The Open Skies treaty allows member states to conduct unarmed surveillance flights over fellow members as a means to provide mutual assurance against the possibility of undetected military actions that could pose a threat.
The US president Dwight Eisenhower first proposed the idea during a meeting with Soviet leaders at the Geneva Conference in 1955 but was rebuffed. The proposal was revived by US president George H W Bush in 1989 and the treaty was signed between the then-members of Nato and the Soviet-led Warsaw Pact in 1992.
Formally known as the Treaty on Open Skies, the pact entered into force in January 2002 after Russia and Belarus completed the ratification procedures. The treaty currently has 34 members following the US withdrawal in November 2020. Russia announced its intention to pull out of the pact on January 15, 2021. Among the prominent member nations are Canada, the UK, Germany, Spain, Turkey, Greece, Norway and Ukraine.
The treaty opens up the entire territory of member states to observation flights by fellow members following prior notification. Data collected during such flights by one state is accessible to other treaty members on request. The only grounds for a member to refuse permission for a mission is flight safety. However, the type of aircraft and sensor equipment used during surveillance flights must conform to specifications laid out under the treaty.
Implementation of the treaty is overseen by the Open Skies Consultative Commission (OSCC), comprising representatives from all members, which meets monthly in Vienna at the headquarters of the Organisation for Security and Co-operation in Europe.