Definition
A block of airspace of defined vertical and lateral limits, assigned by Air Traffic Control to provide separation between specific activities (often military operations) and other IFR traffic. It is established when the activity cannot reasonably be contained inside published special use airspace.
Plain English
A temporary chunk of sky that ATC sets aside for a specific activity, usually military training, and keeps other aircraft out of while it is active.
Context Anchor
You may see ATCAA in airspace descriptions, flight planning information, or ATC coordination related to military or special flight activity.
Why Pilots Care
An active ATCAA can force route or altitude changes and must be avoided unless cleared to enter.
Intuition Check
Do not assume an ATCAA is the same as a restricted area. It is airspace assigned by ATC for separation, not automatically a pilot-prohibited area by itself.
Example Sentence 1
Center advised us we were being vectored south to stay clear of an active ATCAA above FL240.
Example Sentence 2
ATC cleared us to climb through the ATCAA only after the military aircraft had finished their exercise.