Unleaded Avgas: Why UL 91 Isn't "The" Answer

UL 91 is an unleaded avgas already powering aircraft engines in Europe and may within weeks be approved for use in a range of Lycoming engines, but it’s unlikely you’ll see it at your airport soon.

AVweb spoke with Lycoming vice president Mike Kraft, who said the fuel is basically 100LL — without the lead. In essence, any aircraft engine currently burning 100LL that is approved for operation on 80, 90 or 93 octane fuels can operate just as well burning UL 91. But 100LL supplies a one-product solution for a more complete range of engines. And that may be reason enough for distributors to balk at offering the product to users.

Today, of roughly 15,000 airports in the U.S., there are about 400 that offer a lower-octane fuel than 100LL, Kraft said. And for pilots who have opted to run high-grade auto fuels in engines compatible with lower octanes, ethanol requirements and other issues have caused concern. According to Kraft, “100 percent of our concerns with auto gas are addressed with UL 91.” But engines that need 100LL will not be well-served by that product, and distributors would need reason to invest in changing their networks. In short, the availability of an unleaded fuel alternative for aircraft engines in the U.S. does not hinge on the approval of UL 91 alone. Other forces will be required to see that unleaded alternative made available at airports nationwide.

CalPilots Editors Note: It is important to understand that aircraft requiring 100LL are the largest consumers of all of the sold.