The Certificate of Airworthiness (C of A) or Airworthiness Certificate is the formal document issued by the Hellenic Civil Aviation Authority (HCAA) to certify that an aircraft is airworthy. Every individual aircraft has to gain its own C of A which is achieved when it can be shown to conform to the certificated Type Design and is in a condition for safe operation. As a general rule civil aircraft are not allowed to fly unless they have a valid C of A.