The Karlsruhe UAC (Upper Area Control Centre) operated by DFS Deutsche Flugsicherung, Germany’s air navigation services provider, experienced a system failure earlier this afternoon and was briefly zero-rated (no traffic handled), causing several flights to go into holding patterns before reaching the Karlsruhe area (see picture below).
Eurocontrol reports that, at 13h49 UTC, Karlsruhe initiated a backup system and started accepting traffic again.
Frankfurt (FRA) and Berlin (TXL, SXF) airports reported several delayed flights caused by this failure of what is also called the Rhine radar.
UAC Karlsruhe is one of the busiest control centres on the European continent. It manages en-route air traffic over central and eastern Germany.