Glenn,
References to the "iron ring" are in my opinion no longer warranted.
I recall when the term was first used and I believe it was meant to indicate that the CASA CEO and Board were kept in the dark by the secretive group of bureaucrats who controlled the agenda(s). While the senior bureaucrats are very powerful and operate virtually unchecked, they all work towards one aim; to protect the minister. This also protects the public service and their own jobs because they are all contracted staff and serve at the whim of the minister and his departmental advisors. Also do not forget that the present head of CASA is himself a bureaucrat.
The iron ring the, if it could be said to exist I believe is at the very top of the organisation, not CASA, but the executive branch of government; the Department of Infrastructure, Regional Development and Cities <https://www.infrastructure.gov.au>. Aviation is not mentioned however, I quote: "The Australian Government, through the department, contributes to the prosperity of the economy and the wellbeing of all Australians by fostering a viable, competitive and safe aviation industry.The department advises the Government on the policy and regulatory framework for Australian airports and the aviation industry, manages the administration of the Government's interests in privatised airports under the Airports Act 1996, and provides policy advice to the Minister on the efficient management of Australian airspace and on aircraft noise and emissions."
This is where policy is set, plans are made, and orders issued.