THF was a air force base run by the americans with a tiny commercial side. TXL was in the french sector and their base, Gatow (GWW) the british airfield. The transit corridor had no height restrictions, I was on flights of FL 300-350.

The rough ride into THF was more for noise abatement. The approach into TXL was over the soviet sector when the wind direction changed. I remember being on a FRA-TXL PA 727 flight and doing some interesting turns over downtown Berlin (Palast der Republik) before settling in to land