The validity of a certificate of airworthiness requires a valid Airworthiness Review Certificate (ARC) to be attached to it. The ARC is issued for one year at a time following a successful airworthiness review.
An aircraft may be provided to an airworthiness review in advance during the last 90 days of the validity of the previous review without bringing the validity of the new ARC forward. In other cases, the validity of a new ARC is determined based on the date on which it was issued.
If the aircraft has remained in a so-called controlled environment for the entire duration of the validity of the ARC, the approved continuing airworthiness management organisation responsible for the control may continue the validity of the ARC with one year up to two times. An aircraft has remained in a controlled environment if it has been in the possession of the (same) approved continuing airworthiness management organisation and all maintenance has been carried out by an approved maintenance organisation during that time.
In other words, if the continuing airworthiness of an aircraft has been managed by the owner without approval from an organisation (which is fully permissible for privately used simple aircraft not used for commercial air transport), the aircraft has not been operated in a controlled environment. In this event, the validity of the ARC cannot be continued; instead, a new airworthiness review must always be carried out when the validity of the ARC ends. This must also be done if the aircraft has been serviced by some other organisation than an approved maintenance organisation (a maintenance mechanic without an organisation) during the validity of the ARC.
The ARC may be issued by the continuing airworthiness management organisation that carried out the review, or a CAO organisation approved for airworthiness management in accordance with Part-CAO for simple aircraft not used for commercial transport.
In addition to this, an airworthiness review can be carried out on Part-ML aircraft in connection with annual maintenance by a maintenance organisation approved in accordance with Part 145 or Part-CAO or independent maintenance personnel approved for airworthiness reviews according to Part-ML.