During the Cold War era (1945–1991), the West Berlin air corridors, also known as the Berlin corridors and control zone, were three regulated airways for civil and military air traffic of the Western Allies between West Berlin and West Germany passing over East Germany's territory. The corridors and control zone were physically centered on and under control of the all-Allied Berlin Air Safety Center (BASC) in West Berlin. The airspace within these corridors was used by US, UK and French-registered non-combat aircraft belonging to these countries' armed forces and airlines operated by pilots holding those countries' passports. In addition, it was also used by LOT Polish Airlines for regular scheduled services from Warsaw to London and Paris via Schönefeld Airport to the south of East Berlin. History The air corridors connected the three West Berlin airports of Tempelhof, Tegel and Gatow with other airfields/airports. Each air corridor was only wide, while the circular-shaped control zone had a radius, making it in diameter; thus allowing aircraft room to maneuver for weather and takeoff and landing. Aircraft were compelled to fly at a maximum height of . However, on occasion, the height restriction would be raised to in order to accommodate Soviet military exercises. Flight plans, for entry into an air corridor, were handled by the Berlin Air Safety Center (BASC), who in turn would coordinate with the Berlin Air Route Traffic Control Center (BARTACC). Routes Northern air corridor: Hamburg, Bremen, Northern Europe Centre air corridor: Hanover, Düsseldorf, Cologne/Bonn, Western Europe Southern air corridor: Frankfurt, Stuttgart, Munich, Nuremberg, Southern Europe Operating procedures Contemporary air traffic control procedures prohibited overtaking in the air corridors to ensure a safe operating environment inside these narrow air lanes and to prevent aircraft from accidentally straying into East German airspace. This compelled jet aircraft crews to reduce their speed if the preceding aircraft was a slower-flying piston or turboprop plane. This in turn extended the jet's flying time inside the air corridor and resulted in higher operating costs due to increased fuel consumption at , especially on short-haul internal German services covering a maximum distance of . For commercial and operational reasons, the airlines had their flights routed through the centre corridor whenever possible as this was the shortest of the three air corridors, thereby minimising the time aircraft spent cruising at . At such a low altitude, modern jet aircraft could not attain an efficient cruising