Last week, a Virgin Atlantic passenger jet traveled from London to New York powered 100% by sustainable aviation fuel, or SAF.  The low-carbon fuel came from feedstock that included used cooking oil and waste animal fats. Critics call the flight a gimmick, and to be clear, right now SAF makes up a tiny slice of the fuels airlines use to get us places. Marketplace’s Lily Jamali spoke with Louise Burke, an energy analyst and vice president of business development at Argus Media, who says that could change.