Zoom in/out

Hello, I have to do an imagen zoom in/out by a double tap in as3 for android. I have resolve the zoom in and a pan:

map_mc.addEventListener(MouseEvent.DOUBLE_CLICK, fl_MouseDoubleClickHandler);

function fl_MouseDoubleClickHandler(event:MouseEvent):void

{

    map_mc.scaleX *= 2;

    map_mc.scaleY *= 2;

}

/* Evento de toque y arrastre

Permite mover el objeto sujetando y arrastrando el objeto.

*/

Multitouch.inputMode = MultitouchInputMode.TOUCH_POINT;

map_mc.addEventListener(TouchEvent.TOUCH_BEGIN, fl_TouchBeginHandler);

map_mc.addEventListener(TouchEvent.TOUCH_END, fl_TouchEndHandler);

var fl_DragBounds:Rectangle = new Rectangle(0, 0, stage.stageWidth, stage.stageHeight);

function fl_TouchBeginHandler(event:TouchEvent):void

{

    event.target.startTouchDrag(event.touchPointID, false, fl_DragBounds);

}

if(event.phase==fl_TouchBeginHandler.BEGIN){

map_mc.removeEventListener(MouseEvent.DOUBLE_CLICK, fl_MouseDoubleClickHandler);

}

function fl_TouchEndHandler(event:TouchEvent):void

{

    event.target.stopTouchDrag(event.touchPointID);

}

map mc is the image.

How can I do the zoom out by another double tap?

Thank you