G100UL vs avgas
7 min read

The FAA has granted an STC to GAMI allowing use of its new lead-free avgas formulation in all piston engines. That seems like a slam dunk win for lead-free fuel, something that has eluded general aviation for decades.

But there is at least one precedent of how an STC for a vital piston engine fluid can go wrong.

In the early 1980s the general aviation business was flat on its back. Deliveries of new airplanes had plunged from nearly 18,000 in 1979 to a handful in just two or three years. All the major piston airplane makers went bankrupt, or changed ownership, or both. Add to that interest rates topping 18 percent and one of the deepest recessions in many years, and one can understand how the entire GA industry was on the ropes.

Phillips oil

Believe it or not, multi-weight oil was once scorned by the FAA.

Phillips Petroleum was, however, one of a handful of companies still working to improve piston engine flying. In the mid-1970s Phillips created the first successful multi-weight airplane piston engine oil, named Cross Country oil, or X/C for short.

Phillips had pioneered development of a multi-weight oil for diesel engines and determined the same chemical technology that held up to the high lubricating stress of a diesel would also perform in the harsh conditions of an air-cooled piston engine.

Cessna was the first X/C customer for use its newly manufactured airplanes. Often an airplane would be rolled out of the factory and complete its production test flights in one season—hot or cold weather—but not be flown away by the dealer or new owner before the weather changed. That meant the airplane had the wrong oil in the crankcase. Either lightweight oil if it was manufactured in winter, or heavy oil in the summer. The new X/C solved that problem.

Pilots who traveled in their piston airplanes had the same issue. For us in the Northeast, a winter trip to warm southern climes meant departing with lightweight winter oil in the engine that would be running out everywhere like water at the warm destination. X/C was the answer.

The Phillips chemical engineers soon realized that they could make a real anti-wear “package” to add to X/C that would, for the first time in an airplane engine, provide the type of wear protection that makes the 100,000 and many more mile auto engine durability routine.

The key to anti-wear lubrication is microscopic metal particles. Exactly how these bits of metal greatly reduce friction and wear between moving metal parts is beyond me. But those additives scare the bejabbers out of aircraft piston engine traditionalists. The reason for fear is that the minute metallic components of the oil could cling to parts of the combustion chamber where they heat up and cause preignition, which can quickly be fatal to any piston engine.

But Phillips engineers were confident their anti-wear package would not create any threat of preignition, but would, for the first time, actually reduce wear and extend air-cooled piston engine life. The problem was that under standard FAA practice only engine manufacturers can approve lubricants, and fuels for that matter, in their engines. But Continental and Lycoming were almost out of business and they didn’t have the staff or resources left to test the new X/C II and approve it. Phillips people told me at the time that they offered to reimburse the engine makes for the necessary testing, but no dice.

It looked like X/C II and its advanced anti-wear had no hope until somebody asked the FAA if it was possible to get an STC to use the oil. Nobody I knew had ever encountered an STC approval for an engine lubricant, but the FAA couldn’t come up with a reason for why not. Sound familiar to the recent approval of the GAMI lead-free fuel?

To log the necessary hours in use beyond test cell operation Phillips made an agreement with, as I recall, the University of Illinois. At the time the Illini had a long standing, very active, and well-regarded pilot degree program.

The testing went smoothly, X/C II performed very well, and the FAA granted Phillips an STC to use the oil in essentially all piston engines.

G100UL vs avgas

Do you need a new 337 every time you fill up with the new stuff?

Richard Collins immediately switched to X/C II from regular X/C in his Cessna P210 and I did, too, in the Mooney 201 I owned at the time. We both had excellent experience with the oil and it began to grow in popularity among pilots. Thinking back, it now seems odd that we didn’t have an STC document from Phillips certifying approval for the use of X/C II in our engines. I really didn’t think about.

But an FAA principal operations inspector (POI) in Kansas City did think about it. He demanded that a charter operator under his jurisdiction include the X/C II STC paperwork in their aircraft maintenance records and file a Form 337 as would be done for any modification under STC. That was doable.

What wasn’t workable is that this inspector, based on standard practice anytime a modification is performed under STC, required the operator to file a new Form 337 with the FAA at each oil change using X/C II. Get it? Replacing the oil was a new use of the STC. You can guess the next step. Right. A Form 337 every time a quart of X/C II was added between oil changes.

If you’ve had experience with the FAA you know that what people in Washington say doesn’t matter. It really doesn’t matter much what the leadership of the FAA Region you’re in says. It’s the individual FAA inspector you’re dealing with that matters. Yes, you can appeal to the FSDO brass, then the Region, and maybe even to Washington about the decision by the inspector in charge of your operation, but good luck with that. And it will take about forever to resolve.

Word of the interpretation of the X/C II oil regulation quickly spread. Charter operators who are under regular and direct inspection by POIs were scared away from the oil. Maintenance shops, who are also regulated by the FAA and FSDO, became cautious about the oil. Of course the whole thing rippled down to individual airplane owners who began to wonder about the approval and how to comply.

FAA headquarters was supportive of X/C II and there was no ban on the oil or retraction of the STC approval. But since oil didn’t fit into the traditional way all lubricants had been approved, the entire FAA apparatus couldn’t figure out how to interpret rules that just didn’t fit approval of a lubricant.

So X/C II, which held real promise for engine life improvement, died. Not because it didn’t perform, but because it didn’t fit.

What does this experience say about STC approval for avgas? The engine makers haven’t approved the new fuel just as they didn’t or couldn’t approve X/C II. It seems certain any airplane operator who wants to use the new fuel will need to incorporate the STC paperwork into the airplane maintenance records. But will that be enough? The X/C II disaster was a long time ago, but have the FAA rules changed enough?

And what about engine warranties? If you use a fuel not approved by an engine manufacturer does that void the warranty? If the engine has problems do you sue the engine maker or GAMI? As screwed up as our legal system is, it does seem to me that having refused to approve use of something as basic as fuel is a decent defense by the engine maker against liability.

I had forgotten about the X/C II episode until I saw the FAA make a 180-degree turn and issue the blanket STC for all piston engines to use GAMI lead-free avgas. Then it dawned on me: this was simply passive resistance by the FAA. You want an STC for that fuel, you got it. Good luck with that.

Mac McClellan
Latest posts by Mac McClellan (see all)
23 replies
  1. TomC
    TomC says:

    I fail to see how the GAMI STC, or the X/C II STC, is any different than the tired 87 octane MOGAS STC stickers currently residing on the wings of our club’s 150 and 182 aircraft.

    Reply
  2. Ron Cohen
    Ron Cohen says:

    Taking the lead out of fuel will ultimately prove disastrous for older engines which have rotating valves. The tetraethyl lead additive lubricates the rotating valves. All new automotive engines have non rotating valves with critical seals and clearances.

    Reply
    • Gene
      Gene says:

      You are wrong. The fuel has been approved for, I believe, all engines. And quite frankly, if you are flying a relic, go get some lead additive. Why make the rest of the world wait on you stepping up? This happened back in the early 80’s for boats too. People just bought a lead additive. You can fly but you can’t buy an additive????Get real

      Reply
      • Tony
        Tony says:

        I doubt that EPA will allow lead in anything, including additives, since it will still result in pollution outside of the engine itself (which is why all of the fuss over leaded fuels exists in the first place). You’d better buy a lot of additive, and store it in a very secure and secret place, and don’t get caught using it!

        Reply
      • D Neuf
        D Neuf says:

        Just another left-winger bringing our country down with their foolish environmentalism. Truly their religion.
        The miniscule amount of lead from a plane flying over every how often? You get real! Get your thumb out of your mouth.

        Reply
  3. Gene
    Gene says:

    Enough yappin’ about this stuff. It’s made, it’s been approved, now let’s get it into every airport selling fuel in the country. As far as I know, all manufacturers have approved it. It’s stuff like this that is making America a 3rd world country. With all the advances in technology and medicine, what kind of people are keeping this obvious advancement from happening? The STC fees are ridiculous. If a manufacturer says it’s approved, it’s approved. So, now we have to pay a fee to repeat it???? Maybe Bi-Den can get the taxpayers to cover that too. This is a joke. People need to step up and demand action or let’s fire them all.

    Reply
    • John
      John says:

      Calm down. Did you actually read the whole article? It said that none of the engine manufacturers have approved the fuel. The rest of the article was speculative: not so much about what has or will happen as about what may happen based on something that happened 40 years ago. I’d bet that the real impediment to getting into every airport in the country will be more about FBO’s being reluctant to spend the money to make the change unless the FAA or EPA forces them to. Then there’s production and transportation issue. All of this takes money and businesses may be reluctant to invest in something with a limited outlook for improved returns unless they’re required to do it. I’m not holding my breath.

      Reply
    • T-Mex
      T-Mex says:

      Great idea to fire them all, but it won’t ever happen. The ones making the rules are the ones in charge. They’re not about to throw away their cushy tax-paid jobs to please you or me.

      Reply
      • Guppycaptain
        Guppycaptain says:

        It’s obviously not just a cushy tax-paid job when they go into Congress and the Senate poor, and are millionaires a few years later.

        Reply
    • Mac MCCLELLAN
      Mac MCCLELLAN says:

      Hi Gene,
      The problem is that approval of fuel and lubricants has been left up to the engine manufacturer throughout the history of certification. Makes sense. The engine maker’s approval is then adopted by the airframe maker and becomes part of the overall type certificate. Beech, for example, determined the proper torque for a wing bolt, and Continental and Lycoming determined what fuel is appropriate for their engines. Obvious, I think. No FAA skulduggery involved at all.
      So far the piston engine makers haven’t approved a lead-free avgas for all of their engines, particularly high compression high power models. Not the FAA’s fault.
      The STC process has been used to certify use of automotive gas (mogas) in many piston engines for decades. It works for those who go the extra mile to find suitable mogas, but it reinforces the fact that FBOs simply can’t afford to store and deliver a second type of avgas. Volume is everything, and avgas volume is tiny. That’s why avgas is priced so much higher than jet fuel at nearly all FBOs.
      My point in recalling the Phillips X/C story is simply to point out how unsatisfactory–not necessarily unsafe or unsuitable–the STC process is for certifying fuel and lubricants in any engine. Is an STC for lead-free fuel better than nothing? Maybe.
      Mac Mc

      Reply
  4. Terry
    Terry says:

    Hi Mac:

    I appreciate your fine articles over the years. I have some questions come to mind from this one. You refer to XC but then later mention XC II. My recollection is that the original XC had some problems with something (deposits)? It was withdrawn and then XC II was introduced and has been very successful. I use it in my Baron.

    Good points, however, about the certification basis and the silo effect regarding FSDO’s.

    Thank you

    Reply
    • Terry
      Terry says:

      Maybe I have my recollection wrong. Possibly it was XC II that was withdrawn. I remember hearing something about deposits (I don’t know if that was real or imagined). No matter I have been successfully using Phillips 20W-50 for many years now.

      Reply
  5. Stephen Phoenix
    Stephen Phoenix says:

    I recall that the Mobil Oil synthetic oil was a bigger problem and it was approved by all.

    FAA approvals work good, until they don’t work. In past times, a person could perfectly legally use 115/145 octane fuel in a Cessna 150. I’m here to tell ya that it didn’t work that great; way too much lead.
    Our uncontrolled legal system and the population that supports it does have a damping effect on the development of new products.

    Reply
  6. Bob Conard
    Bob Conard says:

    Your comment about flying down to southern climates with lightweight winter oil took me back about 50 years to climbing to altitude in our Beech Queen Air where the climb out would be controlled by cylinder head temperature instead of airspeed.

    Reply
  7. James T. Kirk
    James T. Kirk says:

    It’s kinda’ sad to read comments blaming Biden for the legal problems impacting every facet of our lives. Are any of you Trump lovers ever going to accept that your love-man tried to overthrow the Government of the USA? Lead-free aviation gas will be the least of your worries under a dictatorship. And, yes, I’m a veteran, an aircraft owner, and Pilot for over 50 years. I think this article should remain politically-free, but if you guys insist on polluting it with politics, Let’s go!

    Reply
    • S Johnson
      S Johnson says:

      It is a shame but politics is in everything now because a certain group gone beyond American fundamentals so it will not go away. As for me I am buying every electric extension cord I can so I can continue to fly X/C with my new electric airplane.

      Reply
    • RD Johnson
      RD Johnson says:

      I am so tempted to jump into this head first, but I will hold my breath and count to 10. Time will tell everyone the truth about this, the STCs, approvals, the future of the FAA, the EPA, and Politics. Funny how they are all (how we have allowed them to be) intertwined!

      Reply
  8. Greg F.
    Greg F. says:

    Thanks for the history lesson Mac, I really enjoy your writing. I believe there is significant interest on the part of the engine manufacturers in finding and approving an unleaded fuel for the piston aircraft fleet. The environmental pressure on the entire aviation world to eliminate lead emissions from aircraft is incredible, in fact it threatens the entire industry. Look at the effort and investment being poured into electrification of light aircraft, a solution that will remain over the horizon until energy storage is improved by orders of magnitude. Unleaded fuel will enable the fleet to fly for the next 30 years until a better solution is found.

    Reply
  9. Wild_Bill
    Wild_Bill says:

    I don’t know what the big fuss is all about. The EAA was selling Autogas STC”s for decades with nary a problem. That would have worked fine too, until the whole Ethanol stupidity kicked in. It probably would have been simpler and cheaper to get non-ethanol automotive fuels and just use that original STC. But here we are, Lauding the great advances in Aviation Fuel Science… Nothing really new under the sun.
    It is also entirely possible to remove the ethanol from mogas using a very easy process…

    Reply

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