Definition
An ATC Assigned Airspace (ATCAA) is a block of airspace, typically above FL180, that Air Traffic Control assigns to a specific user (often the military) for activities requiring separation from other IFR traffic. While active, ATC will not route other aircraft through it. It is established and released by ATC as needed, rather than being charted as permanent special use airspace.
Plain English
A chunk of high-altitude airspace that controllers temporarily set aside for one user — usually the military — so other aircraft are kept clear of it while the activity is underway.
Context Anchor
Seen when reading about civilian aircraft operating near special use airspace, especially where military activity and ATC routing may overlap.
Why Pilots Care
Entering an ATCAA without clearance risks conflict with military traffic and violates airspace rules.
Intuition Check
Do not read “assigned” as “owned” or “prohibited to all aircraft.” Here it means ATC has designated a defined area for a specific activity and is using separation procedures to protect other instrument traffic.
Example Sentence 1
Center advised us to expect a deviation around an active ATCAA being used for military refueling at FL250.
Example Sentence 2
ATC routed the flight around the active ATCAA to maintain separation from training aircraft.