Boeing makes the 787's fuselage out of strands of carbon fiber layered around a rotating mold by a computer-controlled robot that looks like a spider.
The thin plastic skin on Boeing's 787 Dreamliner is an engineering marvel, a mix of carbon fibers and epoxy molded into large barrel-shaped sections that are then baked at up to 350 degrees in giant ovens.
An Airbus A350 on the assembly line in Toulouse, France. Like Boeing's 787 Dreamliner, the A350 has a composite fuselage.
But while airlines love how this lightweight concoction saves fuel, the recent fire on a 787 at Heathrow Airport in London provides the first test of how difficult and costly it will be to repair serious damage. It's happening at a pivotal moment for Boeing, which is eager to show that even significant damage to a carbon-composite plane like the 787 can be repaired as quickly and effectively as in the old aluminum models. Each day a jet remains grounded costs an airline tens of thousands of dollars.
Investigators say they believe that the cause of the fire, a pinched wire on an emergency transmitter, was fairly mundane. But the damage was anything but. The high temperatures weakened the supports in a 10-foot stretch at the top of the rear fuselage and seared the paint on the top of the skin, causing the most extensive damage yet to one of the new Dreamliners.
Aviation experts say Boeing will cut out the damaged areas and glue or, probably, bolt a large patch, made of overlapping panels of composite materials, onto the shiny new plane, which is less than a year old. "That's a little like 'Phantom of the Opera,' where the guy had this mask to cover the fact that half his face was missing," said Hans W. Weber, an aviation consultant in San Diego.
Boeing will also need to install new composite supports, and possibly some made of stronger titanium, to hold that mask in place and shore up the structural integrity of the plane, owned by Ethiopian Airlines. If the damage were more extreme, the plane maker could remove the entire 23-foot-long barrel containing most of the jet's rear fuselage and snap in another one, though composite experts doubt that it will do so in this case.
Boeing said it was presenting the repair options to the airline and would not discuss them publicly. Its engineers are running computer models to analyze the costs and other trade-offs, like how much the added weight from the bracing might reduce the plane's heralded fuel savings.
Boeing executives say they have been developing the repair techniques for years, as they gradually increased the use of composite parts in other planes. And many of them are similar to the methods used with aluminum.
"We feel comfortable that we know how to address this issue and most other structural issues as they arise," Boeing's chief executive, W. James McNerney Jr., said last week.
But some analysts seemed more skeptical, saying the fire on the Ethiopian jet raised a wild card that could make the repairs much more complicated than others on the 70 Dreamliners delivered since late 2011. Boeing said it had made smaller composite repairs on a few 787s that had been hit by lightning or bumped by airport service vehicles or mechanics' tools.
Given how crucial the innovative jets are to Boeing's future - it expects to sell thousands of them in the coming decades - "they will do anything at this point to show that that airplane is repairable," said Robert Mann, an aviation consultant in Port Washington, N.Y. "We'll know how long it takes them to fix it, but realistically, we may never know what it costs."
The use of composite materials started on military jets and has grown steadily on commercial planes over the last several decades. Only 1 percent of the weight of Boeing's 747 jumbo jet came from composite parts when that jet was introduced in 1969. That increased to 11 percent by 1995 on the 777, which has an all-composite tail section. Airbus, the European plane maker, has followed the same trend, using composites on the wings and upper fuselage of the double-decker A380.
Composites now account for half of the 787's weight, which, together with more efficient engines, cut fuel consumption by 20 percent. The 787's future rival, the A350, also has a composite fuselage.
Boeing and its suppliers build the 787's fuselage out of long strands of carbon fiber coated with an epoxy resin. Resembling black masking tape, the strands are layered around a rotating mold by a computer-controlled robot that looks like a spider spinning a barrel-shaped web. The fuselage is built in several sections at plants in Japan, Italy and the United States, where the deafening sounds of metallic clanging have been replaced by the electrical whir of robots and automated systems.
These giant sections, the largest of which measures 84 feet long, are then baked and hardened in high-pressure ovens known as autoclaves. The result after several hours is a structure that is lighter than metal but just as strong. The sections are then sent to Boeing's final assembly plants - one near Seattle and the other in Charleston, S.C. - where they are bolted together.
Early on, Boeing struggled to master the new technology, discarding some sections that developed wrinkles. Building the plane with composite barrels also cuts production time and labor costs, as well as weight, by eliminating much of the riveting that holds aluminum jets together. As a result, the 787 has fewer than 10,000 holes for fasteners in its structure, compared with one million on the 747.
Still, the composite materials have created new challenges for airline mechanics, who need new maintenance tools and skills. Unlike aluminum, carbon structures do not dent visibly and require special ultrasound probes to identify damaged areas, and there is a shortage of mechanics with the right training.
To address these concerns, Boeing has devised repair kits to fix common types of damage, like when luggage carts bang against a plane.
To reduce the need for complicated fixes, and cut repair time, Boeing has engineered spare parts that can be bolted onto areas that have been prone to damage on other planes. Those include damage around the plane's nose, from pilots dragging the tail on the runway, or collisions with service vehicles near passenger and cargo doors.
"There are well-established repair techniques that have been developing to repair composite structures but it is fair to say that these recognized techniques are for smaller areas," said Mark Tuttle, a professor of mechanical engineering and the director of the Center for Advanced Materials in Transport Aircraft Structures at the University of Washington.
For minor scrapes, mechanics can make simple repairs by bonding new layers of composite over the damaged areas with epoxy and heat from portable blowers. Other damage might require casting molds, special cutting tools, vacuum seals or small-scale ovens as well as bolts to hold the new composite layers in place.
The biggest problems come with more substantial damage, like on the Ethiopian Airlines jet. In this case, experts said, Boeing has to come up with a custom repair given the extent of the damage and its location at a critical area right in front of the tail, where the vertical stabilizer is attached to the fuselage.
Airbus has taken a somewhat different approach in building its A350 jets. Instead of the barrel-shaped architecture favored by Boeing, Airbus is using 40-foot to 60-foot composite panels for each section of the fuselage. Airbus contends that the process will make for easier repairs.
But as techniques improve, and airlines perfect the ability to cut out and replace damaged pieces within a section of the fuselage, it may not make much difference in the end whether the fuselage is made out of barrels or panels.
For now, though, all eyes will be on the Ethiopian jet and how the repair is handled.
"This is a very important test for the industry and the airlines," said Mr. Weber, the aviation consultant.
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