What do these strips do above the 787 doors?

The strips visible above the Boeing 787 Dreamliner's doors are lightning diverter strips — a critical element of the aircraft's integrated lightning protection system made necessary by its predominantly composite construction. The 787 is approximately 50 percent composite by weight, with its fuselage barrel sections fabricated from carbon fiber reinforced polymer (CFRP) rather than the aluminum alloys used in previous-generation airliners. While carbon fiber does conduct electricity to a degree, it does not dissipate lightning strike energy nearly as effectively as aluminum, which requires Boeing to engineer a multi-layered protection system into the airframe from the ground up.

The 787's lightning protection architecture is layered and distributed throughout the structure. The primary defense is an expanded copper foil mesh embedded directly into the outermost plies of the composite panels during manufacturing, providing a conductive skin that can carry lightning current along the fuselage surface. The diverter strips seen near doors, windows, and other structural discontinuities supplement this mesh by bridging areas where the conductive path might otherwise be interrupted. Door surrounds are particularly vulnerable locations because the cutout creates a break in the otherwise continuous composite skin, and without deliberate conductive bridging, a lightning strike in that zone could arc across the gap, potentially damaging door seals, actuators, or adjacent structure. The strips ensure current follows a controlled path rather than finding its own route through or around critical components.

For flight crews and maintenance personnel operating 787s, understanding the function of these strips has direct operational relevance. Pre-flight walkaround inspections on composite aircraft require a different visual vocabulary than inspections on legacy aluminum jets. On an aluminum airframe, evidence of a lightning strike is often immediately visible — scorch marks, pitting, or burn-through in the skin. On a composite airframe, damage may be subsurface and invisible to the naked eye, and the condition of the lightning protection strips themselves becomes a key inspection indicator. A missing, delaminated, or visibly damaged diverter strip near a door is not a cosmetic defect; it represents a degradation of the certified lightning protection system and requires evaluation before further flight.

The broader engineering challenge the 787 represents has shaped how the entire industry thinks about composite airframe design. Airbus faced similar questions with the A350, which uses comparable composite percentages and likewise incorporates copper mesh and conductive surface treatments. Both programs required extensive certification work with the FAA and EASA to demonstrate compliance with lightning protection standards under 14 CFR Part 25 Appendix F and the associated Advisory Circulars — standards originally written with metallic structures in mind. The certification experience from the 787 and A350 has informed how newer composite programs, including regional jets and advanced air mobility platforms incorporating significant composite structures, approach the problem of electromagnetic effects from the outset rather than as a retrofit.

For corporate and charter operators flying 787-8 or 787-9 variants under Part 91K or as managed assets, awareness of these systems matters at the contractual and maintenance planning level as well. Composite airframe MRO requires specialized inspection capabilities — including eddy current, ultrasonic, and thermographic inspection — that not all maintenance providers possess. Post-lightning-strike return-to-service on a 787 is a significantly more involved process than on a 737 or older widebody, and operators should ensure their maintenance agreements and AOG support contracts reflect the specific inspection protocols applicable to composite primary structure. The strips above the doors, modest as they appear, are a visible reminder of the substantial engineering investment required to certify and maintain a structure that departs fundamentally from aluminum aviation's century-long baseline.