THE United States says China "has raised regional tensions" by creating its air defence identification zone (ADIZ) that covers the Diaoyu islands governed by Japan (which calls them Senkaku), which are also claimed by Taiwan (which calls them Diaoyutai).
China deems its ADIZ to be necessary for its "airspace security". Some 20 other states have ADIZs. What is the status of ADIZs in international law?
"The legalities that govern them are murky at best," Mr Sam LaGrone, editor of US Naval Institute News, claimed recently in a piece reprinted in The Straits Times. In fact, ADIZs can be shown to contravene customary international law as expressed in treaties.
An ADIZ is the airspace over land or water that a country creates by providing its GPS co-ordinates. Once defined, planes flying into an ADIZ must file a flight plan, identify itself and may be subject to air traffic control.
China is not the first to declare an ADIZ. The US created five in 1950. These extend several hundred nautical miles (nm) seaward, much more than China's does. Two US continental ADIZs extend over 300 nm into the Atlantic and over 400 nm into the Pacific. The others extend 350 nm from the Alaskan coast, 250 nm from Guam and 250 nm from Hawaii. By contrast, China's ADIZ is smaller as the disputed islands are only 180 nm from the Chinese shoreline.
In general ADIZs hardly affect international air commerce. As China has taken pains to point out, an ADIZ is not a no-fly zone, so otherwise permitted flights are not precluded. Its procedural requirements are not burdensome. But it arguably does not serve its supposed function - boosting national security - in this day.
When first created during the Cold War, ADIZs may have made some sense since nukes were then delivered by long-range bombers. An ADIZ of a few hundred nm would have afforded a country some time to scramble its interceptor jets and get ready its surface- to-air missiles.
But today, nukes are delivered by ballistic missiles or long-range cruise missiles launched from thousands of kilometres away.
In this context, an ADIZ of a few hundred nm - the distance covered by a Cold War subsonic fighter in 30 minutes, say - affords virtually no buffer in terms of time. For an ADIZ to serve that function with today's supersonic Stealth fighters, it would have to extend a few thousand nm to give you, say, 10 minutes. In sum, ADIZs no longer serve their purported security purposes.
Moreover, they violate customary international law. First think of the seas as territorial waters extending from the shore for 12 nm and then the state's exclusive economic zone (EEZ) extending 200 nm, which are part of the high seas.
International treaties dictate that every state has the right to traverse any EEZ and thus the airspace above it as well as the rest of the high seas and the airspace over them. But an ADIZ could extend into the EEZ and beyond.
When the US first created its ADIZs in 1950, most jurists found them illegal under domestic law. According to McGill University law professor Michael Milde in his 2008 work, International Air Law And ICAO, this was because US law limited its national sovereignty to airspace over the territorial seas of its mainland, its possessions and its trust territories.
This would also be the position of four relevant international conventions, all of which hold that a state has absolute sovereignty over the airspace above its land and its territorial seas (12 nm out) but not that above the high seas.
First, the Convention on International Civil Aviation 1944 recognises that a state, whether signatory to the treaty or not, has "exclusive sovereignty in the airspace above its territory". It then divides the seas - and thus the airspace over them - into territorial waters and high seas only. It holds that the use of airspace over the high seas is to be exclusively under international regulation. That is, a state is prohibited from passing domestic laws to regulate the airspace over the high seas.
It requires that military aircraft of a contracting state shall not "fly over the territory of another state or land thereon without authorisation" and "will have due regard for the safety of navigation of civil aircraft". In 1998, the convention added a clause to ban state aircraft from using weapons against civil aircraft in flight.
Second, the Convention on the Territorial Sea and the Contiguous Zone 1958 speaks about "limiting" the sovereignty of a coastal state to its territorial seas. If a coastal state decides to suspend the innocent passage of ships in its territorial seas, that suspension must not only be factually justifiable but also temporary.
Third, the companion treaty signed simultaneously, called the Convention on the High Seas 1958, specifically prohibits any state from asserting its sovereignty over "any part of the airspace over the high seas".
Finally, the United Nations Law of the Sea (Unclos) 1982 specifically guarantees to all states the freedom to navigate all EEZs. It also gives all states overflight rights of their planes, including military planes, in the airspace above all EEZs.
Unclos allows military planes to engage in surveillance and intelligence gathering and to support naval activities, notes Nicholas Poulantzas in his 2002 book, The Right Of Hot Pursuit In International Law. Unclos also specifies that states have no sovereignty of the airspace above their continental shelf, which may extend far out into and beyond its EEZ.
While nations may downplay it, establishing an ADIZ is tantamount to asserting partial sovereignty in that it asks traversing aircraft to self-identify. Such an act presumes a claim of (partial) ownership. With its unilateral claim of partial sovereignty of the airspace over waters beyond a coastal state's territorial seas, any ADIZ will violate all the provisions above.
When ADIZs overlap as they do above the disputed islands, overlapping partial sovereignty claims emerge, an even stronger reason for all states to stop this practice.
As ADIZs violate the four treaties which express the collective will of the community of nations, they are illegal under customary international law. And as they also cannot serve their supposed security function, all states with ADIZs, not just China, should do away with them without fail.