After Berlin-Brandenburg airport opened, there was a regular (every 2 hours) Intercity train direct to Dresden. It started somewhere on the Baltic coast, I think. A few years back this was disrupted by major works somewhere in the Berlin area. Looking up the DB Navigator app, I can see that this isn't running at present. Does anyone know if this service has discontinued completely, or if there are still works ongoing and we can expect direct trains sometime in the best future?