A certificate of airworthiness (C of A) is issued by the national aviation authority (NAA) of the country in which the aircraft is registered. An aircraft is registered in a single state only. The NAA is responsible for regulating and overseeing aviation safety within its jurisdiction and is typically a government agency or department.
“A national certificate of airworthiness or a certificate of validation issued for a non-EASA aircraft registered in the United Kingdom ceases to be in force if:
(a) the aircraft or any part of the aircraft or such of its equipment as is necessary for the airworthiness of the aircraft has been overhauled, repaired, replaced,modified or maintained…”
Air Navigation Order Section 1 Part 3
All EASA aircraft types that qualify for an EASA Certificate of Airworthiness (C of A) are issued with a non-expiring C of A, which is validated annually with an Airworthiness Review Certificate (ARC).
This annual validation occurs when a new ARC is issued or the validity of a current ARC is extended.