Going to the Moon Was Easy Compared To 100UL


Doing a little back-of-the-envelope math here, it looks like I have spent just shy of half of my entire life writing about avgas. And not just avgas, but the unleaded replacement for it that would ultimately banish tetraethyl lead to the same place we sent dioxin, radium paint, asbestos and the Gilbert Atomic Laboratory Kit for kids that actually contained bits of uranium.

So you’ll forgive me if I was blase about last week’s report from the National Academies of Sciences, Engineering, and Medicine Transportation Research Board recommending what we should do about leaded avgas. Reading it felt a little like a gauzy tour of the 1980s delivered by someone who didn’t know we actually detested ABBA and we all knew that Scratch ‘n Sniff stickers really were disgusting. If you sense a certain black cynicism in my otherwise uplifting prose, I feel certain you will understand. To be fair, there is some wisdom in this report and if you’re paying attention, a warning, too.

As summarized in our news report, the National Academies examined the unleaded avgas problem because of a requirement inserted into the 2018 FAA Authorization Act. And why not? The FAA couldn’t figure this out and neither could the airframers, the engine builders or, so far, the oil companies. Might as well give the academics a shot, right? If you’ve somehow zoned out on all of this—and who could blame you?—the report reviews in great depth how aviation went from being nowhere when lead was phased out of automotive gas in the 1980s and how we have essentially remained right there—nowhere.

But not for lack of trying. As the report notes (barely) and we have reported ad nauseam, the avgas replacement effort accelerated to this-time-gosh-darnit-we’re-serious speed around 2010. And a decade later, we’ve advanced to the very verge of the edge of … nowhere. The FAA put together a four-letter program called the Piston Aviation Fuels Initiative or PAFI. Thus far, it’s not unfair to say this program has been a black box that whirs, clicks and clatters but nothing visible comes out. By statute, because of its interface with the private sector, the FAA can’t talk about PAFI’s findings, so inquiries to the agency are met with the anodyne “work continues” or “progress is being made.”

Such that we know anything, it appears that Shell has a 100-octane unleaded fuel that’s close to being approvable. But the FAA said it fell short of being a drop-in replacement for unstated reasons. One of these could be materials incompatibility issues related to gaskets, seals, O-rings and tank bladders. Swift Fuels was originally in the PAFI program but withdrew to work outside that testing program. General Aviation Modifications Inc. is also working on a 100-octane fuel and has been since 2010. It’s pursuing approval under a novel STC path and reports progress has accelerated in recent months. Phillips is dabbling with its own additive-based fuel, also outside of PAFI.

The National Academies was charged with policy recommendations on reducing lead pollution from avgas up to and including eliminating it entirely. At a meeting in the fall of 2019, according to one participant who attended, there was a discernible tilt toward doing this with mogas and the experts on the board seemed only vaguely aware of PAFI’s existence, much less its activities. In its analysis, the report recognizes that mogas is a non-starter and not likely to have a significant role. So in the time-honored and industry-honed tradition of can kicking, it recommends the EPA conduct more research on the actual health impact of the 468 tons or so of lead aviation spews into the air.

The EPA, you may recall, already has health-risk data and some of it is presented in the report. This has been the basis for the long-awaited Finding of Endangerment that would lead to rulemaking to force the issue for aviation. Without that ruling, the industry has simply had no incentive to get serious about an unleaded fuel, especially one that might require airframe, engine or fuel farm upgrades. Even minimal ones. And one that will certainly cost a little more.

So, again in the grand tradition of loving the problem, the report uses a shotgun approach. It suggests federal agencies should develop training and awareness for the hazards of using and handling 100LL. Whoever wrote that has never cleaned the oily gunk off an oil filter pad with a gas soaked rag. We know this. We ignore it at whatever peril it represents.

The NA data identifies runups as a major contributor to lead pollution. It recommends airports move runup areas away from where they might impact people likely to breathe the lead particulates. Not a bad suggestion, but I don’t know how practical it is.

In place of 100LL, the report suggests 100VLL, which is a tighter spec ASTM-approved fuel with about 20 percent less lead and less octane give away than 100LL typically has. Some refiners can produce this and may actually be. There might be some reticence to do so because of octane shortfalls, but the report says widespread use of 100VLL would reduce aviation lead pollution by 20 to 40 percent if combined with more use of UL94.

As have other researchers, the NA report estimates that up to 68 percent of the GA fleet could burn UL94, a lower-octane fuel that also has ASTM approval. Swift has had some success in marketing this fuel to a few dozen airports and private users, mostly in the Midwest. The researchers recognize that widespread distribution of UL94 is unlikely because airports don’t want to invest in the tankage and owners aren’t demanding this grade of fuel. Regardless of octane, the benefits of unleaded fuel are cleaner plugs and oil and probably less corrosion due to lack of lead salts. That engines might run better and last longer hasn’t resonated enough with aircraft owners to demand a lead-free fuel.

The danger here is this: You may have noticed we had an election and now have a new Democratic president. During the Trump administration, agencies were told for every rule they wrote, two had to be retired. So the agencies have been frozen for four years. The thaw may be coming. An activist EPA could finally stop kicking the can and start kicking out rules once the Finding of Endangerment has been issued. The proportional measures NA recommends may or may not satisfy those rules while we continue to dither on an unleaded 100-octane fuel.

Second, no one really knows if the supply of tetraethyl lead is stable. The U.K.-based Innospec is believed to be the only remaining producer of TEL, although it may also be made in China. Nonetheless, it’s not hard to imagine rules that ban its export or import by a date certain. The number of countries that still allow leaded fuels is a precious few.

That gets us back full circle to the quest for an unleaded 100-octane fuel. Welcome to 1986. Anyone wishing to form a personal opinion about this will be frustrated by PAFI’s opaqueness. Are we close or are we not? GAMI’s G100UL is more transparent, but the marketing and distribution implications of an STC’d fuel are novel. And the FAA has fought this idea and erected barriers for GAMI at every turn, making the FAA’s intransigence instrumental in why we still don’t have an unleaded fuel. This appears to be finally easing.

In the end, the overarching reason we don’t have an unleaded aviation fuel is lack of public policy propelled by the utter absence of will—political, regulatory, scientific and market will. I suspect you’re not clamoring for a lead-free fuel and neither am I. We don’t need, as NA recommends, more study and research. We need leadership and a determination to force this issue with unambiguous policy, not the matrix of half-steps NA offers as a kind of surrender in lieu of doing the right thing. If the unleaded fuel costs a little more or requires some replacement parts in fuel systems, so be it. We need to get this done.

I would recommend reading the report yourself as a means of being more fully informed on the fuel issue, but really because if I’ve spent half my life on this, the least you can do is spend an hour with it. I would urge you to read the section on potential lead toxicity and form your own opinion on whether you think you have a role in reducing that.   

Find the report here.


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  1. For almost 50 years intelligent humans, some of whom worked in government, have been trying to get the lead out, with little progress.
    Todd Petersen, George W. Braly of GAMI, and Lars Hjelmberg of Hjelmco Oil (sweden) collectively have close to 150 years of experience in aviation and fuels. If you want a consensus, and leave out discussion with these GIANTS, everyone will lose.
    Petersen, is the auto fuel STC guru (38 years), including water methanol injection for “100 octane” engines. Braly has contributed to massive reductions in lead emissions by promoting lean of peak (up to 20% reduction in fuel use results in 20% less lead pollution) operations for over 20 years. Hjelmberg has been distributing and selling ASTM D910 unleaded avgas for 40 years now. If we wait much longer, we will have a major brain drain on our hands.

    I downloaded and read the “Consensus Study Report” (CSP) and was extremely disappointed by the lack of research used to present the state of AVGAS. A typical waste of money by government. The valuable information could have been condensed to about 20 pages. I purchased a Swift fuel forever STC and wish UL94 was more readily available, however it feels like the author was paid to promote Swiftfuel. Never is Hjelmco’s fuel mentioned, nor the “marine” grade fuels like REC 90, that many of us use with autofuel STCs.
    Marcellette Cloche published her masters thesis titled in part “Hot Topics in Aviation”, in 2010. http://www.hjelmco.com/upl/files/41143.pdf This document provides an honest and complete overview of unleaded aviation fuel at the time of publication and is still relevant today. Swift’s 94UL was not really in the game at that point, but Ms. Cloche’s document can add quite a bit of understanding to the issue.

    Timeline of Lead Phase-out
    1970: Congress passes the Clean Air Act. The EPA is formed and given the authority to regulate compounds that endanger human health.
    1973: EPA mandates a phased-in reduction of lead content in all grades of gasoline.
    1974: EPA requires availability of at least one grade of unleaded gasoline, in order to be compatible with vehicles equipped with catalytic converters.
    1996: EPA bans the use of leaded fuel for on-road vehicles (leaded gasoline was down to 0.6 percent of 1996 gasoline sales).

    20 years of new vehicle production had minimized the “valve recession” risk, due to better valve and seat materials. After 45 years in the industry, I have seen only one burned valve in an automobile engine built since 1980, ( a turbocharged engine without hydraulic lifters) I suspect a valve clearance issue. In the mid 70s valve issues were relatively common. Unleaded fuels dramatically increase engine life, and could reliably add 50% to aircraft piston engine TBO.

    Particulate emissions are completely ignored by CSP, and a not insignificant amount of lead in fuel ends up in the engine oil. http://www.hjelmco.com/files.asp?f_id=2419
    So, we are still waiting…. Like Obama said, “The kids of Flint, provided that they’ve been tested for lead exposure and are getting continuous health care, are going to be fine” (This is the “science” party).

    I personally believe the best interim solution is regulation promoting road use sale of a single ethanol free “premium” “marine” grade of fuel modeled on Hjelmco’s 91/96 or Swift UL94. These would have an automotive anti-knock index of around 98 and likely could use isobutanol as an oxygenate for smog areas.
    Isobutanol does not absorb water, negatively affect RVP, so should be safe as an aircraft fuel additive. As the current push is for autos to move to higher ethanol content, all lesser grades could be splash blended with oxygenates. These fuels should be able to be pushed through existing oil pipeline infrastructures.
    A federal mandate to preempt 99% of the LOCAL red tape associated with adding a fueling infrastructure (at federally supported airports) for unleaded fuel would put costs closer to $50K. https://www.ufuel.com/aviation.phtml

    • Problem?
      You missed the salient and primary point: they no longer care about small GA; in fact, it’s viewed as a nuisance.

    • I know of only one person with elevated blood levels of lead- he worked in a 50 y.o. lab doing gold assays. Do you know anyone with lead poisoning?

      It is a non-problem with zealots looking for a solution.

      The cost of a new synthetic fuel will be three or four times as expensive as our current low lead fuels.

  2. Lead is bad for engines and people; get rid of it!
    People forget that when lead was introduced, it caused all sorts of engine problems, particularly with valves.
    Now, some still somehow believe that lead is good for engines and valves.
    In my personal experience, engines operated on unleaded Mogas (premium Shell) have at least 50 percent more cylinder life, do not have valve guide or valve problems, and never foul plugs.
    Oil is cleaner. and oil passages do not sludge up.
    Starting is easier in all weather, and some of those engines operate on fuel that may be a year old; still fine.
    No Vapour lock issues, with or without fuel pumps. No problems with seals or leakages.
    Octane is a separate issue, but is not a problem chemically. Octane does not require lead; that is just one way to achieve it.
    What is the hold up? No one will say, except GAMI and SWIFT have fuels that work.
    IF Lycoming and Continental were not scared of liability, and IF they would produce retrofittable “FADEC” ignitions and fuel injections for high compression engines, perhaps the problem would be solved, along with reduced fuel consumption.
    Ford could help, or Toyota, or any engine manufacturer producing current engines with very high compression running on regular gas, let along premium. They build them by the millions; no problem.
    Air cooled engines are more difficult than liquid cooled, but even there, the compression ratios are relatively low compared to modern engines.
    It seems there is no will to solve the problem, and perhaps that the FAA doesn’t even understand the problem.

  3. The fact that Swift Fuels, General Aviation Modifications, Inc., and Phillips have chosen to continue development outside of the FAA’s PAFI program suggests the program itself may be part of the problem. And as Paul pointedly states “… in the grand tradition of loving the problem…” isn’t that what the FAA demonstrates time and again?

  4. Rather than spending more money on writing reports about washing your hands after fueling, I would like to see a grant program to encourage airports to sell lower octane avgas such as Swift. In addition to the fact that 68% of the fleet CAN run Swift, it’s actually better for the engines and creates lower mx costs for owners of a good chunk of the fleet. Just ask anyone with a low compression Continental or Rotax. It’s time to start reducing our lead use with what we have on hand rather than continuing to wait for technology we have not developed yet.

    • It’s a volume problem for the airport fuel providers. Yes, about 70% of the fleet can use low octane fuel, but those are the little airplanes (4-seaters and 2-seaters) that don’t burn a lot of gas. It’s the 30% of the fleet that CAN’T burn low octane (big singles and cabin class twins) that represent the true marketplace because that 30% of the fleet burns (and buys) more than 70% of the fuel. The market will move to serve those customers. It won’t move to serve those of us buying very little fuel. Even if we think it’s so much money we spend. It isn’t. Not for the airports.

    • KGBR (Great Barrington, MA) decided to put in a split tank that contains both AvGas and Swift 94, because the locals were up in arms about them replacing their old fuel tank (required by the state every 20 years, irrespective of condition). One of the arguments brought up at the town meetings was that the airport still sells LEADED gasoline (cue pearl clutching). So now the airport can say, “Actually, we are the first airport in the state to sell an unleaded aviation fuel.” It’s been as much for local PR as anything else.

  5. There’s a subset of fungible, called miscible. THAT’S the unavoidable key issue with ALL of these alternative fuels

    Meanwhile, simply outlawing unleaded fuel would be a form of confiscation – it would comprise a “taking for public use.” What would comprise the constitutionally-required “just compensation?” New engines and fuel systems for all affected legacy aircraft?

  6. Paul. Please reread your column and notice the big picture you talk about. Government BS never ends. People getting paid to do research with never reaching any useful conclusions because their hands are tied behind their backs or they just don’t care about their work.
    But please don’t blame the previous administration because the one before them had 8 years. I didn’t hear a darn thing from that bunch of morons either. Not to support the previous crowd, but at least someone saw the light and determined we need LESS restrictions to be somewhat more productive.
    Hopefully more hands are untied and we move forward on many fronts without costing us an arm and a leg.

  7. I think part of the problem is trying to find a “drop-in solution”. It seems pretty clear at this point that such a fuel does not exist, and that the engines requiring high-octane fuel will need to have some modifications done to support an unleaded fuel. And it seems to me that if most of these aircraft owners choose to spend $10-20k instead of $1500 to equip for ADS-B, surely they can afford whatever it would cost to modify their engines for unleaded fuels?
    It seems like the goal of a drop-in solution is a case of “perfect is the enemy of good”.

    • Those “mods” likely would cost $100k per engine. What’s the value proposition? “The perfect is the enemy of the good,” indeed. Given the miniscule amount of lead that we’re talking about, it seems more like an exercise in virtue signaling, than in planet-saving.

      • I doubt it. Even with new bladders (IF the old ones won’t work), fuel lines, possibly injectors, etc., especially if the FAA paves the approval path for such things. The engine proper will need nothing, and will likely now last longer.
        Still, a fuel that doesn’t require mods would be better, but I’m old enough to remember when the vast majority of airports had two grades of piston fuel. Heck, many airports have two or three tankers, and some have split tankers. Or just have a “lead blender” to mix with the other stuff, for planes that must have it, until a solution (that doesn’t involve the demise of GA high-performance piston engines) is reached.

    • Choose?

      A lot of high performance aircraft are used for business travel. Much less than 20 years ago, but don’t get me started. When they updated the owners did not have a $1500 option. Your argument is based on a misrepresentation of history. My options, until nearly the deadline, were to upgrade minimally for maybe $6k? That option would have upped my value almost zero. OTOH, I could spend much more, but gain most of that in value.
      I wasn’t flying for business anymore, but if I were, I’d have had to get my plane in the shop to avoid a predicted rush near the deadline.

      Now for the rest of your solution, where is it? What does it cost me and how much performance do I lose? Where’s YOUR data?

      I suspect no one will know the answer to how easy it is to modify a plane until a fuel is decided on. And, no bureaucrat wants to be the guy who decided on a fuel and then there was a bad outcome.

  8. Cynical prediction: the ultimate solution will require expensive, invasive changes to most piston aircraft. Not long after the “Unleaded Fuel Mandate” goes into effect, practical and affordable battery (or fuel cell, or ultra capacitor) electrical storage relegates internal combustion engines to the same museum of historical novelties as steam engines.

  9. Car engines routinely have compression ratios (CR) of 10:1 or higher and run fine on mogas. In significant part, it’s because of far-better engine management systems (EMS) which are totally lacking on traditional aircraft engines. But fundamentally, it’s possible only because their small cylinder volume automatically makes pre-ignition much less of a concern. Upgrading from 1928 ignition systems to EMS is technically quite easy and relatively inexpensive, but FAA certification is a byzantine and expensive proposition. Reducing CR with shorter connecting rods is also relatively easy. Turbo engines already have mechanically-lower CR and could be “fixed” by limiting boost. Reducing the effective CR reduces power of course. Expensive true.

    Other regulations presently make adoption of 94UL difficult. A new standard self-fuel installation is very expensive and fuel volume isn’t enough to easily make up costs. (The few in my area charge more for 94UL than 100LL as a consequence.) Numerous and varying local and state restrictions generally forbid having small private fueling options. And, as is the case with me, even with a lead-free loving Rotax, I am required to burn 100LL because that’s what the USA certification certificate requires and the manufacturer has nothing to gain now by changing it, nor is there enough money to be made by going through an STC process, for a tiny number of such aircraft types.

    Overall, a pretty bleak picture.

  10. Hmm… Create a FUEL to run in engines borne in the 1930’s, or create a new engine designed to operate on what’s available (Jet A)? Today’s muscle cars run to power levels never dreamt of in the 1960s. Automotive fuel is largely “contaminated” with Ethanol, which adsorbs water (death to pilots when frozen). So we can’t leverage that source unless we use non-oxygenated fuels.

    This really is not rocket science for those with engine design skills and the will to do it. We just need to have faith, and support those with God given talents for such an exercise. It can certainly be accomplished.

    Godspeed Aviators

    • Lol, Steven is not an airplane owner. If he was then he’d see that certified engine swaps are almost prohibitably expensive. Experimental auto engines swap into certified aircraft is double that. As YARS said, who will pay to re-engineer the fleet and then re-engine the fleet? Yea, that IS moonshot money.

  11. The problem is too many rules already. Agencies being frozen because they couldn’t get rid of rules just reminds me of that thing with monkeys unable to get their hands out of a jar because they won’t release the fruit inside. Pretty sure my dog could work out that level of problem.

    The moonshot was solvable because there wasn’t a mile of preexisting red tape that a majority of normal people found somehow sacred. There merely was a lot of miles physically deadly to humans, and math to be overcome. (Hidden Figures is an awesome movie)

    If lead in aircraft is such a huge deal, just show me the money. I suspect it’s like everything else in the world where it’s only a problem when someone else can be made to provide the time, effort, and money to fix it. In the meantime, we all pay for bureaucrats not to solve anything.

    We are really in this situation because of lack of demand for new light aircraft and their engines. That’s a result of a combination of many things, but much of it is a seeming conspiracy to take the fun and utility out of light aircraft for over half a century. Additionally, innovation gets squashed because flying is so dangerous it justifies many pounds of regulation yet it’s the only industry where manufacturers have a right to build offending products ad infinitum.

    We can do one thing for certain and stop building planes that require 100LL.

  12. The NAS study was directed by Congress to ignore all of the current Unleaded fuels under development. That is in part why it wallows around in half-baked options.. Both the GAMI and Swift UL100 fuels are “Drop-in” replacements with viable formulas able to be produced in existing refineries with existing processes and additives. They are languishing in part because they are designed around a proprietary license model, and haven’t been developed by the producers.. The Shell product had issues with dissolving paint, and the Phillips product (“About 5 years away..”) uses Manganese salts and scavengers that also have health risks.. GAMI and Swift fuels have been delayed by indecision over testing methodology and criteria for actually granting approval for these fuels.. The few refiners brewing 100LL aren’t going to change over until either ordered to by the federal government or forced to by cutoff of Tetraethyl lead supply from Innospec. Most medium to small airports can’t afford to add new tanks, so adoption of UL94 requires arm-twisting to get one of existing tanks/refueling operators to switch.. And it requires distribution infrastructure (transport/storage/deliveries) to mitigate the cost premium away from the Indiana refinery now producing it..

  13. Just spit balling here, could we somehow stop the liability chain from hitting an auto maker whose engine gets modified for aviation use? Hasn’t the weight to power issue been changed a lot recently? Is it still a non starter to modify a high performance auto engine?

    • It isn’t a non-starter at all – a lot of experimentals are using auto conversions very successfully. The devil is in the details, of course, do it wrong and you have an unreliable engine. But if individuals or small groups can do it successfully, then a fully engineered solution should be trivial. But it would require the expense and complication of certification, which has killed many such attempts already, either directly, or by forcing the engine prices so high that ‘I might as well buy the tried-and-true’ engine. Similar reasons why you can still buy brand-new PA-28s and C-172s!

      • So like I said above. The real problem is too many rules.

        Those of us who got through the gauntlet of nonsense to own and fly often just don’t get how unreasonable it all is and what a towering wall it creates keeping so many out of our little club.

  14. It’s already been mentioned that the amount of lead is miniscule–but that will never stop the True Believers that ALL lead must be removed–as Yars quotes–“The perfect is the enemy of the good.”

    How about THIS–Reverse the procedure–instead of modifying existing engines to achieve “lead-free Nirvana”, let the big-government activists fund a program that will WORK!

    If they REALLY believe that lead is that big a problem, let them fund a program to get rid of engines that require it. The Obama administration spent a fortune for “Cash for Clunkers”–buying back a whole generation of perfectly-running cars to advance their agenda. Much as I detest government involvement in ANYTHING, Having a government program to give a pro-rata buyback based on engine hours remaining would settle the issue once and for all–and it wouldn’t take 50 years of “research” by the government to do it.

    With a market this large, Continental, Lycoming, and perhaps some auto engineers would likely have conforming prototypes available in short order–(at least, short, compared to the never-ending “studies.”) Aircraft owners could get be assured that their aircraft wouldn’t be legislated out of existence–the “get out the lead” advocates could stop their hand-wringing. Engine manufacturers would be busy. The FAA could finally move into the 21st century in certifying technology adopted by non-aviation manufacturers in the LAST century. Airplane owners would have some assurance that their airplanes aren’t going to be outlawed.

    The only people this would REALLY affect negatively are those that own aircraft powered by radial engines, or Warbirds–a small but important segment. Perhaps a niche could be carved out for them to have a boutique fuel.

    For the country, we could settle this once and for all–and quit spending money on interminable studies. If I could be assured that my 100 octane powered aircraft could be re-powered with a conforming and modern engine, AND that I’d get a pro-rated buyout of the remaining hours, I’d be all over that!

    • Why pro-rate the buyout?
      If the government opts to outlaw my engine, they should provide me with a new one – installed, with all attendant systems – at NO cost to me. (See 5th amendment.)

      • Yars–you are right, as usual.

        That was my initial take on solving the problem–but I realized that SOMEBODY in the “Puzzle Palace” would shout “Hey, these guys are getting a new engine for NOTHING!” (never mind that the new engine was because of a dubious MANDATE that the government was unable to solve).

        I HAD considered that the FAA would give so many years to replace the engines–and that old-styled engines would no longer be licensed for building–but that would be a great leap of faith in trusting multiple government agencies that have proven to be UNABLE to come up with a sensible solution. It would mean that parts for the old engines would be a problem.

        My solution was that “I will install a new engine in the airplane IF you A. Certify the engine first. B. Have new engines ready for build-up. C. Have spare parts ready to ship. D. Pre-certify the STC to install the new engines. E. Give time for manufacturers to flight test and start installations of the new engines prior to the “Cash for Clunkers Part II” program.
        If they started today, we “Could” have new, fuel efficient, reliable engines that don’t need leaded fuel in 5 year–but with government dithering, it would be 10 years–but at least we would HAVE a solution (unlike the half-century of “development” for a solution that HASN’T PRODUCED RESULTS.
        It would be a fairly simple program–the government gives us a new, compliant, certified engine, with better reliability and systems, and no requirement for lead–and in return, I would pay the remaining hours to TBO at the rate per hour add/deduct as specified in Aircraft Blue Book.
        Best of all, we STOP THE INCESSANT SQUABBLING, DELAYS, AND UNCERTAINTY ON THE PART OF THE FAA. Getting the FAA out of the fuel business and restoring certainty is worth the cost, and safety and utility is upgraded with the ability to utilize modern systems.
        Maybe it wouldn’t be a Continental or Lycoming–maybe it is an FAA-approved auto engine. Remember when the auto manufacturers touted “aircraft style accessories”? The tables have turned–an aircraft engine based on an auto engine MAY be the best solution.
        OR–we can watch the EPA types continue to DEMAND a product that they themselves haven’t been able to produce in 50 years–leaving us all waiting for the next blunder on their part–all the while our aircraft engines use 1930s technology.

      • YARS, you misread the tea leaves. Federal, local, and even unelected officials could care less about keeping little propellor planes flying; much less give you money to keep your “rich noisy” hobby going. No, the simple and cheap and elegant solution is to let you keep your now obsolete toy but on the ground. It’s even “green” that way. Sorry man but small GA is now seen as a threat. Meigs Field? California?

        • Arthur, you’re absolutely right, and that pesky constitution be damned.

          Not so long ago, half of Americans thought that the other half were simply misguided fools. More recently, we’ve been told that half of Americans are “irredeemable deplorables” and “bitter clingers.” This week, we’ve seen open calls to “de-program” and to “de-platform” the deplorables. And open discussions about reigning in the free press, to prevent them from “spewing misinformation and disinformation.” A Truth and Reconciliation Commission. Seriously. Did any of these great leaders read 1984 in high school? A Ministry of Truth?

          Yes, the Greenies will not hesitate to promote “equity,” by grounding all of us little “fat cats.” A small price (for others) to pay, in order to “save the planet” and to promote “environmental justice.” Whatever that is. (I probably should ask Humpty Dumpty.)

          I guess we gratefully but guiltily should fly our little toxin-emitters while we still can. Clearly, we don’t care about anyone but ourselves. Probably the underlying reason why we’re so deplorable. 😉

    • “If they REALLY believe that lead is that big a problem, let them fund a program to get rid of engines that require it.”


      It’s too easy to identify problems, when your paycheck depends on the number of problems identified, not the number of problems solved.

      Kinda like a “safety inspector”.
      Pretty easy to point out problems when you’re not required to solve them.

  15. One of the issues with general aviation is that there are a large number bureaucrats who believe that small aircraft are a problem. We know this, we have seen it. These bureaucrats believe that no individual should have the right to fly an aircraft. When they get around to it and following the typical bureaucratic path, they will mandate lead be removed from aviation fuel in the name of ecological benefit but without a replacement. Thus, the lead in aviation fuel will be used to kill off general aviation. We don’t want to hear this but I see no signs that individual will be protected.

  16. Dana, you nailed it. Small private gas powered GA is no longer viewed as essential or even desired. The will plow runways with big X’s before listening to rational solutions.

    • I want to agree with you guys, but I’m not willing to give up. Besides, I’m not sure they have to do anything at the rate GA is dying, the butchers just have to wait for the beast they’ve cut to bleed out.

  17. What I’m seeing in the business and commercial industry, they are trading out the 100LL engines for turbines. The private owner of an engine that can only burn 100LL are/and will be priced out. The price of the fuel and the insurance will either force the 100LL users out or to trade up. There will be no “drop-in 100LL” replacement. After three decades of controversy, time to take the Rose Colored Glasses off.

  18. The years of looking at fuel problems have fogged the brain (I was too polite to say sniffing the rag was the cause — it is not a fuel problem but an engine problem.
    Look what happened with cars — the governments in their wisdom said they would stop selling leaded fuel.
    The world did not end — manufacturers quickly made engines compatible with unleaded fuel, of all sizes and all power outputs.
    Most found that, actually, in spite of all the fuss, doom and gloom and supposed threats to liberty — doing so was easy. Many used the opportunity to redesign engine plants at the same time and remove the weakest link (humans) from the engine assembly lines. I have one car 16 years old and another 14 years old. Neither has ever had an engine problem. My Dad finds that incredible.
    Simply stop selling engines which use leaded fuel, and the problem will go away.
    Old cubs and the rest with 60 year motors can still fill up with fuel and a dose of lead from the bottle, just as old cars can, if you really want the charm of the old fashioned experience.

    • Brand new cars cost, on average, about $40k. Brand-new personal airplanes? Move the decimal point to the right, then double that amount.

  19. Just finished digging out big chunks of lead out the spark plugs on my O 235. The radial engine in my Nanchang has a minimum octane requirement of 70, so my take on 94UL which is 100LL without any lead is; HeLL yah bring it on!

    But, I get the issue with the big bore turbo engines.

    The biggest danger for those engines may not be government actually getting around to outlawing lead, it is the ONLY plant in the world that now makes TEL has a fire, blows up or just goes bankrupt. 30 days later there will be no 100LL full stop.

    Either a supply chain failure or government regulation means 100LL is gone. As a general comment hard niche problems generally get fixed with the easiest solution, so that would be all existing refineries switch to 94UL, which would be easy.

    Bottom line sadly is GA is subject to a quadruple whammy on this:

    1) Avgas is so low volume it is not even classified as a fuel by the oil companies, it is a specialty chemical. So minimal consequences for oil companies if it is outlawed

    2) Politicians know GA is not a big enough voting block to have consequences if they hurt them

    3) There is basically no “ safe “ level for particulate lead in the environment

    4) There is no easy drop in replacement for TEL. All of the other possible additives have significant issues

    There is no possible happy ending here for any owner of an aircraft that can only burn 100LL

  20. A lot of insightful comments here! We are indeed fighting a lot of inertia, technical issues, and fear of liability here, but the pilot community needs to continue pushing for and demanding a solution. Less than 100 octane is not an option with 70% of the fuel requiring at least that, if not 102 MON. Any unleaded fuel has to meet the stringent requirements set forth by the FAA and OEMs in the PAFI program. This is required to replace 100LL for fleet-wide approval. STCs won’t do it and 94 octane won’t either with only one avgas tank at each airport. If ultra-low lead were acceptable we would have a solution tomorrow, but no-one is ready to throw in the towel, despite the NAS report and suggestion that VLL may be good enough. Not likely for the NGOs who sued the EPA.

    As an insider, I can assure you that your associations have your back, the FAA is genuinely interested in finding a solution, and the OEMs just want to insure they won’t be left footing the bill (or face lawsuits). But there are several fuel suppliers still invested in finding a solution. Some you have never heard of. Keep the faith and the pressure. We haven’t given up on you.

  21. Building on the statement “we need a new engine to solve the unleaded fuel problem”, I’m drawn to alternative engines that burn unleaded fuel. The Yamaha 4 banger liter motorcycle engine come to mind. These engines are ubiquitous, have a very tough service life but are known for reliability. Normal power output of these engines is 140 HP. Change the jetting of the carbs or flash the ECU and these engines easily make 150 HP. Add a turbo and 315 HP is achievable. Google Turbo F1 to see an example. There are probably hundreds of mechanical and reliability reasons why motorcycle engines would not be suitable in aircraft but it is a start. Interesting that the greatest contribution being made by the Samson Sky flying car could be the engine. They have been testing various engines to find the most effective and reliable solution. So far, the Yamaha engine is winning.

    • It’s a better starting point than auto engines. Auto engines are not designed to run endlessly at 75% power settings.

    • I have four of these engines in my garage. There is zero chance they would make good aircraft engines. They make their power at 9000 RPM and above. If you could stand the noise–which you couldn’t–they wouldn’t last long at the 70 percent duty cycle of aircraft engines.

      Don’t forget Rotax tried this with a sophisticated V-6 14 years ago. They abandoned it as untenable. But it could have worked with more development dollars and time. If sorted out, it would have been a lovely engine.

      And all the people here complaining about 100LL and pining for new technology wouldn’t have bought it. Which Rotax fully understood.

    • For years a couple of engineer brothers from Toulouse developed an aero version of the Suzuki Bandit motor, built from the 1980s for 20 years or so — it used spay oil cooling.
      They had some success with European microlights — with a built in reduction gearbox and manual clutch, it did not weigh much more than a Rotax, and had advantages of electronic injection, was quieter and smoother etc.
      But no-one is going to make much of a profit with microlights and when they tried to develop a 150hp model for small Cessnas and the like they were swamped by paperwork and gave up.
      Similarly lots of BMW boxer engines in microlights, at the 100 HP mark with dual ignition, fuel injection, et al, go well, sip fuel and are unbreakable, but difficult to go above 100 HP with them.
      The South Africans linked with the Slinger (?) were developing a V6 related to the old Ford V6 Essex engines, 3 litres, very reliable and updateable, but last I heard they were also mired in the paper work bog.

  22. Since it happened before my time in this business, I wondered what was done to allow some of the big radial powered airplanes that used what was 115/145 octane avgas that was colored purple, when 100LL was introduced? I talked with many persons who were in the military during the 50’s and 60’s who used to work with that fuel. Another suggestion about adapting high powered or turbo-charged may not be workable. Most light twins have marginal single engine climb capability and any reduction in power would result in no single engine climb at all. That would put most pt135 outfits out of business flying those planes. Switching to turbine (using jetA) would not be cheap either. I find it highly unlikely any privately owned ( not government) flight school could afford or actually make a profit on airplanes costing millions of dollars apiece (verses thousands). As far as the constitutional (5th amendment) requirement to compensate those for the government “taking” of airplanes due to leaded fuels being banned, all one has to do is look what has happened to all those businesses lost due to all of the COVID shutdowns and restrictions. As far as I know none of them have been compensated!

  23. Personally I think the only really tenable way ahead for a long term solution is for Continental and Lycoming to create as close to possible a drop in diesel replacement engine for the turbo 520 and 540 series engines. Yes there will be an initial wrenching switch over but 100 octane days are done. When not if, 100LL is euthanized by government fiat or a supply chain failure, I don’t believe there will be any viable affordable replacement and the small and decreasing volume of 100 LL pumped just is not there to interest the deep pockets who could put the kind of resources to solve the problem of how to get 100 Octane without the lead.

    94UL is a proven existing solution for the smaller engines but Jet A is the future for GA high performance piston engines

    • And who will author the hundreds – if not thousands – of type-specific STCs that will be required, to allow these new engines to be installed in airframes? Details.

    • Continental owns the SMH turbo diesel now IIRC. It will work in a 182 or a Cirrus. It’s been done.

      Unfortunately, too heavy for some others because of balance issues.

      • I looked at the SMA turbodiesel having run a TDI in my VW Passat (only part of that car that worked well). I really liked the idea and when it came time to overhaul the O-470R, I looked long and hard at OSH. When the STC installed price came in at more than $70,000 (roughly twice what I paid for the airplane and 4 times the cost of a new limit overhaul), the engine was overhauled. Another issue, at least then was there was talk of a service ceiling limit of around 10k, which didn’t give me enough clearance to get over even the lower passes where I fly and certainly not enough to get in/out of high altitude fields I use, including LXV.

        The mogas STC lives on, and I cart gas to the airport, or land at airports that have mogas all the while badgering my local FBO to give us mogas.

        I’d be happy with a compression fired engine, if the power-weight ration works for the airframe.

  24. How many turbo charged airplanes are viable right now ? Whole swaths of old turbo 310, 320,early 340’s, 401/402, tip tank 414, 421A/B, turbo Aztec’s, early turbo 210, turbo Lances, and high time short body Navajo’s have a sell price less than the cost of the overhaul of their engines. They are going away regardless of the future of 100LL

    When you look at airframes where it is worth spending 60K for an overhaul of the existing turbo big block Continental/Lycoming, the list shrinks substantially. I bet 25 STC’s would cover 90 % of the types which are viable going forward

    • David,
      I’m not sure what’s up in the present market, but that was true of many of those models back when I was still selling planes over a decade ago.

  25. Many comments about auto engines seem to ignore that the three (?) Jet A pistons on the market now are all based on auto engines. Just Say’n.

    If it’s true that innovation is being thwarted by certification, would allowing owners to convert their planes to a new class of experimental use be a solution? If the government won’t make compensation, then it seems it should at least make allowances. Changes to the liability situation and/or regulatory regime would likely result in solutions.

    Also, I’d really like to hear a reaction to my earlier suggestion that we put an end date on letting new 100LL planes get sold. This is just adding to the problem.

  26. The Continental TSIO 550, is certified for 94UL. Virtually all of the IO 520 and IO 540’s will run on 94UL with low compression pistons, a 5 K mod. Yes there is a modest loss of power but in exchange you have fuel certainty for forever.

    Instead of burying our head in the sands how about the alphabet groups lobby for a set in stone drop dead date on 100LL. If we said to everyone that only 94UL will be available as of Jan 1 2024, then everyone can plan accordingly and you have neutered the environmentalist.

    • That modest loss of power may not be acceptable for a twin engine plane due to loss of any single engine climb performance. A lot of the older airframes that are still flying in Pt135 and pt 91 are there because the manufacturers have not produced a replacement for the jobs those airplanes do, or the ones that have been are too expensive to buy or to make a profit with. I do agree with the proposal to stop certifying new airplanes running on 100LL. It would be a good place to start with the final phaseout of leaded fuels.

  27. Read all these noteworthy comments, but one issue that nobody seems to ever talk about is fuel stability. The octane can be there, sure, but will it be there next month? Avgas is, what, mil spec’d for two years? Auto fuel goes south in a month. Yes, my airplane will run on mogas, but if it sits out the winter, it best be drained! As far as auto engines are concerned, there are three local “experimenters” that had belt reduction auto engines which all have experienced at least one crankshaft failure. Anecdotal. yes, but I won’t try that in my airplane, thank you.

    • I’m not so sure this is true. Mogas with 10% and above ETOH is certainly unstable. Shelf life of alcohol laced fuel, is similar to that of an alcohol laced pilot….very very short, less than a month or so. It’s worse when stored in airplanes. gaskets expand, fuel hoses leak, water/etoh extraction corrodes. Not a pretty picture at all.

      ETOH free mogas has a shelf life of about 6 months to 18 months under appropriate storage conditions. It’s not clear how fuel leads to a crankshaft failure as there should not be much fuel in the crank case, and what is there should be evaporated off as soon as the oil comes up to temperature. More likely, the load on the crank shaft and duty cycle on those engines are the culprits. I don’t think I’d put an automotive engine in my airplane either.

      Avgas is usually stable under appropriate storage conditions for about a year, so there isn’t much difference between ETOH free fuel of one or the other stocks.

      As for storage, I believe Cessna has three levels of storage for a/c, flyable, temporary, and long term. Short term is pretty standard, fill the tanks, turn off the switches, tie it down, Fly it for half an hour every 30 days. Amazingly the CSL says if you can’t fly it ground run it for 30 minutes…now I know where that old saying came from…not recommended these days, I think. For long storage, take the plugs out, spray the cyls with anti-corrosion stuff and put the plugs back. Fog the engine compartment through the oil filler, put desicators in the plug holes, exhaust and breather and tape things shut.

      None of these procedures suggest draining the fuel out of the airplanes for the winter. This was written before the hairbrained idea of putting ETOH in fuel came about, so if there’s alcohol in the fuel I’d drain it. I use ETOH free mogas in my farm equipment and it makes the winter just fine with similar preservatives.

  28. We have non-ethanol auto gas available from local gas stations in many places of the country. We haver aviation mogas in several parts of the country. We have a huge number of low compression big inch air-cooled aircraft engines in a very large percentage of current flying in the US that have run on mogas/autogas for decades. Both manufacturers that originally designed and manufactured these 80/87 octane engines are still in business. So why not use what we have already? Between three oft noted mogas STC owner’s exhaustive STC certification tests, we know what works plus have decades of continued use to back up any questions or challenges.

    As Paul pointed out, it is easier and faster to go to the moon using calculators and slide rules combined with 51 year old computers than solve the 100LL replacement. It is not rocket science that GA piston aircraft sales do not offer enough scale of economy to allow FAA certification of EFI, electronic ignition systems, and variable cam timing that is decades use by the auto industry.

    Instead have Continental and Lycoming get some federal grant for resurrection of production of mogas capable engines rather that pay repeated board, commission, or fact finding think tanks regarding both the replacement and repeated inquiries to the miniscule lead exhaust content consequences emitted by GA aircraft. In other words, since we can go the moon, land “rovers” on Mars, and send satellites beyond Pluto while assembling and maintaining an old space station, lets forget the debacle called a drop in 100LL replacement and build what already works.

    Continental E series dry sump engines powered the first 4-5,000 Bonanzas including the E-225-8 installed in my D-35. That solves the borderline bizarre solution to the Cirrus SR22’s narrow cowling design that requires a 0-550 running with a eight quart pan. (yeah…550 cid engine having only eight quarts max with a recommended 7 quart in the sump but no less than 6 for normal flight attitudes to help cool and lube it). Beech needed a low profile powerplant and Continental delivered a slow turning, big inch, dry sump, external 10 quart oil tank which includes its own oil cooler. 470 cubic inches of non-ethanol burning, Walmart 91 octane $2-2.50 cent per gallon autogas. The pressure carb operates very close to throttle body fuel injection. Efficient, rarely has any carb ice issues (never for me so far), great fuel economy, good fuel distribution when you know how to fine tune the manifold pressure.

    Auto fuel extends the life of cylinders because it does not generate all the internal combustion “dirt” that 100LL does making for cleaner oil, less blow by, cooler CHT’s…all properties that extend cylinder life with excellent performance. All the development costs have been born on the first generation Bonanzas. All that is required is dust off the tooling and resume production. Shouldn’t take too much new” technology, dough, and research to dust off old tooling and castings. Yet another piece of 75+ year old engineering that has a proven successful track record of safe, reliable performance on 80/87 avgas and mogas juxtaposed against the decades long quest for 100LL drop in replacement that so far, does not exist.

    Next would be the Continental 0-470 series of wet sump engines that have been installed in many thousands of aircraft since the initial run of the E series dry sump engines. Likewise, proven performance in the 230-260HP range that can run on unleaded non-ethanol auto fuel. All that development technology as also paid for long ago. Just ramp up production.

    Lycoming has 0-540’s that run on 93 octane mogas. A quick call to Pipistrel will verify that was the powerplant of choice for their Panthera. I predict when the Chinese resurrect production of the Continental E-series and 0-470, A65/75/85/90, 0-200, 0-300 engines that also run on mogas, Lycoming will get their 4 cylinder’s approved for mogas very quickly.

    No EFI? No problem! We already have the PS5C pressure carb. No electronic ignition? No problem, we have Slick and Bendix magnetos. No mogas at the airport? Go to Walmart for their “drop in” replacement 91 octane non-ethanol premium. We buy booze, prescription drugs, fast food, via the drive through lanes. All we have to do is readjust our thinking with advanced planning using ancient technology solving the so far unsolvable problem of a drop in replacement for 100LL. We can use a new catch phrase…drive through avgas replacement!

    Car manufacturers installed cupholders, extra power receptacles, coolers, and TV monitors when they realized we live in our cars, raising our kids in the backseat of our cars, living a large percentage of life behind the wheel of our daily grocery getters. It won’t take long for them to install adequate tankage for our drive through auto fuel needs. I predict the EAA will lobby Ford with the Blue Oval offering a 25 gallon aux tank option for the Explorer that can be used for extended range on the road or used for filling up one’s mogas approved airplane, complete with its own fuel pump! All we have to do is drive up and stick the hose in the airplane’s tank.

    I am sure Chinese Cirrus can make a couple of calls to the Chinese Continental headquarters getting an auto-gas approval for the 0-550 series in very short order. It may not be fashionable to buy Walmart fuel for a million dollar airplane. But I am sure some ad agency or PR maven will post proper high end etiquette allowing use of mogas or locally accessed auto fuel preserving all social requirements.

    To move forward in GA, the signs of the times require us to look backward. Forget all the diatribes about govmit red tape, bureaucratic malaise mixed with complexity, and an over abundance of paychecks to boards, commissions, and think tanks. Forget an automotive alternative. Let’s keep GA “pure” from all things new. Lets be thankful, Beechcraft took advantage of all that was learned in WWII, taking advantage of thinking forward because there was little govmit interference in pushing performance boundaries to meet customer expectations, allowing a narrow historical window to actually use innovation for improvement in private airplanes. As a result, we have 185-220mph 4-6 place, all electric airplanes with retractable gear that has influenced and birthed just about every other airplane design outside of the Cub. Today we have new Cub clones and the rest are Bonanza clones. Both have made it possible to fly low and slow or high and fast.

    It appears, 1933-47 were the only years for GA to grow beyond tradition. That narrow window of time has not repeated itself. Consequently, we can either hope for what has been proven historically not to happen eventually squeezing all private aircraft flight to a mere trickle when the EPA wipes out 100LL. Or look backwards, flying 1945-55 technology that still matches or exceeds in many ways the performance of what is currently unaffordable for the majority, but very viable, affordable, and available for far more aviators. Embrace the old. It may be the only way to fly.

  29. “I suspect you’re not clamoring for a lead-free fuel…”

    Oh, but I am. Have been, on and off, since 1986. Now I can’t even schlep mogas to the airport because they won’t sell it without ethanol in it.

    So I keep doing more oil changes and budgeting for higher maintenance costs than I should have to.

    But I’m a small-volume buyer. I get that.

  30. I stated before in another article that the world pumps more unleaded fuel in a day than what leaded fuel gets pumped in a year. That said, how many leaded wheel weights get used and discarded every year on passenger vehicles? Me thinks the EPA needs to focus on other issues and leave aviation to the FAA.