How does the freedom of the high seas apply to aircraft flying above international waters?

Under international air law, the principle of state sovereignty applies exclusively to the airspace above a nation's territory, including its territorial sea. Because airspace is considered an appurtenance of the subjacent territory, it shares that territory's legal status.1

Conversely, the high seas and the airspace above them are open to use by all countries. Under both international customary law and the Geneva Convention on the High Seas (1958), the freedom of the high seas applies to aerial navigation just as it does to maritime navigation.21

When operating over the high seas, aircraft are subject to the following regulatory framework:

• Rules of the Air: Among members of the International Civil Aviation Organization (ICAO), the Rules of the Air established by the organization apply to flights over the high seas.3
• Enforcement and Jurisdiction: Enforcement of these rules and the investigation of accidents occurring over the high seas are the primary responsibility of the state of registry.3
• Legal Accountability: To prevent legal gaps, international agreements—such as the 1963 Tokyo Convention—oblige states to extend their criminal law and jurisdiction to aircraft of their registry when they are outside national territory.4