Not sure it’s as simple as you suggest, JT.
.. and, as I am not routinely involved with the certification system these days, you may well be quite correct .. my observations are based on dated involvement and pertinent reading.
you have to first work out whether an aircraft is or is not a state aircraft, in order to go on to work out whether the aircraft is DGTA’s responsibility or CASA’s responsibility.
Not sure I follow the logic here. Perhaps you can amplify a bit ? If the frame is to go on an ADF registration, it belongs to DGTA .. if VH then CASA although DGTA may exercise some control via the AMO authorisations for the maintainers depending on how the support might be set up.
A CT-4 with ‘VH’ on the tail is only ever flown by PICs that are ADF trainees or ADF instructors, in the course of their duties as ADF members. Which regulator is responsible for the airworthiness and maintenance management of that aircraft?
AirFlite, under contract to BAe, maintains the Victa fleet, as far as I am aware ? and operates under the 059 ? so, I guess, responsibility remains with DGTA. However, the Australian registration would require the usual interaction with the CASA system.
Hawker Pacific, on the other hand, maintain the KingAirs principally to the civil requirements (albeit that they are on the State Register) while complying with DGTA requirements (the 053 - but not the 059) along the way.
As far as I am aware, both fleets are under DGTA control.
I presume that the SPA program is largely civil under the Qantas system ?