By Paul Millner
Oh no! I can hear you thinking. Not another article about unleaded avgas. Haven’t we been hearing about this “coming soon” since the Reagan administration?
Well, yes. Lead was phased out of mogas (automotive gasoline) in the 1980s and early ’90s because of environmental toxicity and its adverse impact on catalytic converters. At the time, the industry wasn’t sure how to meet all the requirements for a safe aviation fuel and achieve the 100-aviation octane required for avgas without lead. (That would equate to a 105-pump octane at your corner service station.) So, the industry launched the Coordinating Research Council (CRC) Unleaded Avgas Development Group in 1991. That group of oil companies, aviation companies, the FAA, and alphabet groups like AOPA worked hard for 20 years looking for a solution that, other than lead content, would meet the existing avgas specification.
Unfortunately, no easy answer was identified. The FAA then launched the Unleaded Avgas Transition Aviation Rulemaking Committee (UAT ARC), which in turn, produced PAFI (Piston Aviation Fuels Initiative) phases one and two, and now has announced EAGLE (Eliminate Aviation Gasoline Lead Emissions). Let’s look at the pillars of EAGLE to better understand the challenge of unleaded avgas.
Develop unleaded fuel
To understand the 100 unleaded avgas challenge, you need to understand a little bit about avgas formulation (put on the lab coats). Generally, avgas has four components: aviation alkylate for octane and energy, light ends for vapor pressure to assist winter starting, aromatics for octane, and an octane booster to get the octane to the 100 specification. For leaded avgas, that booster is lead. For the unleaded avgas candidates, the proposed solutions vary.
The solutions proposed by the five contenders for a new formulation affect the makeup of all but the light ends part of this formula: substitution of novel aromatics and octane boosters compared to the components we’ve been using for the past 90 years in avgas, and tightened quality requirements on aviation alkylate for some of the formulations.
These are not minor changes—these are major reformulations of avgas. Fortunately, most of the hard work is already behind us: aside from the Shell fuel that has been sidelined, the formulations appear not to adversely interact with materials in either our aircraft or our engines; they offer the same or better detonation protection in operation than the existing 100LL; and the manufacturing and handling issues appear to be tractable. But it’s not sufficient for these issues to appear to be solved, they must be proven to be solved to the FAA and industry’s satisfaction, and that’s what is taking the time right now.
The next steps involve determining who and where the new fuel(s) will be produced, and how the existing distribution infrastructure can be adapted or augmented to get these fuels to market. None of these are horribly difficult processes, but they occur stepwise, and require time and resources. For instance, it’s difficult to convince a major oil company to commit to producing an unleaded fuel until that fuel is FAA approved, and there is some operating experience to define any possible requirements that may differ from 100LL. Once there is a commitment, facilities must be dedicated and/or modified to blend the fuel, fuel component supply chains have to be established, and initial operating experiences have to be validated to assure there are no surprises in the product integrity of avgas.
The most hopeful sign from the most recent initiative, EAGLE, is that it is timeframe focused, 2030 or before. All involved hope that before is much before 2030. Up until now, the focus has been on achieving the goal, not on when the goal will be achieved. We’re far enough along now to focus on that finish line. Stay tuned as we keep you updated on developments, and what positive benefits you might expect from the new fuel aside from the environmental improvement.
Paul Millner, a pilot and co-founder of the Cardinal Flyers type club, spent 38 years as an engineer for a major oil company, where he directed unleaded avgas development efforts for a decade.