Passengers often choose an airline because of cheap fares or a good frequent flier program.

Some day, they might pick an airline because it’s environmentally friendly.

Airlines are preparing for that moment by experimenting with a mixture of 10 percent biofuel and 90 percent jet fuel to run their jetliners. Biofuel is a renewable energy source, typically a nonedible crop such as algae, that can be blended with jet fuel for an energy source to improve air quality.

Biofuel could become the Hamburger Helper of the energy business, extending oil reserves just as pasta mixed with ground beef can make a hearty meal.

“One of the few bright points out of the current energy crisis is that it has given alternative energy a kick in the pants,” said Steven Lott, a spokesman for the International Air Transport Association, an airline trade group. The IATA wants alternative fuels to comprise 10 percent of all fuel used by the industry by 2017.

The fuels are still in the experimental stage, and their fuel economy is not known. But they would have to cost no more than jet fuel today. Jet fuel prices in the New York harbor area are up more than a dollar a gallon from a year ago.

Lott said the aerospace industry also must find a fuel that does not freeze at high altitudes and can be used in aircraft that might be in an airline’s fleet for up to 30 years.

Continental Airlines plans to experiment later this year with a biofuel Boeing 737 that will fly around Houston, near the carrier’s headquarters. It would mark the first test of biofuel in a two-engine commercial aircraft, said Leah Raney, managing director of global environmental affairs for Continental. Virgin Atlantic already has conducted a test with a four-engine Boeing 747.

She declined to say what kind of biofuel Continental will use.

“It needs to be environmentally protective and something we can get within our own country,” she said. “We would want the cost to be equivalent to petroleum-based jet fuel.”

Some passengers could decide to become “green” customers just as some are business class customers.

“There is a category of people interested in reducing their carbon footprint,” she said. “If you see the way that Toyota Priuses and other hybrid cars have taken off, that’s a possibility.”

Continental, aircraft maker Boeing and GE Aviation, which builds engines, are partners in the biofuel demonstration.

It could take about a decade for biofuel planes to become widespread in the industry, she said.

Airlines would use a blend of jet fuel – a form of kerosene – and biofuel, said Terrance Scott, a spokesman for aircraft maker Boeing.

“You won’t have to do any modifications to the engine,” he said.

Chevron and Royal Dutch Shell are among the oil companies experimenting with alternative fuels, he said, and airlines such as Air New Zealand, Virgin Atlantic and Japan Air Lines also are studying the concept.

They are part of the Algal Biomass Organization.

“If you can create something that is cost competitive, you can relieve the airlines from the volatility of fossil fuels,” Scott said. “You have a lot of people looking at this.”

UOP, a unit of Honeywell International, is working with Airbus, JetBlue Airways and International Aero Engines to study biofuel use for commercial aircraft.

“We’ve been developing renewable technology for a year and a half,” said Susan Gross, a spokeswoman for UOP. “There is a lot of studying that has to be done. Airbus is hoping to test the fuel on an aircraft in two years and use it on an aircraft in service within three years.”

Companies are working on soybeans, vegetable oils, algae and jatropha, a non-edible, oil-bearing tree, as biofuels, she said.

Jatropha grows on semi-arrid land that is unsuitable for food production and can produce more than 200 gallons of fuel from a single acre. Algae can grow in the desert or in brownfields and can yield 5,000 gallons of oil per acre.

There isn’t enough algae in the world to make enough fuel for the commercial airline industry, said Gross, so a farm supply system would have to be developed.

Any biofuel has to be compatible with the current air transport infrastructure, she said.

“The goal of UOP is to create a drop-in replacement fuel so it can be used in today’s tankers, aircraft and pipelines,” she said.

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