Future Fuels

How regulatory issues affect fuel supply.


Here’s the good news: The industry is stumbling slowly forward with an unleaded replacement for avgas, and in the interim, the 100LL supply remains stable.

Builders of Experimental aircraft and owners of certified airplanes have widely different reasons for owning what they own, but they share one common worry: future fuel availability. An assured supply of 100LL avgas looks promising for the short term, but less so when the timeline is stretched to 10 years or more.

Avgas faces threats on three fronts: direct environmental regulation by the federal government, court challenges at the federal and state levels and the economic reality that refiners are selling it into a declining market.

The industry has finally accepted that 100LL has to go; it’s just a question of when and what will replace it. The FAA has stood up and is funding a working group to manage the regulatory framework to usher approved, unleaded aviation fuels into the market. In this article, we’ll outline the basic regulatory issues, and, in a follow-up piece, we’ll examine some of the replacement fuel candidates.

The bright spot in all of this is that builders of Experimental aircraft are better placed to make both long- and short-term buying decisions with fuel in mind. While owners of certified aircraft are stuck with the engines they have, builders have choices in engines, many of which don’t require 100-octane fuel and some of which are approved for mogas.

There’s a long list of STCs for Lycoming four- and six-cylinder engines approved for mogas; the Rotax models—including the new 912 iS—are also approved to burn either leaded avgas or unleaded automotive fuel. While the STCs for conventional-aircraft engines allow only unleaded fuel without ethanol as an additive, the Rotax series engines can burn automotive fuel with up to 10% ethanol content. More on that later.

Surprisingly, the majority of aircraft engines don’t require 100 octane, but the minority that do—such as this Mooney 231—burn at least 60% of the 100LL sold in the U.S.

A Long History

The reality is that leaded aviation fuel has been threatened since the first iteration of the Clean Air Act in 1970 called for the phasing out of tetraethyl lead as an octane enhancer in all fuels. Today, only a few countries allow leaded automotive fuels, and these are likely to phase it out over the next decade. But aviation enjoyed—and still enjoys—an exemption from this trend because so many engines in the industry require 100-octane fuel, and because the FAA has pitched this as a safety issue, regulators have cast a blind eye on leaded avgas. In terms of total fuel volume in the U.S., it represents less than 1% of all gasoline burned; for three decades, it has slipped under the radar.

But four years ago, the pressure on leaded avgas emerged anew when the EPA announced that proposed lower airborne lead standards might require sharp reductions in allowable lead emissions. Unfortunately, according to the EPA, 45% of all airborne lead emissions in the U.S. come from aircraft burning leaded fuels. To put it bluntly, regulators view aviation as an easy-to-pluck juicy plum that would reduce airborne lead by nearly half, all from a single industry.

Dual-fuel systems for 100LL and Jet A are common at many airports. But FBOs say that the economics of dual-fuel for pistons, say 91-octane and 100-octane options, are a non-starter because of capital and maintenance costs.

Leaded aviation fuel has persisted for one compelling reason: As an industrial compound supremely suited to a single purpose, tetraethyl lead is very much a victim of its own success. Testing and research extending back to the 1920s and accelerated during WW-II revealed that of thousands of compounds tested, TEL was uncommonly effective as an octane enhancer. But it also proved to be highly toxic and difficult to handle safely.

Avgas Threat and Replacement: The Timeline.

Although TEL remained the additive of choice for aviation fuel, by 1970, the first iteration of the Clean Air Act targeted TEL as a bad actor to be eliminated. The real push wasn’t so much about the lead itself as its tendency to foul the catalytic converters that were then coming into the automotive market as a means of reducing overall emissions.

The aviation fuels market was exempted from EPA’s regulatory efforts because the industry convinced regulators that there was no practical substitute for TEL. It promised regulators to carry out research to find a replacement, but nothing meaningful was accomplished.

The good news these days is that almost all fuel installations are above ground, meaning they’re cheaper to install if airports want mogas.

Market conditions, not EPA regulation, actually forced the use of less TEL. For one thing, flight activity has declined steadily since the late 1970s, and for another, the high-lead 115/145 fuel used by the airlines and military was phased out as jets came into wider use. A lower-octane fuel, 80/87, also vanished from the market, a victim of distribution economics as refiners and FBOs found no profit or economy in a two-fuel market. Thus was born 100LL, which delivers just enough octane for the highest-performing engine, albeit more than lower powerplants require. At 2.0 grams of TEL per gallon, 100LL represented a compromise product that served a declining market well enough. It wasn’t a perfect compromise, however. The U.S. has a substantial fleet of warbirds whose turbocharged or turbocompound engines require higher octane. Those engines can operate on 100LL, but only at reduced power settings. Moreover, in an engine that doesn’t require 100-octane fuel, the excess lead in 100LL can become a maintenance nuisance, fouling plugs and trashing crankcases with accumulated lead salts.

Fielding a 100LL replacement isn’t as simple as it seems. To be a near drop-in replacement, specs such as fuel color, compatibility with existing aircraft and FBO pump systems and miscibility have to be well proven before the fuel is approved.

The aviation-piston fuel market remained in stasis until about 1990, when the EPA again got serious about lowering lead emissions. The aviation industry and the FAA pursued research on some 245 possible fuel blends, according to the FAA, but none met the performance qualities of 100LL.

The pressure on 100LL slowly ramped up with the 2006 petition by Friends of the Earth to force the EPA to regulate lower lead standards it already had in place. The EPA itself also issued an update to the National Ambient Air Quality standards for lead. This new standard was adopted in 2008 in response to a court order, requires a tenfold reduction in lead emissions by 2017. Allowable airborne lead content must be reduced from 1,500 nanograms/cubic meter to 150 nanograms/cubic meter.

In the interim, the EPA required the states to set up monitoring programs to both determine their lead emission levels and show where so-called “non-attainment” areas might exist. These requirements specifically included monitors near airports, something that worries groups like AOPA, EAA and GAMA, which are concerned that data showing significant non-attainment of lead emissions standards might result in state or local regulations banning leaded fuel from specific airports. The regional monitoring data hasn’t been released yet, according to GAMA, so we don’t yet know what it will show.

In a parallel project not directly related to the new air-quality requirements, EPA is also conducting what it calls a “finding of endangerment investigation” in response to the Friends of the Earth petition and a formal lawsuit filed in March 2012; FOTE is seeking to have the EPA move more quickly toward a finding of endangerment and a proposed rule to reduce lead emissions.

Meanwhile, in another separate action, a California-based environmental group, Center for Environmental Health, has filed a lawsuit of its own under California’s Proposition 65, otherwise known as the Safe Drinking Water and Toxic Enforcement Act. Unique to California, the law allows plaintiffs 25% of any settlement they’re able to negotiate with the defendant, in this case a group of FBOs selling avgas in the state.

The CEH, which specializes in environmental lead issues, has settled almost all of its suits and reaped cash rewards as a result. The targeted FBO coalition, however, appears not to be in a mood to settle. It countersued CEH, and even though negotiations are still alive, no one is willing to predict an outcome. Although the worst-case scenario is a settlement that prohibits leaded avgas sales in California, this seems unlikely because CEH would have to demonstrate specific damage caused by leaded fuel sales, something that might require an actual trial. If the FBO coalition doesn’t agree to a settlement, a protracted court fight might result.

Although a 100LL replacement won’t necessarily be a seamless drop-in, it also shouldn’t require replacing old fuel systems with new ones.

FAA Action

For the past three decades, the FAA has been marginally involved in finding a replacement aviation fuel. It has committed resources at its William T. Hughes Technical Center in Atlantic City, New Jersey, and the private-sector Coordinating Research Council oversaw tests of many trial fuels, none of which showed much promise. In the absence of pressure from the EPA on lead emissions, the FAA and private-sector efforts lacked urgency.

That changed in 2008 and 2010, when Friends of the Earth ramped up administrative, and later legal, pressure. In parallel, the EPA began sending representatives to general aviation events to explain the potential ramifications of the new air quality standards on lead emissions. At the same time, two high-profile potential replacement fuel projects emerged, Swift Enterprise’s Swift Fuel and General Aviation Modification, Inc.’s G100UL.

Even if 100LL replacements use the same equipment, their chemical properties will be different.

Responding to pressure from both users and the alphabet groups, the FAA in early 2011 chartered the Unleaded Avgas Transition Aviation Rulemaking Committee or UAT-ARC. This group included representatives from the FAA, EPA, the aviation alphabets, engine and airframe manufacturers, companies developing fuels and trade groups such as the American Petroleum Institute, representing refiners as a group. The oil companies, including Shell, Exxon, Chevron and BP, sent their own representatives.

The UAT-ARC has specific marching orders. It wasn’t tasked to propose or find a fuel, but to develop a framework—including testing and regulatory approval—to give the industry a clear path to develop its own alternatives. In early 2012, the committee made its recommendations, and though these hardly seem to either clarify or accelerate the process of finding a new fuel, they at least give the industry something to work with. Lycoming General Manager Michael Kraft, who served on the committee, called the results meaningful progress. “What it does is to give anyone coming to market with a fuel a risk-management plan,” Kraft said. “Nobody’s willing to make the investment if they can’t see the return.”

Specifically, the UAT-ARC devised what it calls a roadmap to a replacement fuel. This sets out avgas readiness levels, essentially a series of 16 hoops through which any candidate fuel must pass on the way to being certified for use. It further recommends centralized testing of all proposed replacements at the Hughes Technical Center in Atlantic City, funded by both FAA and industry in-kind money. There will also be a review board to qualify the feasibility of fuels before they enter the testing process and a collaborative industry-government initiative called the Piston Aviation Fuel Initiative to follow through on the ARC’s recommendations.

The timeline is hardly what anyone would consider short. The UAT-ARC recommended a maximum timeline of 11 years from the date its final recommendations are accepted, or 2023—five years past the EPA’s deadline for new lead emissions standards. However, industry sources say that 11 years is viewed as the longest window in which all fuels might emerge as solutions. Approved fuels may—and probably will—surface well ahead of that deadline, but whether they can be brought to market before the 2017 EPA deadline is anyone’s guess. According to the FAA’s proposed budget planning, the majority of the funding will be spent between two and five years into the program. The UAT-ARC, by the way, has no charter to develop marketing or distribution methods, but only to provide the industry with a means to develop these on its own.

Not so long ago, the price posted on this truck was common throughout the U.S.; now it’s more than double that, although availability and distribution continues to be good.

Interim Supply

The UAT-ARC is not charged with assuring continued supplies of 100LL until the replacement or replacements surface. But none of the sources interviewed said there’s any obvious short-term threat to 100LL availability, other than routine distribution shortfalls related to refiner scheduling and shipping that have occurred in the past.

“I think this [UAT-ARC] is a recommendation to address a future product in a sensible way. I don’t see it impacting supply at all,” said Prentiss Searles, who represented the American Petroleum Institute on the fuel committee. Although 100LL is a declining-volume product for refiners, it’s also a high-margin one, and as long as the products remain profitable, industry providers say it will remain available, though at what price is another matter. It is true that TEL comes from a single source in the United Kingdom, but no one we spoke to would say this represents a potential 100LL supply problem if TEL becomes unavailable.

As for potential 100LL replacements, we’ll cover that in the next article. At least two have proved to meet octane requirements, but volume pricing of these fuels remains a question. Lycoming’s Kraft says that with the ARC’s framework in place and a solid foundation on which to build, he wouldn’t be surprised if more candidate fuels emerge, possibly from the oil companies themselves.

It’s not impossible that a lower-octane certified unleaded fuel could emerge in some local markets. That’s what’s happening in Europe with Total’s UL91, which is slowly making inroads in Europe and the United Kingdom; UL91 is essentially the same alkylate base stock used to make 100LL, but without the lead. In the U.S., there are also efforts underway to increase the availability of non-ethanol high-octane auto fuel on airports. We’ll look at that in the next article as well.

Meanwhile, for anyone hesitant about purchasing an engine for a project airplane, the timeline is still too long to predict what will happen in the fuel market over the next five years. If you’re really unsettled by this, it might make sense to use an engine with auto-fuel approval. There are enough to pick from, and it looks like the fuel may become more widely available. And even if it doesn’t, an approved aviation fuel suitable for all octane requirements probably will be available, possibly within three to five years.


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