Most flyers are single model units, like monsters or characters, but some units of troops can fly too, like Harpies and Carrion. Such units are clearly identified in their army lists. They follow all the normal rules for flyers given above, apart from the exceptions noted below.
Units of flyers operate as skirmishers, except that obviously they cannot fly through woods or other terrain where flying movement is not allowed. If they decide to move on the ground using their Move value, then they move exactly like skirmishers, and ignore terrain penalties.
Models in a unit of flyers always have a unit strength of 1.
Characters can never join units of flyers, even if they ride flying creatures or are capable of flight themselves.