Class help --- checking values on the stage

programming flash
1

Hi I am trying to build a simple class, where my object(s) that get put on the stage continually checks through an EnterFrame Event the y position of an animation on the stage, and if the y pos of this animation is greater than the object doing the checking, then I want to remove it from the stage.
//-- doc class

var s:Sqr = new Sqr();
s.y = 200;
addChild(s);
line_mc.addEventListener(Event.ENTER_FRAME,timer):void
{
    e.target.y += 2;
}

//-- Sqr class

import flash.display.Event;    
public class Sqr extends Sprite
    {
        public function Sqr() 
        {
            this.addEventListener(Event.ENTER_FRAME,timer);
        }
        private function timer(e:Event):void
        {
            // how do I reference line_mc ?
                        if(line_mc.y > this.y)
                        {
                              this.removeEventListener();
                              removeChild(this);
                        }
        }
    }

thanks yo