The flying balloon dates back to the early age of aviation when Jacques Charles held a public experiment in Paris in 1783. A high-altitude balloon is a lighter-than-air aircraft that flies as a result of the reactions of the air. Even though the high-altitude balloon may have different flying characteristics from an airplane, it is still deemed an aircraft under the Chicago Convention of 1944.

Beijing has publicly condemned the United States’ shooting down its balloon as the act is said to be unlawful use of force against a civil aircraft. At the same time, the United States (US) has vehemently claimed that the balloon was being operated for military surveillance purposes and was violating its sovereignty. In the escalating tension of political debates, this blog will try to highlight why the status of the aircraft matters in deciding whether the US’s act of shooting down the balloon violates international law.

Civil and military aircraft are regulated differently

To assess the lawfulness of the shooting down of the high-altitude balloon under the Chicago Convention, the balloon must be classified as ‘Civilian Aircraft' as Article 3 of the Convention limits its scope to civilian aircraft only. However, if the balloon was to be identified as a State aircraft, a more general law regarding countermeasures under the Articles of the Responsibility of States for Internationally Wrongful Acts (ARSIWA) would be applicable. US and Chinese officials have not reached any agreement on whether the balloon was a civil or State aircraft.

Using a ‘weapon’ against civilian aircraft would seriously breach Article 3 bis of the Chicago Convention

Flying the balloon within the US airspace above its territorial water without prior permission is a violation of the complete and exclusive sovereignty of the US. According to US military officials, at the time the balloon was between 60,000 and 65,000 feet (ft) above US territorial waters just off the coast of South Carolina. This means that the balloon was flying within airspace, not outer space. Not to mention that the airspace where the balloon flew was in Class E airspace above Flight Level (FL) 600 (above 60,000 ft). Class E is uncontrolled airspace, thus not controlled by the Air Traffic Controller (ATC).

In the airspace violation, the US cannot directly shoot the balloon as a civilian aircraft. The protocol which amended the Chicago Convention for the inclusion of Article 3 bis (Protocol Relating to an Amendment to the Convention on International Civil Aviation [Article 3 bis] 1984) places an obligation to refrain from using weapons against civilian aircraft in flight. The US is not a party to the protocol, yet the essence of the Article 3 bis norm also binds as customary international law. It has been long international practice that the use of force towards civilian aircraft should, in principle, be prohibited.

Conversely, the US highlighted that the balloon was a Chinese surveillance aircraft. Such a proposition implies that the US saw the high-altitude balloon as a State aircraft operated for Chinese interests. This could exonerate the US from violating the Chicago Convention, as Article 3(a) of the Chicago Convention excludes State aircraft from its scope. Nonetheless, the international law regarding countermeasures under ARSIWA still applies.

US countermeasure

The balloon operation, in this case, has been regarded as a violation of the sovereignty of the US. Sovereignty over airspace is an established right in international law, and it is recognised under Article 1 of the Chicago Convention. The US reiterated that the balloon was in US airspace illegally and conducting an information-gathering operation. On the basis that China violated the US sovereignty over airspace, the shooting down can be seen as a countermeasure for China’s breach.

Resorting to countermeasures must be done in accordance with the proportionality principle under Article 51 ARSIWA. The US must consider the effects of the countermeasure and the injury suffered. The F22 Raptor fired an AIM-9X Sidewinder, a short-range air-to-air missile, to take down the balloon safely, as claimed by the US. As for the effect of the countermeasures, no causalities were reported since the balloon had no pilot on board.

Further, the state of necessity must be present in proportionality considerations. It would be difficult to argue that the action of the US was proportionate without considering the existence of necessity. Article 25(1)(a) ARSIWA stipulates that necessity may not be invoked unless the act is the only way for the State to safeguard an essential interest against grave and imminent peril. Therefore, a closer look at the factual situation is vital for the US to justify the necessity of the shooting. In this case, the US officials stated that the shooting down was justified due to the safety and security concerns of US citizens. The US, indeed, must protect that as an essential interest. However, proving that the balloon posed grave and imminent peril requires a deeper and more comprehensive analysis of what happened.

All in all, a further investigation into the status of the aircraft will give a clearer view of the applicable law and the consequences for both China and the US. On the one hand, if the status of the aircraft was civilian, as China asserts, the shooting down of the balloon is a violation of international law. On the other hand, the US must still provide more factual justification to show that the countermeasure for the balloon as a State aircraft was proportionate and necessary.