Which organization determines the priority of use for an ATCAA?

The organization responsible for determining the priority of use for an ATCAA, or Air Traffic Control Assigned Airspace, is indeed the using agency. This agency typically represents the military units that require the designated airspace for training and operational purposes. They assess their specific needs for access and utilization of the ATCAA and decide how that airspace will be prioritized based on operational requirements and missions.

In this context, the FAA's role is more about ensuring that civilian air traffic is safely managed, while military commands might provide input regarding their training operations but do not dictate the prioritization. The Air Traffic Control (ATC) system, on the other hand, works to coordinate air traffic but adheres to the priorities established by the using agency when managing the airspace allocated for military operations. Thus, the using agency takes the lead in defining how the ATCAA will be engaged effectively in accordance with military needs.