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Lycoming, EU bless UL 91

Soon after the European Union approved its use of UL 91 unleaded avgas, Lycoming Engines announced that it is seeking U.S. approval from the FAA to use ASTM (American Society for Testing and Materials) D7547 UL 91 unleaded avgas in 35 of its engines.

“Our approval of UL 91 supports recent actions by European fuel producers and the European Aviation Safety Agency (EASA) that have resulted in progressively wider availability of unleaded aviation grade fuel supplies for light aircraft,” said Michael Kraft, Lycoming senior vice president and general manager. “We are continuously working to expand our specified fuels list. Distribution of UL 91 has provided a well-conditioned aviation suitable solution for engines originally designed for lower octane leaded aviation and automotive fuels.”

The full list of approved engines is in Lycoming Service Instruction SI-1070R, and posted online.

At this year’s Aero convention, Kraft provided his fourth annual press update on aviation fuels at the event. In response to ecological concerns, Kraft said that all three fuel streams are changing. “In automotive fuels, there are increased levels of E15 ethanol in ground transport fuels. In avgas, UL 91 has entered into production, and there’s continued progress on a potential UL 100 octane unleaded fuel. And with turbine engines there are multiple solutions for blended fuels,” Kraft said.

Lycoming has entered into a collaborative program with the FAA, Shell Aviation, and European refiner TOTAL to examine the long-term effects of UL 91 on purpose-built aviation engines and lubricants. “UL 91 is not auto fuel,” Kraft said. “Premium auto fuel with an anti-knock index (AKI) rating of 91 is not based on the same rating as those used in aviation fuels. Aviation fuels are rated by MON—Motor Octane Number.”

“100LL in an automotive rating would be better than 105 AKI and on the order of some specialty racing fuels,” he explained in an email to AOPA. “UL 91 is not a 100LL replacement, but it is a stepping stone to a UL 100 aviation fuel in the future as we can use its deployment to increase our technical knowledge and address the issues we will face in a UL 100 transition.”

“UL 91 is a very robust aviation-suitable alternative to automotive gasoline at lower prices than 100LL,” Kraft said at Aero.

While SI-1070R immediately enables the use of UL 91 on a range of Lycoming-powered aircraft operated in Europe, UL 91 will require an additional approval by airframe manufacturers to use that fuel in the United States. There are no known distributors of UL 91 in the United States at this time, a Lycoming statement said.

UL 91 is available at 18 airports in the United Kingdom, with another three making arrangements to offer it. In France, 10 airports offer UL 91, with four more making ready to provide it. Switzerland has four airports with UL 91, and the fuel will soon be available in Belgium and Germany. For UL 91 to make any inroads in the United States, Kraft said that Congress must define an FAA requirement for a transition to UL 91 avgas. “The rest of the world is moving first,” Kraft said. “I guess the U.S. is hampered by inertia.”

Thomas A. Horne
Thomas A. Horne
AOPA Pilot Editor at Large
AOPA Pilot Editor at Large Tom Horne has worked at AOPA since the early 1980s. He began flying in 1975 and has an airline transport pilot and flight instructor certificates. He’s flown everything from ultralights to Gulfstreams and ferried numerous piston airplanes across the Atlantic.
Topics: Avgas

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