limiting the swiping area in Air for IOS

Dear Friends,

iam creating an elearning app. In this I have a menu with 50 buttons. I want to swipe this menu vertically. iam using the following code:

Multitouch.inputMode = MultitouchInputMode.GESTURE;

stage.addEventListener(TransformGestureEvent.GESTURE_SWIPE, fl_SwipeHandler);

function fl_SwipeHandler(event: TransformGestureEvent): void {

switch (event.offsetY) {

  // swiped down

  case 1:

   {

    if (menubox.y < 30) {

     var myTween1: Tween = new Tween(menubox, "y", Strong.easeOut, menubox.y, menubox.y + 200, 1, true);

    }

    break;

   }

   // swiped up

  case -1:

   {

    if (menubox.y > -2200) {

     var myTween2: Tween = new Tween(menubox, "y", Strong.easeOut, menubox.y, menubox.y - 200, 1, true);

    }

    break;

   }

}

}

here all are working fine. when I swipe fully to top and bottom, it is coming in staying out of starting area.. I want to make him to stop at bigining of the movielip (initial position of movieclip). how can I limiting  top and bottom position...

Thanks in Advance,

Syed Abdul Rahim