he Office of Airspace Regulation ... is required by Ministerial Direction to implement international best practice in airspace management.
What law says the OAR must comply with ‘Ministerial Directions’, and where is the Ministerial Direction that says the OAR must implement international best practice in airspace management?
It might be worth having a look at what the Airspace Act actually says (here: https://www.legislation.gov.au/Details/C2016C00178 )