The FAA has suspended flight-testing and certain engine trials of the two drop-in unleaded fuel options under evaluation to replace leaded aviation gasoline through the Piston Aviation Fuels Initiative (PAFI) and extended the target completion date of the PAFI program by one year to the end of 2019.
Through the government-industry PAFI research program, the agency had selected fuel options from Shell and Swift to evaluate potential alternatives to the current aviation gasoline. The flight-test program was about one-third complete and the engine test program was about halfway through the trials, the agency estimated.
“Differences in the two PAFI fuels as compared to 100LL are being evaluated for impacts and mitigations,” the agency said. “While these issues are assessed, PAFI flight testing and some engine testing have been halted…Shell and Swift are evaluating options to mitigate the impacts that these differences will present in fuel production, distribution, and operation in the GA fleet.”
This evaluation will push back the timeline for determining a viable unleaded option by one year. In the meantime, the FAA will evaluate alternative high-octane unleaded fuels under development outside the PAFI program for possible leaded avgas replacements. The agency stressed it is committed to evaluating suitable unleaded fuel options for piston engines.
“The FAA and industry are interested in pursuing all alternatives while issues are assessed including evaluating high-octane unleaded fuels currently being developed outside of the PAFI program,” the agency said, adding it has invited other fuel producers to submit their data for evaluation and possible operability and performance testing at the FAA's William J. Hughes Technical Center.
“Fuel producers offering alternatives determined to have potential viability as an unleaded replacement for 100LL will be invited to participate in a Cooperative Research and Development Agreement with the FAA, which will be conducted on a non-interference basis with the PAFI program,” the agency said.
The FAA in 2013 issued a request for proposals for candidate fuel producers to submit unleaded fuel formulations that could be evaluated as potential replacements for the current 100LL. The FAA called the release of the RFP “a significant milestone in a government/industry collaborative effort to find an unleaded replacement fuel for the general aviation industry.”
The agency and industry groups have been collaborating for years on finding a drop-in replacement, recognizing that avgas is the sole remained lead-containing transportation fuel.
Multiple environmental groups have either filed or threatened legal action to prevent its use, and have pressured the Environmental Protection Agency to issue an endangerment finding on leaded avgas that would force limits on its use.
The FAA in 2016 had selected unleaded fuel possibilities from Shell and Swift Fuel for testing. The testing intended to develop data packages to support an ASTM production specification, with wide-scale FAA approval originally targeted for the end of this year.