-approved language goes on to say, “The FAA has, in fact, made a determination that this Specification and Standard for a High Octane Unleaded Aviation Gasoline provides, not only an equivalent, but in fact, an enhanced level of quality control of the properties and performance of the aviation gasoline produced under this specification and distributed throughout the supply chain, as compared to the traditional governmental, military, or industry voluntary consensus based standards which have previously defined and controlled the production and distribution of aviation gasolines used for spark ignition piston engines.” (Italics ours.)
In other words, the traditional Fleet Authorization process as described by EAGLE is less rigorous than the STC process and, in our opinion, is outdated in addition to perhaps even being in violation of FARs. In our research, we note that the quality control requirements for each batch of G100UL delivered from the refiner is more rigorous than for any other avgas developed to date under any system because it requires independent third-party testing of each batch, rather than just in-house testing by the refiner. That was described in detail in our February 2025 issue.
We think that it is wrong for EAGLE to continue to denigrate the STC process by omission of its rigorous testing and, by implication, claim that the Fleet Authorization or ASTM approval processes are better than the STC process.
Modifications?
While EAGLE’s Part 2 notes that under the STC process the aircraft owner has to work with a mechanic to perform the required “modifications” for compliance, it omits that the only modifications required to use the G100UL STC are a sticker to apply next to the fuel filler(s) of the tanks and a placard that is attached to the engine.
Under the Fleet Authorization process, when an approved fuel is determined, the FAA issues a SAIB that identifies the fuel, specifies the aircraft and engines eligible to use the fuel and provides “references and other information to accomplish the alteration necessary to enable the use of the fuel.“
More importantly: “This process may also require engine and other modifications to the aircraft.” The only remaining candidate fuel for Fleet Authorization comes from Lyondell/VP Racing.
Only Candidate Fuel
The publicly available information for that fuel indicates that it cannot meet the “supercharge” requirement that is met by 100LL and required by all high-performance engines. As background, prior to 100LL, all aviation fuels were identified by two numbers, such as 100/130 or 80/87. The lower number was the Motor Octane Number (MON) of the fuel. 100LL under ASTM D910 spec has a minimum MON of 99.6, which is rounded to 100.
The higher number is the “Performance Number” (PN), also called the “supercharge” or “rich” rating, which defines the detonation resistance of the engine at full power with the certified full rich mixture. It’s been part of the definition of avgas for over 80 years. 100LL’s supercharge rating is 130.
By contrast, G100UL’s supercharge rating, during testing, has been typically 160 or higher. That’s better than the old “purple” 115/145 avgas run in WWII fighters, bombers and transports.
In July 2024 Lyondell/VP Racing publicly stated that “There is no such thing as a drop-in unleaded fuel to replace 100 Low Lead.”
In our opinion, no replacement for 100LL that is not approved for the high-performance engines should be funded by taxpayers since we already have 94UL for low-performance aircraft.
However, everything that we have seen publicly available on Lyondell/VP Racing’s fuel states that it will not attempt to get approval for the high-performance engines.
That means that big-bore engines that require 100LL or G100UL for detonation protection (Cirrus series airplanes, Bonanzas, Cessna 200-, 300- and 400-series and Piper Malibu series)—the ones that burn the vast majority of avgas—won’t be approved to use the last remaining EAGLE/PAFI candidate fuel. Why keep spending taxpayer money on this effort?
Any modifications proposed for high-performance engines to use Lyondell/VP fuel would mean those engines will develop less horsepower—which means degraded performance.
We doubt that owners are going to happily accept reduced gross weights. We don’t want to think about how ugly it would be for twins.
A Concern looking Ahead
EAGLE will soon release Part 3, its paper on fuel approval via an ASTM spec and FAA approval. Swift Fuel’s 100R (not part of the PAFI/EAGLE program)is again up for a vote by ASTM’s members soon. As background, 100R, like Lyondell/VP’s fuel, will not meet the detonation requirements of high-performance engines—all of which would have to be derated to use 100R, if that is even possible or practical. Further, 100R is to be tinted green, just like old 100/130, and has the number “100” in the name. That seems utterly foolish, and dangerous, to us.
We’ve been closely following piston-engine misfueling accidents for over 40 years. We are aware that Cessna took the “Turbo System” decals off of its twins back in the 1970s because line crewmembers read them and fueled the airplanes with turbine fuel (Jet A).
Not long after that we interviewed the late Bob Hoover on the subject because it affected him when he flew his airshow Shrike Commander. He was misfueled a number of times. In our conversation he described standing by the airplane, signing autographs, as the line crewmember fueled the airplane from a truck labeled “Jet A.”
We’ve seen enough misfueling accidents to be quite aware that should 100R (green in color and with “100” in its name) be approved for widespread use, it’s going to be put into an airplane that required 100LL—such as a Piper Malibu—and which has not and cannot be modified to run 100R. Following the crash, lawsuits will fly.
ASTM is being asked to vote to approve the green color and the use of “100” in the name for Swift 100R. We think that ASTM International and possible some of its members who vote to approve the Swift candidate fuel with “100” in the name and that’s tinted green will be at significant risk of being sued following the first misfueling crash. The pilots of those airplanes tend to be high net worth individuals. The damages could be substantial.
Conclusion
We ask EAGLE to accurately communicate the facts regarding STC fuel approval and for the FAA to reevaluate whether EAGLE should even support a 100LL replacement that can’t be used on all high-performance engines.