Cost Of Maintaining Composites Can Offset Performance Gains

Cost Of Maintaining Composites Can Offset Performance Gains
Lufthansa Technik has developed a mobile robotic scarfing system under its CAIRE project.

Carbon fiber has a long history in commercial aircraft manufacturing, but its first large-scale application was on the Boeing 787, which features composite materials for half its airframe. Airbus followed Boeing’s lead and used composites for much of the A350’s wings and fuselage, and any future clean-sheet aircraft—as well as upgrades of existing models—will lean heavily on carbon fiber as well.

Composites have several advantages over metals: They are lighter, they don’t corrode, and they exhibit better fatigue resistance. The tradeoff is that metal is easier to fix, so MRO providers need to add new tools, know-how, and processes to ensure they are capable of handling the latest aircraft.

“Before the launch of the 787 and A350, we had mainly been providing composite repair services for wet lay-up repairs of fairings and other secondary structures of an aircraft,” says Ang Chye Kiat, executive vice president of aircraft maintenance and modification, at ST Engineering Aerospace. “With the fuselage and wings of 787s and A350s now compromising composite material as well, we have grown our capabilities to support these platforms not only with repairs but also modification work.”

Inspection and repair techniques for composite materials are developing apace but are still not as mature and well-understood as those in place for common aerospace metals such as aluminum. So in some respects, the performance savings of new materials for airlines are offset by higher support costs, although the greater durability of composites should mean fewer maintenance events.

AAR has expanded its composite capabilities five-fold in the last 20 years, and its senior vice president of repair and engineering services, Brian Sartain, expects further growth as more new-generation aircraft enter service. Sartain acknowledges that composite and metal repairs require different skillsets and tooling, although he disagrees that carbon fiber is intrinsically more difficult from an MRO perspective.

“I don’t believe it has necessarily become more complex as it has driven a shift in skillsets and a greater frequency of replacing parts altogether,” he says. “Older aircraft were very labor-intensive with metal-part fabrication and very expensive in part replacement.”

On top of adding new engineering competencies to traditional metal-working capabilities, MRO providers must keep up to date with a new generation of composite materials, notably carbon-fiber-reinforced plastic (CFRP). This is much more durable than the composite material of 20 years ago but is also more difficult to work with, involving repair processes such as double vacuum debulk, which reduces the porosity in laminate plies prior to the cure cycle that hardens the CFRP.

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