64. In view of my proposed answer to the question referred for a preliminary ruling in so far as the question concerns the principle of sincere cooperation, there is no point in also examining the question in the light of Article 34(1) of the Charter.

65. In any case, even if the Court should hold, contrary to what is suggested in this Opinion, that that principle is not applicable to the main proceedings, the Charter would not be applicable either. It is settled case-law that the fundamental rights guaranteed in the legal order of the European Union are applicable in all situations governed by EU law, but not outside such situations. As the Court stated in the judgment in Åkerberg Fransson (C‑617/10, EU:C:2013:105), situations cannot exist which are covered by EU law without those fundamental rights being applicable. The applicability of EU law therefore entails applicability of the fundamental rights guaranteed by the Charter. Where, on the other hand, a legal situation does not come within the scope of EU law, the Court does not have jurisdiction to rule on it and any provisions of the Charter relied upon cannot, of themselves, form the basis for such jurisdiction. In the present case, it is common ground that the national legislation at issue in the main proceedings, in defining the rules for calculating the old-age pension for employed persons, does not implement secondary EU legislation. In addition, it is clear from the above reasoning that Ms Wojciechowski’s legal situation is purely domestic and is not covered directly by a provision of the Staff Regulations. Thus, it is only if the Court should, as I suggest, find Article 4(3) TEU, read in conjunction with the provisions of the Staff Regulations, applicable to the dispute in the main proceedings that Ms Wojciechowski’s situation would be governed by EU law and the Charter would therefore be applicable.

66. Finally, in the event that the Court should hold that, as the Commission maintains, that article is applicable to the dispute in the main proceedings but cannot be invoked by Ms Wojciechowski, it follows from the judgment in Association de médiation sociale (C‑176/12, EU:C:2014:2) that the Charter would still be applicable. However, I would point out that, in that same judgment, the Court, in contrast to its judgment in Kücükdeveci (C‑555/07, EU:C:2010:21) in relation to the principle of non-discrimination on grounds of age laid down in Article 21(1) of the Charter, held that Article 27 of the Charter could not be invoked independently since, for that article to be fully effective, it must be given more specific expression in European Union or national law.

67. As to the substance, I refer, mutatis mutandis, to the reasoning set out in points 60 to 62 of my Opinion in Melchior (C‑647/13, EU:C:2014:2301). While there is no question as to the ability of Member States, in exercising their power to organise their social security systems, to provide for mechanisms to cap benefits or for anti-overlapping rules, national legislation that, in situations such as the one in the main proceedings, results in eliminating the pension rights acquired by an employed person based on the contributions he made to the national scheme, for the sole reason that he has acquired a whole occupational record in an EU institution entitling him to an EU pension for a period different from that during which he contributed to the national scheme, does not seem to me to be compatible with the principles set out in Article 34 of the Charter.