In an impassioned address to the U˳S˳ Congress on March 16, Ukraine’s President, Volodymyr Zelensky, asked the United States for additional military assistance, including the establishment of a no-fly zone˳
This is a terror that Europe has not seen, has not seen for 80 years, and we are asking for a reply, for an answer to this terror from the whole world˳ Is this a lot to ask for, to create a no-fly zone over Ukraine to save people? Is this too much to ask, humanitarian no-fly zone, something that Russia would not be able to terrorize our free cities? If this is too much to ask, we offer an alternative˳
The address follows on the heels of one to Canadian parliamentarians in the House of Commons the previous day˳ In that speech, he called out Western States for their inaction˳
Can you imagine when you call your friends, your friendly nations, and you ask “Please close the sky˳ Please close the airspace˳ Please stop the bombing? How many more cruise missiles have to fall on our cities until you make this happen?” And they, in return, express their deep concerns about the situation˳ When we talk with our partners, they say “Please hold on˳ Hold on a little longer˳”
Zelensky’s pleas for a no-fly zone have garnered significant support˳ For instance, the Estonian Parliament voted in favor of a resolution that urged “immediate steps to establish a no-fly zone in order to prevent massive civilian casualties in Ukraine,” an understandable position for a small NATO nation bordering Russia˳ In the United States, 27 senior international security experts signed an “open letter” calling on “the Biden administration, together with NATO allies, to impose a limited No-Fly Zone over Ukraine starting with protection for humanitarian corridors˳” Signatories include a former NATO Commander, former Commanding General of U˳S˳ Army Europe, former Under Secretaries of Defense and State, two former U˳S˳ Ambassadors to NATO, and two former U˳S˳ Ambassadors to Ukraine˳ Some members of Congress echo their openness to such an operation (see here)˳
Yet, most States remain opposed to a no-fly zone˳ The Biden administration has made it clear that the United States will not intervene militarily, even by means of a no-fly zone designed to facilitate evacuation of civilians and stop Russia’s targeting of Ukraine’s civilian population˳ White House Press Secretary Jen Psaki explained, “A no-fly zone is escalatory and could prompt a war with Russia, a major nuclear power˳”
Similarly, U˳K˳ Prime Minister Boris Johnson has warned, “This is a time where miscalculation and misunderstanding is all too possible˳” And NATO Secretary-General Jens Stoltenberg has been unambiguous about the NATO position˳
[W]e have made it clear that we are not going to move into Ukraine, neither on the ground, or in Ukrainian airspace˳ And of course, the only way to implement a no-fly zone is to send NATO planes, fighter planes into Ukrainian airspace, and then impose that no-fly zone by shooting down Russian planes˳ And our assessment is that we understand the desperation˳ But we also believe that if we did that, we’ll end up with something that could end in a full-fledged war in Europe, involving many more countries, and causing much more human suffering˳ So that’s the reason why we make this painful decision to impose heavy sanctions, provide significant support, stepping up support˳ But at the same time not involving NATO forces directly in the conflict in Ukraine, neither on the ground, or in their airspace˳
This post first explains the nature of no-fly zones, drawing on five such zones that have been conducted˳ It then discusses the legal bases for conducting such operations, including a possible Ukraine no-fly zone˳ Finally, it highlights the knock-on legal consequences should one be established in Ukrainian airspace˳
No-Fly Zones
It is essential to understand what a no-fly zone is and what it is not˳ A no-fly zone is not an aerial blockade˳ Aerial blockades, such as those implemented during the Gulf War of 1990-1991, are designed to block aircraft entry to or exit from specified airfields or coastal areas that the enemy controls˳ Their primary purpose is to prevent neutral aircraft from transporting material to the enemy (See AMW Manual, sect˳ V; here; and here)˳
Instead, no-fly zones are a three-dimensional piece of airspace in which designated aircraft are prohibited from flying (see my analysis here and here)˳ Such zones have usually been established without the consent of the State concerned˳ For example, Operations Provide Comfort (1991-1997), Northern Watch (1997-2003), Southern Watch (1992-2003), and NATO’s 2011 Operation Unified Protector were mounted without the consent of Iraq or Libya, respectively˳ But no-fly zones may also be consensual, an example being NATO’s 1993 Operation Deny Flight over Bosnia and Herzegovina˳ As these operations illustrate, they may be enforced by “coalitions of the willing” or a regional organization like NATO˳
The purpose of a no-fly zone is usually humanitarian, as was the case with Operations Provide Comfort, Northern Watch, and Southern Watch over Iraq˳ However, it may also be motivated, at least in part, by military considerations˳ For example, it is arguable that Operations Deny Flight and Unified Protector both sought to shift the balance of power on the ground˳ Indeed, the former proved unsuccessful and eventually led in 1995 to direct NATO strikes against Bosnian Serb forces during NATO’s Operation Deliberate Force˳
When a no-fly zone has been lawfully established (see below), it may be enforced with lethal force, subject to international humanitarian law (IHL) rules in an armed conflict˳ Rules of engagement often provide for enhanced means of verification and escalation of force procedures before firing on an aircraft in the zone˳ Yet, lethal force has been used, most notably in 1994 when NATO aircraft shot down four of six Bosnian-Serb aircraft that had dropped bombs while within Operation Deny Flight’s zone˳
And no-fly zones may be established during an international armed conflict, as is being proposed by Ukraine˳ In this regard, the experts who participated in the Manual on the International Law Applicable to Air and Missile Warfare (AMW) project (including me) agreed that,
A Belligerent Party may establish and enforce a no-fly zone in its own or in enemy national airspace˳ The commencement, duration, location and extent of the no-fly zones must be appropriately notified to all concerned…˳ [A]ircraft entering a no-fly zone without specific permission are liable to be attacked˳ (¶¶ 108-110)
The Legal Basis for No-Fly Zones
The possible establishment of a no-fly zone over Ukraine must be analyzed from three perspectives˳ First, any such decision requires consideration at the strategic level˳ Opponents fear escalation, while supporters highlight the human tragedy and worry that failure to act will only embolden Russian President Putin˳ Both views are reasonable, although I lean towards the latter˳
Second, the execution of a no-fly zone is complex operationally˳ Mark Nevitt has made this point based on his experience as a Navy aviator enforcing Operation Southern Watch, as have I in light of my experience as the Staff Judge Advocate (SJA) for the Air Component of Operation Provide Comfort and Task Force SJA for Operation Northern Watch˳ Nevitt and I agree that the fog of war is thick in no-fly zones, as tragically illustrated by the 1994 Blackhawk shootdown in the relatively benign environment of northern Iraq˳
A third perspective from which to consider a no-fly zone is legal˳ A no-fly zone is undoubtedly lawful when authorized by the UN Security Council under Chapter VII of the UN Charter˳ According to Article 39, the Security Council may determine whether a situation amounts to a “threat to the peace, breach of the peace, or act of aggression˳” Once it makes such a determination, and if non-forcible measures to address the situation have failed or are unlikely to succeed, the Security Council may authorize “such action by air, sea, or land forces as may be necessary to maintain or restore international peace and security” under Article 42˳
Such an authorization was the legal basis for Operations Deny Flight and Unified Protector˳ The former was conducted pursuant to Security Council Resolution 781 (1992), while Security Council Resolution 1973 (2011) authorized the no-fly zone over Libya, expressly allowing for “all necessary measures” to enforce it, which is a phrase used by the UN to permit the use of force˳
Because UN Security Council authorization is the clearest basis for establishing and enforcing a no-fly zone, States work hard to justify their operations on this ground˳ To illustrate, Operation Provide Comfort, the first of the Iraq no-fly zones, was justified based on Security Council Resolutions 678, 687, and 688˳ They, respectively, authorized the use of force against Iraq in 1990, set out the terms of the 1991 ceasefire, and condemned Iraq’s attacks on the Kurds as a threat to “international peace and security in the region˳” The three were read together in a creative and therefore controversial justification that held that the initial use of force authorization remained in place, Iraq’s actions violated the ceasefire, and Iraqi attacks opened the door to forcible measures to protect the Kurds˳
As Russia is the aggressor in Ukraine, there will be no Security Council resolution authorizing the establishment of a no-fly zone˳ However, at least in theory, it is possible that such a zone could be established in accordance with UN General Assembly Resolution 377(V), the Uniting for Peace Resolution (see discussion in the Ukraine context here, here, and here)˳ The resolution provides a hotly debated basis for the use of force˳ Its proponents suggest that it allows the General Assembly to authorize action when the Security Council has failed to exercise its responsibility for the maintenance of international peace and security because of a veto by a permanent member˳ Although its use would overcome the Russian veto obstacle, such a resolution is unlikely˳
But UN authorization, either in the form of a Security Council resolution under Chapter VII or a Uniting for Peace Resolution, is unnecessary˳ Ukraine has a sovereign right to determine which aircraft may be present in its national airspace˳ Therefore, it may lawfully invite the combat aircraft of other States into that airspace, and did so in, inter alia, the speech to Congress by President Zelensky˳ The invitation qualifies as “consent,” which is a ground for the preclusion of wrongfulness under the law of State responsibility (Articles on State Responsibility, art˳ 20)˳ And, of course, Ukraine also enjoys a sovereign right to prohibit the entry into its airspace of Russian aircraft unless international law justifies their presence˳ As noted earlier in this symposium, Russia’s justifications for their “special military operation” are without merit˳
However, consent only determines the legal character of the presence of enforcement (lawful) and Russian (unlawful) aircraft˳ Whether enforcement aircraft may use force against Russian aircraft is a separate question˳
First, it is necessary to dispense with one red herring˳ It is sometimes asserted that the use of force by one country (enforcement aircraft) against another (Russian aircraft) in the territory of a third (Ukraine) is a use of force against that country˳ However, there is broad consensus that a State may consent to the use of force on its territory so long as that use is otherwise lawful˳ The debate is irrelevant in this situation˳
Similarly, Ukraine’s consent obviates any need to look to the very controversial doctrine of humanitarian intervention as a basis for establishing a no-fly zone˳ Although a minority of States, including the United Kingdom, are of the view that humanitarian intervention is permissible in extreme cases (which the Ukrainian situation qualifies as now that Russian is directly attacking civilian population centers), resort to the doctrine is only necessary to “preclude the wrongfulness” of the sovereignty violation that the intervening States’ action would otherwise constitute˳ Ukraine’s consent already does that work under the law of State responsibility˳
This brings the analysis around to the crux of the matter, the use of force against Russian aircraft by aircraft enforcing a no-fly zone˳ The law is crystal clear˳ Ukraine enjoys a right of self-defense against Russia’s “armed attack” under Article 51 of the UN Charter and customary international law˳ That right, in my opinion, stretches back to the Russian 2014 operations that resulted in the occupation of Crimea˳ And Article 51 expressly allows for “collective” self-defense at the request, and according to the parameters set forth by, a State that has a right of individual self-defense˳ Ukraine has made that request in the form of a plea for a no-fly zone˳ It makes no difference whether the purpose of the zone would be humanitarian or to support Ukrainian forces, for attacking Ukrainian civilians is no less the continuation of Russia’s initial armed attack than engaging in hostilities against the Ukrainian armed forces˳ Simply put, Ukraine’s request for a no-fly zone allows enforcement States’ aircraft to 1) be present in Ukrainian airspace and 2) employ force against Russian aircraft violating that zone˳
Legal Consequences of a No-Fly Zone
A challenging question is whether a no-fly zone would violate the law of neutrality˳ Wolf Heintschel von Heinegg, Brian Finucane, and I have taken the position, one consistent with the Department of Defense’s Law of War Manual (§ 15˳2˳2), that States do not violate their neutrality obligations by providing arms to the victim of unequivocal aggression by another State˳ Russian action qualifies in that regard, as evidenced by the UN Security Council’s vote on the matter (Russia vetoing) and the subsequent General Assembly resolution demanding an end to Russian operations˳ This being so, it would surely not be a violation to conduct a no-fly zone for humanitarian purposes˳ But even if it were, establishment of the zone would not as such result in the State concerned becoming a party to the conflict˳ Instead, a violation of neutrality obligations is only an internationally wrongful act under the law of State responsibility (see Articles on State Responsibility, art˳ 2)˳
Of course, the question remains whether establishing and enforcing a no-fly zone would trigger an international armed conflict˳ Merely declaring a no fly-zone and operating in Ukrainian airspace, if framed purely in humanitarian terms, would not bring those States contributing enforcement assets into the ongoing conflict˳ However, as soon as their aircraft engaged in combat operations to enforce the zone, an international armed conflict would exist between them and Russia˳
This would be so, for instance, if enforcement aircraft downed a Russian helicopter or military aircraft or conducted “suppression of enemy air defenses” (SEAD) strikes to terminate a Russian threat to enforcement aircraft˳ Relatedly, if the no-fly zone served military purposes, like performing “combat air patrols” meant to deter Russian attacks on Ukrainian forces, the involvement would be at a level where the States concerned would likely be considered a party to the conflict (see my discussion here)˳ And if Russian forces attacked the enforcement aircraft first, an international armed conflict would likewise be triggered˳
Once the international armed conflict was underway, IHL would govern the conduct of hostilities by both sides˳ As noted by the AMW experts, “A Belligerent Party is not absolved of its obligations under the law of international armed conflict by establishing ‘exclusion zones’ or no-fly zones” (¶105)˳
It must be cautioned that, under IHL, the military assets of the enforcing States would be military objectives by “nature” and subject to Russian attack, even if located outside Ukrainian territory˳ Similarly, civilian entities that were being used for military purposes, or even intended for future use, like an airfield used by both military and civilian aircraft, would become military objectives by virtue of their “use” and “purpose” (future use) under IHL˳ Whether Russia would conduct operations beyond Ukraine is debatable, but it must be understood that doing so would be lawful under the law of armed conflict˳
Finally, it is my view that because the enforcement aircraft would be performing a humanitarian mission and lawfully be in Ukrainian airspace, any initiation of hostilities against them by Russian aircraft or ground forces would qualify as a wrongful use of force by Russia in violation of Article 2(4) of the UN Charter and customary international law˳ This is because the aircraft would lawfully be in Ukrainian airspace at the time˳ For instance, the aircraft might be conducting reconnaissance and surveillance in the vicinity of humanitarian corridors and be fired on with Russian surface-to-air missiles˳ Such a Russian use of force might even rise to the level of an “armed attack,” thereby giving the State of the aircraft an independent right of self-defense (separate from Ukraine’s) under Article 51 and customary law˳
Of course, a practical difficulty would be distinguishing enforcement aircraft from Ukrainian combat aircraft, which are lawful targets˳ This is so even though there are means to distinguish the enforcement aircraft, for example, by notifying Russian forces of their presence˳ The point is that the fact that there is an ongoing armed conflict in Ukraine does not necessarily mean that Russia may attack enforcement aircraft˳
Conclusion
Time will tell whether the deteriorating situation on the ground in Ukraine causes States to rethink their position on the establishment of a no-fly zone˳ But if they do, they would be on sound legal footing˳ The issue is the will, or lack thereof, of those States in the face of Russian war crimes, not international law˳
***
Michael N˳ Schmitt is the G˳ Norman Lieber Distinguished Scholar at the United States Military Academy˳ He is also Professor of Public International Law at the University of Reading, Strauss Center Distinguished Scholar and Visiting Professor of Law at the University of Texas, and Professor Emeritus at the United States Naval War College˳
Photo credit: U˳S˳ Air Force
