Propulsion: Energy Sources

Flying on Vegetation: Airlines, aircraft companies, and other stakeholders are taking the long view in developing sustainable alternatives to petroleum-based jet fuels.

Fuel is expensive for airlines. According to sources interviewed for this article, fuel accounts for 30 to 50% of operating costs, depending on the size of the aircraft. And fuel prices remain volatile.

At the same time, there are few alternatives to powering aircraft. While land transport has some available options-think electric vehicles and hydrogen fuel cells-aviation depends on liquid fuels with high energy density. Emissions are another concern. According to the Air Transport Action Group (ATAG), aviation is responsible for 2% of global manmade CO² emissions.