Pan Am & TWA operated a fleet of 727's in Europe till the early 90's not only to provide feeder services for their flights accross the pond but also for flights from various cities around Europe to West Berlin. Before the fall of the wall, the only airlines into and out of West Berlin were US, British and French carriers, no other carriers (including LH
) were allowed by a treaty signed in the late 1940's between the Allies and the Soviets. So when UA
took over PA's routes, it had to continue those services to West Berlin and for a while which they inherited from PA.