Aviation fuel and the 70/30 mantra

Over the past few years, a debate has raged over the best way to reduce our dependence on avgas in North America, one of the last places on the planet where leaded fuels remain in use. There are two “camps” of thought.

The first one, consisting of the leaders of most aviation alphabet groups (with the notable exception of LAMA), contends that the best solution is to find a one-size-fits all, drop-in replacement for leaded avgas. Despite over two decades of searching for an alternative, this group doesn’t appear to be close to finding an affordable solution, but they have attended countless meetings, generated numerous reports and performed a variety of taxpayer-funded studies on the subject.

The second camp, made up mostly of recreational pilots and the managers of the airports they use, favor multiple options including avgas (or its eventual replacement), mogas, and Jet-A. Despite lack of support from the aviation alphabets and avgas suppliers, this second group is making slow, but significant progress towards broader availability of mogas, as this map of airports selling mogas from my co-author Dean Billing shows.

Given the success of the grassroots mogas movement compared to the failure of the well-funded avgas replacement folks, one has to wonder why the latter has not joined the former. Part of the answer, I think, is related to the so-called 70/30 myth of who uses which fuel.

It goes something like this: “While 70% of piston aircraft might be able to use mogas, the remaining 30% burn most of the avgas.” The AOPA repeats this mantra in this Regulatory Brief, but as in all such cases we’re aware of, provides no factual evidence of what appears to be little more than anecdotal evidence.

By comparison, your bloggers decided it was time to find some hard numbers, and this past summer commissioned a study of the FAA aircraft registry, which found that more than 80% of all piston-engine aircraft were capable of operating on mogas.

We still await a comparable, repeatable study from the avgas replacement camp proving their claims. Instead, some of the defenders of the 70/30 myth now refer to a 80/20 ratio; we suspect that if our study would have shown that 99% of all piston aircraft could operate on mogas, there would be those who would claim that the remaining 1% consume 99% of all the avgas!

In his January 2013 monthly editorial, High-Performance Composites Editor-in-Chief Jeff Sloan touches on a similar myth voiced for years by potential users of carbon fiber in the auto industry: “If only carbon fiber were $5/lb.”, then it would be a serious replacement for traditional materials like steel and aluminum, he explains. No one knows who started the myth and whether it is based on hard numbers, but it continues to be repeated as, Sloan contends, an argument for many in the industry to do nothing. “$5/lb has become a mantra mostly by virtue of repetition — and a sort of straw man for some automotive engineers and executives, who, deep down, don’t want to switch to carbon fiber and use the $5/lb threshold as a way to keep the composites industry at bay.” Sound familiar?

Sloan goes on to state that while the real cost for carbon fiber has not dropped, many related factors have, especially the mold cycle time, which for some processes is now down to 60 seconds.

The same can be said for aviation — while many continue to chant the 70/30 mantra, the aircraft industry, dealing with the reality of declining avgas supplies worldwide, has reacted. The fastest growing segment of aviation is Light Sport, aircraft whose engines are designed to operate best on mogas. Virtually all new piston engines are being designed to operate on mogas, including the new AF (Alternative Fuel) series from Lycoming and Continental.

Owners of large-displacement piston engine aircraft have been making the move to light turbine aircraft for years, prompting even small rural airports to add Jet-A tanks in addition to avgas and mogas. Jet-A burning diesels are real contenders these days for high-end pistons, as recent news from Diamond and Cessna shows and Flying magazine described this past summer. Electric-powered aircraft are no longer a novelty, with designs such as Randall Fishmann’s Electraflyer ULS now available for purchase.

Just as the $5/lb mantra among automakers blinds them to progress made in composite fabrication methods, so too does the 70/30 mogas/avgas mantra blind many in our community to the changes occurring in our powerplants that are enabling to us fly efficiently on a variety of fuels, including avgas, Jet-A, mogas and electrons. More choices are always better, especially when free markets — not committees and bureaucrats — determine what is best in each case.


  1. says

    Let’s not totally discount a cheaper alternative to Avgas, although it’s not going to be at your local FBO next month. Maybe as soon as next year, in limited areas. We invited Swift Fuelshttp://swiftfuels.com/ to do a live webinar with the Troutdale Chapter of Oregon Pilots Association and I, among others, was very impressed. It IS a drop in replacement for 100LL, it is being rigorously tested in special STCed aircraft and in stationary engines as well, the FAA is happy with the results so far, so certification looks good. The exciting part is that it can be manufactured in small scale plants that have been used to produce ethanol, from digested bio-mass. They are scaling up to a commercial level of production and will have a more accurate cost assessment but it looks at the moment to be potentially a cheaper fuel than petroleum sourced Avgas AND, the exciting potential is that a small operator could sign a supply contract with a local FBO or two and produce locally. We have a lot of useful biomass in the NW, and Oregon State is already producing Jet A from biomass. We at Oregon Pilots Association have invited Swift Fuels and Oregon State to participate in our annual conference on August 24 in Albany. It’s an exciting prospect, they were asked a lot of practical questions by pilots of all types of craft. The main thing, to my mind, is to keep this product out of the sole control of the petroleum companies or the fuel will cost the same as petroleum avgas. As to the separate equipment issue, they are mixing their fuel with leaded petroleum avgas in various proportions without any problems, so the FBO could buy both types of fuel without requiring special tanks.

    • Bryan says

      For the last 7 years Swift fuel has been ‘just around the corner’. It is a lot of the same hype every year, year after year. When is it going to show up at a pimp near me, or you? Crickets.

      We could have 91UL right now. It is essentially high test Mogas without alcohol, and it is available at some airports, so there don’t appear to be regulatory problems with it like any of the “drop in” candidates. For higher compression engines attempting to burn 91UL, there are existing methanol injection systems to control detonation (http://www.airplains.com/index.php/news-updates/information-articles/121-anti-detonat-injection).

      We need to do this now. The number of certified pilots is not growing and our voices become weaker and weaker. $7 gallon AvGas will continue to reduce the number if hours flown, student starts, and active pilots.

      • Bryan says

        That should say; “a pump near me, or you”. I apologize for inadvertently denigrating our purveyors of fine aviation petroleum products 😉

  2. Edd Weninger says


    In early 2009, I built a small Excel work-sheet to determine if the 70%/30% ratio could be reasonably accurate. My spreadsheet comes up with 67%/33% based on hard data from the FAA via NATA and a few reasonable assumptions on my part.

    If you’d like to see a copy, send me your email address via eddwen…at…aol.com with Kent as the subject line.

  3. R Bettencourt says

    I have been a member of AOPA for 25 years,and on and off of the EAA for aproximately 6 years. The only thing that I get from both is a bill for dues and merchandise to purchase.After watching all this fuel replacement talk I have come to the conclusion that money talks and BS walks! Untill these people that are our so called representative under stand that WE are the reason THEY have a job nothing will change. Maybe the thought of loseing membership would change the way they think.

  4. Kent Misegades says

    One other myth surrounding this issue is the cost of fuel equipment, for any fuel, not just mogas. Many airport/FBO managers believe that an additional fuel system will cost them $100,000 or more. There are a number of fuel equipment makers that offer turnkey, self-service system for well under $50,000. Private financing is not hard to get as they generally pay for themselves in 4-5 years. Whenever you face opposition, ask for hard proof of their arguments. It is generally easy to refute these. Mogas is not a solution for all pilots, nor for all airports, just as avgas and Jet-A aren’t. Not doing something to reduce the cost of fuel however will drive more people away from flying. The FBO that worries about the competition from mogas needs to take Economics 101 and pay attention to the chapter on diminishing marginal returns. Just like taxes, lower the rate and you’ll increase overall revenue. Increase rates and you get less.

  5. says

    Amen. In case anyone missed it, let me say it again: AMEN!
    Kent is right, as he usually is. I have a mogas STC for my aircraft. It can even take 87 octane -as long as there is no ethanol in it. It is still too hard to find, despite the grass roots efforts Kent mentions. Ethanol is usually added to mogas at the point of distribution, not the point of refinement, which means it should be easier to get than it is. Outdated rules and laws mandating ethanol in mogas have hurt corn prices, inflamed politics and done little to reduce the cost of fuel to many drivers. Let’s make things easier on the industry, on the end user and on the environment. Give the 80% access to what we can use, while the 20% switches to diesel/Jet A.
    There is an AD for my engine (Continental O200) that essentially saps a few horses to comply with. I survived. How many high compression aero engines could survive on unleaded 92-94 octane mogas with just a minor loss of horsepower? I am no expert, but have been told many. That seems like only a few percent of engines out there are holding back the growth of mogas as a viable option in most GA airplanes.
    My FBO says costs prevent him from installing a mogas tank. If we took all the money spent on research on the drop-in replacement, and instead gave it to airports to install mogas tanks, we’d probably have enough left over to help the large displacement engine owners convert or adjust!

  6. Jscott says

    While I agree that adding additional tankage for Mogas at most airports would serve most of the flyers, what are the other 20% that require Avgas to do? I know at our local airport the one size fits all solution is driven by the cost of purchasing, installing servicing and insuring an additional tank. Additionally, the view is that any mogas sale would also be seen as an Avgas sale that didn’t happen. I’ve been beating my head against that mentality for many years. For some reason, the end cost to the consumer doesn’t seem to be a factor.

    After burning through $7000 in Avgas in the last year, I have finally given up and am resurrecting my 100 gallon truck tank so I can haul Mogas to my planes. I simply have to reduce the my costs somewhere. Right now the difference in price between premium alcohol free Mogas vs 100LL in our area is $2.03/gallon. If I could burn Mogas all the time, that would reduce my $7000 fuel bill to just a bit over $4200. While I don’t expect to burn Mogas 100% of the time, I do expect this to make a significant dent in my cost of flying. It’s a shame the fuel sales people can’t see this. I’m guessing losing $7000 in my business in the next year will be insignificant to them.

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