14 CFR §25.581
- (a)The airplane must be protected against catastrophic effects from lightning.
- (b)For metallic components, compliance with paragraph (a) of this section may be shown by—
- (1)Bonding the components properly to the airframe; or
- (2)Designing the components so that a strike will not endanger the airplane.
- (c)For nonmetallic components, compliance with paragraph (a) of this section may be shown by—
- (1)Designing the components to minimize the effect of a strike; or
- (2)Incorporating acceptable means of diverting the resulting electrical current so as not to endanger the airplane.