Check if mc reached a certain _y then animate

1

I am sliding a movieclip using easing equations. I need a loop that that steps through the current _y value of that clip and when it reaches the desired position(_yvalue -721) tell another clip to start animating(click_mc)

here is what i have so far

big_mc.cdown.onRelease =  function(){
	_root.big_mc.slideTo(-130, -720, 1.7, "easeinoutquint");
		for(var i = big_mc._y; i > -721; i--){
			trace(i);
			 if(i < -719){
				_root.big_mc.phase1_mc.gotoAndPlay(2);
				_root.click_mc.gotoAndPlay("play");
		 }
	}
}

any ideas?