...
They are mandatory instructions, issued by the Minister of Transport or a any foreign airworthiness authority, that amend an approval document relating to an aeronautical product which may require modification, replacement or special inspection to ensure that it complies with approved design data and is in a condition for safe operation.
They are documents issued or adopted by the Civil Aviation Authority of the State of Registry of a given aircraft. For example, TC will adopt all FAA AD’s issued against Boeing products as the USA is the type certificate holder (TCH) for Boeing, and the Canadian aircraft register contains Boeing products.
...
Canadian ADs are issued by the Minister pursuant to the conditions prescribed in Canadian Aviation Regulation, Part V, Subpart 93 (CAR 593). Pursuant to CAR Part VI, Subpart 5, section 84 (CAR 605.84) and the further details of CAR Standards (Airworthiness Manual) 593 and 625, the continuing airworthiness of a Canadian aircraft is contingent upon compliance with all applicable ADs. Failure to comply with the requirements of an AD causes can cause the certificate of airworthiness of the aircraft to be out of force. Applications for an alternative means of compliance (AMOC) with the requirements of an AD must be made in accordance with CAR Standard 625, Appendix H.
...