The notable thing about the Berlin corridor routes coming up to the fall of the wall is how rapidly they were expanding. TWA came in quite late in the day, EuroBerlin started up, Dan-Air notably expanded their schedules, Pan Am put the A300 on, etc. Nobody seemed to be reducing either. Yet I was at Tegel just maybe two years later and it was a complete rollover, with Lufthansa dominating. Notable also was how services to non-German cities was significantly building up, where previously there were hardly any. I presume the corridor routes subsidy only applied to West German destinations.
Comments above about various holiday charter operators, but as elsewhere they changed emphasis pretty much from year to year and trying to condense it all into a paragraph is not really practical. But I will put in a word for Tempelhof, the main airport for the city until 1975 when the new terminal opened at Tegel and everything transferred over. It had a bit of a renaissance after 1990 and I used a convenient little service on a 146 by Conti-Flug from London City a couple of times. THF was even closer in than LCY, it was like having an airport in Kensington Gardens, just walk out into streets, past the shops and into the U-Bahn on the corner. I was there last year and went to see it; the terminal building is just as always but nothing going on, probably how it was from 1975-90. Shame it's gone; I believe a lot of Berlin thinks the same.