Boeing C-135 OC-135 Open Skies USAFOpen Skies Treaty USAF C 135 aircraft airplane model. The Open Skies Treaty, signed on 24 Mar 92, provides for nearly unrestricted aerial data collection reconnaissance flights over the entire territories of the U. S. and the 26 other signatory countries. Flights are intended to enhance mutual understanding and confidence. The only restrictions on an Open Skies mission are sensor resolution, distance of the data collection flight, and safety of flight