June 14, 2018 — The FAA announced last week that it is temporarily suspending testing of the two potential unleaded aviation fuels within the Piston Aviation Fuels Initiative (PAFI) to further analyze test results from the two candidate fuels under study since 2016.
Those fuels, one each from Shell and Swift, were the final candidates to advance to full-scale engine and flight testing as part of a competitive search for an unleaded replacement for 100 low-lead avgas, which is used by the vast majority of the piston aircraft fleet in the U.S. The goal is to find an unleaded replacement that would satisfy the requirements of the majority of the general aviation piston fleet. The program began with 19 candidate fuels and through a rigorous evaluation process narrowed that field down to the two most promising fuels for engine and aircraft testing.
“The collaborative FAA-industry PAFI program has done exactly what it was designed to do – take promising fuels and subject them to rigorous, standardized materials, engine, fuel system, and aircraft testing to determine their performance characteristics and any limitations they might pose in safely satisfying the breadth of the general aviation fleet,” said Doug Macnair, EAA’s vice president of government relations, who has been EAA’s representative to the PAFI program from its inception. “Finding a fuel that safely and cost-effectively meets the requirements of the GA fleet, and has the confidence of aircraft owners as well as engine and airframe manufacturers, is absolutely essential
“A crucial part of the PAFI process is that it directly involves experts from across the span of the aviation and petroleum industries, including the major engine and aircraft manufacturers, in collaboratively developing test methods and protocols, identifying the test articles necessary to ensure that the worst-case applications for any given fuel property have been examined, and that the fuel can be produced and distributed in an economically viable manner. One thing that everyone involved in the PAFI process agrees with is that any prospective replacement for 100LL will have to eventually be subjected to this level of scrutiny, as the GA community’s safety relies on this kind of broad, in-depth, and transparent testing. It is only through this rigorous testing, which greatly exceeds the minimum standards set forth in the regulations for traditional certification and STC programs, that unforeseen challenges were uncovered that might have resulted in service difficulties in the field had these novel fuels been rushed into the marketplace without exhaustive testing. The fact of the matter is that replacing 100LL with an unleaded fuel of similar capability is a significant technological barrier and the aviation and petroleum industries are continuing to work the problem in collaboration with the FAA.”
While full-scale engine and aircraft testing has been temporarily suspended, work has far from stopped. Differences in the two PAFI fuels as compared to 100LL are being evaluated for impacts on the fleet and potential mitigations are being explored. Development and evaluation of possible mitigations will take time and ultimately affect the schedule of the test program. Based on current projected activities and timelines, the testing completion date for the PAFI program will likely extend beyond December 2019. In the meantime, the PAFI program, through the FAA, has reached out to fuel developers who have either come forward with potential candidate fuels since the closed PAFI process began, or who had previously declined to participate, to do some preliminary screening to determine if further examination of any of those fuels is warranted. In the search for the best possible replacement for 100LL, PAFI wants to ensure that every possibility has been examined.
“What this process tells us is what EAA has maintained for the past 30 years: Finding a high-octane unleaded avgas replacement is a daunting technological challenge,” Macnair said. “EAA joins everyone in the industry in welcoming all potential solutions to take part in this standardized and industry-accepted testing protocol, so together we can find the best and broadest possible solution for the GA fleet.”