No-fly zones are areas in Northrend where flying is not possible. These include the city of Dalaran (except the Krasus' Landing), most of Sholazar Basin except zone's rim; and the whole PvP zone of Lake Wintergrasp. In these you can't mount on any flying mount or shift into Flight Form. When entering one of these by flying, you will get a warning and be forcefully dismounted with a parachute-like buff to prevent dying from falling. However, if you are too high in the air, the parachute will wear off while still high in the air and you'll die nevertheless. Caution is adviced.