With on-going pressure from regulatory bodies and vocal climate activists, the entire aviation industry is working toward a clean air future. For jet operators, the near-term solution is uplift of 100% sustainable aviation fuel (SAF), eliminating the 30-50% mix limits—by regulation—with conventional jet fuel. On the piston-engine side, the path forward has been the replacement of 100LL (low lead) aviation gasoline (avgas) with an unleaded product, rendering the operation of nearly all single and twin piston-engine aircraft completely lead-free. Exhaust gas from 100LL has been cited as a health hazard, mainly for people living near airports with high volumes of general aviation traffic. In fact, according to a statement issued by the Environmental Protection Agency (EPA) Office of Public Affairs—at the request of the Aviation Business Journal—in October 2022, the EPA issued a proposed finding that emissions from aircraft engines operating on leaded fuel cause or contribute to air pollution that may endanger public health and welfare. If the final determination, to be issued by the fall of this year, concurs, the EPA will likely propose and promulgate regulatory standards for lead emissions from aircraft engines. The statement concludes that “the FAA would have a duty to prescribe standards for the composition, chemical, or physical properties of an aircraft fuel or fuel additive to control or eliminate aircraft lead emissions.” Fortunately, unleaded avgas for use in many general aviation aircraft has been available nationwide since April 2015 from Swift Fuels. The West Lafayette, Indiana-based refiner is currently the sole source of that product, identified as UL94. According to Swift Fuels’ CEO Chris D’Acosta, UL94 is FAA-certified and meets ASTM (American Society for Testing and Materials) International Specification 7547 for premium unleaded gas. “UL94 is OEM endorsed by Lycoming, Continental, Textron Aviation (Cessna/Beechcraft), Robinson Helicopter, and many more aerospace manufacturers,” D’Acosta