Ensuring the availability of 100LL avgas at general aviation airports is in the process of being added to the grant assurances required by the FAA’s Airport Improvement Program (AIP).
The FAA published a number of modifications to the program’s grant assurances to the Federal Register on April 25, 2025, giving the public an opportunity to comment.
When an airport accepts an AIP grant, it must agree to certain assurances, FAA officials explained, noting “these grant assurances are incorporated in and become part of a sponsor’s grant agreement for federal financial assistance.”
“As need dictates, the FAA modifies these assurances to reflect new federal requirements,” the notice continues.
Many of the 2025 changes are related to President Donald Trump’s executive orders, but the one that pertains to general aviation is the addition of “Assurance 40: Access to Leaded Aviation Fuel.”
“The FAA has added Grant Assurance 40 that requires an airport owner or operator that made any 100-octane low lead aviation gasoline (100LL) available at such airport, at any time during calendar year 2022, to not restrict or prohibit the sale of or self-fueling with 100-octane low lead aviation gasoline,” the update reads.
This requirement remains until “the earlier of Dec. 31, 2030, or the date on which the airport or any retail fuel seller at the airport makes available an unleaded aviation gasoline that has been authorized for use by the administrator of the Federal Aviation Administration as a replacement for 100-octane low lead aviation gasoline for use in nearly all piston-engine aircraft and engine models; and meets either an industry consensus standard or other standard that facilitates the safe use, production, and distribution of such unleaded aviation gasoline, as determined appropriate by the administrator.”
The update added that “violations are subject to civil penalties.”
As the search for an unleaded avgas continues, the agency wants to ensure that 100LL is available to all general aviation aircraft owners.
Two airports in Santa Clara County in California — Reid-Hillview of Santa Clara County Airport (KRHV) and San Martin Airport (E16) — banned 100LL in 2022, but after aviation advocates filed a complaint, the FAA ruled in March 2025 that the ban violated obligations the county agreed to when receiving $6.8 million in federal airport development assistance between 1983 and 2011, among other federal funds.
Public comments on the latest proposed changes must be submitted by May 9, 2025 on the Federal Register.
Same old story it seems…
… AUTOGAS works for MY plane so that is all we need.
… UL94 fuel works for MY plane so that is all we need.
… xxx fuel works for MY plane so that is all we need.
Great, aviation is a small group, the plan seems to be by some to make it an even SMALLER group. We need a standard fuel that covers everyone.
… 100LL works for MY plane, so that is all we need.
No we don’t need just one grade of fuel. We need at least 2 grades of fuel just like we once had but we gave it up which was a big mistake. By doing so we used a fuel that had so much lead in it we endangered ourselves with fouled spark plugs that has probably caused many accidents. The lead had also resulted in lower TBO’s, valve damage do to lead deposits, increased need for oil changes that have increased maintenance costs in all the aircraft that could have used a lower octane fuel. The higher octane we didn’t need also cost more to buy. I would guess it probably would be about one dollar more based on what the current cost increases would be to buy the Proposed UL100 that is coming in our future.
Keep in mind, JimH, the larger the cylinder bore diameter the greater the need for fuel to resist detonation. Radial engines with bore diameters between 5.5 and 6.5 inches use high octane fuel to slow the burn rate across the combustion chamber, and those engines are often fitted with 6:1 compression pistons or lower.
Likewise, any engine breathing compressed air must account for the heat generated, especially at altitude where the turbo-supercharger is working the hardest to supply the required boost. High octane fuels are vital to maintain detonation margins, regardless of the level of boost needed, when operated in these environments.
In a way it’s kind of sick that the FAA is pushing 100 low lead like a drug dealer. Wish they were requiring UL 94 so we can get past the dangers that come with using 100 LL, which include lower TBO’s, oil contaminated with lead, spark plug fouling, and danger to the public from lead pollution. This seems like bad public relations on the part of the FAA to be pushing hazards lead.
100LL is required for high compression and turbocharged engines , so UL94 is only ok for low compression engines, and is available at a few airports in California.
100LL has be used in aircraft since it was developed in 1930’s and was required for the US WW2 fighter aircraft.
Turbocharge engines are not high compression engines. Almost all of the current turbocharge engines are 7 1/2 to one compression ratio not high compression.
Yes, turbo engines start with low compression pistons, but the turbo boosts the intake pressure, in some aircraft to 36 inches….requiring the 100 octane fuel to prevent detonation.
My comment was meant to say; high compression engines, 9:1 and greater, AND turbocharged/ supercharged engines.
BTW, some aircraft engines are turbo-normalized, maintaining sea-lever intake pressure to a critical altitude, so may not need 100 octane…
Rotax engines are all high compression engines (10.5:1 typically) are are designed to work on UL91 and UL94 fuel —- and are placarded against using leaded fuel (100LL), except as a last resort
Yes, like modern car engines, the electronic ignition system will retard the ignition timing to prevent detonation. Many have detonation sensors as well.
Our magnetos are fixed timing, while some after market electronic ignitions will advance the timing somewhat, they also us manifold pressure to adjust it.
I’ve read the Rotax fuel recommendations are for unleaded 93 octane, and up to 10% ethanol….auto gas.
They allow the use of 100LL, but the oil change interval and spark plug service is greatly reduced.