Running on Empty

When the Environmental Protection Agency began phasing out leaded gasoline in the 1970s with the passage of the Clean Air Act, aviation got a pass. Because lead was needed to boost octane levels and prevent detonation (also known as “knock”) in high-­compression piston aircraft engines, leaded avgas was exempted from the law. Lead is a fantastic octane enhancer, but it destroys catalytic converters in automobiles and it’s toxic to humans. Today, 100 low-lead aviation gasoline is the only transportation fuel sold in the United States that still contains lead. If the EPA gets its way, soon there will be no leaded transportation fuels sold in this country, and 100LL will be history.

The EPA will weigh whether to issue a formal endangerment finding for leaded avgas based on data collected during an ongoing investigation that has involved setting up lead-monitoring sensors at 17 general aviation airports around the country. The agency says it will publish a notice of proposed rulemaking next year based on its findings, with a final determination of the fate of 100LL expected in 2018. The consensus in the aviation industry is that the EPA will call for the phaseout of leaded avgas soon after its endangerment finding is filed.

That’s why the FAA and industry partners are moving swiftly to identify alternative unleaded fuels that can provide the same anti-knock qualities of 100LL while costing about the same at the pump. The new fuels also must be compatible with virtually every piston aircraft engine ever produced, from a Franklin flat six in a 1940s-era Aeronca Sedan to a turbocharged TSIO-550-K in a brand-new Cirrus SR22T. Finally, the newly formulated fuel cocktail can’t be more environmentally harmful than the tetraethyl lead that is an additive in avgas today.

The research program, known as the Piston Aviation Fuels Initiative (PAFI), kicked off in June 2013 as a government-industry collaboration to identify potential unleaded replacement fuels that could be used as a drop-in substitute for 100LL avgas. A primary goal of the program is to provide blanket approvals rather than require supplemental type certificates for each and every airplane and engine combination in existence.

The FAA in September 2014 selected four candidate fuels for testing, one each from Shell and Total, and two from Swift Fuels. After successful Phase I laboratory and rig testing concluded this past fall, the agency will select two fuels in March for an extensive flight-test program set to begin later this year. The agency will soon announce which fuels it has selected to participate in further PAFI testing. The next phase will involve more rig testing and actual test flights using 19 piston-aircraft engines and 11 airplanes at the FAA William J. Hughes Technical Center in Atlantic City, New Jersey, as well as at industry partner sites around the country.

Those evaluations won’t consider octane rating alone, but also how the fuels perform in the cold at high altitude, how they fare in extreme summer heat, their engine-start performance, and whether they cause damage to any engine components, such as seals and O-rings.

You might be surprised to learn that the replacement fuel you’ll be putting in your tanks next decade probably will consist of more chemicals than actual gasoline. To achieve the octane rating that a small amount of lead can provide today, the new fuels contain from 40 to 70 percent octane-enhancing chemicals, notes Peter White, the head of the Alternative Fuels Program staff at the FAA.

“The candidate replacement fuels we are testing are quite a bit different from traditional aviation gasoline,” he says. “We can’t discuss what the fuel blends are because they are proprietary, but we’re looking at much higher contents of chemicals, somewhere in the range of 50 percent or higher.” That obviously begs the question of whether the cure to our 100LL woes will be worse than the disease. White says the replacement fuels should be quite a bit less harmful to humans than leaded avgas. “So far, the toxicity looks OK,” he says.

Leaded aviation gasoline was linked in a 2011 study related to elevated levels of the toxic metal in children living near general aviation airports. The data was used to bolster arguments in a lawsuit against the EPA, filed by the environmental group Friends of the Earth, to force tighter regulation of lead in aviation gasoline. The EPA ultimately agreed to test for lead in the air around GA airports.

Leaded aviation gasoline was linked in a 2011 study related to elevated levels of the toxic metal in children living near general aviation airports. Shutterstock

So far, the EPA’s monitoring program has found that lead levels were below National Ambient Air Quality Standards at 15 of the 17 airports studied. The EPA has denied a petition from Friends of the Earth that seeks an immediate endangerment finding, saying it will continue to investigate the degree to which aircraft emissions may pose a public-health threat. Any endangerment finding, the EPA told the group, will be based on data collected during its ongoing investigations.

The FAA is treading carefully in the debate, pointing out that flight safety is of paramount importance in the switch to alternative fuels while also acknowledging that the piston aviation fleet in the United States inevitably has to transition to an economically viable unleaded future. The questions of when and how this transition is carried out, however, could lead to some prickly confrontations as the EPA and FAA balance the need for environmental safety against aviation safety.

“There is always a natural tension that exists between agencies that have different regulatory interests and environments that they’re operating within,” says FAA Administrator Michael Huerta, “but I don’t think anyone at the EPA is interested in doing anything that is unsafe. At the same time, they want to ensure that we and the aviation industry are collectively doing what we needto do to move the fuel research program to an area where they can see an end of leaded fuels.”

Increasingly, local communities are putting pressure on airports to eliminate lead emissions as well. So while the EPA has yet to propose a ban of 100LL (and it indeed can’t take unilateral action without FAA involvement), nearly everybody agrees that the era of leaded aviation gasoline is nearing an end. Still, don’t think for one second that the switch to an alternative aviation fuel will be easy.

Cost is a major concern, as is the production, distribution and availability of any replacement fuel. There is the question of whether or not 100LL can be mixed with the new fuel during the transition before all airports make the switch. And, of course, there are unanswered considerations about the impact that completely new fuel chemistry will have on every aircraft engine built from the 1920s until today.

“Octane requirements really are just the tip of the iceberg,” White says. “There’s no getting around the fact that this is an immensely complicated undertaking.”

Soon to be outlawed, 100LL aviation gasoline is used in about 170,000 piston-powered airplanes in the United States. Shutterstock

Phase I of PAFI testing evaluated the business case for producing alternative fuels and identified a host of properties, such as fuel density, vapor pressure (the fuel can’t be allowed to vaporize at high altitude), freezing point, distillation curve, corrosiveness, flash point and many others. Carburetor icing is a key challenge that researchers have been studying as well. Storage in fuel tanks and trucks over time in temperature extremes also must be considered.

The real testing starts this March when Phase II engine and aircraft flight trials kick off. Most testing will be ­performed in a range of engines, from carbureted four-cylinders to turbocharged and fuel-injected six-cylinders, with a selection of radial engines thrown in as well. The airplanes involved in flight-testing will include two-seat ­trainers up through piston twins and helicopters. The test card will include inflight engine restarts, high-altitude operations, hot- and cold-weather operations, and everything in between.

The overriding goal of the PAFI program is for the FAA to identify candidate fuels that can be approved on a fleet-wide basis. The plan is to publish eligibility lists in the Federal Register of aircraft/engine combinations that can fly with the new unleaded avgas formulations, which aircraft owners would then add to their operating limitations.

There is a problem with this approach, however. It will require an act of Congress, literally, to change the federal aviation regulations so that this unique method can be applied.

“The traditional approach of going engine by engine to get approval would be monumental,” White says. “That method won’t get us there.”

So far, Congress has been fully supportive of PAFI, authorizing $12 million for testing through the end of 2018, which is when the new fuels are expected to receive approval. As a result, the program has managed to stay on schedule, and the FAA intends to keep it that way. PAFI participants agree that the timeline is ambitious, but the EPA’s endangerment finding that’s due in 2018 is on an aggressive schedule as well. With nearly everybody bracing for an unleaded avgas requirement from the EPA in 2019 or thereabouts, there’s precious little time to waste.

Getting the Lead Out: What Will It Take?

The Piston Aviation Fuels Initiative (PAFI), a joint industry-government partnership that has been tasked with testing and approving avgas alternatives suitable for the existing piston fleet, will develop new ASTM (American Society for Testing and Materials) specifications within the next three years for refining and delivering safe and affordable unleaded fuel to your airplane.

The move to replace 100LL ­avgas began in 2006 when the environmental group Friends of the Earth filed a petition with the EPA that sought an outright ban on leaded aviation gasoline.

PAFI emerged at the 2010 AirVenture Oshkosh airshow as a coalition of aircraft and engine manufacturers, and aviation groups, including the Aircraft Owners and Pilots Association, the Experimental Aircraft Association, the General Aviation Manufacturers Association and others, which realized the EPA was serious about banning 100LL before the decade was out.

The FAA’s Unleaded Avgas Transition Aviation Rulemaking Committee worked out a roadmap for PAFI goals over the next four years and a timeline for achieving them. Ultimately, four candidate replacement fuels were selected for Phase I PAFI testing. Phase II flight-testing that involves two of those fuels in 11 real airplanes starts this March.

If all goes well (still a big “if”), testing will continue through 2017, and ASTM specifications for the alternative unleaded avgas will be released in December 2018, ahead of the EPA’s schedule to outlaw 100LL by as early as 2019.


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