The distance flyers flee is based on their flying move rather than their ground move. The normal flee distance for flyers is therefore 3D6" in common with all models whose move is more than 6". If flyers must flee along the ground due to some constraint which prevents them flying, then they flee 2D6" or 3D6" depending on their Movement characteristic value like other troops. For example, if they are in the middle of a wood, or if they are under some magical influence which prevents them flying.
Flyers pursue fleeing enemy in exactly the same way as ordinary troops. Their normal pursuit rate is therefore 3D6" and the same comments apply as for fleeing.