Just when you thought it could only happen in Britain, large parts of Berlin's S-Bahn (local train) network have been closed down for safety checks!
In particular the entire S9 service to Schonefeld Airport is suspended.
For detailed info see the local transport authority at
http://www.vbbonline.de/start.php?id_language=2
The S-Bahn company has issued an emergency map showing replacement bus services and the VBB has done the same - except their bus services are different!! The VBB has also issued a press release that mentions the first set of buses (routes SXF1, X7 and 171) but it's timetable service is currently crashing if you ask for details (I wonder why!).
Any travel info regading use of S-Bahn in guidebooks should be double checked (at least) locally.
Deutsche Bahn's local trains to the airport are running about twice an hour and local tickets are valid (within relevant zones).
Best of luck.......
Update
Slight improvement expected from Monday 3rd August. S9 will resume running to Schonefeld Airport every 20 minutes but all S-Bahn trains are still running short length with possible overcrowding. SXF1 express bus remains available to local ticket passengers between airport and SudKreuz. Latest estimate for normal service to resume (all trains running with correct number of coaches) is early December.