On 11 May 1991, in Bucharest, Romania and Hungary sign the Agreement on the Establishment of an Open Skies Regime — the world’s first bilateral “Open Skies” treaty.

The text provides for reciprocal surveillance overflights to assess military forces, as a confidence-building measure after the violent clashes at Târgu Mureș in March 1990 between Romanians and Hungarians.

Authentic languages: Romanian and Hungarian. Entry into force: 27 February 1992. A demonstration flight took place in June 1991. The agreement expired on 31 December 2001 when the multilateral Treaty on Open Skies entered into force (1 January 2002), to which both states are parties.

The political motive: demonstrating stable relations amid Transylvanian tensions and the post-communist transition. The Bucharest–Budapest model was a precursor of the NATO–former Warsaw Pact Open Skies regime.

UNIDIR documentation and studies on military transparency cite the agreement as a pioneer of bilateral aerial inspections in Central Europe.

For Romania and Hungary, bilateral Open Skies was a détente signal before NATO and EU accession.

The Romania–Hungary Open Skies Agreement of 11 May 1991 remains the first treaty of its kind and the precursor of the 2002 multilateral regime.

Image: Bucharest / Budapest; Wikimedia Commons. Cropped to 16:9.

Source consulted: Open Skies Treaty between Hungary and Romania. Treaty text: Romania–Hungary Open Skies Agreement (legislatie.just.ro).