Virgin Atlantic conducted the world's first commercial flight powered by biofuel yesterdayin an attempt to show that the fuel can produce less carbon dioxide than normal jet fuels.

"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 Heathrow Airport to Amsterdam's Schiphol Airport.

"The demonstration flight will give us crucial knowledge that we can use to dramatically reduce our carbon footprint," he said.

Some analysts praised the jumbo jet test flight as a potentially useful experiment. But others criticized it as a publicity stunt by Branson, and noted it comes as scientists are questioning the environmental benefits of biofuels.

"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.

Sunday's flight, which landed safely in the Netherlands, was partially fueled with a biofuel mixture of coconut and babassu oil in one of its four main fuel tanks.

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 is just 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 everything from finding alternative jet fuels, to developing engines that burn existing fuels more slowly, to 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 US 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 said greenhouse gas emissions from aviation account for about 3 percent of the total in the European Union 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 will take readings and analyze data to estimate its greenhouse gas emissions.

The world is currently rushing to develop biofuels, especially ethanol from corn and cellulosic feedstock such as switchgrass and woodchips, as a substitute for gasoline.

But recent scientific studies have found that almost all biofuels cause more greenhouse gas emissions than conventional fuels, if the full emissions costs of producing these "green" fuels are considered.

To support biofuel development, a large amount of natural land is being converted to cropland globally. The destruction of natural ecosystems releases greenhouse gases into the atmosphere when they are burned and plowed, and deprives the planet of natural sponges that absorb carbon emissions.

(China Daily February 25, 2008)