adiz

area of secure airspace extending upwards from the surface (especially along a border)

An Air Defense Identication Zone is defined as "the area of airspace over land or water, extending upward from the surface, within which the ready identification, the location, and the control of aircraft are required in the interest of national security." Typically, aircraft entering an ADIZ is required to radio its planned course, destination, and any additional details about its trip through the ADIZ to a higher authority, typically an air traffic controller. ADIZs typically occur along international borders, but can also surround areas of high security, such as the airspace above the American capital of Washington, D.C. ADIZs are commonly used as part of international airspace control arrangements in many countries, including the United States, Australia, and Japan.
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The area of airspace over land or water, extending upward from the surface, within which the ready identification, location, and control of aircraft are required in the interest of national security. Air Defense Identification Zone (ADIZ) locations and operating and flight plan requirements for civil aircraft operations are specified in FAR Part 99. (FAA4)

Air Defense Identification Zone
  

(See AIR DEFENSE IDENTIFICATION ZONE.)