Conventional aircraft made of aerospace aluminium alloys have been in operation for decades. To improve structural safety and reduce operating and maintenance costs - particularly addressing fatigue, durability and damage tolerance – hybrid or multi-material solutions have been developed. Successful solutions are for example Fibre Metal Laminates (FMLs) like GLARE put as primary skin material on the Airbus A380, and carbon fibre reinforced polymer composites as skin material on Boeing 787 and Airbus A350.

These hybrid and composites material technologies took several decades from first development towards certification of primary airframes. Along the initial development direction, many proposals for further hybridization have been made. They aim at changing constituents and lay-up configurations in FMLs, adding micro- or nanoscale interface features in composites, or working with ultrathin plies in composites to further improve performance.

While the initial developments are successfully certified, these follow-up developments seem to end up on shelves, either because they are uneconomic, or manufacturers do not know how they can be certified. While still under constructions, the new incentive to transit to clean aviation and circular economy, puts new objectives on the table. The first Airbus A380 tear down takes place raising the question how to recycle hybrid materials like GLARE. Within few decades composite aircraft will raise similar questions.

It seems that the more hybrid materials and structures become, the less recyclable the final products. Hence, structural and material engineering will find itself within a tension field: improve performance to create a more sustainable operational phase at the cost of recyclability, or aim for circular economy, at the expense of operational performance. Either way, the quest remains: how to certify the technology, and at what cost?