Fact Sheet: The Treaty on Open Skies

Click here for a printable PDF. 


The Treaty on Open Skies allows for states party to the treaty to conduct unarmed observation flights over the territory of other states to foster inter-military transparency and cooperation. The United States, Canada, and 22 European countries including Russia signed the treaty in Helsinki on March 24, 1992. The United States Senate ratified the treaty on November 3, 1993, and it entered into force on January 1, 2002. Today 34 states are members of the Treaty on Open Skies.

The concept for the agreement was originally suggested by President Dwight Eisenhower in 1955. Believing that increased transparency between the United States and Soviet Union would reduce the risk of direct conflict between the two superpowers, he proposed cooperative aerial observation flights. Although this proposal was unpalatable to Moscow at the time, the glasnost-era Soviet Union under General Secretary Gorbachev, and later the Russian Federation, became more amenable when George H.W. Bush revived the idea in 1989.

Why it Matters

The Treaty on Open Skies increases transparency, communication, and cooperation between its members by allowing states to use unarmed aircraft to conduct observational flights over the territory of other states parties. In theory, increased openness between militaries will reduce tensions between states and limit the probability of conflict. In addition, the Treaty on Open Skies provides additional means of verifying states’ compliance with other arms control agreements.

What the Treaty Does


States Parties to the Treaty on Open Skies are assigned “passive” and “active” flight quotas, which are based loosely on the size of their territory. A state’s passive quota is the number of flights that it is required to allow over its territory, and its active quota is the number of flights it may conduct over the territory of other states. Each state’s passive and active quotas are equal. A single state may not conduct more than half of the flights another state is required to accept. For example, Spain has a flight quota of 4, so no single state can conduct more than 2 flights over Spain.


Observation flights are allowed over the entirety of a host state’s territory. An observing state must provide at least 72-hours’ notice of its plans to conduct an overflight. The observing party is required to provide a mission plan to the state it will fly over. The host state may propose changes to the flight plan for safety reasons, but may not restrict access to territory for any other reason. The mission must be completed within 96 hours of the observing party’s arrival.


The treaty regulates the types of sensors that may be used on observational flights. The technology used on Open Skies flights has a maximum resolution of 30 centimeters, which is less detailed than commercially available 25 centimeter resolution satellite imagery. A Russian Open Skies aircraft (the An-30) was certified to use digital technology in 2014, and most states are beginning to transition from film to digital technology on observation flights. Modernization largely reflects a transition to digital film, and does not introduce additional capabilities. In order to incorporate new technology on its flights, a state must have it certified by the Open Skies Consultative Commission and it must be commercially available to all states.


The Open Skies Consultative Commission (OSCC) meets monthly at the Organization for Security and Cooperation in Europe (OSCE) headquarters in Vienna. The Commission is charged with responding to questions about the implementation of the treaty, and resolving concerns about compliance. The first treaty review conference was held three years after the document entered into force, and subsequent conferences are conducted every five years.

Concerns about Compliance

In 2016, Russia submitted a request to equip its Tu-154 observation aircraft with digital electro-optical sensors. Some argued that this technology would give the Russian Federation an advantage over other states by allowing it to gather more precise intelligence. Others have argued that the move towards digital technology is inevitable, and that the benefit to Russia is minimal considering that all states party to the treaty can purchase the data collected on overflights. On June 28, 2016 the United States authorized a Russian jet equipped with the technology to conduct an overflight.

Russia has also been accused of violating the spirit of the Treaty on Open Skies by restricting access to some sections of its territory. These limits include the denial of overflights over Chechnya or within 10 kilometers of its southern border with Georgia, a limitation on the maximum distances of flights over Kaliningrad, and altitude restrictions over Moscow.

Sources: Congressional Research Service, Defense One, U.S. State Department, Federation of American Scientists, Brookings Institution, Organization for Security Co-operation in Europe, CBS News, Radio Free Europe