Complex sentence: In addition to the normal crew of Captain, First and Second Officer, there were two additional check captains: the captain who was being trained as a Check Captain (CC) and the Supervising Check Captain (SCC) who was training the CC.
Split into simpler sentences: In addition to the normal crew of Captain, First and Second Officer, there were two additional check captains. The captain who was being trained as a Check Captain (CC) and the Supervising Check Captain (SCC) who was training the CC.