 The world's longest volumeproduction airliner touched down safely on the rain-soaked airfield northeast of Paris at 5.35pm last Monday. The sheer scale of the updated Boeing 747-8 - which, at 250ft long, is nearly one and a half times the size of Nelson's Column - drew admiring glances from onlookers at the Paris air show.  The interesting stuff, however, was happening out of sight. This was the first transatlantic flight of a large commercial aircraft powered by a green jet fuel.  The plane flew from Everett, Washington state, to Le Bourget close to the French capital, with all four engines powered by a blend of 15% biofuel mixed with 85% traditional jet fuel.  "It was an important mental leap to make, to show this is a safe fuel and in many ways superior to traditional jet fuel," said Darrin Morgan, director of sustainable aviation fuels at Boeing.  He also said the plane maker was only "weeks away" from getting official approval to use a 50-50 fuel blend for commercial flights.  a few months ago, the US Navy flew an F-18 on a 50-50 blend - without a hitch and with no impact on the fighter jet's performance.  The supersonic military flight added to Morgan's confidence that the days of jetting round the world on 100% biofuel are only a "year or two" away.  Boeing's transatlantic flight used fuel derived from camelina, a crop grown in Montana by farmers every three to four years, which allows the land to be recharged with nutrients. Camelina, which needs little water, looks like wheat. It produces seeds, which are gathered and crushed to produce triglyceride oil. This is then refined to produce synthetic kerosene that can be used as a fuel.  Boeing has also set up a biofuels partnership with the Gulf carrier Etihad and the Masdar Institute of Science and Technology, established by the abu Dhabi government and the Massachusetts Institute of Technology.  The partners are running a pilot scheme to test the effectiveness of biofuel derived from halophytes - plants that flourish in hot, desert conditions and which thrive on salt water instead of fresh water. These also produce oil seeds that can be crushed and refined to produce green fuel.  Morgan said scientists in Eritrea, in the Horn of africa, first discovered the potential to develop a sustainable biofuel from the plants. But a bloody coup against the government led to the research being abandoned and all the documentation was lost. Boeing's green fuels guru said the partners in the abu Dhabi pilot are looking for the scientists involved in the original study to piece together their findings.  Morgan is excited about the potential of this project because the plants can be produced on desert land instead of displacing food crops on arable land, and they can be irrigated with sea water.  He noted the vast swathes of desert that may be available to grow the large amounts that would be needed for commercial production in australia, China, africa, the Middle East and parts of america.  Just as important as proving the effectiveness of the fuel is establishing a robust supply chain to produce and distribute it.  Morgan added that there is now a groundswell of support across the globe. Projects are starting in China, the Middle East, australia and Europe, where governments, airlines, manufacturers, financiers and academic institutions are now coming together to establish green fuel networks.  Last week, the European Commission, the plane maker airbus, leading airlines and biofuel producers signed up to an aviation biofuel accord with a target of producing 2m tonnes a year by 2020.  Pierre-Henri Gourgeon, chief executive of air France KLM, said: "The suitability of biofuels for aviat 