Airworthiness is the state of a plane being fit and safe to fly — not “this pilot is skilled” and not “the weather is fine,” but “this machine, as it stands, meets the rules for flying.” Aviation authorities issue airworthiness certificates; engineers inspect a plane for airworthiness; after a scare, news asks about the airworthiness of the fleet. It is a legal, technical noun, not a dinner-table word. The related adjective is airworthy: a plane that is airworthy is safe to fly. This word is that safety treated as a quality you can check, fail, or certify. Though actually, people sometimes use it loosely to mean “this plane feels trustworthy,” but in real aviation it is a paper-and-inspection matter, not a feeling.

適航性。正式航空用語；「適航證明」就是證明這架飛機可以安全飛。