Uses of Force against Civil Aircraft

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Dr Kimberley N. Trapp is lecturer in law at Newnham College, University of Cambridge.

On 18 June, South Korean marines (stationed on Gyodong Island, to the west of South Korea) fired 99 rifle rounds at an Asiana flight en route from Chengdu (China) to Seoul International Airport (BBC report).  Asiana aircraft are registered to South Korea, but the flight was mistaken for a North Korean military aircraft as the marines apparently believed the plane was flying north of the normal civil aviation corridor. Mercifully, the Asiana flight was out of rifle range and sustained no damage, landing safely – blissfully ignorant of the threat it had faced.

While it is relatively uncommon for civilian aircraft to be the object of direct attack by military forces – it does happen (particularly where tensions are running high as on the Korean peninsula) – and raises some interesting questions as to the applicable legal regime.  This post will use the Korean incident as a starting point for its analysis – exploring some of the issues that might have arisen had the use of force been more serious than it (very happily) was.

There are three legal regimes that might be implicated in assessing the lawfulness of a use of force against civilian aircraft: the jus ad bellum; the Convention on International Civil Aviation (the ‘Chicago Convention’) and the Convention for the Suppression of Unlawful Acts against the safety of Civil Aviation (the ‘Montreal Convention’) – each of which will be addressed in turn.

UN Charter

In reference to the South Korean incident, there is no breach of Article 2(4) of the UN Charter.  The Asiana aircraft was a South Korean plane flying over South Korean territory – and there was therefore no use of force against the territorial integrity or political independence of another UN Member State.  There were probably foreign nationals on board the flight – particularly as it was travelling from China to South Korea – but a use of force in South Korean territory (and on board an aircraft registered to South Korea) which affects foreign nationals does not fall to be assessed under the UN Charter, although it may well have human rights implications (which are beyond the scope of this post).

Had the aircraft been registered to a foreign State, any use of force against it would have been assimilated to a use of force against the State of registration, and would therefore have amounted to a breach of Article 2(4) of the UN Charter (which should be read to prohibit all uses of force in international relations – not only those the object of which is to gain territory or undermine political independence).  Let’s imagine for the sake of argument that Asiana is registered to China (from which country the flight was travelling).  The Chinese civil aircraft was mistaken for a North Korean military jet and fired upon by South Korean marines. Let’s accept (again for the sake of argument) that the South Korean use of force was intended to be in self-defence, to prevent an imminent attack by North Korea – not the craziest thing in the context of recent North/South Korean relations. Given the mistaken identity, the wrongfulness of South Korea’s use of force could not be precluded on the basis of self-defence – and would therefore amount to an unlawful use of force.  Nevertheless, the mistake would inform the extent to which China could itself respond with defensive force against South Korea, given the completion of the attack and the absence of any continuing threat.

Chicago Convention


The Chicago Convention sets out the constitutional framework of the International Civil Aviation Organization (the ‘ICAO’) and the general regime of air navigation between State Parties (including rights of over-flight and measures to facilitate air navigation).  A 1984 protocol to the Chicago Convention [Article 3bis: Non-use of weapons against civil aircraft in flight], to which South Korea is a Party, “recognize[s] that every State must refrain from resorting to the use of weapons against civil aircraft in flight and that, in case of interception, the lives of persons on board and the safety of aircraft must not be endangered.”   In its recognition, Article 3bis suggests a codification of customary international law or the re-iteration of a widely ratified treaty provision – which is indeed what the travaux préparatoires indicate some ICAO Member States considered themselves to be doing.  And for the most part, they were right.  A use of force against a foreign registered civil aircraft is assimilated to a use of force against the State of registration, and therefore a breach of Article 2(4) of the UN Charter and associated customary international law.  Article 3bis, however, goes beyond both because it is not limited to foreign registered civil aircraft –the prohibition must be read to include uses of force against civil aircraft registered to the State using force.  This interpretation of Article 3bis is the most consistent with the object and purpose of the Chicago Convention – which is (in part) to promote the safety of all international civil aviation.  The conduct of South Korean marines being plainly attributable to South Korea – its use of force against the Asiana flight (whether as the actual South Korean airline or the above hypothesized Chinese airline) is a clear breach of Article 3bis of the Chicago Convention.

Interestingly, Article 3bis is not to be interpreted “as modifying in any way the rights and obligations of States set forth in the Charter of the United Nations.”  Article 3bis picks up on the prohibition in Article 4 of the Chicago Convention (not to use civil aviation for any purpose inconsistent with the aims of the Convention), and permits the use of “any appropriate means consistent with relevant rules of international law” where civil aircraft is nevertheless so used. In the particular case at hand, there is no justification for the use of force as self-defence in reliance on Article 51 of the UN Charter given the mistaken identity of the aircraft.  But to the extent that a civil aircraft is in some way posing a security threat (for instance – if it were being used as a suicide weapon), Article 3bis recognises that the normal rules of self-defence apply – conditioned by necessity and proportionality, which will naturally raise very difficult issues given the civilian nature of the target.

Montreal Convention

The Montreal Convention requires States to prevent the unlawful and intentional destruction of a civil aircraft in service, or the causing of damage to the aircraft which renders it incapable of flight or endangers its safety in flight.  The Convention applies to all international flights (i.e. those which are flying from or to the State of registration via another State), and therefore certainly applies to the Asiana flight between Chengdu and Seoul.

The Montreal Convention does not expressly prohibit States from destroying civil aircraft in service or from damaging such aircraft in a way endangers their safety.  In its Bosnia Genocide Case judgment, however, the ICJ held that a State’s obligation to prevent genocide under the Genocide Convention necessarily implies a prohibition of the commission of genocide by the State itself.  The Court was of course very careful to restrict its reasoning to the particular circumstances of the Genocide Convention, but the decision nevertheless strongly suggests that the obligation of prevention in the Montreal Convention could equally imply a prohibition on State conduct.

The question remains whether State military force was intended to be included or excluded from the scope of the Montreal Convention (or indeed whether negotiating States failed to turn their minds to the possibility of uses of military force against civil aircraft at all).  Unlike other Terrorism Suppression Conventions, the Montreal Convention as presently in force does not expressly exclude military force from its scope of application[i] – but State practice in the application of a treaty may be relevant to its interpretation (Art. 31(3)(b), VCLT).

The difficulty in relying on Article 31(3)(b) VCLT as an interpretive tool in reference to the Montreal Convention is that the State practice is split – depending on whether States were publicly condemning the conduct, or whether they were in need of a jurisdictional hook on which to hang their litigation hats before the ICJ.  In reference to Israel’s downing of a Libyan airliner on 21 February 1973 over occupied Egyptian territory; the USSR’s downing of Korean Airlines flight 007 on 1 September 1983; the Iraqi air force’s shooting down of an Iranian passenger plane on 20 February 1986; and the shooting down by the Cuban air force of two private US civil aircraft on 24 February 1996, injured States, the ICAO and (occasionally) the Security Council condemned the use of force on the basis of general international law and the Chicago Convention, without any reference to the Montreal Convention.[ii] Indeed, when the international community became convinced of the need to codify general international law prohibiting a State’s use of military force against civilian aircraft (in response to the USSR’s downing of KAL 007 on 16 September 1983), the amendment was to the Chicago Convention (in the form of Article 3bis discussed above), not the Montreal Convention.  While the practice does not unequivocally indicate that military conduct was intended to be excluded from the scope of the Montreal Convention, it strongly suggests that States do not consider the Montreal Convention to be a relevant instrument.

But for the purposes of international dispute settlement (discussed further below), States have invoked the Montreal Convention as a source of legal obligation in disputes regarding direct State responsibility for military activities against the safety of civil aircraft.  In its suit against the US, Iran invoked the Montreal Convention as the basis of US responsibility for the destruction of civilian flight IR 655 by surface-to-air missiles launched from the ‘USS Vincennes’ – killing all 290 passengers and crew aboard.  As has been its consistent position, the US fiercely disputed that the Montreal Convention applied to State activity against civil aircraft.  The case was settled by negotiation.  The DRC equally invoked the Montreal Convention (alongside the Chicago Convention) in its suits against Uganda, Rwanda and Burundi as they related to the downing of a Congolese Airlines aircraft at Kindu Airport on 10 October 1998. The applicability of the Montreal Convention was never settled by the ICJ because the DRC’s suits were either discontinued (Burundi), the Montreal Convention was not pleaded on the merits (Uganda), or the ICJ determined that it did not have jurisdiction based on the DRC’s failure to meet the procedural requirements of Article 14(1) of the Montreal Convention (Rwanda).

This approach to treaty interpretation by some States, when the ICJ’s jurisdiction hangs in the balance, prompted the ICAO to adopt a legal position on the question of the applicability of the Montreal Convention to State activities.  In 2007, the ICAO Legal Committee, in the context of a working paper regarding the effectiveness of the existing ICAO terrorism suppression conventions (in particular the Hague and Montreal Conventions), claimed that ‘[i]n [the] ICAO, it has been widely understood that the aviation security instruments which criminalize certain acts [against civil aircraft] are not applicable to [ . . . ] military activities’.[iii]

In keeping with this position, the ICAO recently adopted the Beijing Convention (consolidating the Montreal Convention and 1988 Protocol to the Montreal Convention, in addition to requiring States to criminalize the use and transport of explosives and BCN weapons from civil aircraft) – which contains a military exclusion clause identical to that contained in the Nuclear Terrorism Convention:

The activities of armed forces during an armed conflict, as those terms are understood under international humanitarian law, which are governed by that law are not governed by this Convention, and the activities undertaken by military forces of a State in the exercise of their official duties, inasmuch as they are governed by other rules of international law, are not governed by this Convention.[iv]

Plainly, the South Korean marines were acting in exercise of their official duties.  And while their conduct in not governed by the UN Charter (because the civil aircraft was registered to the State using force), it is governed by Article 3bis of the Chicago Convention – thereby satisfying the ‘governed by other rules of international law’ requirement for exclusion from the scope of application of the Convention.  But the Beijing Convention is not yet in force (it was adopted in September 2010 and requires twenty-two ratifications before entering into force).  In reference to uses of force against civil aviation by non-military State officials, however, there is nothing in the State practice examined above or the exclusion clauses in the 2010 Beijing Convention to suggest that the Bosnia Genocide Case analysis is inapplicable. As a result, acts against the safety of civil aviation committed by States through secret service agents or non-State actors should, subject to a Bosnia Genocide Case analysis, be prohibited as a matter of the Montreal Convention.


Implementation of State Responsibility and the ICJ

Assuming that the South Korean incident had (goodness forbid) damaged or endangered the safety of the Asiana flight, the possibility of invoking the Montreal Convention and the Chicago Convention as a source of both South Korea’s responsibility and the ICJ’s jurisdiction raise some interesting issues.

The first issue is that of standing.  Asiana aircraft are registered to South Korea and the use of force was in South Korean territory.  Unlike other Terrorism Suppression Conventions,[v] the Montreal Convention does not expressly permit States to establish jurisdiction over crimes committed against their own nationals, and the Chicago Convention does not contain any relevant provisions which indicate how questions of interest should be resolved.  Nevertheless, China (assuming Chinese nationals on board) could almost certainly claim to be an injured State on which basis it would be entitled to invoke South Korea’s responsibility.  This is supported by the preambles of both Conventions which note the extent to which they address matters of concern to the international community as a whole (on which basis there might also be Article 48 ILC Articles on State Responsibility standing).

The question would then arise as to whether the Montreal Convention contains substantive obligations which South Korea, though it use of force against a civilian aircraft, could be held to be in breach of.  On a Bosnia Genocide Case analysis, the Montreal Convention prohibits States from engaging in the very activity they are required to prevent and punish (without reference to the nationality of the aircraft).[vi] The Court could only give effect to the ICAO’s understanding of the Montreal Convention (now reflected in the exclusion clause added through the Beijing Convention) if it ‘interpreted’ an implied military exclusion clause into existence.  Such an interpretation would limit its jurisdiction and undermine the substantive basis of the claim – but the Court’s approach to treaty interpretation in cases where it would not otherwise have jurisdiction has arguably been expansive rather than restrictive. As such, attempts to implement a State’s responsibility for the conduct of its armed forces meeting the elements of the offences defined in the Montreal Convention could well be successful, until the Beijing Convention is in force between relevant States.  Once in force, as between State parties, the only regimes which can be invoked before the ICJ as a source of State responsibility for the use of military force against foreign owned civil aircraft are the UN Charter (and parallel customary international law) and the Chicago Convention.

In reference to the Chicago Convention – Iran’s suit against the US, and the DRC’s trilogy of suits (in which the Applicant States invoked the Montreal Convention as a source of State responsibility for the military downing of a civilian aircraft, rather than relying on the more directly relevant Article 3bis of the Chicago Convention) should not be read as suggesting anything negative about the potential scope of responsibility under the Chicago Convention.  In both cases, relevant States (the US and the DRC) were not State Parties to the Chicago Convention Article 3bis Protocol.  That said, the ICJ’s jurisdiction under the Chicago Convention is appellate only, for the purposes of reviewing a prior decision by the ICAO Council on a ‘disagreement between two or more contracting States relating to the interpretation or application of [the Chicago] Convention’ (Art. 84, Chicago Convention).  As South Korea is a party to the Article 3bis of the Chicago Convention, the use of force against the Asiana flight would first need to be put to the ICAO Council before the ICJ would have jurisdiction to consider the matter.

The relatively simple (yet alarming) facts which gave rise to the analysis in this post highlight the potentially complex interaction between general international law and the particular regime of law geared toward the safety of international civil aviation.  If the Montreal Convention is interpreted in keeping with pronouncements by the ICAO and the intention of ICAO Member States expressed through the adoption of the Beijing Convention, the ICAO regime should not affect the applicability of the jus ad bellum.  The Bosnia Genocide Case analysis, however, raises the possibility of an overlap in substantive treaty obligations.  To the extent that this overlap is approached by the ICJ with a sensitivity to intended regime interaction (perhaps interpreting the ‘unlawful’ element of the offences defined in the Montreal Convention as a window through which the jus ad bellum and the right to use force in self-defence might be given interpretive effect) – the overlapping treaty regimes should be viewed as a positive in that they increase the potential bases for implementing State responsibility through the peaceful settlement of disputes.

[i] The Terrorist Bombing Convention and the Nuclear Terrorism Convention contain clauses which exclude (i) the activities of the armed forces during an armed conflict when such activities are governed by international humanitarian law; and (ii) the activities of State military forces governed by other rules of international law, from their scope.

[ii] See Trapp, State Responsibility for International Terrorism (OUP, 2011), 165-68.

[iii] ICAO Assembly 36th Session, Legal Committee, Acts or Offences of Concern to the International Aviation Community and not Covered by Existing Air Law Instruments, ICAO Doc. A36-WP/12, LE/4 (2007), para

[iv] Article 6(2), Beijing Convention, available at

[v] see 6(2)(a), Terrorist Bombing Convention, available at

[vi] There is the further question (beyond the scope of this post) as to whether South Korea could be held responsible under the Montreal Convention if it fails to submit the two marines to prosecution – which would also require an analysis of the excludability of military activity from the scope of the Convention.

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Ian Henderson says

June 28, 2011

Dear Dr Trapp,

Thank you for a very interesting post.

At one point, you write: "Given the mistaken identity, the wrongfulness of South Korea’s use of force could not be precluded on the basis of self-defence – and would therefore amount to an unlawful use of force." I take this to mean that where a State genuinely and reasonably relies on national self-defence under article 51 UN Charter, but due to a mistake of facts (eg, misidentification of an aircraft as hostile), the State is precluded at law from asserting a legitimate claim of national self-defence. Put another way, national self-defence is available not only where a State genuinely and reasonably believes a certain set of facts to exist, but those facts must actually exist.

If I have correctly understood your view, I would be very grateful for a reference/citation for that view as this is a point I have not previously had occasion to consider.

Kimberley Trapp says

June 29, 2011

Dear Ian,

That is indeed my view – which emerges from (i) Article 51 of the UN Charter; (ii) Article 21 of the ILC Articles on State Responsibility; and (iii) the Court’s decision in Oil Platforms. Article 51 of the UN Charter applies ‘if an armed attack occurs’. This has been interpreted to include imminent attacks, but certainly not imagined ones (even if imagined in good faith). Article 21 of the ILC Articles picks up on this – self-defence is a circumstance precluding the wrongfulness of an otherwise unlawful use of force if the self-defence is lawful, that is to say complies with the requirements of necessity and proportionality. Finally, in Oil Platforms, the Court held that “the requirement of international law that measures taken avowedly in self-defence must have been necessary for that purpose is strict and objective, leaving no room for any ‘measure of discretion’” (¶73). The Court’s pronouncement was in response to the American argument that it considered in good faith that its attacks on the platforms were necessary (an argument made in reference to Article XX(1)(d) of the 1955 US/Iran Treaty of Amity, but which the Court treated as equally relevant for the purpose of deciding the self-defence point). The Court’s decision suggests that a State’s good faith belief (or more specifically absence thereof) may be relevant evidence in establishing the objective elements of self-defence, but is not in itself dispositive (¶76).

As a result, a good faith, but mistaken, view as to whether the elements of lawful self-defence are met (armed attack, necessity and proportionality) does not preclude the wrongfulness of the use of force. Good faith should, however, inform the extent to which a response to the now unlawful use of force (mistakenly intended to be in self-defence) is itself lawful self-defence for the reasons I mention in the post.

Ian Henderson says

June 30, 2011

Thank you for the comprehensive reply.

Dapo Akande says

July 1, 2011


Another way in which mistake might be at play in a self-defence scenario is where it is the original attacker that is mistaken. In other words, State A's forces attack installations or forces of State B but either by accident or with the intention of attacking the forces of State C. The question there is whether State B is entitled to act in self-defence. In the Oil Platforms case, the ICJ suggested that there is no armed attack on a State if the attacker did not intend to attack that State. I think this is misguided. If it is correct then the attacked State (State B) has no right of self-defence. Whether there is an armed attack or not should be a question of fact. In my view, the key issue here should be one of necessity. It may well be that State B has no right of self-defence but that will be because in cases of mistake or lack of intention it is more likely that it is unnecessary to use force as (a) the attacks are unlikely to continue once the mistake is realised and (b) it is more likely that the dispute can be resolved in some other way. But this should not mean that in principle there is no right of self-defence. For example, the attacked State should be able to respond in the heat of the moment, while the attack is underway to put an immediate end to it.

Ian Henderson says

July 1, 2011

Dear Dapo,

Thanks for the follow up. I’m recalling why I prefer the jus in bello to the jus ad bellum.

I suspect part of the problem is that many actions in self-defence are actually taken after the initial attack has finished — eg, the circumstances of the Oil Platforms case. I am struggling though with the idea that an honest and reasonable mistake of fact (as opposed to a subjective assessment of how to respond) could vitiate a legitimate claim of self-defence. An example that comes to mind is where State A masses its forces and feints an attack on State B. Assuming based on past practice and intelligence that State B genuinely and reasonably thought an attack was commencing and that it was not a feint, then to suggest that State B’s claim of self-defence is barred because of State A’s deception plan seems peculiar.

Of course, I am not saying that you or Dr Trapp have misinterpreted the law. It more seems that the current state of the law may have been unduly influenced by ‘post-attack’ responses. There may also currently be an inadequate distinction between the concept of State B’s assessment of the facts and State B’s assessment of what is a necessary and proportional response.

Kimberley Trapp says

July 1, 2011

Dear Ian,

Really interesting issue – hopefully not one that arises too often, although in the context of N./S. Korean relations, who knows... I think we need to draw a distinction between two scenarios here: The 1st in which State B mistakenly believes that an attack is imminent based on faulty intelligence (WMDs anyone??), and the 2nd in which State B mistakenly believes that an attack is imminent because of State A’s feint. It seems absolutely right that State B bears the risk of faulty intelligence in the 1st scenario – if State B gets its assessment of the facts wrong (in that an armed attack is not imminent), then it is responsible for an unlawful use of force against State A. And while I think you are correct to note that the circumstance precluding wrongfulness of self-defence does not distinguish between Scenario 1 and Scenario 2 in its requirement of an objective assessment of the facts – this would not necessarily produce the unfair result you expect. This is because of the ‘clean hands’ doctrine – or the general principle of law that “one Party cannot avail himself of the fact that the other has not fulfilled some obligation or has not had recourse to some means of redress, if the former Party has, by some illegal act, prevented the latter from fulfilling the obligation in question, or from having recourse to the tribunal which would have been open to him” (Factory at Chorzow, Jurisdiction, Judgment, PCIJ Series A, No. 9 (1927), 31; cited with approval in Gabčíkovo-Nagymaros Project (Hungary/Slovakia), Judgment, [1997] ICJ Reports 7, ¶110). State A should not be able to avail itself of the fact that State B has used force unlawfully if State A, through its ‘feinted’ use of force (amounting to a threat), has been the principal cause of State B’s use of force. The clean hands doctrine is one that is very fact sensitive, so it would depend on the particular circumstances of the case, but if the facts you outlined above ever came to the International Court (and the feint was somehow provable), there is every likelihood that the Court would apply the doctrine so as to preclude State A from invoking the responsibility of State B.