Aircraft Sustainability Constrained by Long Life, High Cost, and Massive Fuel Consumption

The “greenness” of a manufactured product is determined by multiple factors, including its material composition and the environmental impacts of the manufacturing process, as well as the lifecycle impacts of the product itself. Aircraft, however, are distinct. A plane is a very large, very expensive object that lasts for decades and, most importantly, consumes a tremendous amount of fuel during that lifetime. This means that, in aircraft manufacture, sustainability efforts inevitably focus on the fuel efficiency of the plane. The drive to reduce emissions, coupled with increasing prices for crude oil, means manufacturers have strong incentives to develop fuel-efficient aircraft.

It’s not easy to find information about the lifecycle and environmental impacts of a single airplane, but consider the following back-of-the-envelope calculations:

  • Boeing delivers a net average of about 731 aircraft a year. The company emitted 1.25 million metric tons of carbon dioxide equivalent (CO2e) in 2011. That’s roughly 1,709 tons of CO2e for the manufacture of each plane.
  • American Airlines has a fleet of about 605 planes. The company had direct CO2e emissions of 26.85 million metric tons in 2011. That averages out to roughly 44,382 tons of CO2e per plane per year.

Consider that an aircraft can easily last 30 years, and you can see that the environmental impacts of manufacturing a plane make up a very small percentage of that plane’s lifecycle impacts. In the big picture, it’s not making aircraft that causes concern; it’s running them.

The Air Transport Action Group (ATAG) says the global airline industry has committed to improving fuel efficiency by 1.5 percent per year through 2020, capping total industry CO2 emissions starting in 2020, and reducing emissions by 50 percent by 2050, relative to 2005 levels. The group says that in 2011, air travel globally emitted 676 million tonnes of CO2, about 2 percent of total global emissions.

Global airline fuel efficiency commitments. Credit: ATAG.

Global airline fuel efficiency commitments. Credit: ATAG.

New Technologies Achieve Continuous Improvement in Fuel Efficiency

The International Civil Aviation Organization (ICAO), a United Nations agency, operates a system of standards for air transport emissions that has been setting increasingly strict emissions targets. These standards are driving continued improvements in the emissions performance of aircraft.

Aircraft manufacturers have a strong record of responding to the call for greater fuel efficiency. In its 2011 Environment Report, Boeing says that “Improved fuel consumption is at the core of our research-and-development efforts.” Conserving one gallon of fuel prevents 21 pounds of CO2 emissions, or 3.16 kilograms (kg) of CO2 for each kg of fuel.

ATAG believes that out of all measures on the table, “technology has by far the best prospects for reducing aviation emissions.” This is being achieved through such means as “revolutionary new aircraft designs; new composite lightweight materials; radical new engine advances; and the development of sustainable alternative jet fuels which could reduce CO2 emissions 80 percent, on a full carbon lifecycle basis.”

Aviation consultant John Goglia, former aviation professor and member of the National Transportation Safety Board, said in an interview that two basic measures have made jet engines more fuel efficient. One, he said, has been to improve “the technology of the nozzle that sprays the fuel,” configuring “the size of the droplets and the spray pattern to get the maximum thermal efficiency.” The other measure “has been to raise the temperatures inside the engine to get the maximum thermal efficiency out of every ounce of fuel.” In new engines, Goglia stated, “the temperatures inside the burner cans can be higher than the melting temperature of the base metal itself. The flame is actually suspended in the middle of the burner can.” This allows for a higher combustion temperature. “The technology has really advanced,” he said, “and that’s where the real fuel savings come from.”

Four Boeing 787 Dreamliners in final assembly. Credit: Boeing.

Four Boeing 787 Dreamliners in final assembly. Credit: Boeing.

Boeing says its new 787 Dreamliner (recently grounded because of problems with the lithium-ion batteries used in the planes), “with its composite fuselage and wings, is designed to be 20 percent more fuel-efficient than [previous] airplanes of comparable size.” The company’s 747-8, the newest version of the Boeing 747, “with its advanced engines and systems,” has “the lowest seat-mile cost of any large commercial jetliner…, provides 16 percent better fuel economy and 16 percent lower carbon emissions, and generates a 30 percent smaller noise footprint than the 747-400,” which was first delivered in 1985.

These kinds of improvements are part of a long-term trend toward fuel efficiency in aviation. Compared to earlier jetliners, such as the 707, built from 1958 to 1979, Boeing says “today’s commercial airplanes generate 70 percent fewer emissions and have a 90 percent smaller noise footprint.” The company is “committed to deliver at least a 15 percent improvement in fuel and CO2 efficiency with each new generation of commercial airplane.” The company is now flying an ecoDemonstrator 737 to test new low-emission and low-noise technologies. The program is exploring such technologies as “ceramic matrix composite acoustic engine nozzles, advanced inlets, and adaptive wing trailing-edge flaps that can help reduce fuel consumption and noise during the takeoff, climb and landing phases of flight.”

Improvements in fuel efficiency are driving purchases of new aircraft. American Airlines says that in July 2011 it placed “the largest aircraft order in aviation history” for 460 narrow-body jets from Boeing and Airbus for delivery between 2013 and 2022, along with 465 option positions. The company says this order will put it on track to assemble “the youngest, most fuel-efficient fleet in North America in roughly five years,” reducing “the average fleet age from 14.8 years today to 9.5 years by 2017.”

The fuselage of the Airbus A350 XWB is constructed more than 70 percent with composites, titanium and advanced aluminum alloys that produce a lighter aircraft. Credit: Airbus.

The fuselage of the Airbus A350 XWB is constructed using more than 70 percent composites, titanium and advanced aluminum alloys that produce a lighter aircraft. Credit: Airbus.

Composite materials are being used increasingly to make aircraft lighter and more fuel-efficient without sacrificing strength. According to ATAG, “The aviation industry has been using carbon fiber composite materials for around 30 years to manufacture certain parts of an aircraft structure.” But now, manufacturers “are using composites to build entire sections of the main body of an aircraft.” The group says the Airbus A350 and the Boeing 787 are made substantially from composite materials.

In its 2011 Southwest Airlines One Report, its corporate citizenship report, Southwest describes measures it has been taking to improve fuel efficiency for its fleet. Winglets — angled extensions on the ends of wings — reduce drag at the wingtips, thus helping with fuel efficiency. Southwest has installed winglets on 102 of its Boeing 737-300 planes and on all of its more than 400 737-700s, for an estimate annual savings of 42 million gallons of fuel. Auto-throttle technology on Southwest’s -700s is saving the airline 67,000 gallons annually.

While most of the focus in aircraft manufacturing is on greater fuel efficiency, some manufacturers report efforts to incorporate “greener” materials into their planes. Airbus, for example, says it is pursuing “environmental innovations” such as “a chemical-free milling process for fuselage panels; more environmentally-friendly painting processes; and steps to minimize energy and water consumption” during the production cycle. The company has introduced painting practices that “significantly reduc[e] the volume of paint necessary per aircraft” and that reduce the use of solvents to clean painting equipment by 90 percent.

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