Fleeing Flyers

From page 68 of the 7th edition rulebook:

Flyers always choose to fly when fleeing, and so 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".

Flyers can flee over interposing terrain and units, but if their move ends inside impassible terrain (including woods) or non-fleeing enemies, they are destroyed as normal.

So the odd sounding event that Darth described where the fleeing flyers went over the Bretonnian knights was in line with the rules.