A NASA-led team conducted a series of choreographed flights over California in order to find out how aircraft emissions differ when using petroleum fuels or biofuels. Early results from the Alternative Fuel Effects on Contrails and Cruise Emissions (ACCESS II) experiment confirm that blended biofuel is the cleaner-burning fuel. During the ACCESS experiment, scientists took advantage of the aircraft's segregated fuel tank, switching the fuel type sent to each of the four engines. The engines burned either jet fuel, or a 50-50 blend of jet fuel and a renewable alternative produced from camelina plant oil. With each change of fuel, three other instrumented aircraft took turns lining up in the DC-8's wake to gather data. The photo was taken from Langley's HU-25C Guardian jet as it descended toward NASA's Armstrong Flight Research Center after a successful three-hour sampling flight behind the DC-8.