Flying Too Low?

Artificial islands have become central flashpoints in maritime disputes, particularly in the South China Sea. Their strategic use by coastal states raises difficult questions under international law, especially regarding the rights of foreign aircraft to conduct overflight. While the legal position of maritime zones generated by natural features is relatively clear under the United Nations Convention on the Law of the Sea (UNCLOS), the legal consequences of constructing artificial islands remain contested. The issue becomes even more complex when artificial islands are built not on “rocks” (Article 121(3) UNCLOS) but on low-tide elevations (LTEs) or submerged features.

This article examines the right of overflight above artificial islands by distinguishing between features originally classified as rocks and those classified as LTEs. It argues that while overflight above artificial islands constructed on rocks is restricted by the territorial sea regime, the situation for LTEs remains unsettled, creating a grey zone in international law. To illustrate these challenges, the article also considers Subi Reef, a major Chinese-built installation in the South China Sea, as a case study.

Ambiguous Status of Artificial Islands

The status of artificial islands, installations, and structures as “territory” is ambiguous in international law. Whilst it is clear they do not generate maritime entitlements under UNCLOS, whether they themselves can be regarded as territory in a broader legal sense remains unsettled.

The ambiguity persists. Unlike ships or oil platforms, artificial islands may be large, permanent, and host civilian or military populations. They might resemble territory in both function and symbolism. States, therefore, often treat them as extensions of sovereignty. The gap between legal doctrine and state behaviour is particularly acute when it comes to the airspace above these structures. If artificial islands are viewed as territory, foreign aircraft should have no right of overflight. If, however, they are treated as installations located within the EEZ or continental shelf, the freedom of overflight should apply. UNCLOS offers little direct guidance, leaving states to assert competing interpretations.

Rocks and Territorial Seas: The Fiery Cross Reef Example

Where artificial islands are built on rocks, their legal effect is relatively clear. Rocks, as defined by Article 121(3) UNCLOS, can generate a 12-nautical mile territorial sea, even if they cannot sustain human habitation or economic life of their own. Within a territorial sea, foreign ships enjoy only the right of innocent passage, which does not include the right of overflight for foreign aircraft. The rock basis matters: the territorial sea exists by virtue of the natural feature, not because of subsequent reclamation.

Fiery Cross Reef illustrates this point. Widely regarded as a rock that, at most, can generate a 12-nautical mile territorial sea, Fiery Cross was transformed by China into a major artificial island with military facilities. Although the 2016 South China Sea arbitral tribunal did not specifically rule on Fiery Cross, its natural condition makes it unlikely to qualify as a fully entitled island. When U.S. military aircraft conducted overflights in 2015, Chinese authorities issued warnings to leave. From a legal standpoint, China could argue that the rock’s territorial sea excludes unauthorized overflight, even if sovereignty over the feature itself remains disputed.

LTEs and Submerged Features in the EEZ or Continental Shelf

The situation becomes more complicated when artificial islands are built on LTEs or submerged features. LTEs located within the territorial sea of a coastal state can be assimilated into its baseline regime. However, when located in the exclusive economic zone (EEZ) or on the continental shelf, LTEs generate no maritime zones of their own (UNCLOS Article 13).

Artificial islands on LTEs in these zones are governed by Article 60 of UNCLOS. While coastal states have the right to construct, authorize, and regulate such installations in their EEZ and continental shelf, the Convention is explicit: these structures do not possess the status of islands and do not generate territorial seas. The only recognized protective zone is a maximum 500-meter safety zone around them. This safety zone is designed to protect navigation at sea, and might not to exclude aircraft from overflight. Freedom of overflight, one of the high seas freedoms preserved in the EEZ by Article 58, therefore arguably continues to apply.

This interpretation highlights a striking asymmetry. Ships must respect a 500-meter navigational safety zone around such installations, but there is no equivalent rule for aircraft. In principle, aircraft may fly directly above these structures without violating UNCLOS. For coastal states, this legal vacuum is uncomfortable—particularly when installations host critical military infrastructure. The next question, then, is how far this right of overflight extends in practice: if freedom of overflight exists above the safety zone, how low can foreign aircraft fly? Could they operate at sea-skimming altitude, passing within meters of the installation, without breaching international law? Unlike ships, which must respect the 500-meter exclusion zone (UNCLOS Article 60(6)), UNCLOS does not prescribe a comparable vertical buffer for aircraft. This difference underscores a regulatory gap: coastal states can lawfully enforce clear limits on vessels, but when it comes to aircraft, the line between lawful overflight and provocative conduct is left undefined.

A Scenario: Subi Reef

Subi Reef illustrates the stakes of this ambiguity. Subi Reef is a low-tide elevation on the high seas that China has transformed into a large military base with runways, radar, and missile systems. Under the 2016 South China Sea Arbitration, Subi Reef was confirmed to be an LTE. Crucially, this LTE is located beyond any state’s EEZ. It also lies outside the 2009 Malaysia–Vietnam joint submission to the Commission on the Limits of the Continental Shelf (CLCS). In 2019, Malaysia submitted a claim to an extended continental shelf (ECS) that would encompass Subi Reef, though the CLCS has yet to issue a verdict. The Philippines may also include Subi Reef in a future ECS submission. Pending such determinations, or if the CLCS were to reject all claims, legally speaking, Subi Reef remains an LTE situated effectively in the high seas.

This raises the sharp question: does the United States have a right of overflight over Subi Reef? Given that Subi Reef is legally an LTE and artificial islands do not generate a territorial sea, there appears to be little in international law that would provide a basis for prohibiting U.S. aircraft from overflying the feature. At most, China could claim the 500-meter safety zone under Article 87(d) in conjunction to Article 60(5), but this provision is aimed at maritime navigation, not aviation. In the absence of sovereign airspace, freedom of overflight should continue to apply, making U.S. military overflights lawful.

This scenario underscores the gap between law and geopolitics. China, by transforming Subi Reef into a massive base, acts as though it possesses sovereign control, warning foreign aircraft and vessels. Yet international law continues to classify Subi Reef as a legally insignificant LTE, incapable of generating territorial seas or sovereign airspace. The tension between physical control and legal status makes Subi Reef a textbook example of “uncharted territory” in international law.

Fiery Cross and Subi Reef thus present different legal dynamics. Overflight above Fiery Cross can be legally restricted due to its status as a rock with a territorial sea, whereas overflight above Subi Reef might not.

Implications for Customary International Law

Could new state practice reshape the law? The answer is uncertain. For a new customary rule to emerge restricting overflight above artificial islands, two elements are required: widespread and consistent state practice, and opinio juris (a belief that such practice is legally required). At present, practice is limited.

Absent broader adoption, the orthodox interpretation remains: the freedom of overflight continues to apply. Still, as more artificial islands emerge, especially with military significance, pressure will grow for states to assert control. The law will evolve only if enough states converge on a restrictive practice.

Conclusion

The right of overflight above artificial islands exposes a profound gap in UNCLOS. When built on rocks, the law is relatively clear: territorial seas exist, and unauthorized overflight is prohibited. But when built on LTEs or submerged features—particularly those in the EEZ or high seas—the law is unsettled. Subi Reef highlights this uncertainty: despite being transformed into a major military base, it remains legally an LTE without territorial seas or sovereign airspace. U.S. overflights above Subi Reef, therefore, should be considered lawful. For now, freedom of overflight endures—yet it does so against the grain of geopolitics, leaving the skies above artificial islands as contested as the waters around them.