cs4 Using root properties in a class

1

i have a class .as file which extends MovieClip. inside the .as file there is a public function and when called upon it needs to change the value of a property that is on the maintimeline

package
{
    import flash.display.*
    public class TEST extends MovieClip
    {
        public function TEST()
        {
            this.x = 500;
        }
        public function changeGears(){
            this.parent.gear_num += 1;  
        }
    }
}

problem is this error

1119: Access of possibly undefined property gear_num through a reference with static type flash.display:DisplayObjectContainer.