For forty-five years, the only legal way to fly into West Berlin was down one of three lanes twenty miles wide, drawn across hostile territory by a committee in 1945. Stay inside them and you were untouchable. Drift out and you could be shot down, and three American officers were.

The corridors were not airways in the normal sense. They were a legal fiction with a ceiling on it, held open by nothing more than four signatures and the willingness of airline crews to fly through jamming, searchlights, chaff and fighters that came close enough to rock the wings.

Between 1945 and 1990, US Air Forces in Europe logged 733 separate harassment events in and around those lanes. Not one Western airliner was ever brought down in them. That record is the whole story.

Three lines drawn on a map in 1945

Berlin sat 100-odd miles inside the Soviet zone. The four occupying powers had agreed the city would be governed jointly, but nobody had written down how the Western garrisons and their civilians were supposed to get there. On 30 November 1945 the Allied Control Council fixed that with three designated air corridors, each twenty miles wide, running from Hamburg in the north, Bückeburg near Hanover in the centre, and Frankfurt am Main in the south.

The geometry was deliberately simple. Twenty miles wide meant a crew could hold the centreline with 1940s navigation aids and still have ten miles of margin on either side. That margin mattered more than anyone realised at the time.

Twenty miles wide, and not an inch more

The same 1945 agreement created the Berlin Air Safety Centre, staffed round the clock by American, British, French and Soviet controllers sitting at the same table. Every flight plan into Berlin passed through it. The Soviets never walked out, not even at the height of the blockade, because the BASC was the one place where four-power Berlin still formally existed.

Around the city the Berlin Control Zone extended twenty miles from the centre, up to 10,000 feet. Inside the corridors, civil aircraft flew between 7,000 and 10,000 feet, with military traffic tucked below 7,000. The ceiling was occasionally lifted to 13,000 feet when Soviet exercises demanded it, but the working rule for four decades was blunt: low, slow, and no deviation, for weather or anything else.

For jet airliners this was expensive nonsense. A Boeing 727 burning fuel at 10,000 feet over 100 miles of Brandenburg is doing everything an airliner is designed not to do. Crews flew it anyway, several times a day, for twenty-five years.

733 ways to make a point

The serious disruption campaign began shortly after the Wall went up in August 1961. In January 1962 the East German government announced it had the right to force down any aircraft over its territory, four-power agreement notwithstanding. The following month the Soviets began demanding through the BASC that one or more corridors be reserved for their exclusive use. The requests were logged, and ignored.

What followed was a catalogue of pressure short of shooting. Radio jamming. Chaff dropped to blind Western radar. Barrage balloons allowed to drift into the lanes. Parachute drops staged across the flight path. Searchlights aimed at the cockpits of aircraft on night approach to Tempelhof. Soviet fighters buzzing Pan Am, Air France and British European Airways airliners, and going supersonic over West Berlin so the sonic booms rattled windows below. USAFE counted flak, air-to-air fire, rocketing and bombing among the recorded incidents.

In June 1963 the United States announced that President Kennedy’s flight to Berlin would be escorted by F-105 Thunderchiefs, described by an Air Force spokesman as armed and ready for business. The escort was as much a statement as a precaution, and it was understood as one.

What happened if you left the lane

The corridors worked because both sides treated the boundary as real. Twice in 1964 that was demonstrated the hard way, and both times the aircraft were outside the lanes.

On 28 January 1964 an unarmed USAF T-39 Sabreliner on a training flight strayed over Erfurt in East Germany and was shot down by a Soviet MiG-19. All three American officers aboard were killed. Six weeks later, on 10 March, an RB-66 reconnaissance aircraft from Toul-Rosières went down near Gardelegen after being intercepted; that crew ejected and survived.

Neither aircraft was in a corridor. That is exactly why the harassment inside the corridors stayed at the level of jamming and buzzing: the Soviets were making a political point about the lanes, not disputing that the lanes existed. A shot-down airliner would have collapsed the four-power framework the Soviet Union still wanted in Berlin.

The airline that treated it as routine

Because German carriers were barred from Berlin, the internal German routes belonged to Pan Am, British European Airways and Air France. Pan Am’s Internal German Service carried roughly 60 per cent of the traffic in and out of the city and became a world of its own inside the airline: a few score American flight crew, German cabin and ground staff, and an operating culture built on the assumption that something odd would happen today.

When Pan Am opened direct flights from the United States to Berlin in 1964, Moscow made pointed noises about consequences. Pan Am kept flying. The IGS ran until 1990, when reunification let Lufthansa into Berlin and ended the arrangement that had made the service necessary.

The corridors themselves had already carried the city once, in 1948 and 1949, when the same three lanes handled an aircraft every few minutes for fifteen months. That was the exception. The other forty-four years were the quiet version of the same standoff.

The lanes close

On 3 October 1990 Germany reunified, the four-power rights lapsed, and the Berlin Air Safety Centre closed after forty-five years of continuous operation. The corridors stopped existing overnight. Aircraft flying to Berlin climbed to cruising altitude and went the short way, as they had never been allowed to do.

What the corridors proved is worth keeping. For forty-five years a hostile state could have closed them any week it chose, and the only thing stopping it was that the West kept flying them as though they were ordinary airways. Routine, repeated often enough, became a fact on the ground. Or rather, at 10,000 feet.

Sources: Pan Am Historical Foundation, “A Dangerous Game: Flying to Berlin during the Cold War”; Wikipedia, “West Berlin Air Corridor”, “Berlin Air Safety Centre” and “1964 T-39 shootdown incident”; US Department of State, Foreign Relations of the United States 1945 vol. III and 1964–68 vol. XIV; The Aviation Geek Club on the March 1964 RB-66 shootdown.