Art 66 of the EASA regulation allows non-EU countries to join [stay in] EASA if they have a treaty with EU applying EU aviation law.
This is the ECAA treaty, text here - eur-lex.europa.eu/legal-content/…
First, Art 16 requires non-EU states to allow *some* jurisdiction of ECJ if their national courts receive disputes about EU aviation law. This can be less than EU members provide for, but it can't be non-existent (Annex IV).
a) Art 20 ECJ role isn't mandatory
b) Art 16/Annex IV gives option for non-mandatory use of ECJ
c) no explicit mention direct effect/supremacy (Art 3)
But it's a very fine line...*ends*