On 22 July 2011, we were able to detect telemetry data anomalies. BEESAT had entered safe mode of operation automatically and was still functional in this mode. After examination of the fault scenario, which was cross-checked with our engineering model a couple of days, we have decided to activate the cold redundant on-board computer. The controlled switching took place on 29 July. Although all telemetry data are plausible again, we still continue to investigate the cause of the malfunction. After 1 year and 10 months of satellite operations for the first time redundancy became necessary on BEESAT.