Mobility

Efficient aviation: The sky is the limit

Air travel's popularity is soaring, a problem for the climate. To reduce fuel use and carbon emissions airlines and manufacturers must find smarter ways to fly.
SAS Norway has reduced top speed during some of its flights to reduce fuel burn and CO2 emissions .../ Credits: SAS Norway

Every driver knows that a heavy foot on the pedal guzzles more gas than cruising down the highway at a sensible speed. If you want to save money, go easy on the gas. Up in the skies, the Norwegian division of Scandinavian airline SAS has done exactly that. It has slowed down its fleet of Boeing 737s, reducing fuel use and consequently carbon dioxide (CO2) emissions by seven to eight percent.

“The Oslo to Bergen flight [about 360km] normally produces a little over five and a half tons of CO2,” explains Helge Hafftad, environment manager at SAS Norway. “We saved just under half a ton of CO2 by reducing the standard cruise speed from 860 to 780km/h. The entire journey lasts only three minutes longer.”

Hafftad's target is is a six to seven percent reduction in total emissions. He's hopeful of beating it by not only flying slower, but also taxiing on one engine and other fuel-saving measures.

This is the kind of innovation the industry desperately needs. Aviation is the fastest growing source of global transport emissions. Successful efforts by the industry to improve fuel efficiency have been largely outpaced by explosive growth so that global CO2 emissions from airplanes continue to rise by about three to four percent annually, according to the the UN Intergovernmental Panel on Climate Change. Aviation is responsible for about two percent of global CO2 emissions and 13 percent of CO2 from transport.

One kilogram of aviation fuel (kerosene) produces about three kilograms of CO2. In addition, aircraft also produce other gases that lead to climate change, water vapor and nitrogen oxide for example. And because they are emitted at high altitude those gases have a disproportionate effect. So by 2050, the IPCC estimates, the global aviation industry will emit about three  percent of CO2 emissions but be responsible for about five percent of the potential warming effect.

At the same time, the increasing price of oil has elevated fuel costs above labor and maintenance as airlines’ largest expense, and the European Union is in the process of bringing airlines into its carbon emissions trading scheme, effectively a a carbon tax.

All of these factors are prompting airlines and aircraft manufacturers to look harder for ways to burn less fuel. In 2008, the aviation industry agreed to continue to improve fleet fuel efficiency by 1.5 percent per year until 2020.

Operational improvements

How will they do it? Airlines cannot wait for the next generation of lighter, more aerodynamic planes, or super-efficient engines running on biofuels, says Helge Hafftad. They must find imaginative ways to act now. “It’s all about the art of the possible,” argues Ian Poll, professor of aerospace engineering at Britain’s Cranfield University. “It will take 20 years to see the benefits of new technologies. Operations should be the first place to start.”

Operations covers everything the airplane does from switching on its engines at the departure gate to shutting them down at the arrival gate. Optimum operational performance requires close coordination between airlines, airport operators, local authorities, and air traffic controllers. The International Air Transport Association (IATA) maintains a list of best practices that include:

Reducing tankering: Different countries have different prices and taxes for kerosene. To save money, aircraft fill up in cheaper countries with much more fuel than they need. This ‘tankering’ weighs the plane down so it burns two to four percent more fuel. With less tankering, less fuel is wasted.

Fitting winglets: Small vertical winglets attached to the end of the wings reduce drag in the air. These could cut fuel consumption on SAS Norway’s flight from Oslo to the Canary Islands by as much as five percent.

Lightening up: Refitting aircraft with lighter seats saved one airline 900kg in weight (2.1 percent of the aircraft’s total) which prevented an estimated 3,700 tons of CO2 emissions.

Using ground power: Air conditioning, lighting and other cabin functions are often powered by engine fuel while the plane is on the ground. Using power from the airport instead, one airline saved 10,000 tons of CO2 emissions in a year.

Reducing taxiing: IATA says that up to six million tons of CO2 could be saved by reduced aircraft engine taxiing on the ground, either by towing  or using only one engine.

Descending continuously: Traditional approaches involve airplanes descending, then leveling off, and descending again, repeated several times. This may be more comfortable for passengers and air traffic controllers, but it wastes fuel. Continuous descent approaches (CDA) tested by SAS Sweden at Stockholm airport saved 100 kilograms of fuel per landing.

Several of these measures are largely dependent on efficient air traffic control, a key focus for the industry. IATA calculates that reducing flight time by even one minute globally would save 4.8 million tons of CO2 every year. But because of the tangle of national air traffic control systems, safety considerations, congestion, and reserved military airspace, many flights take circuitous routes. In Europe, the average extra distance flown is 9 to 11 percent of the total flight distance.

In Australia, the Flex Tracks system allows pilots to adjust their routes based on optimum winds. In the first 50 days of operations between Singapore and the Australian east coast, the estimated CO2 emissions reduction was 1,580 tons. In a similar vein, Boeing is testing a "flight trajectory optimization" system that can be handled from the cockpit. The entire aviation industry is pressing authorities for more direct routes.

Notwithstanding all these measures, it is increasingly difficult to find new operational improvements, admits Hafftad. Ian Poll also fears that such improvements will be “eaten up” by runaway growth in aviation.

Operational changes are not enough. They must be acccompanied by technological advances to the aircraft themselves.

What are aircraft manufacturers doing?

Although we may have to wait for them, more sustainable aircraft are of course enormously important. And manufacturers are responding to the demand. For example, Virgin Atlantic’s says its new Airbus A330 aircraft are up to 15 percent more fuel efficient per passenger than the aircraft they replaced. From the end of 2012, Airbus plans to introduce large vertical wingtips, called Sharklets, on its A320 model which, the company says, will reduce fuel burn by 3.5 percent over long distances. Airbus claims that more than 90 percent of its R&D investments are for the benefit of the environment.

Airbus's main rival Boeing has meanwhile kitted out a 737 jet, the "ecoDemonstrator", with new technologies that will, it predicts, reduce fuel consumption by as much as two percent, lower noise, and validate sustainable materials.

These include: wing trailing edges that change shape to suit a particular phase of flight, thereby increasing aerodynamic efficiency; a hydrogen fuel cell to power airplane electrical systems thereby minimizing the need for the engine to burn fuel to power fridges or lighting: carpet tiles made of recycled materials; and flights using biofuels.

Airlines and manufacturers are betting big on aviation biofuels, currently blended with kerosene. Airbus believes that by 2030 biofuels could provide up to 30 percent of all commercial aviation jet fuel and argues that sustainable, non-foodstuff biofuels should be reserved for the avaition industry. 

Biofuels are currently blended with kerosene in aircraft engines and over 1,500 commercial flights have been flown on biofuels to date. Now 50/50 blend biofuels have been certified for commercial flights and the industry goal is a 100 percent aviation biofuel.

Looking even further ahead, Airbus has some radical visions of the future of flight, including aircraft made of lightweight bionic structures, passenger jets flying in formation and runway platforms that catapult planes into the air.

For Ian Poll, there is another even more revolutionary path to change. “Get rid of the gas turbine engine,” he says. “Nuclear is the obvious candidate. The U.S. Air Force researched this until the 1960s. We’ve been there before.” It is theoretically possible, but tens of thousands of mini-nuclear reactors hurling across the skies and landing at an airport near you? The public might need some persuading.


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