Fuel from the weed jatropha powered an Air New Zealand jet on a two-hour flight today—the world's second flight of a commercial jet on biofuel. One out of the four Rolls Royce engines on an Air New Zealand Boeing 747-400 burned a 50-50 blend of regular jet fuel and a bio-version made from jatropha.

The flight more than doubled the air time of the first biofuel flight—a 40 minute jaunt between London and Amsterdam in February. The plane climbed to an altitude of 35,000 feet and the engine performed normally, according to chief pilot Capt. David Morgan.

Jatropha—a weedy bush from Africa that produces seeds rich in oil—was selected because it is not a food crop and can be grown on land unsuitable for food production. The roughly three tons of liquid jatropha biofuel came from plants grown in India, Malawi, Mozambique and Tanzania, the airline says.

UOP, a division of Honeywell, refined the jatropha oil into a synthetic jet fuel using a process similar to that for refining typical petroleum fuels. As a result, the fuel is functionally the same as petroleum-based fuel, including not turning freezing until -70.6 degrees Fahrenheit (-57 degrees Celsius)—above the Jet A1 specification of-52.6 degrees F (-47 degrees C), according to chemist Jennifer Holmgren, UOP's general manager of the renewable energy and chemicals business.

"We can use any kind of vegetable oil—palm, jatropha—they all have the same [chemical] backbone," she says. "We just adapted what we tend to do in a [oil] refinery for this application. This is not rocket science, we feel very comfortable scaling this up."

She adds, however, that this fuel is not a "drop-in replacement" for Jet A1. That's because jet fuel from petroleum contains so-called aromatics—hydrocarbon rings—that interact with the seals in current engines, helping swell them shut. "We don't make aromatics through the vegetable oil route," she says. "If we wanted to fly on 100 percent [biofuels], there are issues around O-rings and things like that."

The appeal of such biofuels is that the growing of the plants ostensibly absorbs as much carbon dioxide (CO2)—the most common greenhouse gas warming the planet—as is emitted when the fuel is burned. Although airplane travel contributes only 3 percent of global greenhouse gas emissions, according to the U.N. Intergovernmental Panel on Climate Change (IPCC), the emissions are of particular concern because they occur high in the atmosphere.

The flight, originally planned for Dec. 3, had been delayed due to an unrelated Air New Zealand-owned plane crash in November. On Jan. 7, Continental Airlines plans to fly a similar two-hour flight out of Houston with an engine burning a 50-50 blend of petroleum-based jet fuel and biofuel from algae and jatropha. Japan Airlines plans to fly on a biofuel made primarily from camelina—an oilseed plant—on January 30.

Though environmentally sound, however, economics may delay a switch to the alternative fuel. Plant-derived fuel is now significantly more expensive to produce than the fossil fuel variety thanks to a drop in oil prices, making it a less attractive alternative than when Virgin Atlantic conducted the first commercial biofuel test flight in February. It remains to be seen whether that will affect Air New Zealand's goal that biofuels make up 10 percent of its nine million barrel-a-year fuel use by 2013—or the broader industry group the Air Transport Association's goal of 10 percent of all aviation fuel by 2017.

"Eighty-five percent of the cost [of the biofuel] is the feedstock," Holmgren says. "It's pretty hard when the jet fuel made from oil sells at a lower price than soy."