Considering the No-Fly Zone Prospects in Ukraine


In light of Russia’s ongoing aggression across much of Ukraine and the growing number of civilian casualties and refugees, there is increasing pressure for the United States and NATO to create a no-fly zone over portions of Ukraine. Ukrainian president Volodymyr Zelensky called on the international community to implement a no-fly zone to protect civilians and deny the Russian air force the ability to gain air superiority. Recently, as of last week, several former U.S. officials—including previous supreme allied commanders of Europe—have supported humanitarian-based no-fly zones. The United States and NATO, however, are refusing to impose a no-fly zone over the risk of escalating to a direct conflict with the possible implications of a nuclear threat. Policymakers need to be clear-eyed in their understanding of the tactical challenges, the desired end state, and escalation risks of any form of a no-fly zone.

Q1: What is a no-fly zone and what is the historical experience?

A1: No-fly zones are one form of exclusion zone in U.S. military joint doctrine, specifically in the air. They are established to “prohibit specified activities in a specified geographic area.” Thus, enforcing one obligates clear publishing of the excluded activity and associated geography to establish confidence that all parties are aware of the prohibited details and the promised consequences for violators. No-fly zones can take many forms to fit the context at hand, like those established in U.S. airspace over key areas and cities immediately following terrorist events of September 11, 2001. No-fly zones are intended to be temporary, limited in scope and geography, and are not equal to the defense of the entire sovereignty of a nation’s airspace. They are declared policy, often requiring a third-party state to justify (legally or ethically) their establishment of an exclusion zone inside another’s sovereign airspace. The U.S. experience with the legal basis for these actions has historically been through UN Security Council authorization. 

Historically, the United States has established and supported no-fly zones in Bosnia, Libya, and Iraq through sustained operations, such as both Northern and Southern Watch as well as Provide Comfort. These examples, however, differ in three key ways from the proposed no-fly zones over Ukraine. First, in these historic examples, the United States established the boundaries of each no-fly zone over an aggressor nation rather than a nation that is being supported. Second, those offending nations did not possess nuclear weapons—more specifically tactical nuclear weapons as a means of escalation as is the case of Russia. Finally, those nations did not possess the kinetic or non-kinetic striking power to impose costs on the nations supporting the no-fly zones.

No-fly zones are rife with complications that can create unintended consequences—history should remind us of the tragic Black Hawk shootdown by friendly fire in a very uncontested airspace over northern Iraq in 1994. More recently in Syria, where many argued for the U.S. establishment of no-fly zones, the challenges faced by the U.S.-led coalition and Russian airpower was more of deconfliction than denial of airspace. While Russian strategic objectives in Syria were very different from those of the U.S.-led coalition, in the conflict over Ukraine, these objectives are in direct opposition.

Q2: How might a no-fly zone over Ukraine lead to conflict escalation?

A2: A no-fly zone, even in its most basic form over airspace that is not contested, is a highly complicated act, involving far more than just fighter jets to patrol the skies. It requires a 24/7 movement of fighters, refueling aircraft, airborne early warning systems, and command and control platforms plus hundreds of ground maintenance, security, and support personnel that are usually stationed across multiple airbases. This same no-fly zone in an airspace that is contested by modern militaries with advanced surface-to-air missile systems (SAMs)—as is the situation over Ukraine—requires another level of air assets to suppress adversary air defenses at a greatly increased risk to the defensive air assets.

Even in a best-case scenario of tacit agreement by Russia to avoid a no-fly zone, armed U.S. and NATO fighters, as well as support aircraft flying in very close proximity to armed Russian fighters and SAMs, create a potential for an inadvertent engagement or miscalculation. Actions can spiral out of control rapidly, especially when pilots are traveling near the speed of sound off the border of a heavily armed adversary. Shifting conflict boundaries that are easily recognized on a map are less obvious on a radar screen. A mistake as simple as an aircraft turning right instead of left or accidentally shining radar energy on an adversary fighter can be misunderstood as an act of aggression. The inherent right to self-defense for a fighter aircraft perceived to be in a threatening situation means that the nuances of a strategic diplomacy can be overcome in a moment by a single tactical decision. This is not an environment that garners strategic stability, and as such, a no-fly zone should only be pursued with a clear-eyed understanding of the risks that is tied to a direct objective.

Q3: How might a no-fly zone over Ukraine produce different results than those of the past?

A3: A no-fly zone would likely bring the United States and NATO into direct conflict with Russia. Despite the laudable intent of signaling resolve or providing proactive defense for humanitarian response, a no-fly zone would cede initiative to Russia. Escalation decisions would be in the hands of Russia with an ability to leverage aircraft—by targeting them—in the no-fly zone with possible deniability of ill intent. Over the risk of inadvertent (or intentional) tactical escalation, the establishment of a no-fly zone could be perceived by Russia as a new encroachment of the West—potentially triggering an escalatory response.

Previous no-fly zones were often implemented without a modern military to counter them. Operation Provide Comfort’s no-fly zone was lauded for the reassurance to generations of Kurds without a single engagement, largely due to the military overmatch of the forces defending the airspace against Saddam Hussein. The military forces patrolling a no-fly zone over Ukraine will not hold a similar monopoly on power. In addition to the possible miscalculation outlined above, coordinated U.S. and NATO military operations will require the formation of a coalition military command structure, expanding President Putin’s possible target list.

A no-fly zone should also consider how to protect against or respond to threats to Ukrainian forces and humanitarian zones from munitions launched from Belarus, Putin’s claimed Donbas region, or even from Russia itself. These situations create questions of what to do with cruise missiles, ground-launched ballistic missiles, and other threats originating across political borders aimed at targets inside the no-fly zone without formal declarations of war. As the former air commander of operation Northern Watch, Lt. Gen. (ret.) David A. Deptula notes, “[a no-fly zone] is not some magical way to disperse an enemy without bloodshed.”

Additionally, the broad range of threats that could transverse a no-fly zone, from aircraft to cruise and ballistic missiles, complicate the defensive response. While defending fighters may have minutes to detect, intercept, and engage adversary aircraft, this timeline can be reduced to seconds for cruise missile at low altitude. Ballistic missiles and artillery—which have seen considerable use by Russia against targets in Ukraine—are not targetable by fighters. These no-fly zone enforcement challenges will likely create frustrations in the international community when missiles and shells—albeit reduced in number—are still falling on Ukrainians.

Q4: What impact do rules of engagement (ROE) have on the effective use of a no-fly zone and the chance for escalation?

A4: Rules of engagement (ROE) are the authoritative guidance given to the pilots and air defenders to restrain their actions under the international Law of Armed Conflict and proximal political constraints. While a pilot may have the tactical opportunity to engage an adversary violating the boundary of a no-fly zone, the strategic risk of conflict escalation if they engage may drive a highly restrictive form of ROE. This type of politically charged ROE can require a high-level approval for each tactical action. While policymakers may assume in theory that each decision is carefully considered in light of escalation risk, the practical outcome is that pilots are left in a dangerous position of needing to make split-second decisions while also not holding the authority to make that decision. This tense situation is rife with risk for miscalculation or inadvertent engagement while waiting for a decision from on high. 

This risk only increases when considering the U.S. and NATO pilots’ right to self-defense—an inherent right inside ROE derived from international law and national policies. An aggressive act (whether perceived or actual) from Russia against a defending aircraft invites a response to stop the aggression—even if this means destroying the aggressor. This important right also increases the chance for misperception, inadvertent engagements, and conflict escalation.

The United States and NATO will need to decide if their political objectives are mature enough from which to derive militarily effective ROE. Even if Russia temporarily honors a no-fly zone, U.S. pilots can expect to see Russian fighters routinely pushing or incrementally crossing the published no-fly borders to assess the United States and NATO’s tactical response or to trigger a U.S. response that could be used to legitimize Russian escalation. A no-fly zone should not be viewed as simple deconfliction of air activity, as was the case in Syria through coordination hotlines. Furthermore, once the basic no-fly zone objectives are achieved, as was the case for Deny Flight in Bosnia, the coalition may face the political pressure to loosen the ROE to include disrupting or punishing atrocities taking place underneath the airspace—which, in the case of Russia, may include targeting Russian ground forces. Even with the clearest written ROE, U.S. and NATO pilots will need to rapidly assess intent and make decisions with strategic consequences.

Q5: Could the United States and NATO achieve air superiority over Ukraine by establishing a no-fly zone?

A5: Yes, but it would be very costly. Russian advanced SAMs, such as S-400s that can reach well into Ukraine, are difficult to suppress and increase the complexity of defense and risk to the defending aircraft. Each 24/7 defended area in a no-fly zone would require more than an entire fighter squadron and multiple tankers and early warning systems. An effective no-fly zone may require several of these air patrols operating simultaneously. Air superiority over Ukraine would involve a major undertaking for NATO and the United States, requiring coordinated airborne and ground-based air defense across multiple areas of the country. Intense coordination would be required between the United States, NATO, and Ukrainian command elements. The placement of aerial tankers; intelligence, surveillance, and reconnaissance (ISR); and early warning aircraft is critical, as they add to the list of assets to defend, even if some are to remain well outside Ukrainian airspace.

The United States and NATO, particularly with defense spending improvements since 2014, maintain the capability to successfully conduct a no-fly zone. Since the Cold War, the United States has flown on average 20,000 to 30,000 sorties per year (60-100 missions per day) in no-fly zones, equating to the 24/7 output of 3-5 installations across the span of combat to support missions. Policymakers, however, must accept that a no-fly zone in Russia may only achieve limited objectives, given that the ranges of Russian offensive and defensive missile capabilities will allow them to continue operations without placing assets in Ukrainian airspace, and may be costly in terms of risk to force and escalation.  

Q6: Is it possible to have a “limited” no-fly zone to assist humanitarian corridors?

A6: The simple answer is no. The logic of using force to prevent an adversary from entering certain airspace is agnostic to the type of operations happening on the ground. While the intention for such a humanitarian no-fly zone may be to signal defensive strength and reduce suffering, the potential for tactical miscalculation does not appreciably change. Additionally, the effectiveness of such a no-fly zone to effect better humanitarian support would be limited. Russia has launched over 1,000 missiles at targets in Ukraine, with the vast majority originating inside or on Russian and Belarusian airspace and soil. While these weapons can cause substantial indiscriminate harm, the fighter aircraft in a no-fly zone have no ability to intercept most of these munitions and have limited capability against the cruise missiles that are likely flying at low altitude.

Q7: How is Russia enforcing a no-fly zone over Ukraine?

A7: On March 18, 2022, Russia announced a no-fly zone over the Donbas region in Ukraine. The absence of third-party states and the contained nature of the conflict between Russia and Ukraine make this declaration largely inconsequential to the tactical and operational levels of the ongoing conflict, but it most likely serves as posturing to further dissuade the possibility of the international community and NATO’s involvement in Ukraine.

Q8: What other air defense options could better assist Ukraine’s resistance to Russia?

A8: SAMs, especially those that are highly mobile, have achieved considerable success in contesting Russia’s use of the air over Ukraine. While larger SAMs, such as the S-300, gain significant press (including some targeting attention from Russia) and have successfully engaged Russian aircraft like SU-25s and SU-35s, the highly portable Ukrainian shoulder-launched SAMs (such as Stingers and Iglas) have proved to be a far more effective air defense tool so far. The United States and NATO should consider the utility of man-portable air-defense systems (MANPADs), which come in many varieties that exist across NATO, are easily transferred, and require little training to operate effectively. These would be an excellent choice for additional support to Ukraine over MiG-29s and in addition to higher-end SAMs like S-300s.

While the prospect of creating a no-fly zone over Ukraine may signal defensive resolve of the United States and NATO against Russia, it is rife with the potential for unintended consequences. The historical record of no-fly zones is one of tactical realities failing to meet political objectives, leading to mission creep. Policymakers should approach such actions, even if done to protect humanitarian response, with a clear-eyed understanding of the high potential that it could lead to direct conflict with Russia. A decision to enact any form of no-fly zone should only be made if it links to a strategic objective and the policymaker can clearly answer: To what end?

Matthew Strohmeyer is a military fellow with the International Security Program at the Center for Strategic and International Studies (CSIS) in Washington, D.C. Christopher Reid is a military fellow with the International Security Program at CSIS. Grace Hwang is a program coordinator and research assistant with the Burke Chair in Strategy and Transnational Threats Project at CSIS.

The authors give special thanks to Seth Jones, Mark Cancian, and Oliver Lause for their outstanding comments.

Critical Questions is produced by the Center for Strategic and International Studies (CSIS), a private, tax-exempt institution focusing on international public policy issues. Its research is nonpartisan and nonproprietary. CSIS does not take specific policy positions. Accordingly, all views, positions, and conclusions expressed in this publication should be understood to be solely those of the author(s).

© 2022 by the Center for Strategic and International Studies. All rights reserved.

Grace Hwang

Christopher Reid

Matthew Strohmeyer