2. Without prejudice to Article 30(5), Member States shall define, before the start of a reference period, the charging zones for air navigation services and shall identify the air traffic service providers falling under the scope of each charging zone. The Commission shall adopt an implementing act to define the conditions under which Member States may modify or establish a new terminal charging zone during a reference period. That implementing act shall be adopted in accordance with the examination procedure referred to in Article 48(3).