were under Allied control by the quadripartite Berlin Air Safety Center. According to permanent agreements, three air corridors to West Germany were provided, which were open only for British, French, or U.S. military planes or civilian planes registered with companies in those countries. The airspace controlled by the Berlin Air Safety Center comprised a radius of around the seat of the center in the Kammergericht building in Berlin-Schöneberg – thus covering most of East and West Berlin and the three corridors, of the same width – one northwestwards to Hamburg (Fuhlsbüttel Airport), one westwards to Hanover, and one southwestwards to Frankfurt upon Main (Rhein-Main Air Base). The West German airline Lufthansa and most other international airlines were not permitted to fly to West Berlin. Flights by Lufthansa or the East German airline Interflug servicing connections between East and West Germany (such as between Düsseldorf and Hamburg in West Germany and the East German city of Leipzig) began in August 1989, but these routes had to go through Czechoslovak or Danish airspace. Traffic between West Berlin and East Germany Until 1953, travelling from West Berlin into East Germany (German Democratic Republic (GDR)) fell under Interzonal traffic regulations overseen by the three Allied military governments (the Soviet Military Administration in Germany (SVAG), the Control Commission for Germany – British Element, and the Office of Military Government/United States (OMGUS)). On 27 May 1952, East Germany closed its border with West Germany and its -long border with West Berlin. From then on West Berliners required a permit to enter East Germany. East German border checkpoints were established in East German suburbs of West Berlin, and most streets were gradually closed for interzonal travel into East Germany. The last checkpoint to remain open was located at the Glienicker Brücke near Potsdam, until it was also closed by East Germany on 3 July 1953. The checkpoint at Staaken's Heerstraße remained open only for transit traffic to West Germany. This caused hardship for many West Berlin residents, especially those who had friends and family in East Germany. However, East Germans could still enter West Berlin. A number of cemeteries located in East Germany were also affected by the closure. Many church congregations in Berlin owned cemeteries outside the city, so many West Berlin congregations had cemeteries that were located in East Germany. For example, the Friedhof vor Charlottenburg (in Cemetery in front/outside of Charlottenburg) was located in