Bjorn’s Corner: Aircraft Structures Part 14. Automated prepreg layup.

Bjorn Fehrm's latest installment in Leeham News' aircraft structures series shifts focus from manual dry-fiber infusion to automated thermoset prepreg tape layup, the dominant production method for primary structural components on the Boeing 787 and Airbus A350. The piece details how Automated Tape Layers (ATL)—large gantry-style machines exemplified by the M Torres equipment used on the A350 wingbox cover—apply unidirectional prepreg tape in precisely controlled ply orientations, with the Airbus example requiring more than 250 plies at the wing root tapering to roughly 40 at the tip. The article walks through the full process chain: frozen prepreg tape rolls that must be thawed and applied within controlled time windows, tacking via heat sources, vacuum bagging to compact plies and remove air pockets, and finally autoclave curing at 180°C and 7 bar pressure. For the A350 wingbox cover specifically, this cure cycle takes 13 hours, followed by an additional 8 hours to co-bond stringers—a process requiring autoclaves costing roughly $50 million each and substantial nitrogen and energy inputs.

For pilots and operators, this deep dive into composite manufacturing may seem far removed from the flight deck, but it directly explains why the airframes they fly perform as they do and why production ramp-up constraints persist across the industry. The 787 and A350 fleets—now core to long-haul widebody operations for major carriers—derive their weight savings, fatigue resistance, and maintenance characteristics from exactly this prepreg/autoclave process. Understanding the labor- and capital-intensive nature of this manufacturing method helps explain persistent delivery delays and production bottlenecks that have plagued both Boeing and Airbus widebody programs for years, directly affecting fleet planning, aircraft availability, and lease/purchase decisions for airlines and corporate flight departments alike. Bjorn notes that tape-laying itself consumes less than 30% of total layup cycle time, with inspection and other steps consuming the rest—a detail that underscores why widebody composite airframes remain expensive and why manufacturers have been racing to automate inspection and reduce non-value-added process time.

The broader significance lies in the article's closing observation that current autoclave-based processes are calibrated to a widebody production rate of only 10-15 aircraft per month—a pace that has become a critical constraint as both Boeing and Airbus attempt to meet substantial order backlogs stretching into the next decade. This bottleneck has real consequences for airline network planning, as delayed widebody deliveries force carriers to extend the service life of older aircraft, adjust route economics, or lean more heavily on secondary lease markets. The series' trajectory—moving from manual to automated methods—also signals where the industry is headed: continued investment in faster, less labor-intensive composite production (including thermoplastic matrices, which Bjorn flags as a parallel technology using PEEK/PEKK resins that can be melted and reformed rather than cured) may eventually loosen these production constraints. For business aviation and general aviation manufacturers watching this space, advances in automated composite layup could eventually filter down to lighter, more efficient airframes at lower unit costs, though the enormous capital investment required (autoclaves alone running $50 million) currently confines this technology to the highest-volume commercial programs. Pilots flying today's composite widebodies are, in effect, operating the output of an industrial process still constrained by 20th-century curing physics, even as manufacturers push toward faster, more automated alternatives explored in the remainder of this Leeham series.