Regulation (EU) No 1321/2014
(a) For the purpose of this Annex (Part-66), the competent authority shall be:
1. the authority designated by the Member State to whom a person first applies for the issuance of an aircraft maintenance licence; or
2. the authority designated by another Member State, in case it would be different, subject to agreement with the authority referred to in point 1. In that case, the licence referred to in point 1 shall be revoked, all the records mentioned in point 66.B.20 shall be transferred and a new licence shall be issued on the basis of these records.
(b) The Agency shall be responsible for defining:
1. the list of aircraft types; and
2. what airframe/engine combinations are included in each particular aircraft type rating.
AMC1 66.1(a) Competent Authority
ED Decision 2023/019/R
A competent authority may be a ministry, a national aviation authority, or any aviation body designated by the Member State and located within that Member State. A Member State may designate more than one competent authority to cover different areas of responsibility, as long as the designation decision contains a list of the competencies of each authority and there is only one competent authority responsible for each given area of responsibility.
The purpose of 66.1(a)2 is to allow the possibility for a person who already holds a Part-66 licence issued by one Member State (i.e. Member State X) to replace it by a Part-66 licence issued by another Member State (i.e. Member State Y).