Lightweight design remains the main focus when making cabin interior equipment more environmentally friendly, as weight savings translate directly to fuel burn and, hence, emissions. But airframe and equipment manufacturers are also looking at new materials with better recyclability and more efficient production techniques.

The long life-cycle of cabin furnishings - seats stay typically with their initial operator for six years, while galleys, lavatories and overhead bins stay on board longer - means the weight reductions and respective fuel savings dwarf any benefits of environmental initiatives during the equipment's production period, says René Dankwerth, vice-president research and development at seat manufacturer Recaro.

Selecting light materials is an obvious strategy to cut equipment weight. But while composites have found increasing application on new aircraft - and have always been dominant in the interiors arena - Dankwerth sees no trend in the foreseeable future towards a seat made primarily from carbonfibre-reinforced plastic (CFRP). "Carbon makes sense [in certain areas]," he says. "But this depends heavily on the components and applications."

Italian seat manufacturer Aviointeriors has switched from plastic to metal for some highly stressed parts, such as rub strips on the side cover of aisle seats. The bumpers sustain regular impact from passenger luggage and galley trolleys, and not only did metal prove to be more durable than plastic, but it can also be more easily recycled when it has been damaged beyond repair.

Francesco Varriale, Aviointeriors' technical director and head of research and development, says the manufacturer has been able to approximately halve the weight of the aluminium backrest structure of its Columbus economy class seat by switching to a higher-specification alloy. But he adds that the designers use CFRP for secondary structures such as armrests. Armrests previously comprised a metal hinge mechanism with a polycarbonate cover, but the component is now made as a single CFRP piece, saving around 40% weight.

Varriale says the company cut total weight for standard economy class seats by around a quarter to 9kg (20lb) per passenger, although he adds that the final weight depends on the airline's individual seat customisation.

Today's benchmark per-passenger-weight for a standard economy class seat is around 9kg. But French interiors group Zodiac Aerospace claims it has produced the industry's lightest coach class seat thus far at 7.5kg. The "Dragonfly" seat was introduced in 2012 after its designers cut part count by around 30% from the previous seat generation, including the recline mechanism. If operators prefer not to have the standard fixed seat back, a recline mechanism can be installed, which brings the weight to 8.2kg (18lb).

Reduction on core functionalities - such as installing fixed backrests - is one of four ­approaches which, combined, should lead to optimum lightweight engineering, Dankwerth says. The other three avenues are component design improvements, careful material selection and enhanced manufacturing methods.

Dankwerth questions whether the "substantial" weight penalty of the recline mechanism is justified on short-haul routes with less than two hours' flight time where, he argues, passengers tend not to use the recline function. Air France selected Recaro's SL3510 economy class seat with a slightly more angled than usual (15˚) but fixed backrest for part of its A320-family fleet in 2010.

Dankwerth admits that such minimalism would not be appropriate on longer flights. But Boeing's director for environmental ­performance, Jeanne Yu, is more categorical about the matter, saying that the "green" objectives should come neither at the expense of passenger comfort nor at a prohibitive price premium when the operators purchase the equipment. "This is not a question of either/or," she says, "but of function and [at the same time] being more environmentally progressive."

More sophisticated component design has, for example, been achieved for the footstep on the seat's aisle side to reach the overhead bins. Recaro fixed a U-shaped metal step to the seat structure in the past, but the company's engineers have redesigned the plastic side cover to serve as a step, thus abandoning the need for a separate component. Instead of a conventional passenger footrest made from aluminium and steel that weighs 1.3kg, the manufacturer developed a foot net that is largely made from elastic fabric, cutting down the part's per-passenger-weight to 0.4kg.

US interior group B/E Aerospace has slashed the weight of its latest-generation galley inserts by "well over 10%" in a typical widebody passenger cabin, says Grant West, vice-president for sales and marketing for interior systems. The coffee-makers, ovens, wine chillers, etc, are part of the company's "Essence" product line, which has been developed as buyer-furnished equipment for the A350 and will become the manufacturer's main platform for different aircraft, although additional types have yet to be determined.

In the galley arena, too, the use of carbon­fibre and other plastics has been central in cutting equipment weight. But this was a challenge, says West, as inserts such as ovens need to accommodate excessive temperatures while ensuring around 20% higher reliability than previous product generations.

Lower weight was not the only environmental objective. The engineers also reduced electricity consumption by around 10-15%, with a respective impact on fuel burn. But higher performance and efficiency had to be achieved while at the same time the equipment had to become more aesthetically attractive. West emphasises that given their vicinity to doors, galleys give passengers the first impression of the aircraft during boarding. Especially during long-haul flights, they also become gathering spaces for passengers. The aim was thus to create more ambience for what used to be mere utilitarian workspaces for the crew.

While composites have driven down aircraft weight, the synthetic material thus far remains a bugbear in recycling terms. Given the historically high use of composites in aircraft cabins, Jeanne Yu says that "one of the areas where we have been most challenged is in the interiors". While metals and components such as avionics can be easily returned to new uses, she says that composites - particularly plastics with fibreglass or carbonfibre re­inforcement - are "very difficult to recycle".

Part of the problem is that cabin interior equipment has evolved in conjunction with the materials used for the respective components - in other words, interior equipment design and materials developed in mutual dependence. It is therefore challenging to introduce alternative materials that meet all desired characteristics of their predecessors - which had been honed over decades - and yet are essentially different in their make-up to allow better re-utilisation. "It will take some time to develop [new] materials with equivalent performance," says Yu.

A part's recycling value is evaluated via three approaches: whether it contains any recycled material; to what extent it can be recycled itself; and whether the re-utilisation will lead to a product of the same or lower quality.

Boeing tested interior components, such as seat back panels, armrests and stowage bins, that were made from carbonfibre scrap material from its airframe production. Not only has this proved to be technically possible, says Yu, but the process is also less costly and energy-intensive than fabricating the parts from virgin material. She adds that Boeing considers the recycling method "certainly a great opportunity", but declines to comment when it might be employed for serial production.

One of the issues, she says, is to ensure a sufficient and reliable supply of scrap material for interior part manufacturers. Another hurdle is protection of engineering know-how. Yu says that scrap material from Boeing's airframe production needs to be cut into sufficiently small pieces to prevent disclosure of intellectual property about the original part's structure and manufacturing methods.

Composites from Boeing's production line have been tested to make parts for the automotive industry, and the US airframer has entered a research partnership with BMW for manufacturing and recycling composite materials.

Thus far, recycled plastics have not found any application in the serial production of interior equipment. Other industries have long been using shredded plastics as part of the source granulate material to fabricate components in thermoplastic injection moulding processes. But this option is not available for aerospace products because of current certification standards.

Zodiac says that 85% of the "Dragonfly" seat can be recycled. But the regenerated material has to be taken up by other industries for non-aerospace goods - and seat manufacturers today do not provide the recycling processes and infrastructure to reuse their products at the end of their lifetime. Christian Novella, member of Zodiac's executive committee and chief executive of the company's seat division, says that because of the requirement to trace aerospace material for aviation products all along the supply chain, "there is no way" to employ recycled material from other sources.

Giorgio Santero, Aviointeriors' head of industrial design, also doubts that recycling materials could be employed in future to produce components such as seat backs or tray tables for aircraft seats. He believes that the quality of such parts will not satisfy the continuously rising demand for high-performance products.

Aviointeriors focuses on employing recyclable seat covers and avoiding foams for seat cushioning as the polyurethane-based material can only be reused for related products such as mattresses. The company, based in Latina, outside Rome, uses new natural leather breeds with increased durability as well as synthetic leather and microfibre textiles as seat covers. While the lightweight synthetic leather includes recycled material from the leather industry, the suede-look microfibre is made from polyester products such as T-shirts and polyethylene terephthalate bottles.

Natural fibres have been evaluated for side panels for years. But thus far, the organic material does not fulfil certification requirements, particularly with regard to flammability criteria. Another hurdle is to develop suitable resins because, as Yu points out, the fibres' ability to decompose naturally has no benefit if the resin - in which the fibres are embedded - is not biodegradable.

Boeing continues to research the employment of natural fibres. Yu says it is still unclear when certification could be met, but she adds that her team should have a clearer picture in about a year's time. Novella thinks that natural fibres will find wider use - beyond leather covers - in seat padding and surfacing over the next five years. But he also foresees their employment as reinforcement fibre in composite parts.

Better environmental performance is not just a question of changing materials, however. More efficient use of resources can also be achieved by changing the mode of employment. Boeing and US low-cost carrier Southwest Airlines are trialling the use of carpet tiles as opposed to conventional rolls. This allows quick replacement of worn-out areas - such as the front end of the cabin aisle - locally while other, less stressed areas remain in place for further utilisation.

Source: Air Transport Intelligence news