14 C.F.R. § 39.5 : Aeronautics and Space — FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION — AIRCRAFT — AIRWORTHINESS DIRECTIVES — When does FAA issue airworthiness directives?
FAA issues an airworthiness directive addressing a product when we find that:
(a) An unsafe condition exists in the product; and
(b) The condition is likely to exist or develop in other products of the same type design.