Preparing for the end of 100LL

Here’s the bottom line: 100LL is going away.

“Don’t fool yourself,” warned Alan Klapmeier, co-founder of Cirrus Aircraft. “The industry hoped 100LL would survive, but it is going away.”

What does that mean for you?

That’s what the industry and federal agencies are trying to figure out now.

The demise of 100LL was a hot topic at this year’s AOPA Aviation Summit. It was discussed during the opening general session, as well as in several forums throughout the show. While a lot of uncertainty exists about the future of aviation fuel, one thing is certain: A change is coming.

“And we will be ready for it,” said Rhett Ross, president of Teledyne Continental Motors, who noted the company has tested “all different types of fuels.”

It’s also a top priority at Lycoming Engines, where officials warn that this is one of the most complicated issues facing GA today.

“Be wary of the five-minute sound bite,” said Michael Kraft, senior vice president. “We have just one shot at this, so we need to make the right decision.”

“Certification costs in time and money are such that the industry can only afford to make this change once,” added Earl Lawrence, vice president of industry and regulatory affairs for the Experimental Aircraft Association. “Whatever change we make, it better be right. We need to move deliberately.”

But why do we need to change?


Tetra-ethyl lead (TEL) had been added to fuel since the 1920s. After it was identified as a neurotoxin, it began to be phased out in the 1970s. In 1990, the Environmental Protection Agency (EPA) mandated that it be gone by 1995. “It is considered one of the EPA’s biggest successes,” said Glenn Passavant, director of the EPA Nonroad Center.

Through lobbying, avgas was exempt from that mandatory phase out because the aviation industry said it just wasn’t ready.

“Avgas isn’t mogas — it’s anything but that. It is made in specialty batches and transported separately. It’s the only fuel with TEL added at the terminal,” he added, noting that it’s an important ingredient to increase octane, which prevents knocking. “It’s especially important to higher compression engines. When you need that octane, you need that octane.

That said, “20 years is a long time to not have a solution,” Passavant noted.

Time is officially running out. New national air quality standards are set to take effect soon, while the EPA is expected to make a finding on a three-year-old petition from the Friends of the Earth that claims avgas endangers the public health and welfare. “The petition requires the EPA to take action,” he said.

He estimates findings from the EPA’s investigation will result in rulemaking in the next 12 to 18 months, while the agency is looking at the “2016-2017 time frame” for a final solution. “There’s still a lot of work to be done,” he said.


That’s an understatement. As the EPA investigation continues, the aviation industry is searching for an alternative fuel, as well as developing engines that will fly safely on that fuel, whatever it is.

The big concern for the engine manufacturers are not the new engines — they know they can develop those. It’s the existing fleet that cause for worry, according to TCM’s Ross.

Making sure the existing fleet isn’t grounded by the demise of 100LL is the focus of the Future Avgas Strategy & Transition Plan — known as FAST — which is being developed to determine how the industry will get from “where we are today to the new fuel,” Passavant said.

The plan, expected to be complete this year, studied the viability of potential fuels, including low-octane 87-89 mogas — which was determined to be unacceptable — mid-octane UL94, which would require a lot of engine modifications and result in a loss of performance, and high octane synthetic or biofuels, such as the one being developed by Swift Fuels.

“That is very promising,” he said. “It is the equivalent — or better — than 100LL, but it is still in development, so it’s not available. Also, there’s no infrastructure, so it’s a complete uncertainty.”

That’s why the industry keeps coming back to UL94, which would require “some minor changes” to how aircraft owners operate, as well as some modifications. Those modifications could range from something simple, like a belt-on ignition, with a price tag of $5,000 to $10,000, to a requirement for electronic controls, which come with price tags up to $30,000, according to Passavant. “There also may be a portion of the fleet that can’t be modified,” he warned.

UL94 would be the easiest replacement for 100LL as the distribution structure is in place and it can be “more easily certified, which is an important point,” TCM’s Ross said.

But will it be compatible with your engine?

“There’s been substantial testing in low-compression engines,” Ross said. “Some will need just minor modifications — some changes could be just a change to the POH. For most normally aspirated engines, if 100LL went away today, they could be converted.”

There are some engines, however, that will require substantial — read expensive — modifications.

The assessment of UL94 continues, especially in the areas of performance and certification. “It will affect operating cost and range,” Passavant said.

So what’s next? A lot of work for everyone involved.

A fleet impact assessment is needed, as well as a transition plan. Then the modifications will have to be developed and certified — and installed and paid for.

Meanwhile, the industry also has to continue developing new engines and new fuels.

All this so we can “keep ’em flying,” said the EAA’s Lawrence.

“This is really, truly here,” he said. “I feel like the boy who cries wolf, because I’ve been saying this is coming for 20 years now. What’s different now is that the EPA and FAA say it is going away.”

What’s taken so long, he said, is that when one problem is solved — a fuel is identified that will get an engine to run safely — another pops up — like “how are we going to make it work in the distribution system?” he said. “There’s a lot bigger picture here. That’s what we’re struggling with.”

EAA’s position is that it will support as many alternative fuels as possible, to ensure that a safe fuel is available — and perhaps more important — affordable.

Another important point: “No one says we must go to a zero lead fuel,” said the EPA’s Passavant. “If there are going to be multi-billion dollar effects, there must be another way to do it. Let’s come up with a creative solution.”

Thinking about fuel is a whole new ball game for the FAA, added Mark Rumizen, a reciprocating engines/fuels specialist with the agency. “We had one fuel, historically, and airplanes and engines were designed and optimized to operate on 100LL. We didn’t have to think about fuel certification.”

When the EAA and others started developing autogas STCs, the emphasis was still on making the fuel fit the engines, he noted.

“But with the unleaded fuels and Swift Fuel, we’re working backwards,” he said. “It creates a challenge. We have to think differently.”

The FAA is depending on ASTM to develop fuel specifications, he said, adding the industry should look for a notice of proposed rulemaking (NPRM) in 2010.

Meanwhile, the FAA’s 2011 budget includes funding for research on alternative fuels for GA. The agency also is working with the X-Prize Foundation to develop a contest for alternative fuels. “That should help spur development in this area,” he said.


Swift Enterprises, Ltd. is developing an unleaded 100LL replacement fuel, called 100SF, that exceeds the energy content and octane number of 100LL, according to company officials. The new fuel contains two chemical components that, when mixed together, meet or exceed most performance parameters of 100LL. Because of this, 100SF requires minimal engine modification to run in the current GA fleet.

100SF can be produced from any organic matter that contains sugar of cellulose, company officials add.

For more information:


  1. narby says

    Noting the link at the bottom of the page, is this a news article, or a paid advertisement by Swift Fuel?

    The end of 100LL will require me to spend about 1/3 to 1/2 the value of my aircraft for a completely different engine. This is because of the particular airframe and performance requirements to use it at the airpark where I live. I will fight the end of 100LL as hard as I can.

    The discussion of a second round of environmentally mandated fuel changes (the first being from green 100 octane/red 80 octane to 100LL), strikes me as crony capitalism. Getting the government to mandate changes so that fuel manufacturers, engine manufacturers, rubber hose manufacturers, tank manufacturers, all can sell more stuff to people who otherwise are doing just fine. In other words, it appears to be corruption, using the environment as an excuse.

    Doesn’t the government have anything better to do? Maybe plug the gusher in the Gulf or something?

    Leave us alone.

  2. says

    Up front I’ll state that I’m an aviation “spectator”. I have 36 years of “in-the-trenches” time in the Marine (boat) industry, and have a love of all things reciprocating, including Aero-engines. Over the years I have acquired some experience that may be relavent to aviation/fuel, as regarding alcohol use in fuels, if or when such a shift may occur. Our industry began dealing with the effects of alcohol blend fuels in the mid 70’s when alcohol replaced TEL in Mogas. In the 80’s, MTBE replaced alcohol in Mogas, ending “alcohol” issues, but bringing a host of other environmental issues with it. The ban of MTBE in Mogas a couple years back meant the return of alcohol, and thus our alcohol “issues” returned. We have found FOUR major alcohol concerns that should be addressed. FIRST is material compatability with fuel system components. Some metals, especially certain aluminum alloys suffer corrosive effects when exposed to alcohols, particularly, methanol. Fuel hoses (and rubber fuel components in general) suffer plasticizer depletion from the higher solvent aspect of alcohol, harden and suffer a condition similar to dry-rot cracking as a result. Conversely, certain grades of rubber absorb alcohol and can swell becoming mushy. Alcohol always permeates through rubber. The rate and effect are what is relavent. In the Marine industry, when leaded fuel was phased out, to be replaced with Ethanol and Methanol as octane controllers, the US Coast Guard mandated special alcohol resistant hose be used, which limits (note: does NOT entirely eliminate) alcohol permeation through rubber hosing, be it for liquid OR vapor application. These are certified as Type A1 (liquid exposure) or Type A2 (vapor use). This may effect older aircraft in that hosing and rubber components may need to be upgraded to alcohol resistant types, a phase we went through in our industry. SECOND, and least worrysome for aviation (I would hope) is the increased solvency of alcohol as a fuel additive related to “cleaning” of deposits on tanks and other components. Fixed contaminants from these components may be disolved or dislodged into solution in the fuel. THIRD, and of considerable significance, is the shift in stoichiometric ratio brought about by alcohols. While adding octane to a fuel, alcohols also have the effect of being an “oxygenate”, that is, adding oxygen to the fuel air mixture by way of its chemical nature, in effect, partially displacing a portion of “fuel” with “oxygen”, thus effectively leaning out the fuel mixture. Until January 2010, our engines (marine) have been either carbureted, or non-feedback fuel injected. In either case, the engines combine fuel-air at a pre-determined ratio, and do not self compensate for a “lean” shift in “fuel” content as related to the liquid proportion of air/fuel. Simply, they measure X volume of fuel to Y volume of air, regardless of result. In our case, with the shift to alcohol blend Mogas, carbureted engines generally did not suffer terribly, as they typically trended “rich”, though in some rare instances, the leaner condition pushed some engines over the edge, resulting in piston melt-down. This phenomenon was generally not predictable by engine type or model, but proved sporadic throughout most existing product. More significantly effected have been fuel injected engines. Our “dumb” non-feedback EFI engines inject fuel per a pre=determined speed/density data table, with no ability to self compensate. EFI engines have inherently been designed closed to the “edge” of air/fuel ratio for emissions and fuel economy. The addition of alcohols to fuels as a replacement for MTBE octane additive pushed many of these engines over the edge (lean), resulting in significant performance issues, requiring recalibration /reprogramming of their computers to compensate for the shift. As Mogas alcohol content was further increased specifically to capitalize on the oxygen adding property of the alcohol (oxygenated fuel), some of these engines required a second reflash of their computers. What is relavent is that air fuel ratio shifts with the proportion of alcohol, thus, engines that can’t self adjust, have to be “adjusted”, be it carburetor re-jetting, or computer reprogramming. Note: automotive EFI engines and marine gas motors after 2010 do not exhibit symptoms of this problem as they are “feed-back” engines thru the use of oxygen, and or air/fuel sensors in the exhaust down stream, which detect and allow the engine management computer to compensate for rich/lean shifts. FOURTH is the hydroscopic nature of alcohol. Alcohol LOVES water. Much more-so than gasoline. Alcohol absorbs moisture from exposure to air. Moisture initially couples to the alcohol of the alcohol/petroleum blend, remaining suspended there, – – up to a saturation point. When the blend becomes saturated, the water laden alcohol drops out of suspension in the fuel blend, and settles in the tank as a non-combustible water/alcohol mess. The process is known as phase separation. Two issues arise. Water in the fuel tank, and, as alcohol provides “octane”, when it goes, so does octane. This process will happen with exposure to air/moisture. How rapidly is a function of humidity, air exchange through tank venting, particularly thermal expansion/contraction of tank air through ambient temperature rise and fall (daily temp changes), and duration of exposure. Duration is a function of how long fuel is “stored”, that is, not consumed, be it in the storage tanks at the fueling station, or in the aircraft. In our industry, incidents of fuel degradation have occurred in as little as a couple weeks.
    I hope this has provided some practical insight from a sister industry that may have some implications for the aviation industry. I have no doubt that whatever the final fuel resolve will be, all these factors will be considered and addressed when Avgas is re-formulated.

  3. Greg Morton says

    Re: Preparing for the end of 100LL Nov. 29, 2009

    It was a very informative article. It left me with some questions; Why would we continue to go with a petroleum based fuel such as 94UL that will require great modification expense for a large portion of existing aircraft, especially in high performance engines using 94UL that would then run hotter and produce less power? Why would we choose a non-renewable fossil fuel with a carbon footprint that continues to add to our dependency on imported oil? Wouldn’t these issues suggest that an affordable alternative renewable fuel that requires minimal engine adjustment (no FADEC needed), with 100+ octane, no carbon footprint and no foreign oil dependency, such as 100SF, be a much better choice? Oh, and by the way, the 100SF we use here in the USA would be 100% produced in the USA. The profits would go to the U.S. economy, not to OPEC or other foreign countries. We must think in the long term in regards to an aviation fuel replacement, not a convenient quick fix that would not serve aviation’s best interests in the long term.
    NO MORE FORIEGN OIL FOR AVGAS! Doesn’t that sound good?
    Thank you, Greg Morton

    Here is Swift’s web site if you would like to learn more:

  4. Craig says

    Sorry, but this article gets a zero for informing the GA community about the demise of 100LL. Anyone with a pulse knows that 100LL is going away. What we need to know is exactly what engine compression ratio will run on 94UL (7:1? 8.5:1?) and whether or not the existing fleet of Lycoming and Continental engines will run on unleaded fuel without modification. Your article doesn’t answer either of those questions. Try this: “If you have an engine with a compression ratio of X:Y, or if your engine has electronic ignition, you should be in good shape to make the transition without opening your wallet to the tune of $5000 to $10,000” or whatever the truth of the matter happens to be. Sure, it’s complicated, but it can’t be that hard.

  5. JB LeTourneau says

    The old 80-87 avgas is looking better all the time, it had 1/4 the lead of 100LL and was better on the valves leaving less deposits yet still providing the lead needed to cushion the valves against the valve seats. I’ve been burning 1/4 100LL,3/4 auto fuel (yes I have the STC) for years, it works good but you have to test every batch of auto gas to make sure the distributer haven’t put in any ethanol or got the batch mixed up with the “no ethanol” fuel at the state motor pool station I get my gas from.

    From what I’ve heard the UL94 will just be a high spec auto gas with no ethanol, no lead for the valves and not much good on turbo charged or high compression engines without anti-knock detectors and variable timing (read “less power” to keep the engine from knocking). Makes me glad I stuck with the old low compression engines.

    In your article it was quoted that “no one said we must go to a zero lead fuel”, then don’t just go back to the old 80-87 avgas spec and Swift 100SF for the high compression/turbo charged engines(good article in the AOPA magazine last month about an RV owner doing alternate fuel flights), one fuel may not be the answer even if it’s what they would like. If gas stations can carry 2 or 3 different grades of fuel then why can’t airports carry 2 fuels (3 if the have jet fuel as well), one for the high compression engines and one of the low compression engines that were designed for the old 80-87 octane spec? Just as a antique Piper cub isn’t for everyone neither do we all want to fly around in Beech A36’s.

  6. says

    You’ve heard the expression, “Damned by faint praise.”, I assume? Well, you’ve just done it – multiply. The only thing left to determine is whether it was done with malice aforethought. 96 UL is not the frontrunner; it is neck and neck with 100SF according to the ASTM, the people who write the specs. You do mention that mods to engines for 96 UL will be expensive in some cases and not needed in others, but then you erroneously report there needs to be “minor” modifications with 100SF. There are NO required modifications with 100SF. You talk about compatibility with tankage, lines, etc. and put that squarely in the pluses for 96UL, but it is equally true for 100SF; a fact that went unreported. This was a biased piece.

  7. Oscar says

    The thing is:
    What Sugar makes is alcohol …
    Are we going to be Flexibilizing the motor?
    So, by this way, the answer is: Put more alcohol in the gas and run the engine at full mix, should we change the valve seats, piston rings, chromatise the carburator internally??
    What about the lubrication benefit that lead gives in the hot internal engine components, of old powerplants (valve seats, piston rings, etc)?
    Maybe the Swift fuels could answer that.

  8. Oscar says

    The thing is:
    What Sugar makes is alcohol …
    So the answer is: Put more alcohol in the gas and run the engine at full mix, should we change the valve seats, piston rings, chromatise the carburator internally??
    What about the lubrication benefit that lead gives in the hot internal engine components, of old powerplants (valve seats, piston rings, etc)?
    Maybe the Swift fuels could answer that.

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