Control Tower Establishment
Rosso
In years gone by, DCA/CAA used to rely on simple aircraft movement and traffic mix critieria to determine whether a control tower (or a flight service unit) was required or not e.g. total number of aircraft movement per annum, number of RPT movements pa, percentage of IFR vs VFR movements etc. These movement considerations were then overlaid with a subjective assessment of environmental factors that could impact on safety e.g. presence of terrain, adverse weather effects, complexity of surrounding airspace etc. It should be noted that there were also traffic movement criteria for discontinuing a control tower or a flight service unit.
In subsequent years, this simple establishment/discontinuance process matured to include basic collision risk modelling and societal impact modelling to determine the impacts of not only implementing a control tower but understanding the potential consequences of not establishing a tower. Proposed changes were also subject to a cost benefit assessment to ensure (safety and efficiency) benefits outweighed the cost of any new service. My recollection is that all ATS units were eventually subject to regular review but I can't recall the timing.
My understanding of the process today is that CASA now uses the aircraft movement data as a simple "trigger criteria" i.e.to determine whether a more detailed and comprehensive aeronautical study is required to support changes to airspace classifications or the air traffic service to be provided (e.g. CTAF (R), Unicom, CA/GRS or control tower). The aeronautical study conducted by CASA will establish the level of risk at an airport after consideration of all the factors listed above and make a recommendation as to the appropriate airspace classification and/or air traffic service to be provided at the airport to reduce perceived risk to acceptable levels. CASA's recommendations are then reflected in an airspace change proposal that is subject to a CBA and consultation with industry stakeholders before implementation.
Once coordinated and approved, the changed arrangements are implemented. My understanding is that CASA formally reviews the risk profile at certified airports at 5 year intervals.
Quite happy for others to correct me if my understanding of the process is incorrect as it has been some time since my involvement in such matters. But it might also be useful for you to ring CASA and ask to speak to someone in the Office of Airspace Regulation who will certainly be able to give you guidance on the correct process.