Balloons are Not Always Joyful: The Legality of Downing the Chinese Spy Balloon


| Mar 10, 2023

Chinese Balloon

On January 28, 2023, a Chinese high-altitude balloon (HAB) entered U.S. airspace near Alaska and, after transiting Canadian airspace, continued its voyage from the west to the east coast. On February 4, 2023, the United States shot down the HAB over the territorial sea off South Carolina. Chinese authorities complained about an over-reaction by the United States because the balloon was of a civilian nature used for scientific/meteorological purposes that had entered the U.S. national airspace due to force majeure. The Chinese authorities claimed that they had not intended to violate the territory or airspace of any sovereign country.

So far, several authors have provided assessments of the legality of the downing of the Chinese HAB under both U.S. domestic law and international law. According to the position taken here, some of the arguments provided in those assessments are not as helpful as they might be and should be reconsidered.

Classification of the Balloon

Whereas China contends that the HAB was a civilian aircraft, it may well be that it was operated by Chinese authorities or by an entity under direct Chinese government control. According to U.S. government officials, the HAB “had collection pod equipment, including high-tech equipment that could collect communications signals and other sensitive information, and solar panels located on the metal truss suspended below the balloon,” that is, equipment “clearly for intelligence surveillance, including multiple antennas […] likely capable of collecting and geo-locating communications.” Moreover, “video of the balloon showed small motors and multiple propellors that allowed China to actively maneuver the balloon over specific locations […] and it was steered by rudder.”

Although an FBI investigation is still pending, it is very likely that the HAB shot down on February 4 was not a meteorological balloon or a civil aircraft. In that context it is important to bear in mind that the altitude at which the balloon was operating is characterized as “near space,” which is of considerable strategic and other military importance. Accordingly, it is safe to believe that the HAB was operated by Chinese authorities or by entities under the effective control of Chinese authorities for exclusively governmental non-commercial purposes (i.e., espionage) and it, thus, qualifies as a State aircraft. It is important to emphasize that Article 3 lit. (b) of the 1944 Chicago Convention does not provide an exhaustive list of categories of State aircraft. Aircraftother than those “used in military, customs, and police services” equally qualify as State aircraft if they are operated by a State organ for exclusively government non-commercial purposes (rule 1).

Violation of U.S. Sovereignty

It has been rightly stated that even if the HAB had been a civil aircraft, its unauthorized entry into the national airspace would have violated the 1944 Chicago Convention. However, the Convention, according to Article 3 lit. (a), “shall not be applicable to state aircraft.” Accordingly, the legality of the HAB’s presence in U.S. national airspace must be assessed under customary international law.

There can be no doubt that the entry of a foreign State aircraft into the national airspace of another State without that State’s prior authorization qualifies as a violation of territorial sovereignty. The purpose of such entry is irrelevant. Accordingly, the fact that espionage is not prohibited under international law does not change anything. Interestingly, China implicitly admitted it had violated the territorial sovereignty of the United States, by claiming the HAB had been driven into the national airspace by force majeure. Claiming a circumstance precluding wrongfulness, such as force majeure, means that the State relying on it agrees that its conduct would otherwise qualify as an internationally wrongful act.

According to Article 23(1) of the International Law Commission’s Draft Articles on State Responsibility, the

wrongfulness of an act of a State not in conformity with an international obligation of that State is precluded if the act is due to force majeure, that is the occurrence of an irresistible force or of an unforeseen event, beyond the control of the State, making it materially impossible in the circumstances to perform the obligation.

Seemingly, China may rely on force majeure, if the HAB had been driven into U.S. national airspace by the prevailing weather conditions, probably in combination with a malfunction of the steering controls. However, Article 23(2) of the Draft Articles excludes an invocation of force majeure if: “(a) the situation of force majeure is due, either alone or in combination with other factors, to the conduct of the State invoking it; or (b) the State has assumed the risk of that situation occurring.”

Using a balloon at high altitude, whether or not equipped with steering technology, always implies the foreseeable risk of the balloon being exposed to changed weather conditions and, thus, forced from its (allegedly) original course. Moreover, the use of a balloon for espionage always implies the risk of detection. Obviously, China had hoped the balloon would remain undetected and did assume the risk of changed weather conditions and a loss of control due to technical malfunctions. The primary aim was to conduct an intelligence operation in U.S. national airspace. Therefore, invoking force majeure is impermissible and it does not preclude the wrongfulness of the unauthorized entry into U.S. airspace.

Legality of the Shoot-Down

Even if one were prepared to concede a situation of force majeure, this would not result in the illegality of the downing of the Chinese HAB.

While in U.S. national airspace, the HAB was still operative and continued its spy operation. Of course, espionage is not prohibited under international law. However, this does not prevent the target State from applying and enforcing its domestic law. The lack of an international prohibition of espionage implies the warning not to get caught in the act. Accordingly, the U.S. government was entitled to terminate the HAB’s intelligence operation while it was in U.S. national airspace, including by a use of force. Other measures to terminate the violation of U.S. territorial sovereignty, such as intercepting the HAB, were not reasonably available. Accordingly, the downing of the Chinese spy balloon was a lawful enforcement of U.S. domestic law within sovereign U.S. territory. Because the HAB was unmanned, “elementary considerations of humanity” could not exclude a use of force.

The fact that the balloon may qualify as a State aircraft does not result in the illegality of the shoot-down of February 4, 2023. In principle, State aircraft enjoy sovereign immunity. Any exercise of jurisdiction over a foreign sovereign immune vehicle will violate international law. Arguably, sovereign immunity must also be respected if the foreign aircraft is in the national airspace and territory of another State. However, this only applies if the aircraft’s presence is authorized or otherwise permissible. A foreign aircraft engaged in an intelligence operation while in the national airspace of another State has forfeited its sovereign immunity and may, therefore, be subjected to enforcement jurisdiction by the affected State.

Necessity of a Justification?

It has been argued that the legal basis for the downing of the Chinese spy balloon could be either self-defense or reprisal.

In that context, it may be added that espionage by a foreign aircraft while in the national airspace will hardly qualify as a use of force or armed attack. Invoking reprisals in times of peace is not helpful at all. Firstly, reprisals as dealt with in para. 18.18.1 of the DoD Law of War Manual are a means of enforcing the law of armed conflict, not peacetime rules of international law. Secondly, if at all, countermeasures according to Article 22 of the ILC’s Draft Articles should have been referred to as another circumstance precluding wrongfulness.

These considerations, however, miss the point. It is important to emphasize that there is no need to rely on either self-defense or on another circumstance precluding wrongfulness. The downing of the Chinese HAB was a lawful enforcement of U.S. sovereignty and, thus, not an internationally wrongful act. It may be recalled that the invocation of a circumstance precluding wrongfulness is an implicit recognition of the illegality of the respective conduct were it not exceptionally justified. There is, therefore, no necessity of invoking either self-defense or reprisals which could prove to be counterproductive.

While the incident involving the Chinese HAB is now in the past, the enduring utility of balloons for espionage and other military purposes means that the legality of the shoot-down may have continued relevance into the future.


Wolff Heintschel von Heinegg holds the Chair of Public Law, in particular Public International law, European Law and Foreign Constitutional Law at the Europa-Universität Viadrina in Frankfurt (Oder), Germany.


Photo credit: U.S. Department of Defense