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Unleaded Aviation Gasoline

Fuel Testing (2:31)

At a Glance

  • Two unleaded aviation gasoline formulations are being tested through the Piston Aviation Fuels Initiative.
  • The FAA and its partners are seeking unleaded alternatives to leaded aviation gasoline.
  • The FAA's goal is to authorize the use of these new fuels to as much of the general aviation fleet as possible without significant engine and supply infrastructure modifications.

A primary benefit of NextGen is a cleaner environment. One way to realize this is by developing an unleaded alternative to the 100 octane low-lead aviation gasoline (avgas) that powers more than 167,000 piston-engine aircraft in the United States. The FAA, Environmental Protection Agency, and industry are partnering to identify an unleaded fuel.

Avgas contains lead to prevent detonation that can damage engines and result in sudden engine failure, but it is a toxic substance. Since lead was eliminated from automobile fuels and is the only remaining leaded transportation fuel, avgas emissions have become the largest contributor to the relatively low levels of lead emissions produced in this country.

Unleaded Aviation Gasoline Today

The FAA supports alternate fuels research at the William J. Hughes Technical Center (Tech Center) in Atlantic City, NJ. The agency works closely with aviation associations, aircraft and piston engine manufacturers, fuel suppliers, and the Environmental Protection Agency to research and evaluate unleaded replacement fuels.

The agency originally hoped for a "drop-in" fuel replacement, one that requires no modifications to existing engines. However, extensive research determined that this was not feasible. The goal, therefore, changed to evaluating fuels to find ways to mitigate their implementation impact on the general aviation fleet, as well as on the manufacturing and distribution infrastructure.

A pilot in a small cockpit.

The FAA's goal is to authorize as much of the general aviation fleet as possible to use new unleaded fuels without significant engine modifications.

In 2016, the FAA began testing two high-octane unleaded fuel formulations that delivered the least impact. The testing constitutes Phase 2 of a two-phase Piston Aviation Fuels Initiative (PAFI) fuel testing program at the Tech Center. The formulations, one from Shell and the other from Swift Fuels, were chosen based on the results of Phase 1, which was completed in 2015.

Phase 2 testing is generating engine and aircraft test data to authorize the use of the two fuels to fly aircraft. About 20 engines, including those manufactured by Continental, Lycoming, Pratt & Whitney, and Rotax, are being tested on 10 aircraft models, the Beech Bonanza, Cirrus SR22T, T-6 Harvard, Robinson R44 helicopter, and various Cessna and Piper aircraft.

Unleaded Aviation Gasoline Ahead

Identification and evaluation of resolutions to issues discovered during PAFI testing are under way with the fuel providers. Industry in-kind support is providing much of the flight and engine testing data. PAFI expects to announce in 2018 when it plans on completing testing and issuing final reports.

The FAA is also seeking a new authority for its administrator to conduct engine and aircraft approvals for the PAFI program. The agency is planning to submit that request to Congress as part of the FAA reauthorization. PAFI created a deployment working group composed of the FAA and industry stakeholder representatives who are focused on planning for the implementation, production, and deployment phases of the new fuels. The working group plans to take on legislative and regulatory issues and requirements, engine and aircraft modifications, manufacturing capability, distribution system and airport deployment, communications, and training.

Female pilot refueling her aircraft.

The FAA is determined to deliver alternatives to unleaded gas through traditional processes and the PAAFI program.

The FAA continues to work directly with other fuel producers seeking unleaded avgas engine and aircraft approvals through traditional procedures. The agency also recently issued a Special Airworthiness Information Bulletin clarifying that unleaded fuels with minimum octane ratings of 94 or 91, known as UL94/91 grade fuels, meet the requirements of the operating limitations of aircraft and engines approved to operate within those grades of leaded avgas, or in low compression engines approved to operate on fuel with an octane rating of 80, known as grade 80 avgas, which was phased out in the late 20th century.

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