The future of fuel

“We have to stop loving the problem and just fix it.” Those words, spoken by Lycoming’s Michael Kraft at the 2010 AirVenture, may sum up best the quest to find an unleaded replacement for 100LL.

Ostensibly, the industry has been working since the early 1990s towards finding a solution, but efforts didn’t really get serious until a few years ago. Many place the turning point at the AOPA Summit in Tampa, Florida, in 2009 when Glenn Passavant of the EPA made it very clear that it was time for the industry to get to work.

That was followed by a true wake-up call in April 2010 with the release of an advanced notice of proposed rule making from the Environmental Protection Agency, giving the GA community an opportunity to comment on data collection regarding lead and possible new environmental standards.

The folks at General Aviation Modifications Inc. (GAMI) in Ada, Okla., as well as the forces behind Swift Fuels, didn’t need that additional wakeup call — they were already hard at work in the search for an unleaded alternative.

At this year’s AirVenture, George Braly, who started GAMI in 1993 with fellow aerospace engineer Tim Roehl, described how the two spent the flight home from that eventful AOPA Summit sketching out ideas for an unleaded fuel.

They went to work in the company’s engine test facility and within a year began testing the new G100UL in the company’s Cirrus SR22.

By the spring of 2010 — right about when the EPA’s advanced notice came out — GAMI had a fuel that worked, Braly said.

Dubbed G100UL, the fuel fits the design requirements for an unleaded aviation fuel, he said. While GAMI officials won’t divulge what’s in the fuel — calling it a secret formula like the formula for Coca-Cola — Braly noted “there is nothing in it that hasn’t been running in airplanes in the past.”

In fact, G100UL can be mixed in any percentage with 100LL, so if a pilot wants to top off a fuel tank that already has 100LL with G100UL, there will be no problem.

“The fuel in the plane will still retain its spec and integrity and there will be no degradation in performance,” Roehl said.

The fuel has been flown by officials at Cirrus Aircraft, Lycoming, Continental Motors and the FAA. Embry-Riddle Aeronautical University has used the fuel in its Cirrus and Cessna 172s. In September 2012, G100UL was successfully tested for use in high-compression turbocharged aircraft, with four FAA officials there to witness the test, according to Braly.

All of the data shows that the fuel performs just as well as 100LL, GAMI officials noted.

The FAA has since approved G100UL for all certification testing activities, Braly added.

The company and the FAA recently reached an agreement on the list of airplanes that have to be tested to receive AML-STC (Approved Model List Supplemental Type Certificated) approvals.

Braly estimates the company will have the testing completed in about a year. “When we are through, we should have an STC list for all the airplanes in the FAA database,” he said.

The folks at Swift Fuels in the Purdue Research Park next to Purdue University in Indiana took a different tack, creating a new fuel — 100SF — through a mixture of two hydrocarbons. In English: 100SF is a biofuel, made of renewable sources, such as sugars and starches.

After seven years of R&D, the company is now transitioning to production. In fact, the company announced at this year’s AirVenture that officials had sent in the Swift Fuel research report to ASTM for FAA and OEM review and approval.

“The vote outcome is expected in several more weeks,” said Chris D’Acosta, CEO, on Sept. 3.

100SF has been tested in the Embry-Riddle fleet, as well as in all kinds of aircraft engines, from Pratt & Whitney to Lycoming to Continental to Hirth, Swift officials reported at Oshkosh. In fact, the engine test section makes up about 200 pages of the 400-page report submitted to ASTM.

That report also includes a materials compliance study from the University of Dayton Research Institute, which shows that 100SF is fully compliant with the engine, fuel systems and composites used in modern aircraft. Another test, conducted by researchers at Clemson University and Lewis University, show that 100SF is far and away less environmentally toxic than 100LL.

After all, Swift officials said at Oshkosh, “what good would it be if we put something in there that was as harmful as lead?”

While the industry continues to argue over the solution, there is one thing that everyone agrees on: Getting the lead out of avgas will benefit aircraft owners.

“All the positives we saw in cars we’ll see in aviation,” says Lycoming’s Kraft.

Once we get the lead out, there will be decreased maintenance costs because lead by-products affect the engine, as well as contaminate the oil. We’ll see increased equipment life and perhaps longer TBO times, industry insiders promise.

“Remember when we transitioned from leaded to unleaded autogas?” Braly asked the Oshkosh crowd. “We went from changing our spark plugs every 10,000 miles to every 80,000 miles. The lead in fuel is not good for anything except to protect the engine from detonation.”

In fact, Lycoming’s Kraft said the company would “love” to get rid of TEL — Tetraethyllead, the highly toxic additive in avgas — noting that in the company’s iE2 FADEC engine, the lead “messes up the sensors.”

Kraft, who has been at the center of the search for a 100LL replacement as a key member of the Aviation RuleMaking Committee, is pleased with the progress the industry has made over the past few years.

“We’ve learned a hell of a lot and with that knowledge, we’ve changed the outcome,” he said.

The debate has finally switched from fighting the EPA about keeping lead to finding new fuels for GA, he noted.

“There is a technical solution,” which must be music to the engineer’s ears.

Lycoming has made it very clear that it is more than willing to revise its Service Instruction 1070, which lists the approved fuel for its engines.

“Every time we revise SI1070 it is a signal to the fuel manufacturers that if you product a new fuel, we will approve it,” Kraft said. “If you throw us a fuel, we can tell you within two weeks if it will work.”


While all this is getting sorted out, pilots and aircraft owners need not worry about being grounded.

“There will be no precipitious end to 100LL,” said Doug Macnair, vice president of government relations for the Experimental Aircraft Association (EAA). “There is a methodical process in place that brings prudence to the industry.”

The process will begin with evaluating all candidate fuels on a level playing field. Initial candidate fuels must be submitted to the FAA, which will then choose the fuels that will actually be tested at the FAA’s William J. Hughes Technical Center in Atlantic City, N.J.

Testing of the fuels to identify the most viable replacements for 100LL won’t even begin until 2014, with certification not expected for several years beyond that. Some peg 2018 as the date to expect fleet-wide approval of the new fuel.

“We’re still talking years, not months,” Macnair said. “This is not going to happen overnight, nor should it.”

The lengthy process of standardized testing is critical, he added.

“This takes all the opinion and conjecture out,” he said, noting the fuels will be judged on “purely technical and economic factors.”


  1. Venus Savage says

    General Aviation is already reaching the tipping point. And flight training is one of the few things which America seems still to do well.

    That said, why not hasten the decline of GA with potential cost increases and futher uncertainty about its future?

    • says

      Venus, you should apply for a job with the ObamaCare death panels for your community. :)
      I think we are talking about fuel for planes not for suicide.

      My research does agree that America is this the best place to have Asian pilots trained. It is a lucrative business right now. However, that business may get over saturated quickly as PanAm Flight School is now owned by ANA Holdings, the parent of All Nippon Airways.

      Just like the China buying Smithfield, they will buy the the hog to get the bacon. But, don’t expect them to stay long, raising hogs in America is another government burdened business that they don’t want any part of it. We will be importing our Bacon soon.

  2. Clint Newell says

    Trying to lower the octane requirement for large displacement aircraft engines introduces multiple problems. The process of modifying and recertifying those engines to lower performance standards is unrealistic. It’s much more sensible to go with the 100 octance unleaded fuel that has already been developed. To speculate on the cost of that fuel at this point is premature. It will depend on how many companies and refineries choose to produce it, which is likely to be much less limited than what we see today with 100LL. The market will determine the price.

    • Greg W says

      Lowering the octane requirement of an engine is as simple as lowering the manifold pressure. Many of the large radial engines were certified to run on multiple grades of gasoline at different manifold pressures. This will change the horsepower produced but does allow the engine to safely operate. The modification required would simply be an amendment to the operating manual and test program on the engine with the lower grade fuel.

      • Stanley Stewart says

        This procedure, using a lower manifold pressure, could work for single engine airplanes but would make most twin engine GA airplanes useless, as the single engine performance would be so degraded that the airplane would not be able to fly at any usable gross weight. The single engine performance of most twin engine GA aircraft is marginal when the engine can produce 100% power, reduced power would negate any ability to climb on one engine.

        • John Mininger says

          I’ve heard this argument for years and I wonder if it holds up if the twin is fitted with V.G.s. I’m just curious.
          You are right though. Most stock piston twins have extremely marginal single engine performance at gross weight. If the engines are de-rated, the gross weight will probably be reduced to a level that it would not be practical to operate the aircraft.

        • Greg W says

          My intention was to point out that operation at lower M.P. could allow operation on lower octane rated fuel, as has been done routinely in the past with the radial engines. Would performance go down?,yes. The airplane however would still be usable while the replacement fuel or ADI system or replacement engines were funded and installed. The point is with a paperwork change and operational change,(lower M.P.), the airplane would not just be sitting. An additional fuel stop may be needed because “full” fuel could not be carried at a possible lower gross weight at the reduced power. But would that not be preferable to just letting the airplane sit? Many, or most, light airplanes, single or twin, cannot fill the seats and the tanks at the same time.

  3. Andrew Briseno says

    I always try to be “practical”. I have to ask a very simple question. Why? We all know that there are far fewer hours being flown in aircraft that burn 100LL than there have historically have been. We all have to also recognize, unless we stupidly CHOOSE TO LIE TO OURSELVES that the extremely tiny contribution of pollutants into the world by aircraft that burn 100LL has no statistical impact on the Earth’s atmospheric lead pollution levels. Because of that, why are we spending so much time and energy coming up with a lead free Aviation Gasoline that is reducing the life of very expensive aircraft engines at a time when everyone is hurting for cash because of the Depression that has been in place since late during George W. Bush’s term; it has only gotten progressively worse.

    So again I ask, WHY? We must choose to not be volunteer idiots and argue for the only rational position: the elimination of 100LL aviation gasoline is a stupid, expensive and unnecessary exercise in politically correct idiocy. My two cents.

  4. Bob Jamieson says

    There is no mention of valve lubrication provided by TEL in this article. I ran autogas in my Cessna 150 with a Peterson STC and wiped out the valves. Do these alternatives provide adequate valve lubrication or will we have to revalve all our engines as older cars did when lead disappeared from autogas?

    • Ernie Ganas says

      There is no lubrication provided by TEL, that is an Old Wives Tale. Numerous studies including one where the FAA ran an Aero Commander 500 with on engine using 100LL and one engine using unleaded gas of the same octane. Engine teardown showed no difference in the valves or Valve guides

  5. Jim Hiatt says

    91/96 is not really an answer! The aircraft that burn 80% of the avgas are high performance working planes that require 100 octane. Sure, 80 % of the planes can burn 91/96, but the volume of gas they use is not enough to make 91/96 avgas a viable fuel. FBO’s will not invest the $150K ++ to carry two fuels, especially when one of them is only going to be 20% of the fuel sales.

    • Greg W says

      “The aircraft that burn 80% of the avgas are high performance working planes that require 100 octane.” While I agree in theory my own experience is that this number will get smaller each year. I worked at a part 135 airline that operated Beech 18’s, Piper Chieftains and Cessna 310’s today the airline is doing fine but they do not fly any piston aircraft. The 310’s may be flying somewhere but the twin beeches are sitting. What this means is the hundreds of gallons of 100LL that they used per day has been replace by jet A. A Cirrus running LOP or Beech G36 even running R.O.P. will not come close to replicating the fuel use of a R-985 @ 25gph cruise or R-1830 @ about 66gph at cruise. Add to that those users are twins,(Be-18,DC-3) so double the fuel use and it takes a lot of “big bore high performance engines” to replace a single old freighter that has been replaced by a turbine.

  6. Carl Froehlich says

    91/96 Avgas is the product available now, that rides on the huge automotive fuel market and infrastructure, and has a growing certification base with aircraft and engine manufacturers. 91/96 Avgas directly addresses the #1 threat to the average Joe General Aviation population – the cost of flying. Current estimates for all unleaded 100 octane drop in fuel replacements have a range of $0.50/gal to $1.00/gal price increase over the current sky high 100LL price. This means the singular focus by our aviation community champions for a drop in replacement miracle fuel for 100LL will only accelerate the general aviation death spiral.
    Time now for AOPA and EAA to promote FBOs deciding what their customers want – an economical 91/96 Avgas or an expensive specialty fuel that serves an ever shrinking customer base.

    • JLG says

      GA is on a death spiral not because of fuel, expense ect. It’s on a spiral because of people. Young men and woman do not find the joy or challange in flying these days. Blame it on video games or ???.
      To me it seems the generations born from the 70’s on are just not interested. I travel to many small town airports. Most of them are like ghost towns. The ones that go have somewhat of a crowd hanging around are pilots who do more prop polishing than flying. Shame. JG

  7. says

    Kent and Dean,

    In English, I’m a little “confused” by this article and the subsequent dialogue. I’m told by my Cessna FBO that they are seeing SHORTER TBOs from the burning of ethonol in today’s 100LL avgas. This apparently due to the residual byproduct of combusting biofuel in a piston engine, namely water and it’s corrosive effect on internal engine components. So, economics aside, how do you get HIGHER TBOs out of a newly overhauled engine like my O470U burning this new experimental fuel? Like Breaking Bad, isn’t it all in the chemistry? And if it is, what is in the “new” chemistry that replaces lead and yeilds equivalent performance while extending, not shortening, conventional piston aircraft engines like mine?

    • Stanley Stewart says

      The water in the bio fuel is a non-issue. Urban myth status. Fuels are hydrocarbons, which contain hydrogen, carbon and other combustables. You get approximately one gallon of water from every gallon of gasoline burned as a result of the hydrogen in the fuel combining with oxygen in the air and that becomes H2O, or water! This is why you see water dripping out of automobile exhaust systems for a few minutes after start up, the cold exhaust system condenses the water in the exhaust onto the cold parts. After warm up, the water evaporates and the combustion by product of water passes through the warm exhaust system without condensing. This is also why it is a bad idea to start and run an airplane engine on the ground without flying it to thorougly warm up the oil and evaporate out the H2O (water) that has condensed on the inside of the engine.

    • Michael Thurland says

      Rich, there is no mention of ethanol in the article, it talks about lead. There is no ethanol in Avgas 100LL. Also, even though the new Swift fuel can be based on biological sources, it has nothing to do with ethanol. Without lead in the new Avgas fuels, they say that “perhaps longer TBO times” may be expected, as lead has some negative effects (like fouling spark plugs and contaminating oil).

  8. Sarah A says

    There was no mention in this article but in past coverage they talked about the problem of having a propriatary formulation for the 100LL replacement. The refiners in the US were not interested in such a deal and wanted someting that was essentially “Open Source” like the rest of the fuel mixtures they refine. If out 100LL replacement is only available from one or two specialty sources what is the transportation cost going to add to the end user cost then. It is one thing to have a tanker truck bring fuel from a few hunderd miles but consider the cost when you have to ship it all they across the country. I am not sure if our small quantities would justify the use of pipelines for transportation over long distances.

    As Kent mentioned in his comment we already have the solution for 80% of the general aviation fleet. We just need to start getting alchol free Auto gas into more airports so it is commonly available. The rest will have to work out their own solution whatever that may be. It almost sounds like they want to use the 80% to help keep the cost down and assure a replacement for their own limited applications. At one time there was a very high octane blend generally refered to as 115/145 but that went away and the big engines adapted to what was available. Maybe it is time for history to repeat as we make another step down towards what is commonly (and reasonably) available in the auto fuel market.

    • Clint Newell says

      It’s my understanding that G100UL developed by GAMI doesn’t contain anything that isn’t currently inside the fence at any US refinery. Therefore, production would be possible at any refinery in the US that wanted to produce it.

      • John Mininger says

        It is my understanding that G100UL gets its high octane without TEL by using more higher grade aromatics. It’s also my understanding that currently at least; these higher grade aromatics are only produced in the quantity needed to produce G100UL at refineries which are currently refining 100LL.

    • ted says

      Sorry to rain on your parade but THEY as you call them, use 80% of all aviation fuel. If you didnt have the guys with the big engines, there wouldnt be enough use to even justify airports, much less fuel.

    • Stanley Stewart says

      If the contention that 80% of the GA fleet can burn alcohol free automotive fuel were a relevant fact, we would not have seen the elimination of the old 80-87 octane aviation gasoline, as a result of poor sales/usage. In real data, the 20% of the fleet that requires 100 octane performance fuel actually consumes 70-80% of the aviation fuel that is refined. By the way, 80-87 had up to 1/2 gram of lead per gallon, and 100LL has up to 2 grams of lead per gallon, depending on how much lead is needed to bring a batch of fuel up to the octane performance. In reality, most have less lead than the maximum allowed.

  9. says

    “In English: 100SF is a biofuel, made of renewable sources, such as sugars and starches.” This statement is patently untrue and Swift admits it. 100SF is NOT a biofuel. A precursor to one of the molecules can be acetone which can be made from bio-mass.

    Considering all of the hype about these two possible “drop in” replacements for 100 LL it is interesting to note that neither company is willing to speculate what the fuel is going to cost at the airport.

    • Ernie Ganas says

      I believe the GAMI folks have indicate less than 10 cents a gallon cost increase or even possibly a slight cost decrease since the special refinery tanks, lines and delivery vehicles used for 100LL will no longer be needed. Any refinery equipment that has lead in it contaminates the refinery equipment, tanks and lines which then have to be expensively cleaned before they can be used for lead free MOGAS. All of that will be unnecessary with the G100UL product.

  10. Kent Misegades says

    This problem has been solved. Over 80% of all piston aircraft can legally and safely burn 91+ AKI mogas, which is available in enormous volumes compared to Avgas and Jet-A. All one needs is to have the Avgas suppliers bring it to airports from terminals, which are far more plentiful than the handful of avgas producers. For the remaining 15%-20% for whom an STC does not exist, why not work through your type club to fund the STC testing at Petersen Aviation? For the very small group who still need a higher octane fuel, there is the INPULSE water-injection system, FAA-certified and proven on tens of thousands of aircraft in WWII.

    • says

      Kent, that is too logical and practical. Sorry, but there is no money in your solution. We need these other proprietary solutions that require an enormous investment to the supply chain where there will be lots of profit takers including the FAA who has a huge budget to spend on this “problem”. Sarcastic speaking of course.

    • Ernie Ganas says

      The problem is that the 20 percent that can’t use the european 91+gas (not certified in the US) buy 80 percent of the 100LL sold in the US and they create the infastructure for the aviation maintenance services and support that piston GA, their use helps make the services and support available to all of us. The INPULSE system make the assumption that you only need it during take off and climb and it isn’t cheap nor is the ADI fluid available unless you roll your own. Had a pilot on the field look at the system and he figured about 10-12K for the system and a dollar a gallon to the Mogas cost.

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