Reference: Regulation (EU) No 965/2012 on Air Operations, Annex III (Part-ORO)
The Essential Requirements (ER) are as applicable as the implementing rules.
The operators are responsible for checking that they comply with all the Essential Requirements contained in Annex IV of the Basic Regulation (EC 216/2008).
Some implementing rules make a direct reference to the Essential Requirements. This is the case when an ER is not further developed in the implementing rules.