a350msn001airbuspmasclet.jpg P. Masclet

Views Diverge On Bonded Repairs To Primary Composite Structures

Regulators only allow bolt-on metal repairs to primary composite structures on the latest generation of aircraft—just like standard metallic-build versions—because of concerns over the strength, quality and durability of manually bonded repairs.

MADRID—Executives from Air France Industries KLM Engineering & Maintenance (AFI KLM E&M) and Bombardier Aerospace agreed there is still some way to go before bonded repairs will be accepted on primary composite structures.

Regulators only allow bolt-on metal repairs to primary composite structures on the latest generation of aircraft—just like standard metallic-build versions—because of concerns over the strength, quality and durability of manually bonded repairs. 

“There is still the debate between bonded and bolted repairs. We need both,” James Kornberg, AFI KLM E&M aerostructures product and business development general manager, said during a panel at MRO Europe. 

While Lufthansa Technik is working with Airbus and other industry stakeholders to automate and standardize bonded composite repairs as part of the Composite Adaptable Inspection and Repair (CAIRE) project team, Kornberg is unconvinced. 

“It is very interesting, but practically this system cannot be used because it is not validated. Today we don’t think [it] necessary to have robot to repair these aircraft,” he said.

Kornberg argued it is too tricky, while in the field, to get the proper tooling for bonded repairs and recreate the conditions needed, so bolted repairs will continue to take the lead. 

“You cannot do bonded repair on very large areas,” he noted. “It is technically not possible, so there is a limit. It is case-by-case. You have the right have to push for bonded repairs, but it will not always be possible.”

Michael Curran, director of engineering and component services for Bombardier, agreed with Kornberg’s assessment. 

“We’re doing a huge amount of work on bonded repairs,” he said. “For instance, if something needs fixing during the manufacturing process it’s not going to be done with a bolted repair. But we have the advantage of clean rooms, autoclaves and perfect vacuums. The difficulty is reproducing that in the field.”

Both executives agreed that the prime objective is returning the aircraft to service as quickly as possible, with a minimum cost of repair, adding that bonded repairs lend themselves more to secondary structures, like nacelles and fan cowlings.

“You don’t want to touch it again. That works with bolted repairs,” Curran said.  “There is no limit to how many bolt-on repairs you could do.”

The metal fix, which carries a weight and strength penalty, will then fly with the aircraft until the end of its life, or until the structure is replaced. Curran described this as “fit and forget.”

Bombardier is working to establish bolt-on repair procedures for the CSeries, testing potential events such as heat exposure and lightning strikes. 

“The big message to take out of this is we’re not going to be doing carbon-type repairs,” he said. “These are metallic repairs that bolt-on to the structure, which should make it easier for MROs and airlines. It is not necessary at this point to do carbon repairs everywhere.”

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