It emerges from the judgment of the Court of 29 November 1959, in Case 8-55, Fédération charbonnière de Belgique/High Authority, that the High Authority enjoys a certain independence in determining the implementing measures necessary for the attainment of the objectives referred to in the ECSC Treaty or in the Convention on the transitional provisions which forms an integral part thereof.

The AETR judgment shows that powers which, at the outset, have not been conferred exclusively upon the European Community may become so progressively through the exercise of those powers by the Community. In this case, the implementation of a common transport policy by the Community, through the laying down of common rules of an internal nature (adoption of a regulation), excludes the possibility of concurrent powers on the part of the Member States throughout the sphere of transport. The Court of Justice, while aware that the system of internal Community measures may not be separated from that of external relations, concludes that Member States may no longer enter into agreements with third countries in this field.

In its judgment of 5 November 2002, in Case C-469/98, Commission v Finland, the Court of Justice emphasises that, even if the Community's external competence in the field of air transport may arise by implication from provisions of the Treaty, this case does not disclose a situation in which the Community's internal competence could effectively be exercised only at the same time as its external competence and, therefore, the Community could not validly claim that there was an exclusive external competence to conclude an air transport agreement with the United States of America.