The unleaded fuel disaster – what it means for pilots

Can a story simultaneously be underreported and overreported? The transition from leaded avgas to an unleaded future has been decades in the making, and countless articles have discussed everything from the certification process to the chemistry (Paul Bertorelli at Avweb has done some of the best work). And yet many pilots don’t know how bad things are right now, as other topics like ADS-B, drones, and user fees have sucked up most of the attention. It might be going a little too far to say the general aviation fuel system is in crisis, but it’s certainly troubled.

The key problem? Right now there isn’t much of a plan to transition to unleaded avgas, at least not in the way most pilots think about it.

The best hope, until recently, was the FAA’s Piston Aviation Fuels Initiative (PAFI), a government-sponsored program to evaluate different fuels in a consistent and rigorous way. The goal was to avoid competing standards from companies more interested in market share than technical compatibility. PAFI’s goal is not to “certify” a fuel, but to offer the test data that would allow a candidate fuel to prove compliance with an ASTM specification. Things were moving along steadily (if excruciatingly slowly) until this summer, when the FAA stopped all testing. The press releases were vague but essentially the problem was that none of the fuels were meeting the hoped-for standard.

Swift Fuels
Swift Fuel is going it alone by pursuing an STC.

Following that announcement, Swift Fuel, one of the PAFI participants, pulled out and announced their intention to pursue an STC outside of the FAA’s complicated process. They will join similar efforts from Phillips 66 and General Aviation Modifications, Inc. (GAMI). That leaves Shell as the lone PAFI participant, although how long that lasts remains to be seen. The FAA agreed to restart testing in late August, but no firm plans have been announced and the deadline has already slipped by more than a year. Optimism is in short supply

Other powerplant options

Given this mess, what are the alternatives? The slow death of PAFI doesn’t necessarily mean an unleaded fuel won’t happen – both Swift and GAMI seem firmly committed to the STC path, and have spent years working on their product. But even if these eventually make it to your local FBO, the distribution will be fractured and the decisions for pilots will be confusing. Is GAMI fuel approved for your engine or only Swift? Which kind of fuel is available at your destination? Can they be mixed (a key issue in the PAFI testing, apparently)? All those questions come before a more prosaic concern: how expensive are these new fuels going to be? All of these are new questions to consider, and so far nobody knows the answers.

An idea that once seemed quite promising was the diesel engine, which can run on widely-available Jet A. Just a few years ago, Continental was promoting a new line of diesel engines, Cessna was working to certify a diesel-powered Skyhawk, and Redbird was overhauling 172s with a modified Mercedes diesel engine. Today these projects are either dead or on the back burner. It turns out diesel engines, while efficient and reliable, are also heavy and expensive. The math just doesn’t work unless you plan to fly a lot of hours (probably over 200 hours per year), and pilots have voted with their wallets.

Much of the excitement that once surrounded diesel has moved on to electric aircraft. There are dozens of models being promoted right now, which range from somewhat reasonable to utterly ridiculous, but even the most conservative designs are many years away from going mainstream. Certification rules need to evolve and battery technology needs to make dramatic (some say impossible) progress. Both of those may happen, but it’s far too early to place any bets.

It’s probably safe to say that – eventually – electric airplanes are the future, at least for flight training and small general aviation airplanes. That’s exciting for many pilots, but it also has the potential to kill off much of the remaining interest in diesel programs, and may even give unleaded fuel boosters second thoughts. Why invest time in money in a niche fuel when it will get leapfrogged in a decade?

Muddle through?

The depressing conclusion from the PAFI debacle is that there simply isn’t a drop-in replacement for 100LL, a fuel that could be used in a wide variety of airplanes without major changes to ground infrastructure or airplane performance. That means some previously unappealing ideas may get another look.

SR22T
The SR22T from Cirrus was designed to run on “a wide range of fuels.”

One possibility is that airplane engines will have to run on unleaded auto gas in the near future. That would solve a lot of problems with distribution and infrastructure – it’s widely available in the US, a clear standard already exists, and it solves the lead problem – but it will come at a high cost. Most high compression engines (think TSIO-550) simply can’t run on 94 octane unleaded gas without changes to operating limitations and thus performance. Would you run your Cessna 310 at 50% power instead of 75% power? That’s the type of tradeoff pilots may have to confront.

Where operating limitations don’t solve the problem, engine modification might be required. That would present aircraft owners with some tough financial decisions. One notable example of planning for the future is Cirrus, which introduced the SR22T model in 2010 with a lower compression turbocharged engine. It is widely assumed that one reason for the company’s design choice is to accommodate unleaded fuel if that becomes necessary. That’s great for new airplanes, but it does nothing to address the tens of thousands of 40-year old Cessnas and Pipers that still fly all over the US. And even new airplanes would struggle with many of the ethanol blends sold at gas stations – even auto gas isn’t much of a “drop in” solution!

Electronic ignition, the standard in cars for many years, would be a great way to increase the number of high compression engines that could run on unleaded avgas, but the FAA has been astonishingly slow in approving these systems for certified airplanes. While experimental airplanes increasingly sport these systems, they are very rare on certified airplanes and one magneto is retained anyway. With an installed price of over $7,000, it’s not an inexpensive upgrade.

The only sure thing in this confusing world of regulators, oil companies and airplane owners is that timing of this transition (whatever transition it ends up being) is uncertain. 100LL has remained in use decades after cars ditched the lead, and there’s reason to believe that can continue for many more years. However, the EPA could easily declare leaded fuel a danger to public health in the near future. They have held off for years now, partly because they believe there is a serious effort on the part of the FAA and industry to replace leaded avgas. If that process apears to be failing, such patience may evaporate. That would start the clock ticking and all the carefully planned processes might go up in smoke.

34 Comments

  • I’m not at all surprised to learn that vendors are choosing means that limit interaction with the FAA. In its effort to become a kinder, gentler version of itself (we’re here to help!) the FAA is slowly becoming irrelevant. The recent crash of the Lion Air 737 Max in Indonesia is yet another indicator. I see two possibilities from that crash; either the FAA approved Boeing’s plan to keep operators in the dark about the MCAS flight control system installed on the aircraft, or it didn’t know that Boeing had installed the system on the aircraft. I don’t know which of those is worse.

  • IMHO it’s going to come down to one of a few things (or some combination thereof) (most likely to least likely):

    1. The aging GA fleet of 100LL airplanes will pass a critical mass of low ownership where the oil companies will no longer have the facilities to produce the fuel, at which time they will tell GA that the end is very near and the price will spike to the point where it will be inevitable where no one can afford to fly anything 100LL.

    2. The EPA will eventually grow tired of waiting for the alternatives to arrive and start making forcible actions to eliminate 100LL

    3. Electric Power plants in aircraft will overtake piston engines in power and range.

    4. Any legacy aircraft left behind will be relegated to the museums.

  • We’ve had leaded fuel in small quantities for so long it is unfathomably illogical and unconscionable to ban 100LL, but I agree with you John, EPA will eventually do it anyway. It’s just accelerating the inevitable though, as that one-and-only plant producing TEL in the UK won’t last forever. For most of us, 93UL will be the answer, my engine loves that fuel. For most of the piston aviation hours flown, i.e. big bore engines, the answer appears to be that they’ll have a choice: turbines or … WATER INJECTION. WI demonstrably works and is running on a 300hp engine experimentally. If we really think the UL initiative is going to fail we need to take a good look at WI.

  • I’m not as pessimistic as some of the posters.

    The reason lead is in avgas is to improve detonation margins. Electronic engine management systems can address detonation issues using autogas in most operating regimes. For the exceptions, some operating limitations could apply, or mechanical mitigation like water/alcohol injection.

    This is expensive now, but five years ago a basic electronic attitude indicator was 5K (before installation) and an ADS-B upgrade was 10K. When the FAA became invested in these outcomes the price plummeted and aviation ECM boxes will do likewise. Remember the affected engines comprise a large percentage of the part 135 on-demand cargo fleet and no one who builds automobiles or does organ transplants is going to allow them to go away.

    I think the final rendition of unleaded avgas will be straight autogas (without oxygenates) out of the refinery, formulated with an aviation additive package at the distribution point to control vapor pressure. That base stock already conforms to an ASTM standard so mixing fuels from different manufacturers won’t be a problem.

    What is lacking right now is a firm deadline for the transition as John suggests. The rest will follow.

  • Buongiorno,
    io sono propietario di Piper Warrior 161hp.
    dal 2004 funziona con Mogas 100 ottani, raramente riempio con Av, anche a quote alte non fa blocco di vapore , io da questo ho girato 1200 ore, buone compressioni e stesso rendimento,
    grazie
    Denzio

  • Not to take away (much) from the UL discussion which is important, I’ve not seen any ADSB discussion of the continuing cost of compliance. We can get full databases from ForeFlight that can be used on 2 devices for a reasonable annual amount of $150 or so. I just upgraded to Avidyne and am now presented with two $500 annual payments to Jeppson so the avionics will work and it will talk to iPad. I tried to get information for both Avidyne and Jeppsen but neither would reply about these costs – until after I installed the new equipment. These fees are exorbitant, unreasonable and outrageous.

    • The GPS output required for that (raw GPS coordinate data) is independent of any Avidyne or Jeppesen subscription. Your ADS-B equipment will continue to work just fine without a subscription. (It’s all the OTHER capabilities – such as being legal for IFR – that would suffer.)

      And while I agree that the Avidyne / Jeppesen subscription costs are far too high (they are using data the government supplies to the for zero cost!), I was able to find the cost of the subscriptions online in a matter of minutes. Your dealer who did the install should also have been able to answer your questions before you selected that equipment…

    • Garmin makes a great GPS, however the yearly subscription makes it very cost prohibitive, ForeFlight is a great alternative, I have used it for many years, the 179 a year is good.

  • One critical factor which appears to be routinely overlooked is that the lead in the fuel also acts as a lubricant for critical engine components such as intake and exhaust valve guides. The lead also makes it way past the piston rings lubricating the cylinders and camshaft as well as providing corrosion protection to these components. This is especially important in aircraft which are not routinely flown on a daily basis.

    • Dan – Can you cite an engine manufacturer spec for lead as a lubricant and corrosion inhibitor?

      Aero-engines burning mogas stay cleaner than aero-engines burning 100LL: Lead salts emulsify into sludge that collect in oil galleries. Look at the lead sludge that collects in the crank nose bore of a constant speed engine. If it sloughs off, it can clog oil galleries. Have you had an engine that responded poorly to prop cycling on the first runup of the day? It could be sludge blocking the passage until the prop governor pump pushed the glob into the prop dome.

      Lead deposits cause sparkplug misfire. If you burn mogas it doesn’t happen. Lead salts are a large part of the reason why we change oil so frequently.

      • Redbird;
        While lead creates the potential for some plug fouling (and that thin black film inside your engine), I have never had it clog the oil galleries on a properly maintained engine. This being said, unleaded fuel is still an issue for vintage cars owners. Exhaust guides in particular, originally received most of their lubrication from the tetraethyl lead. Without the lead, stock cast iron guides wear rapidly and eventually cause valve seat & face problems simply because of the excess wear in the stem area. (http://www.mossmotoring.com/unleaded-gas/). Unfortunately, most of us burning 100LL today are doing it with an engine that was designed over 50 years ago – – just like a vintage car…

        • Dan: Thanks for the reply. Your summary of the article and the article are interesting, but is it true?

          Here is the control group for this experiment: How many vintage auto engines burning leaded mogas and operated identically had valve seat recession and guide problems? How does that compare to identical engines burning unleaded?

          How many models of aero-engines have cast iron valve seats and valve guides?

          Why do valves in vintage diesel engines survive without lead?

          Why do experimental aircraft burning mogas survive with the same or less valve problems than those burning 100LL?

          Does lead really act as a sacrificial anti-wear material on valve seats?

          Does lead really form a lubrication oxide layer on valve guides and stems?

          Do you really know what that black layer is?

          To me, the article reads more like a puff-piece advertising ReLead, not actual engineering data.

          When EPA proposed removing TEL from fuel, it was to prevent ‘poisoning’ of catalytic converters. If engine manufacturers had a problem with it, they would have said so during the comment period using engineering data, not speculation. Is there a record of that? Data might be more convincing than an opinion piece masquerading as tech data.

  • I’m not nearly as pessimistic as the author and I do not think the word “disaster” is an accurate descriptor of the problem. The current EPA leadership could care less about lead in avgas and I think that’s one reason for the slow down. Should the EPA get new leadership and press the issue, I think you’d see progress towards a 100LL substitute pick up. I agree with Kim Hunter – this is not a hugely difficult technical problem – and I believe the FAA is our ally. I think we are going to see them become more friendly towards things like electronic ignition.

    Finally I think GA has more political clout than we think. After all we’ve kept ATC privatization and user fees at bay since the 1960s. This will at least help us buy more time to solve the problem.

  • Money, Money, & more money, that is what is lacking in all this. The people responsible for the mfg. of fuel haven’t come up with a way to continue ripping us off that is the bottom line. Our technology today can mfg. any type of fuel we need for what ever usage is needed. During the 2nd. world war the U.S. needed 130 & 150 octane for the heave bombers, it was made in a matter of a cpl. of months, no problem, & that was with the 1941 technology. In the 1950s we could by Chevron car gas starting with 93 octane, 95 octane and then the custom supreme, white pump was 100 octane leaded gas for $.39 a gallon. All this BS about not being able to come up with unleaded fuel for aircraft is crap!! Even 94 octane unleaded gas fuel would work with no problems. Fuel is mfg without lead, the lead is added later to increase the octane to what ever is needed, This is an insult to my intelligence.

  • I am continually appalled at how reticent wealthy people are to do something that is helpful, good for all, good for the planet and just plain the right thing to do because it might cost them extra money. They typically have to be dragged kicking and screaming into compulsory, imposed action by fiat where a simple voluntary act would have begun the ball of change and improvement rolling. If GA is snuffed out here, while continuing to be viable elsewhere, it only has the stubborn, change-resistant 1% to blame.

  • And the FAA is NO ONE’S “ally.” It exists to restrict, impose, interfere and intrude. And not terribly competently at that.

    • Yes, it seems the FAA is out to destroy general aviation, while making suppliers richer. Kinda like the FDA exists only to protect and insure the profits of big pharma.

  • I can’t understand why enterprising people need the FAA to hold their hands before they do something bold and innovative.

    Why isn’t there an auto fuel that could be boosted to 100 octane without lead and ethanol. Sounds like a simple solution.

    The auto fuel at my airport at my airport works very well in a Rotax 503. Occasionally I use Super Shell auto gas and it also works well, though I cringe when I add ethanol to the engine. I guess aero engines are just old primitive designs. No incentives by the three oligopoly engine manufacturers to be innovative.

  • “Why isn’t there an auto fuel that could be boosted to 100 octane without lead and ethanol?”

    Because modern automobile engines don’t NEED 100-octane fuel. Many aircraft engines DO. And not just high-performance birds – my 125 hp Tomahawk requires 100-octane fuel.

    The awful truth is that there may be NO chemistry that will solve this problem. Just new engines. And most light GA owners can’t afford that.

  • 91/96UL is 100LL without the lead. Quote: “In November 2010, the European Aviation Safety Agency (EASA) based on about 20 years of trouble-free operations with unleaded avgas 91/96UL produced by Hjelmco Oil cleared this fuel for all aircraft where the aircraft engine manufacturer has approved this fuel.[23] ” end quote
    https://en.wikipedia.org/wiki/Avgas#Phase-out_of_leaded_aviation_gasoline

    It is claimed that 70% of the fleet run fine with 91/96UL. For those engines that need higher detonation margins, is there a way for the user to add Tetraethyl lead to the fuel at the tank? In my poorly informed mind, that solves the problem.

    Then there is mogas. Peterson and EAA have STCs for that. A few airframe/engine combinations don’t pass testing due to vapor lock (fuel boils in the pumps) and hydro -lock (fuel boils in the carb). options include relocating fuel pumps away from heat sources or replacing them with pusher pumps submerged in the tank. Systems that recirculate fuel back to the tanks cool hoses, carbs and pumps. This works fine in experimentals burning mogas, so it’s well tested.

    Why aren’t these alternatives part of the discussion?

  • John Z wrote “The depressing conclusion from the PAFI debacle is that there simply isn’t a drop-in replacement for 100LL.” He might have added an additional qualifier “based on petroleum sources” which is where PAFI seems to be. The big oil companies haven’t yet been able to check all the boxes and therefore the testing was halted for a year or so to provide more time to develop a more robust product.

    Swift and GAMI apparently have passed the tests, but since they developed products utilizing plant derivatives rather than petroleum, they will not be allowed to disrupt big oil’s avgas markets with non-petroleum products. Instead, Swift and GAMI are being forced to market their products through the STC process, a slow, agonizing and costly method. In the interim, big oil and their NATA cohorts will continue to produce and market 100LL (which by the way is suitable for the current fleet despite the objections about lead) and the existence of the PAFI project will be enough to pacify EPA for an indefinite period.

    In summary, don’t expect any changes in the avgas market that will eliminate lead or reduce prices — it’s not going to happen unless big oil and NATA are at the table with products and services that protect their generous profit margins and existing infrastructure. It’s just the way the world works whether we like it or not!

  • Getting the FAA involved was a mistake. All that was required was a date after which leaded fuel could not be sold. If there is still anyone out there that believes in a free market economy, it would get sorted out to everyone’s satisfaction that still wanted to fly. It might be perceived to be better or worse than we have today, but that would be irrelevant.

    My experience with diesels leads me to believe there are several problems there:
    1. The engines are expensive to build.
    2. The engines are expensive to install in existing airplanes.
    3. The jet-A infrastructure really isn’t set up to sell small quantities of fuel to small diesel airplanes.
    4. The current Jet-A specs are not adequate for diesel engines.
    5. Jet-A fuel smells bad (and it’s hard to wash off).

  • Dan,
    I’m not a metallurgist but I am a automotive machinist & mechanic. I can tell you that lead has little to do with guide wear, it’s fuel mixture control or lack of that causes most wear. As for valve seats the exhaust is primarily affected by the lack of lead, however induction hardened seats and stellite facing on the valve reduce wear to the point of 140k mile durability on an engine that works hard and 240k or more on a lightly loaded engine.

  • While everything that Stephen said is true, it appears that there is NO chemistry that offers a fungible replacement for 100LL.

    If ANY existing aircraft/engines can’t find a replacement fuel, then THEY will have to be replaced with ones that can use whatever witches’ brew emerges from the post-PSFI swamp.

    Any effort to minimize this fiasco, by noting that “MOST existing engines can burn automobile fuel,” is a narcissistic assertion of “I’m aboard; pull up the ladder.

    • Tom,
      I would liken the situation more as: “This whale oil works great in our lamps, why would we want to change”?

      Your statement that there is no possible chemistry is probably in error. Both GAMI and Swift fuels have enough confidence to spend significant money on the STC process for their brew. There has been no mention of changing engines; maybe some materials changes in the fuel system?

      I personally would like to see the lead go away not only as a cooperative member of society but also because I would like to see extended oil change intervals and I’m tired of cleaning lead out of the plugs all the time.

      • Stephen:
        It’s all about fungibility. So far, nothing has worked. And a LOT of effort has been provided by a lot of very smart people. That’s why I say that there MAY be NO chemistry that will provide the required fungibility.

        Which is why there’s now so much discussion about moving the goalposts.

  • 100LL should remain the standard. In the grand scheme of things, lead is no big deal. 100LL is not going to cause any more illness or environmental damage than cheeseburgers, ice cream, over population, and natural disasters.

    • Unfortunately, environmental extremists are uninterested in your grand scheme. To them, lead (and anyone who defends its uses) is an evil that must be eradicated.

  • “the EPA could easily declare leaded fuel a danger to public health…
    That would start the clock ticking and all the carefully planned
    processes might go up in smoke.”

    The Supreme Court ruled that EPA must leave avgas regulation to the FAA.

    Getting lead out of mogas was justified because it poisons catalytic converters, which reduce CO and NOx coming out of an engine. Lead wasn’t a direct health concern, tho NGOs pretended it was, and EPA never rushed to correct the misperception.

    Aero and off road engines don’t have catalytic converters, so the EPA rules don’t apply. Nascar burned leaded fuel until recently, then converted to alcohol for PR purposes. https://en.wikipedia.org/wiki/Racing_fuel

  • How about the “Bush Pilot Emergency Blend”: 50/50 mix of Coleman Fuel and Marvel Mystery Oil? (Works in everything……sometimes…..!)

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