Special use airspace includes: restricted airspace, prohibited airspace, military operations areas (MOA), warning areas, alert areas, temporary flight restriction (TFR), national security areas, and controlled firing areas, typically up to FL180 or 18,000 ft above sea level. In addition there is often an Air Traffic Control Assigned Airspace (ATCAA) from FL180 through FL600 in which ATC plans for military operations. ATCAAs are generally not depicted on charts because flights above FL180 are subject to mandatory instrument flight rules operation requiring continuous contact with ATC.