At almost 1,000 degrees Celsius, yellow-orange flames shoot out of the blow­torch to a length of some 30 centi­meters. For nearly two minutes now, the flames have been relentlessly barbe­cuing the air­craft seat from the left-hand side. Then, after precisely 120 seconds, the torch goes out. Any remaining pockets of embers are immedi­ately extin­guished and a light veil of smoke fills the test cabin. Once it clears, we can see the extent of the damage. How much remains of the seat cushion, backrest and cover will decide whether or not this par­ticular mix of materials will get its wings. As per FAR/CS 25.853, the flamma­bility regulation that applies to Europe and the United States, the fire must not spread more than 43.2 centi­meters from the source. That’s the width of the narrowest aircraft seat.

“All textiles used in aircraft cabins must be flame-retardant,” says Daniela Grunder, Director Brand Communi­cation & Product Manage­ment at Lantal Textiles AG. Based in Langenthal, Switzerland, the company specializes in fabrics for the aviation industry and manu­factures products including seat covers, carpets, curtains and wall coverings. All the major air­craft manu­facturers as well as more than 300 air­lines—including Swiss Air, Lufthansa, Delta and China Airlines—place their trust in the expertise of this company located in the Canton of Bern. This makes Lantal a world leader in its industry.

Every decigram counts

According to Grunder, having flame-retardant properties is just the first require­ment fabrics must fulfill if they are to be used in air­craft cabins. “Aircraft textiles should also be wear-resistant, stain-resistant, non-toxic and—most importantly—as light as possible,” she says. After all, the lighter the air­craft, the lower the airline’s fuel con­sump­tion and, in turn, its CO₂ emissions. Extrapolate that to the level of an entire fleet of some 100 air­craft and reductions of even a tenth of a gram per seat cover can quickly result in six-figure savings. Still, more light­weight textiles have their drawbacks; for example, a slimline aircraft carpet is thinner and often less resistant to wear than its heavier counter­parts. Plus, the more lightweight versions tend to get dirtier faster.

Look and feel

Another key factor for seat upholstery is that it feels good against the skin. Wool does this best, partly because it absorbs moisture and as such doesn’t feel “sweaty,” Grunder explains. But com­pared to artificial fibers like polyamide or poly­ester, fabrics made from natural fibers can be heavier. “Given the many, often varying, require­ments that air­craft textiles must fulfill, there is no one best fabric or carpet for every case,” Grunder says. “The decision as to which material or material blend gets used and where depends on the individual customer’s require­ments.” While one customer might place greater emphasis on comfort, another will be more con­cerned with reducing fuel con­sump­tion—and yet another will want both.

But occasionally it’s simply a matter of taste: when it comes to carpets, European air­lines almost always favor products with a very high wool content, while US air­lines are just as adamant about having the synthetic material polyamide. “A more tech­no­logical look simply goes over better in that market,” Grunder says. A blend of wool and polyamide is the standard for seat covers, with wool fibers ac­counting for 89 to 95 per­cent of the fabric. Grunder says polyester’s use in seat upholstery is dependent on being combined with what are known as fire-blocking materials. This may for instance be Kynol®, a special heat- and flame-resistant fiber used for electrical insulation in high-per­for­mance electronics as well as other applications.

Fighting fire with physics

What sets this high-performance textile apart is its high limiting oxygen index, or LOI for short. Expressed as a per­centage, this describes the oxygen concen­tration in the air at which the fibers start to burn. Kynol® has an LOI of 30. Oxygen generally makes up 21 per­cent of the air we breathe; at that con­cen­tration, this special fiber won’t even smolder. Wool has an LOI of 25. This is why poly­amide and poly­ester—with their LOI of 20—are blended with a very high pro­portion of wool; it’s the natural material that makes this fabric flame-retardant. “How well textiles burn can, however, be influenced by the tech­no­logy used to make them,” says Wilko Reinck, Chief Aviation Engineer at safety belt manu­facturer Schroth, based in Neheim, Germany. “Tightly woven fabrics allow very little oxygen to reach the surface of the fibers, which keeps fire from spreading.” In addition, tech­nical weaves can be given a flame-retardant coating. This is just one method Schroth employs to make its polyester safety belts fire-retardant as well as extremely mech­anically robust: its belts can withstand loads of at least 2.2 metric tons.

Safety and security thanks to the Fly-Bag

If worst comes to worst, even higher demands are placed on the four-layer aramid fibers used in the Fly-Bag. Made from the same fiber used in the better-known DuPont brand Kevlar®, this flexible luggage container is designed to provide pro­tection from explosions. The basic idea is that items of luggage or suspicious objects are placed inside the Fly-Bag. Should a hidden explosive device detonate, the high-tensile layers of heat-resistant aramid make sure the blast waves, heat and shrapnel remain inside the bag. “What the Fly-Bag does is dissi­pate the energy of the explosion, which in turn prevents the air­craft from sustaining major damage such a hole in its fuselage—the very thing that caused the Lockerbie air disaster in 1988,” says Heike Illing-Günther, Research Director at the Sächsisches Textil­forschungs­institut (STFI), Chemnitz University’s institute of textile research. Illing-Günther, who played a major role in the develop­ment of the Fly-Bag, believes that a compact version for use in the air­craft cabin could enjoy success on the market.

“In addition to being lighter than the large versions, the main advantage of a small Fly-Bag is that it wouldn’t affect loading procedures,” she says. The larger safety bags designed for the hold add at least one step to the process: the cargo has to be put into the bag, which must then be sealed. This costs time, which is enough for the airlines to reject the idea. A small Fly-Bag wouldn’t have to be loaded, making it simply another way to increase safety. “If an unclaimed object—say a mobile phone—is found in the cabin after takeoff, current safety protocol is for the aircraft to land imme­diately,” says Illing-Günther. But if the crew could put the suspicious object in a small Fly-Bag, the airline would have the option of allowing the flight to proceed as planned.

Smart textiles

Regardless of whether the Fly-Bag makes it on board, Thomas Stegmaier, Research Director for technical textiles at the German Institutes of Textile and Fiber Research Denkendorf, says we can all expect a great deal from the devel­opment of textiles for aircraft applications. “What’s going to be really interesting are smart textiles with additional functions,” says Stegmaier. Take the work currently being done on self-illu­minating textiles, which incorporate metal fibers that emit light when electrified. “Upholstering the aircraft cabin ceiling with this kind of fabric would mark a signi­ficant reduction in weight,” says Stegmaier. “Ulti­mately, that’s what all devel­opments in textile tech­no­logy are trying to achieve.”