1. The Commission shall assess the adopted draft performance plans referred to in Article 23, including the consistency of performance targets for en route air navigation services with Union-wide performance targets, in line with the criteria and conditions laid down in the implementing acts referred to in Article 28, point (b), and the allocation of common costs between en route and terminal air navigation services according to the general principles referred to in Article 21(4), point (l). The assessment of the consistency of performance targets for en route air navigation services with Union-wide performance targets shall take into consideration performance improvements over time. The Commission shall review the performance targets for terminal air navigation services in light of the elements specified in the implementing act referred to in Article 28, point (b).