Whereas the right of a state to establish an air defence identification zone (ADIZ) in national airspace falls squarely within its sovereignty, the question whether coastal states may claim such zones outside national airspace remains a matter of controversy. The latter category, referred to as ‘offshore ADIZs’, usually do not amount to sovereignty claims over the open airspace outside national airspace or involve threat or use of force. The right of coastal states to identify aircraft in the open airspace near coastal areas has arguably become part of customary international law. This customary right, however, only extends to ‘passive identification’ by radar detection, radio communication or close visual checks, which thus is only capable of justifying the establishment of offshore ADIZs for this purpose. The identification of aircraft in offshore ADIZs, through either voluntary or passive measures, is nevertheless within the parameters of the obligation of paying due regard to the freedom of overflight. This explains why ‘passive identification’ is ‘permissible’ under customary international law, while ‘voluntary identification’ is at least ‘tolerated’ albeit in the absence of a permissive customary rule.

中文翻译：

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在国家领空外设立防空识别区是否符合国际法？

虽然一国在国家领空建立防空识别区（ADIZ）的权利完全属于其主权范围，但沿海国是否可以在国家领空之外主张此类区域的问题仍然存在争议。后一类被称为“近海防空识别区”，通常不构成对国家领空以外空域的主权主张，也不涉及威胁或使用武力。沿海国在沿海地区附近的开放空域识别飞机的权利可以说已成为习惯国际法的一部分。然而，这种习惯权利只延伸到通过雷达探测、无线电通信或近距离目视检查的“被动识别”，因此只能证明为此目的建立海上防空识别区是合理的。尽管如此，通过自愿或被动措施识别近海 ADIZ 中的飞机仍属于适当考虑飞越自由的义务范围内。这就解释了为什么“被动识别”在习惯国际法下是“允许的”，而“自愿识别”至少是“允许的”，尽管没有允许的习惯规则。