Computer screens display a map showing the outline of China’s new air defense zone in the East China Sea on the website of the Chinese Ministry of Defense.
    Associated Press

    The latest flashpoint for the U.S.-China rivalry is something called an Air Defense Identification Zone, or ADIZ. China announced over the weekend that it set up an ADIZ over the East China Sea that overlaps with similar zones maintained by Japan, South Korea and Taiwan–all U.S. allies or partners. It’s an extension into the air of disputes playing out at sea. China’s move riled the region, especially Japan. The U.S. flew B-52 bombers through the zone on Monday. The back-and-forth has thrown a spotlight on a complex set of international agreements and unilateral policies that govern how one country’s military aircraft operate around another’s borders.

    What distinguishes an ADIZ from a country’s national airspace or Exclusive Economic Zone? The technical definitions lie in the small print scattered through complex treaties and national laws and regulations. Here’s a rough lexical guide to help make sense of the key terms:

    AIRSPACE – Under international law, a country’s sovereign airspace extends to the outer limits of its territorial waters, 12 nautical miles from its coastline. Most countries require all foreign military aircraft to obtain permission to enter their airspace and reserve the right to take military action, including shooting them down, if they do not. China and Japan both claim the disputed East China Sea islands known as the Senkaku in Japan and Diaoyu in China as part of their territory. They also claim sovereign airspace above them and over the waters extending 12 nautical miles around them.


    EXCLUSIVE ECONOMIC ZONE (EEZ) – According to the U.N. Convention on the Law of the Sea, each signatory state can claim an EEZ that gives it special rights to exploit marine resources up to 200 nautical miles from its coastline. When EEZs overlap, signatory states are supposed to negotiate an agreed boundary. Most countries allow freedom of passage for foreign vessels through their EEZ. However, some countries disagree on whether non-aggressive foreign military operations – such as reconnaissance patrols — should be allowed in their EEZ. The U.S. says yes; China says no. China often intercepts and tracks foreign military planes over its EEZ, but usually does not try to repel them or force them to land.

    AIR DEFENSE IDENTIFICATION ZONE (ADIZ) – An ADIZ has no basis in international law and is not overseen by any international organization. So definitions and rules vary between different countries. Typically such zones extend well beyond a country’s airspace to give its military time to respond to potentially hostile incoming aircraft. Several countries have declared them unilaterally, including the U.S. and Japan. Many of those countries require foreign military aircraft to identify themselves and their flight plans on entering their ADIZ. They will often intercept and escort foreign military aircraft in their ADIZ but will usually not repel them or force them to land unless they consider them a threat. The U.S. says it only applies ADIZ procedures to foreign aircraft intending to enter its airspace. China’s ADIZ is unusual in that it overlaps with Japan’s, South Korea’s and Taiwan’s and covers disputed territory.

    –Jeremy Page

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