China’s Declaration of an Air Defense Identification Zone in the East China Sea: Implications for Public International Law

Jaemin Lee
August 19, 2014

On 23 November 2013, China declared an Air Defense Identification Zone (ADIZ) in the East China Sea,[1] leading to ongoing grievances of other states.[2] An ADIZ is an additional zone of aerial control beyond territorial airspace, allowing the declaring state to identify approaching aircrafts before they enter that airspace. Before China’s declaration, as many as 20 states had adopted contiguous ADIZs, mainly for the purpose of meeting national security needs.[3] China is now reported to be considering another ADIZ in the South China Sea, despite growing criticism from other states.[4] In particular, the United States and Japan contend that China’s ADIZ in the East China Sea is contrary to international law, and specifically the law of the sea. In the International Civil Aviation Organization (ICAO) Council meeting held in Montreal in March 2014, the United States and Japan submitted that China’s ADIZ contravenes the principle of “freedom of overflight” in high seas as codified in Article 87 of the 1982 United Nations Convention on the Law of the Sea (UNCLOS).[5] The controversy over China’s ADIZ has continued to escalate and the issue has become a focal point of recent statements and reports issued by countries being affected by the declaration including the United States, Japan and Australia.[6]

The legality of an ADIZ per se is relatively well settled: in principle, states have a legal basis for declaring an ADIZ adjacent to their airspace.[7] Given the frequency of this practice over several decades with relatively few objections, the legal basis is arguably found in customary international law.[8] The more difficult question, on which this Insight focuses in respect of China, is whether a particular state’s implementation of a declared ADIZ stays within the parameters of the relevant legal norms.[9] That question gives rise to broader systemic issues to be resolved in public international law, including as regards the interpretation of silence in international law and the significance of the presumption of good faith.

Military Enforcement in the East China Sea ADIZ

While the details of ADIZs differ from country to country, they share key features. In the ADIZs declared to date, aircrafts are required to submit their Instrument Flight Rules (IFR) or Defense Visual Flight Rules (DVFR) flight plans to air traffic control and report their location on request by control.[10] These ADIZs are thus mainly for flight information and identification purposes in conjunction with national security. In principle, aircraft within the ADIZs are subject to administrative or regulatory penalties in accordance with the general statutory mandate of national aviation authorities. However, these ADIZs do not provide for a direct military response or countermeasures against incoming aircraft.

The East China Sea ADIZ of China, on the other hand, arguably replaces the information gathering function of other ADIZs with a military enforcement function by formulating the ADIZ as a military emergency action plan. For instance, the relevant Chinese declaration states:

China’s armed forces will adopt defensive emergency measures to respond to aircraft that do not cooperate in the identification or refuse to follow the instructions. . . . [T]he Ministry of National Defense of the People’s Republic of China is the administrative organ of the East China Sea Air Defense Identification Zone.[11]

The shift within the Chinese ADIZ away from information gathering and towards military response is what has raised concerns about its compliance with international law.

Freedom of Overflight Under UNCLOS

To the extent that China’s ADIZ restricts flights of foreign aircraft, it may fall within the scope of China’s obligation as a coastal state under Article 87 of UNCLOS, which provides that freedom of the high seas includes the freedom of overflight. The military response to incursion in the China ADIZ that is contemplated in the Chinese declaration seems direct enough to infringe the freedom of overflight in that zone. Yet China has argued that its promulgation of the ADIZ is within its sovereign rights,[12] emphasizing that many other states, including the United States and Japan, have declared ADIZs over the years. Ultimately, China’s compliance with UNCLOS may depend on how it implements its ADIZ declaration: whether as an enhanced flight information gathering scheme (albeit for national security purposes) or as a tight military control and surveillance scheme.

The Defense of National Security or Necessity

In response to an apparent violation of UNCLOS Article 87, China could argue that a territorial airspace of 12 nautical miles (flowing from the territorial sea stipulated in UNCLOS Article 3) is too limited to defend a state from foreign aerial threats, particularly given the extraordinary velocity of modern aircrafts. Thus, as with the contiguous zone in the law of the sea,[13] some additional buffer zone is necessary to deter aerial aggression.[14] The International Law Commission’s Articles on State Responsibility do permit a state to justify the violation of a treaty by referring to “necessity” when an “essential interest” faces “a grave and imminent peril,” subject to specific conditions.[15] The increasing military tension in East Asia could play a role in supporting or refuting a necessity argument in this context. Moreover, a disproportionate military response by China to non-compliance with the ADIZ could lead to a lawful or unlawful countermeasure by another state, as seen in the 1984 U.S.-Libya conflict regarding Libya’s demarcation of “the line of death” in the Mediterranean.[16]

States’ Discretion in the Absence of Legal Norms

In the debates concerning China’s ADIZ, the problem is that the specific conduct of China is not explicitly permitted, regulated, or prohibited in public international law. In particular, we need to interpret the absence of specific norms regulating a state’s declaration of contiguous aerial blocks for various policy objectives. The United States’ position may suggest that the absence of a specific right to declare such a zone renders it a violation of international law, whereas China’s position may suggest that the absence of a specific prohibition renders its conduct allowable.

The law’s silence on particular conduct may create similar difficulties in a range of fields, as international law sometimes lags behind developments in the global landscape, due to the time taken to conclude treaties or establish customary international law. Significantly, states are presumed to act in good faith, in accordance with international law.[17] Therefore, until legal norms emerge for a particular challenge facing the international community, a state may be deemed to have acted within the parameters of international law. However, as in the case of China’s ADIZ, a measure affecting the rights of another state that are preserved in a related area of international law may still be argued to constitute a violation.


Although the legality of an ADIZ per se has now been arguably settled, the consistency of an individual ADIZ with applicable rules of international law falls to be determined on an ad hoc basis, according to its design and implementation. Since last November, the Chinese ADIZ declaration has taken center stage in the increasing geopolitical tension in East Asia, and intense debates on its legality continue. Depending on how China’s ADIZ plays out, other countries in the region may choose to follow suit by declaring their own ADIZs. As illustrated by the recent frenzy over “stealth” fighters and bombers,[18] the (military) aviation industry is engaged in rapid technological development, which may enhance the appeal and perceived necessity of ADIZs, particularly for coastal states. This factor is also likely to increase the complexity and urgency of ADIZ discussions in the future, especially if technological development continues to outpace legal development.

About the Author: Jaemin Lee, an ASIL member, is Associate Professor of Law and Associate Dean for Planning & International Affairs at Seoul National University.

[1] Statement by the Government of the People’s Republic of China on Establishing the East China Sea Air Defense Identification Zone, Xinhua News Agency, Nov. 23, 2013. 

[2] See, e.g., Press Statement, John Kerry, Secretary of State, Statement on the East China Sea Air Defense Identification Zone (Nov. 23, 2013), available at

[3] See Demetri Sevastopulo, Q&A: What Is an Air Defence Identification Zone?, Financial Times, Nov. 29, 2013, available at The 20 ADIZ declaring states include Canada, Iceland, India, Japan, Norway, the Philippines, South Korea, Taiwan, the United Kingdom, and the United States. The first ADIZ was declared by the United States in 1950. The declared ADIZs are sometimes adjusted reflecting changing circumstances. See Press Conference, Katsuya Okada, Minister for Foreign Affairs of Japan, Revision to Air Defense Identification Zone (ADIZ) Line (Jun. 25, 2010), [hereinafter Katsuya Okada Press Conference] available at

[4] Beijing Hesitant on Setting ADIZ in South China Sea, The Asahi Shimbun, Feb. 26, 2014, available at

[5] Press Release, Ministry of Foreign Affairs of Japan, 201st Session of the Council of the International Civil Aviation Organization (ICAO) (Mar. 11, 2014); U.S., Japan to Raise China ADIZ at U.N. Meeting, The Japan Times, Feb. 27, 2014; S. Res. 412, 113th Cong. (as passed by Senate, July 10, 2014).

[6] See Office of the Secretary of Defense, Annual Report to Congress: Military and Security Development Involving People’s Republic of China 9, 12–13 (2014); Itsunori Onodera, Japanese Minister of Defense, Japan’s New Security and Defense Policy: An Enduring Partnership in the U.S.-Japan Alliance, Remarks at the Center for Strategic and International Studies (Jul. 11, 2014); China’s Unilateral ADIZ Escalating Tensions, Tokyo Defense Report to Say, The Japan Times, Jul. 17, 2014; Japan Defense White Paper Targets ADIZ, Exaggerates ‘China Threat, The Global Times, Jul. 18, 2014; Media Release, Julie Bishop, Australian Minister for Foreign Affairs, 5th Japan-Australia 2+2 Foreign and Defence Ministerial Consultations (Jun. 12, 2014).

[7] J Ashley Roach, Air Defence Identification Zones, in 1 The Max Planck Encyclopedia of Public International Law 232 (2012).

[8] See Peter A. Dutton, Caelum Liberum: Air Defense Identification Zones Outside Sovereign Airspace, 103 Am. J. Int’l L. 1, 16–17 (2009).

[9] See Roach, supra note 7, at 233; Dutton, supra note 8, at 1.

[10] See Canadian Aviation Regulations, SOR/96-433I (2014) (Can.); Security Control of Air Traffic, 14 C.F.R. § 99 (1988); Air Traffic Management Procedures (Taiwan); Enforcement Ordinance of the Civil Aeronautics Act, 56 Ministry of Transport (1952) (Japan); Civil Aeronautics Act, 231 Ministry of Transport (1952) (Japan); Katsuya Okada Press Conference, supra note 3; Amendment of the ADIZ, Government Gazette (Gwanbo) (2013) (Korea) (in Korean).

[11] Announcement of the Aircraft Identification Rules for the East China Sea Air Defense Identification Zone of the P.R.C., Xinhua News Agency, Nov. 23, 2013, available at (emphasis added).

[12] See Ministry of Foreign Affairs of the People’s Republic of China, Foreign Ministry Spokesperson Hong Lei's Remarks on US Secretary of State’s Comments on China’s Establishment of the Air Defence Identification Zone in the East China Sea (Feb. 8, 2014).

[13] United Nations Convention on the Law of the Sea, art. 33, Dec. 10, 1982, 1833 U.N.T.S. 3.

[14] See Statement of Chinese Foreign Ministry Spokeswoman Hua Chunying (Feb. 21, 2014).

[15] International Law Commission, Draft Articles on Responsibility of States for Internationally Wrongful Acts, art. 25 (2001), available at

[16] For the chronological development of 1986 U.S.-Libya military conflict and positions of the two countries, see Edward Schumacher, The United States and Libya, Foreign Aff., Dec. 1, 1986, available at See also Patrick E. Tyler, In Qaddafi’s Realm, Shadows of the Caesars, N. Y. Times, Mar. 7, 2004, available at

[17] See Case Concerning Fisheries Jurisdiction (Spain v. Canada) 1998 I.C.J. 432, 505 (dissenting opinion of Vice-President Weeramantry); The Corfu Channel case (U.K. v. Albania) 1949 I.C.J. 4, 119 (dissenting Opinion of Judge Ad Hoc Ečer).

[18] See Julian Barnes, U.S. Ups Its Show of Force in Korea, Wall St. J., Apr. 1, 2013, available at; Eric Talmadge, Commander: Stealth Fighters 100 Percent ‘Safe,’ Air Force Times, Aug. 30, 2012, available at; Sean Callebs, Hagel: Stealth fighters not intended to provoke DPRK, CCTV English, Mar. 29, 2013, available at