For every complex problem,” the eminently quotable H.L. Mencken opined, “there is an easy answer that is clear, simple and wrong.”

So it could be said of the ongoing attempt to find an alternative to leaded aviation gasoline that can meet provisions of the Clean Air Act while still providing protection against detonation in high-compression piston engines. The magnitude of the necessity for a replacement can best be appreciated when one reflects on the fact that avgas — now available in only one grade, 100 low lead (LL) — remains the sole transportation fuel in the U.S. still containing lead. The “problem” with replacing it is indeed complex, fraught with technical, regulatory (both the Environmental Protection Agency and FAA), economic, human health, environmental and logistical considerations. Decades of research to find an unleaded replacement fuel that works without adverse impact on engines and fuel systems and which can be certificated for fleet-wide use — a huge financial undertaking for any one manufacturer or refiner — have shown that there are no easy answers here. Justifying just the economic case in light of the relatively small market for avgas is daunting.

Getting the Lead Out

But now, after years of discussion within the aviation, petroleum and chemical industries; aviation advocacy groups; the FAA; and segments of the environmental movement, a definitive and formalized step has been taken that could result in a solution to not only “get the lead out” of aviation gasoline but also approve an affordable replacement fuel that can be safely and reliably burned by the existing fleet of piston-engine aircraft. “Clear and simple” it may not be, but hope runs high that it will be both “right” and supportable by a viable business case.

This is the Piston Aviation Fuel Initiative, or PAFI, a joint industry-government partnership to test and approve an unleaded avgas suitable for the existing fleet, develop a new ASTM (American Society for Testing and Materials) specification for refining it and address the business case for deploying it into the field. Note that the emphasis here is to come up with a 100-octane fuel that the approximately 230,000 piston-engine aircraft worldwide (about 170,000 of which are U.S.-registered) can safely use without modification or — the worst-case scenario — being permanently grounded until a whole new class of large-displacement engines is developed capable of generating 320 to 400 hp on diesel fuel (or auto gasoline without ethanol — see below) and retrofitters can earn STCs to install them.

A principal factor galvanizing the industry and FAA to cooperatively seek an unleaded avgas solution was the 2006 petition to the EPA by the environmental group Friends of the Earth to outright ban lead from general aviation by eliminating 100LL fuel. The petition stated that if there were a determination by the EPA that it could not ban lead in avgas — i.e., that there was no alternative fuel that achieved 100 octane without relying on lead additives — then the EPA should conduct an “endangerment finding” that lead emissions from general aviation can cause or contribute to human health maladies. Four years later, the EPA announced an advance Notice of Proposed Rule Making (NPRM) on lead emissions for general aviation aircraft and began soliciting comments from the public and industry. (The way the EPA/FAA relationship works is that the former sets the environmental standard — in this case, the reduction of lead in the atmosphere — and the latter then mandates compliance, again in this case, a transition to an unleaded replacement fuel.)

“Fundamentally, the industry position is that it is important that we find a safe replacement before we reduce or eliminate lead emissions from airplanes,” said Walter Desrosier, vice president, engineering and maintenance, at GAMA, “so the issues are safety and economic impact if you have to start grounding airplanes.”

Largely in response to the EPA action, PAFI emerged at the 2010 Experimental Aircraft Association AirVenture fly-in at Oshkosh as a coalition of OEMs, general aviation “alphabet groups” (the AOPA, EAA, GAMA, NATA and NBAA), the American Petroleum Institute (API), and the FAA, which was asked to take the lead in forming the government/industry partnership. During the succeeding four years, the FAA administrator commissioned an Unleaded Avgas Transition Aviation Rulemaking Committee (UAT ARC), which worked out:

A roadmap of PAFI objectives and a timeline for achieving them;

A process for soliciting and selecting promising unleaded avgas candidates from the petroleum and chemical

A two-phase program for evaluating and approving at least one fuel from which an ASTM “spec” could be derived;

Studies of the business case for fuel production, marketing and logistics of distribution and storage.

The deadline for submitting fuels was set for July 2014. Ultimately, five candidates were submitted, from which four were selected in September, two from Swift Fuels and one each from Shell and TOTAL. Last month, Phase 1 of the program began at the FAA Technical Center in Atlantic City in which the candidate fuels will undergo a comprehensive series of laboratory tests described further on in this report. Phase 1 is scheduled to be competed in fall 2015, whereupon data compiled in the testing will be turned over to the PAFI Technical Evaluation Committee, composed of industry and government experts vetted for conflicts of interest “within areas of expertise necessary to evaluate fuels to criteria,” which will pick the fuel (or fuels) that will progress to Phase 2, actual flight testing in appropriate aircraft, scheduled to begin in 2017. If all goes as planned, a final report will be compiled from the extensive data gathered from the testing, allowing ASTM to release a fuel specification for production in the 2018 timeframe. The assumption here is that at least one of the candidates will demonstrate that it can be safely used in existing engines, not affect aircraft fuel systems adversely, and meet financial, production and distribution objectives.

The FAA has been successful in winning the support of Congress for the unleaded avgas research initiative, which has appropriated $6 million to cover the program through FY2014. Further, both the House and Senate Appropriations Committees have proposed advancing a second $6 million tranche in FY2015 to carry the initiative forward to conclusion.

The component in leaded avgas that establishes the octane level is tetraethyl-lead, or TEL, an additive used in small quantities to raise the ignition point of the fuel so that it doesn’t pre-ignite under compression before the spark plugs fire during the ignition cycle. That pre-ignition, or detonation (“knock” in auto engines), can tear aero engines apart at the high power settings at which they operate. So TEL allows the fuel to deliver high performance, and the octane number is a measure of how well it can protect against the onset of detonation.

“One of the big differences between automobiles and aviation is the performance of the engines,” Desrosier pointed out. “In a car, you are demanding the highest performance of the engine under load. However, in 80 to 90% of your driving, you are not demanding a lot of power from the engine. But in an aircraft, you are demanding a lot of power from the engine all the time. You are flying through the air with a lot of drag and are always under a high load/power condition. You are always under load in an aircraft.”

Avgas 100LL is one grade in ASTM Specification D910 that covers multiple grades of aviation gasoline, e.g., 80/87, 91, 100, 115, et al. They essentially are all the same except for the octane rating. While many piston-engine aircraft were originally certificated for specific octane grades other than 100LL, their operators today have no choice but to fuel them with 100LL. “Out of all the grades that are identified and approved, the only one that is currently available is 100LL,” Desrosier said. “We have in the fleet a large number of engines — about 44%, or 82,000 airframe installations — that require that higher octane fuel to operate without damage to the engine.”

Avgas Is Now a ‘Specialty Fuel’

When commercial aviation transitioned to turbine-powered aircraft that burned a derivative of kerosene in the late 1950s and early 1960s, the consumption of avgas gradually declined. “And it has continued to decline ever since,” Doug Macnair, vice president, government relations at EAA, observed. “The market is continually shrinking, so we have seen consolidation of grades down to 100LL, a function of volume to make them economically viable. The same reason why 80/87 is no longer produced is because of its low volume. Only 100LL is available today and produces lead fouling in smaller engines, so eliminating lead will be a good thing.”

Added Desrosier, “In terms of the market, 25 years ago you could get two or three grades of avgas; however, due to the relatively small general aviation market, the industry can no longer justify a lot of grades, so today, it is a ‘specialty fuel.’” The small market, then, is an economic factor in the continued availability of avgas. But this is compounded, as any fuel farm manager knows, by the necessity for a fairly complicated storage and distribution structure where a high level of quality must be maintained and verified by frequent testing of samples. “You have to maintain separation between the fuels and absolutely avoid cross contamination,” Desrosier said. “You can’t use the same trucks, railroad tankers, barges, pipelines or storage facilities. And this raises the cost of the product. A significant part of the cost of
avgas is transportation, storage and

And the fact that it is leaded brings in the environmental issue. “The U.S. has gotten rid of leaded fuel in every other application, and other countries have announced schedules for its curtailment, as well,” Desrosier said. Thus, the market for leaded avgas has diminished so much that only one supplier of TEL remains: Ethyl Corp. And, of course, this adds uncertainty to the ongoing availability of the additive if aviation represents its sole use. Auguring a declining market for TEL, Ethyl Corp. has joined the industry side of PAFI. “They have a business plan to make TEL available,” Desrosier said, “but need to plan ahead for the eventual elimination of it. There was an initiative for aviation to eliminate lead when the auto industry did, but there were factors that prohibited that — the principal one being the need for high performance [in aero engines] all the time.”

As Desrosier pointed out, more than 15 years of research were invested by the industry to find another way to make high-octane fuel without lead as an anti-detonation additive, a so-called “drop-in” replacement, meaning the fuel would have all the characteristics of the original fuel but without TEL. “What they found,” he said, “is that it isn’t technically feasible. There is also a higher safety issue involved here.”

In other words, there is no solution that would allow the existing 100-octane fuel to be unleaded and continued to be used. An entirely new type of gasoline would have to be developed to meet the octane anti-detonation requirement plus all the other necessary properties implicit in a fuel that must operate properly (and safely) at altitude, not to mention its effect on the aircraft’s fuel system.

“We are pursuing a high-octane replacement that will not ground or require the affected airplanes to be re-engined,” Desrosier continued. “That’s our approach today. Because of the environmental factors, the industry is looking for another fuel to replace avgas, but it is nothing that will resemble gasoline. It is all chemicals.” That’s a bit of an exaggeration . . . but not quite. 

“Generally,” Desrosier explained, “gasoline contains approximately 85% petroleum, and the replacement that we’re looking at breaks down to a much higher content of chemicals, somewhere in the area of 50%.”

It Ain’t Just
the Octane

The complexity of developing and approving an alternate unleaded fuel can only be appreciated when considering the ancillary requirements in addition to octane, i.e., the performance measures and properties. The more critical of these include:

Vapor pressure, as the fuel cannot be allowed to vaporize at high altitudes;

Freezing points;

Materials compatibility with the fuel’s different chemical components, examples being whether they could dissolve the seals or adversely affect gaskets in the engine, hoses, pumps, tubing and bladders in the fuel delivery system, etc., all requiring extensive testing;

Electrical conductivity, which is necessary for proper functioning of modern fuel-level gauges;

Impact of the distillation curve or when the energy is produced in the combustion cycle.

As Macnair put it, “Every material it touches has to be evaluated against the effect of the fuel. You have to look at the whole fuel system. Materials have to be evaluated even in the old antique aircraft dating to the 1920s — we have to find the cross section of materials that will represent the fleet and particularly the corners of the envelope in terms of the sensitivity of the fuel. That’s the complexity. We can’t test them all [the materials] but will try to test as many as possible to determine which are the most crucial.” Thus, literally hundreds of materials will be evaluated against the candidate fuels.

This testing, currently underway in the FAA Tech Center labs under Phase 1 of PAFI, involves simple exposure of fuel to materials and more sophisticated rig testing of fuel system components mounted on boards and cycled repeatedly. Suppliers have been asked to submit 100 gal. of each candidate fuel for this phase of the evaluation. “What you want to do first is determine which fuels are the most viable,” Desrosier elaborated, “and those that work will be moved on to Phase 2 testing of full-scale engines and airplanes . . . to generate the FAA compliance data for the overall approvals.” Suppliers of unleaded avgas candidates selected for Phase 2 will be asked to contribute 10,000 gal. of each of their fuels for engine test-stand runs and actual flight trials for that year-long evaluation process.

An underlying premise of PAFI is the understanding that any solution to the leaded avgas conundrum has to apply fleet-wide, that is, it has to be usable by any aircraft/engine combination. This addresses the economic issue that, otherwise, each engine/airframe OEM would need to partner with a fuel refiner to individually pursue development of an unleaded fuel and seek FAA approval for it plus STCs to use the fuel in its products. Prior to launch of the PAFI program, this was “the real roadblock” to a serious attempt to find an unleaded alternative, John McGraw, director, regulatory affairs, for the NATA, told B&CA. “PAFI puts the FAA in a place where it is taking the initiative to determine the equivalence of the new fuels with leaded avgas and use them in existing aircraft,” he said. “If successful, it will be a boost for the use of the alternate fuels in today’s fleet.”

If manufacturers had to apply to the FAA to get this approval, it would be “impossible,” McGraw continued. “This is a fleet-wide initiative to provide equivalence, with the industry and government pulling together. The role the government is playing is allowing the OEMs and refiners to make an investment with a chance of success. Having the funding available to show equivalence has made this something the OEMs can invest in.”

Creating a Fleet-Wide Market

PAFI is also designed to address economic impact on the general aviation industry, as well. “If you don’t have an approval, you have no market [to sell fuel], so an EPA-compliant replacement has to be approved,” Desrosier observed. “The FAA is doing all the testing, relieving the suppliers from having to do that.” So the program creates the market while assessing the safety of the fuel for every engine type in use, identifies the differences from the current 100LL avgas, and then develops a data package that can be applied to the approval for use in all the engines. “We know the engines that require the highest octane, so if it works in those,” Desrosier said, “it will work in the ones that require less
octane. . . .”

Part of PAFI’s charter is to identify “the critical corners” of the performance envelope to make a replacement fuel as broadly applicable to the fleet as possible, the EAA’s Macnair elaborated. “You test on the applications that require the highest octane [i.e., the large high-compression engines], with the understanding that it will work on the others.” Identifying the necessary parameters and testing for each of them in order to develop the data package necessary to support a transition to an unleaded 100-octane avgas is “an extremely complicated process, but it’s achievable,” Macnair contends. The depth of the industry/government team brings a lot of talent to the table to make that possible. “We have the brain trust to make these evaluations because so many actors are in it.”

A misconception continues to circulate among the avgas user community, Macnair insisted, “and it is that there is a small room of omniscient people tucked away somewhere who are determining the fate of avgas. The PAFI process is designed to be collaborative between government and industry, and it has tapped the breadth of the aviation and petroleum industries for input.” The initiative’s Technical Advisory Committee, which vets the full compendium of tasks associated with the objective, has been drawn from experts in their respective fields: engine, airframe, petroleum, even the distribution chain and materials support. “So it is not a closed-door process,” Macnair said, “it is an open one intended to bring together all the technical resources available from the industry to reach an unleaded future.”

Once the PAFI Technical Evaluation Committee has determined that at least one unleaded avgas candidate meets all the performance and properties requirements, ASTM will issue a “consensus standard” for the new fuel, which can be broadly produced as a commodity. This sets the requirements and characteristics that any refiner could use to develop a competing fuel. The FAA will then be able to issue approvals for every engine type and model in the fleet and remove any limitations stated in the AFMs for the aircraft they power, e.g., “Use only leaded fuel in this aircraft.” “These are the challenges in finding an alternative,” Desrosier said, “a fleet-wide initiative to determine if the fuel is safe.”

The approvals may be available in 2019, but whether or not the market will support the production and distribution of the fuels is unknown at this time. “We expect that the EPA will have issued its NPRM [identifying lead emissions from avgas as a health hazard] by then,” Desrosier predicted. “But we don’t know if that NPRM will set a hard deadline for setting an emissions standard. The FAA would then have to do a separate rulemaking to impose the standard on the aviation industry. But there is an obligation through the Clean Air Act requiring the FAA to implement a standard in such a way that it would not impact safety or noise, so to me that means the FAA has the authority to determine under what timeline and approach to issue the

“Once we know the viable replacement, then we can talk about a reasonable transition if a regulation is required,” he continued. “I think the industry has a strong interest in transitioning in as timely a manner as possible to minimize the impact. If you delay it too much, you have a greater risk of something happening to the existing supply of TEL. There are other potential environmental activities like Prop 65 in California [see sidebar]. That’s why it’s so important to find a viable alternative.”

Then there is the step from approval of an unleaded formulation to actual refining by potential suppliers. “Probably as the reality sets in that there is a fuel that will work and therefore a potential market for it,” NATA’s McGraw observed, “there will be a lot of discussion around it being real and therefore a viable commodity and worth the investment in refining and distribution. But everyone is waiting to see how successful the testing is.”

And What if There Is No Solution?

As Phase 1 of the PAFI process gets underway, hopes run high that an unleaded replacement fuel will be found and certified for production by the end of the decade . . . but what if, for the sake of discussion — especially after $12 million of taxpayer money and years of research — the program fails to isolate a viable substitute for 100LL avgas? “The high-octane fleet would be effectively grounded,” Macnair said, unhesitatingly. “The marketplace would be even smaller for fuel, and even the low end would be scrambling to find low-octane auto gas that would not contain ethanol [see sidebar discussing auto gas and its limitations]. So there would be significant dislocation.”

Roughly 30% of the piston fleet burns 70% of the avgas today, Macnair pointed out, “and that segment is the large end, the commercial part of the fleet, with a high-octane demand, because they’re flying the most. In the absence of an avgas that satisfies the whole fleet, the Cessna 172 operator would be paying a lot more for small quantities of a niche fuel, that is, auto gas without ethanol [or so-called ‘mogas’].”

If the aviation community burns 400 million gal. of avgas a year, and overnight demand was reduced to 100 million gal. a year, “that remaining portion would be very expensive because you still have to deliver it to the same number of airports in smaller quantities,” Macnair said. “To maintain the integrity of the marketplace, we have to satisfy the largest portion of the fleet as possible, or 100% in a perfect world.”

But no matter the uncertainty of whether a leadless replacement aviation gasoline is a viable possibility in a declining market, the consensus in general aviation is that failure cannot be an option if piston-engine aviation is to survive. “Avgas was an evolutionary product,” Macnair said. “It evolved to control specific performance parameters in the real world. Now all of those parameters are back up in the air and have to be met. We don’t have the benefit any more to learn as we go — now we have to pull the rug out from under the entire aircraft fleet and install a whole new one to support both the fleet and safety while we are doing it. Every engine out there was designed to known fuel, one at a time. Now we are trying to change the fuel for everything at once — an immensely complicated task that has never been attempted before. It is vitally important that we do this right and do it once. We cannot afford to do it haphazardly. It has to be methodical.”

McGraw at the NATA believes PAFI is “the most promising advance we’ve seen since this discussion started. There was not a lot of progress until this initiative, and we are glad to support it. Hopefully, we will continue to get support from Congress. I am optimistic that this is real progress and not just talk, real funding, and a commitment from the FAA. We are pleased.” B&CA

This article was originally published February 1, 2015.