Case C-413/20: Judgment of the Court (Ninth Chamber) of 18 November 2021 (request for a preliminary ruling from the Tribunal de première instance francophone de Bruxelles — Belgium) — État belge v LO and Others (Reference for a preliminary ruling — Air transport — Regulation (EU) No 1178/2011 — Technical requirements and administrative procedures related to civil aviation aircrew — Points 9 and 10 of Subpart A of Appendix 3 to Annex I — Training course for the issue of a commercial pilot licence — Flying training — Instrument ground time — Calculation — Simulator training — Skill test — Principle of legal certainty — Temporal limitation of the effects of a preliminary ruling)