As from 28 September 2003, the European Union Aviation Safety Agency (EASA) has acted as the state of design authority for type-certified aviation equipment designed in EU Member States. Before that date (or the date of accession of the Member State, if later), ADs concerning aviation equipment were issued by the national authority of the Member State in question.
The ADs issued by EASA have been published in the EASA Safety Publication Tool (External link), where users can search for directives concerning specific aviation equipment.
The ADs issued by the Federal Aviation Administration (FAA) of the United States are published on the FAA website (External link), where directives can also be searched by the type certificate holder of certain aviation equipment. (NB! The holder of a type certificate may change because of mergers and acquisitions, for example. The current holder of a type certificate may not be the same company that originally manufactured the aviation equipment.)