Virgin Atlantic carried out the world's first flight of a commercial aircraft powered with biofuel on Sunday in an effort to show it can produce less carbon dioxide than normal jet fuels.
Some analysts praised the jumbo jet test flight from London to Amsterdam as a potentially useful experiment. But others criticized it as a publicity stunt and noted scientists are questioning the environmental benefits of biofuels.
"This breakthrough will help Virgin Atlantic to fly its planes using clean fuel sooner than expected," Sir Richard Branson, the airline's president, said before the Boeing 747 flew from London's Heathrow Airport to Amsterdam's Schiphol Airport.
He said the flight would provide "crucial knowledge that we can use to dramatically reduce our carbon footprint," he said.
Sunday's flight was partially fueled with a biofuel mixture of coconut and babassu oil in one of its four main fuel tanks. The jet carried pilots and several technicians, but no passengers.
Virgin Atlantic spokesman Paul Charles predicted this biofuel would produce much less CO2 than regular jet fuel, but said it will take weeks to analyze the data from Sunday's flight.
"It's great that somebody like Richard is willing to put some of his billions into an experiment aimed at reducing the climate change impact of aviation," said James Halstead, an airline analyst at the London stockbroker Dawnay Day Lochart.
"But there are a lot of unanswered questions about the usefulness of biofuels in the battle against global warming," he said.
The flight is the latest example of how the world's airlines are jumping on the environmental bandwagon by trying to find ways of reducing aviation's carbon footprint.
These efforts have included finding alternative jet fuels, developing engines that burn existing fuels more slowly, and changing the way planes land.
The experiment by Virgin Atlantic and its partners — Boeing, General Electric and Imperium Renewables — also comes at a time when high oil prices and the U.S. economic slowdown are promoting consolidation in the airline industry.
Aircraft engines cause noise pollution and emit gases and particulates that reduce air quality and contribute to global warming and global dimming, where dust and ash from natural and industrial sources block the sun to create a cooling effect.
About a year ago, the European Commission, the executive of the European Union, said greenhouse gas emissions from aviation account for about 3 percent of the total in the EU and have increased by 87 percent since 1990 as air travel cheapened.
Charles said Virgin's Boeing 747-400 jet and its engines did not have to be redesigned to use biofuel on the test flight.
He said CO2 emissions on a normal flight are generally three times the fuel burned, and that technical engineers on the test flight would take readings and analyze data to estimate its greenhouse gas emissions.