The Strato Avis has a simple attack pattern: it will attack twice, then on its next turn use Tornado to reduce a party member to critical HP.
The party should begin by having Rosa group-cast Slow on the enemy party, then have Cecil and Cid take out the Cockatrices and then move on the Strato Avis. The player can use their Machine Break Band if they wish. Rosa should focus on healing Cecil with Cura and buffing him with Protect. Cecil will automatically use Cover to intercept attacks on weakened allies, so the player only needs to focus on healing Cecil in this fight. If Rosa and Cid are hit by Tornado, Cecil will protect them from the Strato Avis's physical blows, and Tornado cannot kill them. The player must keep Cecil healthy, because if he himself is reduced to critical health, he will no longer use Cover.