A Flyby is the camera movement you first see when beginning a mission. If the FlyBy is not adjusted for the city you are on it will give you strange result like a car floating in the air. To get rid of this you can either edit the FlyBy to adjust the position for the city you're in or you can remove it. You can also Restore a previously deleted FlyBy from the FlyBy Menu.
To edit the current FlyBy, start the editor from the FlyBy Menu or by pressing the FlyBy Button on the Edition Tools. If there is no FlyBy currently defined, you will have to select 'Create Flyby'.