We have successfully demonstrated the protection-switching operation of photonic cross connect (PXC) triggered by the performance degradation threshold of the bit error ratio monitored with FEC in S-LTE for optical submarine cable networks. We confirmed that once the monitored errors exceed the threshold of the submarine line terminal equipment this immediately generates the loss of signal to initiate PXCs to trigger protection/restoration-switching. With the implementation of this technique, the appropriate switching operation of PXCs against the performance degradation of optical signals and the error free operation were confirmed by the 9,000-km test bed with 4 optical nodes.