FAA: No Discernible Progress On Approving G100UL Avgas


Despite promising to issue a full STC for G100UL avgas in May, the FAA still hasn’t announced expanded approval for the fuel and the agency has declined to answer AVweb’s queries on when the approval process will be completed. General Aviation Modifications Inc. completed test work on G100UL and submitted the STC test package earlier this year. Recall that a limited number of engines were approved for G100UL last summer during AirVenture. The test package submitted in February would expand the number of engines under an Approved Model List to virtually all the powerplants in the GA fleet.

After the expanded STC application was submitted, the FAA ordered a Technical Advisory Board review of the certification work done by the Wichita Aircraft Certification Office. The TAB report wasn’t released by the FAA, but GAMI’s George Braly told us it appears not to call for additional testing but asks GAMI to provide so-called issue papers to explain detonation testing protocol, engine endurance testing, materials compatibility, hot weather operations and use of an independent fuel specification not recognized by ASTM. Braly said with the exception of an independent fuel specification, all of these areas were addressed in depth during the STC program under FAA-approved testing methods.

Although the 100LL avgas is refined to meet the industry standard ASTM D910, the FAA’s own guidance says an independent specification for fuels and oils is specifically allowed, Braly said. Further, language in the 2018 FAA Reauthorization Bill clearly allows fuels to be approved under STC.

Braly said the TAB also recommended that the GAMI project incorporate “lessons learned” in the FAA’s aborted Piston Aviation Fuels Initiative, which terminated in 2018 after concluding that the two fuels it had examined—one from Swift Fuels and one from Shell—weren’t suitable as drop-in replacements for 100LL. Shell has since stopped public work on a replacement fuel and Swift exited PAFI. PAFI’s findings, although supported with government funds, were not made public and thus weren’t available to GAMI during its fuel trials.

GAMI began work on G100UL in 2009 and was almost five years into the project when the FAA announced PAFI in 2014. The agency invited GAMI to join the PAFI program but the company declined because the program didn’t allow changes to fuel blends to meet test requirements during the program and because the FAA refused to credit GAMI for test work it had done in the four years prior to PAFI’s establishment.

When we asked the FAA about the TAB’s recommendation for issue papers on FAA-approved testing already done, the FAA declined to provide any details. “We do not comment on ongoing certification projects. The FAA has approved unleaded fuel for use in some aircraft. The agency continues to work with the general aviation industry and fuel suppliers to develop and test additional unleaded fuel options,” an FAA spokesperson said.

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  1. Can’t help but wonder:
    * Is there still some small issue / concern that GAMI (a private company) won’t publicly disclose.
    * Some small issue / concern the FAA (the bureaucracy) can’t disclose.
    Not exactly some greenie-weenie but I’m all for get’n da lead out for a whole bunch of reasons. Is it lead that causes stuck exhaust valves? Just dealt with a scary encounter regards that.

    • Yes, stuck exhaust valves, burned exhaust valves, cylinder scoring, ring wear, valve guide wear, valve rotator failure, etc…
      Lead is about the worse thing you can use in fuel for octane boosting due to the damage it does.

      • When lead was first used in ICE engines (I’m sure before you were born) its primary function was to lubricate the valves. But they discovered that the lead also boosted the octane of the fuel. They hadn’t planned on that. But times have changed and now lead is the villain. When 100LL first came out it WAS the cause lots of problems with valves. It was the lack of lead that caused the problems. Just trying to bring you up to speed on history.

        • Randy, sorry that’s not exactly correct. Tetraethyl lead ,Pb(C2H5)4, is an organometallic compound, and as such is NOT a lubricant of any kind. If anything, it may be slightly abrasive. It was introduced in the 1920s SOLELY as a detonation preventative measure. It turns out the chemistry MAY have some capability to prevent the formation of “micro-welds” on soft valve seats and faces, but that isn’t settled science. The “valve recession” problems of the early 1970s were a result of the loss of octane, and subsequent higher internal cylinder pressures, not a loss of “lubrication” from the lack of TEL. Getting the TEL out of avgas, but retaining the same octane performance, will result in transparent useage to the engine, other than it will be cleaner.

          • “The “valve recession” problems of the early 1970s were a result of the loss of octane, and subsequent higher internal cylinder pressures, not a loss of “lubrication” from the lack of TEL.”

            Absent any detonation, are you suggesting that a reduced octane level inherently increases combustion chamber pressure?

        • If you re-read the history of tetra-ethyl lead, you’ll find that its discovery was as an octane booster right from the start.

          But that’s all it does. Everything else about lead is a problem in an engine. In fact, gasoline has additional additives to get rid of lead once it’s finished with its job of boosting octane. It was never a ‘valve lubricant’. In fact, it contributes to valve deposits and problems.

          Airplane engines have always used hardened valve seats. So lead had no ‘cushioning’ benefit there, either.

          If there were anecdotal reports of valve problems when 100LL was introduced, it was likely in aircraft that were designed to burn 80/87 and now were using a fuel (100LL) that had four times as much lead. It wasn’t the lack of lead, it was too much lead leading to deposits and valve problems.

          Most importantly – none of this information is ‘new’. Even in the 1920s when lead was first used to boost octane all of these problems were common knowledge in the scientific and engineering communities.

          • Exactly. And one of the reasons for the “valve lubrication” Myth is because supposed “experts” such as Ben Visser repeatedly trumpeted that nonsense in publications such GAN. After a decade of objections from readers he has apparently abandoned that B.S.

  2. Why bother waiting for people who clearly are incapable of doing their high-paying jobs at our expense? All these questions were answered in the early 80s when the EAA gained approval for Mogas in its C150 and then over the decades by Peterson with their dozens of Mogas STCs. I wrote for the EAA and GA News on this topic for several years and was able to interview EAA Mogas team members as well as Paul Poberezny and Todd Peterson. All confirmed that the FAA opposed Mogas and they placed tougher testing requirements for the STCs than on the avgas, engine and airframe manufacturers. Yet the Mogas STCs have had a stellar record of safe, lower-cost, lead-free use. The world’s largest airframe and engine makers, Tecnam and Rotax, have a policy that all products run on Mogas. It’s time to nullify (ignore) incompetence in the federal government and just do what’s right. The aviation alphabets including the EAA have failed miserably for lack of leadership and defiance of the obviously incapable, unelected bureaucrats of the FAA.

    • Hmm – could people take up a collection to pay Braly for the formula, so he can retire (he’s getting rather long in the face 😉 then each make it themselves?
      Like moonshine?

      Albeit documenting experience would not be possible.

      • Oh! my g,d,r did not appear as I put it in chevron brackets which causes HTML to ignore it.

        Well, if use is allowed under an STC, which these days can have a long list of allowed uses (GAMI 100NL has an Approved Model List but so far only few models on it) then experience can be documented.

        Or is the problem FAA refusal to expand the AML? Have I lost the picture?

        The approved Flight Manual Supplement does detail higher density of G100UL than 100LL – 4.167%, even to the detail of instructing to increase unusable fuel amount by 4%. And it instructs on different color including when mixed with 100LL.

        • Well, the SG is higher, but what is the actual energy density? What is the stoichiometric mixture compared to 100LL?

          • Approved FMS says use existing manuals data for performance including fuel flow, but G100UL has higher energy density than 100LL by 1-2% so may have slightly lower fuel flow. Effectively saying it is better but use existing data to be safe.

            gami com for details.

    • Since when are “unelected bureaucrats” more reliable than “elected” ones that are stooges for lobbyists? I trust the judgement better of those whose opinions are not influenced by monied interests.

      • They may not be any more reliable, but they are easier to fire. They messed up when they limited the number of representatives to 435. Everyone should know someone who knows their representative. I say they messed up, but of course it was the voters messing up by letting them get away with it.

  3. It is like a toilet that will not flush. Just keeps spinning ‘ round ‘n round.
    The FAA and its TAB team will embellish this until either GAMI drops out or is turned down completely. Then the FAA will drag this out until 2030 and folks will ultimately end up with a forced engine / aircraft modifications deal, for a non STC’d , but rather an FAA / EPA / Government / Congressional mandate of some magical lead free fuel blend .

    • “It is like a toilet that will not flush.”

      What an apt analogy! One wonders if it is the “product” (Mogas) that causes the problem–the “paper” (money)–or the design (FAA inablilty to take action).

  4. Meanwhile, it appears politicians have managed to stall or possibly halt altogether) the part 13 investigation with Santa Clara County (RHV/E16). It’s been crickets chirping for 2+ months with no communication of status and continued harm occurring to business and pilots at those airports.

  5. I saw an interview with the president of Lycoming shot at AirVenture. He said due the problems with lead causing damage to engines and then not making it to TBO, Lycoming is 100% behind getting the lead out.
    They not only want their engines to making to TBO, but they would also like to extend the TBO times. WIth 100LL that will never happen

  6. “provide so-called issue papers to explain detonation testing protocol, engine endurance testing, materials compatibility, hot weather operations and use of an independent fuel specification not recognized by ASTM.”
    This is precisely why feet are dragging. Impartial, independent consensus standards (like ASTM) are useful to the certification process and provide the FAA with a better understanding of the testing used and the goals expected. In the absence of such standards, the applicant must shoulder the burden of IPs to address what is missing-or unknown.

  7. Perhaps it is time for AvWeb to make a FOIA request for the bits that the FAA will not disclose……..

      • HA! No, it’s Pete’s fault. Those idiots want all electric planes. Oh wait, no range and jets don’t run on electricity Pete. Who cares, we don’t need to travel. That’s only for rich elites.

  8. If you thought the FAA was bad before, wait until we get Biden’s new appointment. The guy can’t even fly a paper airplane. Like any Government agency, we’re getting gipped on our tax money. Need new leadership at all levels.

  9. I’m not close this at all but I wonder if GAMI’s refusal to join the FAA sponsored PAFI thing back in 2014 is coming back to bite them. Perhaps the FAA is saying “we’ll show you not to join our government program.”

    • Kurt, there is a fair amount of “not invented here” at play, but there are also a few folks in the FAA with an axe to grind and malicious intent stemming from events that predate PAFI. Some of those individuals have been reprimanded more than once for their interference, but still manage to gum up the works through the whisper network.

  10. Follow the money. Someone somewhere is paying lawyers to fight this sub rosa. Big Oil? Who really knows but its fairly obvious in my not so humble opinion that there is a money trail.

    • Having worked in refining for a career I can assure you avgas is just a blip on the radar for big oil. Not worth their time to fight it. If somehow 100UL made it uneconomic for them they would just blend it into the mogas pool and not make it.

      Maybe the company that makes the TEL but I doubt they have that much influence.

      • I can confirm this. They really, really, do not care. I’m not saying they only make the stuff out of charity, it’s something more like they do it out of habit.

  11. This is what I think is happening here: No one at the FAA wants to be blamed if one plane has trouble in flight with G100UL. Put another way, this is a massive CYA maneuver by members of the FAA. It is not good enough for the FAA that G100UL has been tested to the nth degree already. What is important to the FAA is that they have all the paper in place to prove everyone at the FAA did their job. No scapegoats. This has nothing to do with solving the problem. It has everything to do with protecting the FAA from future problems.

  12. Do not be fooled. The FAA is dragging its feet, knowing that the EPA is immanent of declaring 100LL illegal. The entire GA piston fleet will grounded. The FAA is the enemy of GA.

  13. “GAMI began work on G100UL in 2009 and was almost five years into the project when the FAA announced PAFI in 2014. The agency invited GAMI to join the PAFI program but the company declined because the program didn’t allow changes to fuel blends to meet test requirements during the program and because the FAA refused to credit GAMI for test work it had done in the four years prior to PAFI’s establishment.”

    THIRTEEN YEARS OF TRYING TO GET GOVERNMENTAL APPROVAL! It’s a good thing these people weren’t around in WW II–WE WENT FROM BIPLANES TO JETS IN 5 YEARS–mobilized the entire country–built the plants to produce what was needed for the war–trained the workers to produce the products, trained the military–built military bases in places that nobody had even HEARD OF, deployed the products around the world……..(but then, one of the first things they did was suspend the normal government rules and “protection.”–sarcasm)

    • I retired from Lockheed. One time a crusty engineer was complaining about being behind schedule. Due to bureaucracy. He jumped up and said “GD. Lockheed designed, built and delivered 10,000 P38’s in four years. If we had been working under the policies and procedures of today the last one would still not be delivered yet.”

      It was better to follow policies and procedures and fail than to achieve while not following policies and procedures.

      • THIS is the best that Government can come up with?

        Social Security take 15% of the national payroll (7.65% from BOTH the employer and employee)–yet is always broke–even though they pay a piddling amount for retirement. A private company with that poor return on investment would be investigated for fraud.

        Medicare–same thing.—but WORSE. Take “contributions” from workers and employers–and deliver a substandard “product”.

        If you WANT mandated retirement and medical care, go ahead and mandate it–just leave the option to buy what you NEED from the private sector instead of forcing us to buy a substandard “one size fits all” from the government.

        “National Defense”–a paragon of “government efficiency?” You’ve obviously not spent time in the military!

        Let’s face it–government ought to be a “last resort” if there are no private markets that will accept the risk. It used to be said that “the business of government is to defend the borders and deliver the mail”–we found out how efficient the Post Office is compared to the private sector–that leaves “Defend the Border” as being questionable as well! (smile)

  14. Has anyone, EVER, done a scientific study as to exactly WHY premium mogas won’t work? Cut the emotional hype and BS, just the facts please.

    I’ve heard something, decades ago, about vapor pressure and vapor lock in fuel lines. If that’s all it is, a simple fuel pump near the tank would’ve solved it.

    Bertorelli? Berge? Anyone?

    • Vapor pressure is certainly an issue, but it isn’t the biggest one. The biggest problem with premium mogas is that the octane rating is just too low for the 8.5:1 and higher compression ratio engines to operate without detonation. Unlike car engines that operate at higher RPM and have smaller combustion chambers, the ~260+ HP aircraft engiens really need 100 Motor octane. Premium mogas is a 91-93 (R+M)/2 octane rating, which coorelates to about a ~86 Motor octane rating.

      • Most of that issue is the crappy cylinder head design, not the engine speeds. My twin-turbo will get double-digit boost at low RPM, no knocking.
        Ethanol is another issue; it’s everywhere, and it adds a few points of antiknock, and some parts in older planes don’t like it.

    • Octane is the issue with mogas. In higher output engines, it will detonate. No additional study is needed. This is a fact. Distribution is a secondary issue. Only about 100 airports have it now and getting more of it out there has been daunting because buyers aren’t demanding it and some airports are constrained by exclusive supply contracts with avgas suppliers.

      UL94 is also an option, but very limited distribution of that. Still wouldn’t serve the high compression engines.

      • “Still wouldn’t serve the high compression engines.”

        Just to expand on this point a bit – while roughly 70% of the fleet can burn mogas, they only account for 30% of fuel sales. The 30% of the fleet that requires 100-octane fuel is mainly a working fleet, flying far more hours at higher burn rates. They account for 70% of fuel sales.

        In effect, a mogas solution only solves 30% of the problem.

      • Jethro,
        I couldn’t reply to you in the thread above (too many nested replies, maybe?) I probably could have worded what I said better. The lower octane didn’t cause higher ICPs inherently, but did lead to constant low levels of detonation in the late 60s high compression auto engines. Very low levels of detonation aren’t inherently bad, and may have a slight cleaning effect on the combustion chamber, but like a slow drip on a rock causes eventual erosion, so very low levels of detonation caused recession of the valves in to the seats. The solution was two-fold. 1) harden the seats to resist the recession and 2) lower the compression ratio. The mid-70s “malaise-era” cars did both and the problems went away. Later developments such as unique piston dome and combustion shapes, knock sensed timing, and direct injection at just the right time have allowed cars to bump the compressions back up.

  15. I was told that the oil companies don’t even refer to Avgas as “gasoline”, instead it is considered a specialty chemical. I would suggest that their GAF over the future of Avgas is not high.

    Whatever is easiest and cheapest is the way they will go which is why when the dust settles they will just make UL94, that is 100LL without the TEL. No change required to make or distribute = easy.

    The fact that some airplanes can’t use it is irrelevant to them other than total volumes will go down which means distribution will be reduced to higher demand areas.

    Of note the 2 highest profile users are the big airline puppy mills flight schools pretty much all of which use airplanes that can use 94UL and Alaska which is full of 80 octane Supercubs, Cessna 180’s and Beavers.

    Since there is no minimum safe level of lead in the environment, I think it will be banned soon, certainly before 2030

    • If you’re referring to leaded 100-octane (i.e.100LL) fuel, then no, no one wants a leaded fuel. Lead is bad for the engines (other than the octane boost it provides), it is bad for the environment, it is bad for humans, and it’s a logistic nightmare to keep it fully separated from all fuels that are not 100LL. These are all undisputed facts.

      The only thing 100LL appears good for is for the FAA to receive government funding for a program that has been rendered obsolete from the start by private industries (and not even Capitalism, because I presume GAMI and Swift have not earned any appreciable income from their programs).

  16. I remember that, back when UL fuel was mandated for autos beginning in 1975, I almost immediately began encountering current-model cars having valve-burning issues on fairly low-mileage engines (I owned and operated a car repair shop at the time). So, when the switch was made to UL fuel, some manufacturers had obviously not adequately prepared their products for the change. But, back then, spark plugs only lasted for 12000 miles, and oil had to changed way more often. Engines ran very dirty on leaded gas. Now, with high-voltage electronic ignition, lead-free gas, more exotic materials used in spark plug electrodes (platinum, iridium, etc.), spark plugs routinely last 100000 miles, and oil change intervals have been extended. Our automotive fleet has been fully adapted to unleaded fuel, and there is almost no downside to the use of it. As long as our aircraft engines can mechanically withstand the elimination of lead, the change is LONG overdue.

  17. Take the lead OUT of ordinary AvGas and let those of us who can use that do so. Let the big monied guys with the big airplane engines pay for this argument.

    • Yeah, that’s just about as fair as they next move where they take your access to fly leaving your airplane on the ground with all the other cars, rich guy. Really, who “needs” an airplane.

  18. Great idea! Produce avgas without lead–a product MOST can use–and put a “lead dispenser” on the pumps at a higher price for those who need it and are willing to pay the premium.

    Eliminates the vagaries of “what kind of product are we REALLY getting from the local gas station” (and “how was it handled?”) and it puts this entire issue to bed.

    The amount of lead in the atmosphere is reduced, and certified fuel is available almost anywhere. Best of all, we can stop the arguing and “virtue signaling.”

  19. Yet another program. Insanity: dong the same thing over again and expecting a different result.

  20. “We do not comment on ongoing certification projects.”

    What?! Like it’s some DOJ criminal investigation? I’m weary from hearing bureaucrats across our government using this excuse to do whatever they want in secret.

    Is all this secret conversation within the FAA subject to a FOIA request?