When an aircraft has a structure made from composite materials, how is protection provided against lightning strikes?

• A. The composite is coated with paint
• B. The composite material contains a layer of conductive material
• C. The aircraft uses a separate metal skin
• D. Lightning protection is not needed

Answer: (B)

Lightning can cause severe damage to a non-conductive composite, so a low-impedance path for the current must be provided. The protection comes from embedding or attaching a layer of conductive material within the laminate—such as a metal foil or a conductive mesh—so the lightning current can spread across a broad area and flow into the aircraft’s bonding network rather than concentrating in one spot. This conductive layer acts as a path that carries the current away from the resin and fibers, protecting the structure from overheating and delamination. Painting the surface, which is typically nonconductive, does not establish this path and thus isn’t sufficient by itself. In some designs a separate metal skin is used, but the standard, effective method for composites is to include a conductive layer in the material itself.