ActionScript 3.0 :: Removing An Object When It Reaches A Certain Point

I have a rounded rectangle that the x and y values will always stay the same. However it rotates around and it's height is increased (it follows moving targets). (Think of it as a turret that shoots out a beam of light that will always be anchored to the turret on one end but it gets longer and rotates so that it constantly tracks the moving targets) I want to remove the object when it moves off the screen.

Normally I would just do this with:

(if myObject.x >= 550){
removeChild(myObject);
}

and the same for each other direction of the screen. However, as mentioned, it's not the x and y values that are changing - it's the height that's changing.

Now I've tried just swapping out 'x' for height:

(if myObject.height>= 550){
removeChild(myObject);
}
etc. for the rest.

But the problem with that is that if my turret (the anchor point for beam of light) is closer to the edge of the screen (i.e. it's x is 500), then it will take a couple of second's for the light beam's height to reach 550.