Reference: Regulation (EU) No 1178/2011 on Aircrew and its amendments, Regulation (EU) No 965/2012 on Air Operations and its amendments
When Regulations are published in the Official Journal of the European Union they invariably include several dates. The date of entry into force is usually expressed as the 20th day following publication of the Regulation in the Official Journal of the European Union. It means that the EU rules have been adopted and published - thus producing legal effects -, but are not necessarily mandatory on the date of entry into force. The date when they become mandatory is the date of applicability.
The Aircrew Regulation applies from 8 April 2012.
The Regulation (EU) No 965/2012 on Air Operations applies from 28 October 2012. Its further amendments have different dates of entering into force and of applicability.
However, since Article 12 of the Aircrew Regulation and Article 10 of the Air OPS Regulation include several opt-out provisions, this means that entire Annexes and/or specific parts of the Annexes will not be applicable until the end of the out-out periods, in case Member States take up this possibility. This means that the entry into force and applicability dates are common to all Member States, but due to the possibility of opt-outs, concrete implementation of specific provisions of Annexes or entire Annexes may vary among Member States. Please find Derogations to Aircrew Regulation ((EU) No 1178/2011, (EU) No 290/2012) and Air Operations Regulation ((EU) No 965/2012 and (EU), No 800/2013) here.