China has been in the news recently for constantly breaching into Taiwanese "Air Defence Identification Zone", which apparently includes a huge chunk of space far beyond their territorial waters. At the same time it seems like the ADIZ concept is not legally binding for foreign aircraft that is headed elsewhere:

The ADIZ is simply a unilaterally established set of procedures followed by one country's air defense forces, and does not have to be "accepted" by other countries if they are prepared to have their aircraft intercepted. The US military as a matter of policy does not comply with ADIZ procedures of other countries, as this would amount to announcing planned movements of warplanes. Non-acceptance in whole or in part by other countries will keep China quite busy scrambling, and this does increase the risk of miscalculation.

However the US military itself is frequently complaining about Russian jets in the US ADIZ:

A rise in Russian military aircraft venturing near North America is straining Air Force crews who must meet them in the air. U.S. Air Force units stationed in Alaska, near America’s frozen border with Russia, say intercepts rose to 60 a year in 2020, up from just 10 in 2015, according to Air Force Times. While the aircraft in Russia’s Aerospace Forces don’t actually come near Alaskan airspace, they do require the Air Force to sortie a number of planes, from F-22 Raptors to tankers, to meet them.

So why don't countries simply sign an agreement between each other on formally respecting each others ADIZs? Without a formal agreement it looks like only civilian aircraft are actually encumbered by identification procedures while military aircraft fly wherever they wish (outside of territorial waters) and completely ignore it in practice.

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – JJJ
    Oct 10, 2021 at 0:49

4 Answers 4


You're mentioning the US stance on this but generally speaking the US is not so high on reciprocity and they have enough clout to demand or get away with things they wouldn't tolerate, from access to airspace to inspections of sensitive sites, intervention in various matters in other countries, or even clandestine or special military operations. If one of the biggest player wants to retain both the ability to fly wherever they please without permission (and they do that, even with friendly neutral countries like Austria) and the ability to ban foreign military aircraft from their own airspace, then the incentive to commit to some complex new international scheme is very low indeed.

In the specific case of Taiwan, any practical solution to make these zones internationally recognized and legally binding would entail agreeing on sovereignty over various contested territories. Between two countries that do not even recognise each other's right to exist at all (even if the idea seems to have become more acceptable in Taiwan at the end of the 20th century). That's also a complete non-starter.

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    I am curious about "even if Taiwan has recently gone much further into that direction than the PRC" -- what are you referring to?
    – cpast
    Oct 9, 2021 at 15:46
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    @cpast I am thinking about the fact that "independence" can be and is being advocated openly in the country and that high-level office holders have made gestures towards the idea of not contesting the PRC's sovereignty over the mainland (admittedly without ever making it official government policy, AFAIK). Recently might be a bit misleading, I meant since the 1990s as opposed to the beginnings of the country.
    – Relaxed
    Oct 10, 2021 at 15:52
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    @Relaxed, the confusion (mine too) stems from the fact that in your wording "that direction" seems to relate to "do not even recognise each other's right to exist". Of course, they both (PRC/ROC) start from that position. If you mean that Taiwan "has gone further" on the path of declaring independence, it implies that it also came closer to recognising PRC's "right to exist".
    – Zeus
    Oct 11, 2021 at 0:03
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    @uhoh You seem to have some issues with this statement but I am frankly unable to tell what it is as you have provided many unrelated, at times absurd or contradictory objections. To me this statement is completetly unremarkable, not at all an opinion I would care about or try to push in any way, but simply a small nuance that seemed relevant since the relationship between the two states is an integral part of my answer (and not in any way incidental to the question). Care to explain what actually bothers you about this?
    – Relaxed
    Oct 11, 2021 at 7:06
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    @Zeus Yes, that's exactly what I mean, the direction in question is “recognis[ing] each other's right to exist”, without the negation, as they indeed both start from the opposite position (which I assumed to be both completely obvious and implied by the sentence). I will rephrase, thanks.
    – Relaxed
    Oct 11, 2021 at 7:15

The ADIZ is simply a unilaterally established set of procedures followed by one country's air defense forces, and does not have to be "accepted" by other countries if they are prepared to have their aircraft intercepted.

The keyword is unilaterally. Countries are free to declare whatever air defense identification zone they want. Indeed, you can declare an ADIZ that crosses into the airspace of another country (Taiwan's ADIZ covers parts of mainland China).

If you have an agreement to formally respect each other's ADIZ, what's stopping the other country from declaring an ADIZ that covers your entire country, thereby grounding your aircraft? Because that would never work, you need an agreement to have a mutually acceptable ADIZ, which in China/Taiwan's case would also never work.

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    And accepting China's ADIZ would probably see it including the Spratleys. Oct 8, 2021 at 8:14
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    @ItalianPhilosophers4Monica And Taiwan. Oct 10, 2021 at 6:51
  • @ItalianPhilosophers4Monica Taiwan also claims The South China Sea and even has a garrison there. Oct 11, 2021 at 12:11

Without a formal agreement it looks like only civilian aircraft are actually encumbered by identification procedures

This is precisely the point of an ADIZ.

The basic idea is that a country wants to establish a "buffer zone" around its territory so that incoming aircraft, which may be hostile bombers, can be seen and intercepted before reaching the mainland. Therefore any target crossing into the ADIZ must be investigated.

It would be impossible to scramble interceptors to meet every target entering the ADIZ, so commercial traffic is required to pre-identify themselves via prior coordination (for example, filing a flight plan, or establishing radio communications with a civilian or military control facility a certain number of minutes outside the zone).

Any targets which are not identified in the proper way are then considered potentially hostile and must be investigated further, perhaps to the point of interception.

Of course, having unilaterally established such an identification zone, it is then the responsibility of the establishing country to police it and enforce its interception procedures. The ADIZ concept is useless if unidentified targets are allowed to continue without being investigated or challenged. This necessitates scrambling interceptors when necessary and makes it impossible to establish any arrangement where they will not be! You cannot expect two countries to sign an agreement saying "In times of peace we will respect each other's ADIZes, and of course when we come to bomb your country after declaring war we will be sure to file a flight plan letting you know 24 hours in advance."

Instead the ADIZ is continually defended against unidentified intruders, both for practice on the part of the defenders and to demonstrate to the intruding country that the defenders are, in fact, present. As has been pointed out in the comments, Russia does this to the US and the US also does it to Russia.

  • An ADIZ does not necessarily require the establishing country to actual do anything active. Its an Air Defence Identification Zone - this means that the establishing country just wants to identify all movements in that zone, not that they have any authority to defend it or prevent its use (hint - the Taiwanese ADIZ extends well over mainland China, but that does not give Taiwan any authority over movements there).
    – user16741
    Oct 10, 2021 at 20:38
  • @Moo I think that's covered by "must be investigated further, perhaps to the point of interception". It's not about having authority over the area, it's about having full knowledge in that area. Obviously, Taiwanese fighters performing an intercept over mainland China would be unlikely, but being ready to intercept a flight path as it leaves mainland China in the direction of Taiwanese territory would be sensible. And doing so when the plane in question is actually commercial would be a waste of time, hence the "identification" part.
    – IMSoP
    Oct 11, 2021 at 9:29

A significant part of the problem is the location of a given ADIZ. In the case of the North American ADIZ, operated jointly by the United States and Canada, there's very rarely any reason to be there unless you're either intending to enter the airspace of at least one of the United States or Canada or are just there to test NORAD's defense capabilities. Simply due to geography, there are very few direct routes between other countries that involve penetration of the North American ADIZ, but not of the actual national airspace of the United States or Canada.

This is in stark contrast with, for example, China's relatively-recently-announced East China Sea ADIZ, which lies across many very busy air routes that are important for both commercial and military traffic that have absolutely nothing to do with China, having no intent to either enter its airspace, nor to test its defenses. For example, all flights into Taipei from Korea, Japan, or North America would need to transit the East China Sea ADIZ. Granted, the People's Republic of China considers Taipei to be part of its territory, but, obviously, the people who live there generally disagree.

The enforcement of the East China Sea ADIZ would mean that all traffic across this very busy international corridor - which includes both lots of scheduled commercial flights and regular military operations of Korea, Japan, Taiwan, the United States, and others - would be required to file a flight plan with China and follow instructions of Chinese air traffic control. You can probably see why the militaries of Korea, Japan, Taiwan, and the United States wouldn't want to do that.

Another part of the problem that is sometimes overlooked is that different countries have quite different ideas of what an ADIZ is or what can be required in one. China is attempting to apply its rule to all traffic in the East China Sea ADIZ. However, as Secretary of State John Kerry noted at the time of the announcement of the East China Sea ADIZ,

Freedom of overflight and other internationally lawful uses of sea and airspace are essential to prosperity, stability, and security in the Pacific. We don't support efforts by any State to apply its ADIZ procedures to foreign aircraft not intending to enter its national airspace. The United States does not apply its ADIZ procedures to foreign aircraft not intending to enter U.S. national airspace. We urge China not to implement its threat to take action against aircraft that do not identify themselves or obey orders from Beijing.

The United States Navy's Commander's Handbook on the Law of Naval Operations further expounds on this:

International law does not prohibit nations from establishing air defense identification zones (ADIZ) in the international airspace adjacent to their territorial airspace. The legal basis for ADIZ regulations is the right of a nation to establish reasonable conditions of entry into its territory. Accordingly, an aircraft approaching national airspace can be required to identify itself while in international airspace as a condition of entry approval. ADIZ regulations promulgated by the United States apply to aircraft bound for U.S. territorial airspace and require the filing of flight plans and periodic position reports. The United States does not recognize the right of a coastal nation to apply its ADIZ procedures to foreign aircraft not intending to enter national airspace nor does the United States apply its ADIZ procedures to foreign aircraft not intending to enter U.S. airspace. Accordingly, U.S. military aircraft not intending to enter national airspace should not identify themselves or otherwise comply with ADIZ procedures established by other nations, unless the United States has specifically agreed to do so.

It should be emphasized that the foregoing contemplates a peacetime or nonhostile environment. In the case of imminent or actual hostilities, a nation may find it necessary to take measures in self-defense that will affect overflight in international airspace.

In order for there to be formal reciprocity in following the rules of an established ADIZ, countries would have to first agree on what an ADIZ even is and what traffic it can apply to, which they currently do not.

  • "there's very rarely any reason to be there unless you're either intending to enter the airspace of at least one of the United States or Canada" But parts of the Alaska ADIZ are closer to Russia than NA.: upload.wikimedia.org/wikipedia/commons/thumb/2/2f/… Oct 12, 2021 at 19:29
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    @KeithMcClary Some of it is, but there are also some U.S.-owned islands out there that don't show up well or at all on that map, so there's more U.S. national airspace out there than it might appear from just that map. At any rate, the statement remains. There's generally no reason to be flying there from Russia if you aren't planning to enter U.S. airspace. There's nowhere else to go but the U.S. from there once you've entered the ADIZ. And, as noted in the answer, aircraft not intending to enter U.S. or Canadian airspace aren't required to comply with the ADIZ procedures anyway.
    – reirab
    Oct 12, 2021 at 22:00
  • @KeithMcClary There are also spots out there where Russian airspace comes closer to the U.S. than to Russia. Some of that just has to do with making the lines straighter/more convenient for mariners and aviators.
    – reirab
    Oct 12, 2021 at 22:04

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