public static function flipHorizontal(obj:DisplayObject):void {
    var m:Matrix = obj.transform.matrix;
    m.transformPoint(new Point(obj.width * .5, obj.height * .5));
    m.tx = (m.a > 0)?obj.width + obj.x:obj.x - obj.width;          
    m.a = -1 * m.a;
    obj.transform.matrix = m;
}
       
public static function flipVertical(obj:DisplayObject):void {
    var m:Matrix = obj.transform.matrix;
    m.transformPoint(new Point(obj.width * .5, obj.height * .5));
    m.ty = (m.d > 0)?obj.y + obj.height:obj.y - obj.height;
    m.d = -1 * m.d;
    obj.transform.matrix = m;
}

http://www.nightdrops.com/2010/quickreference-flipping-displayobjects/

Flipping DisplayObjects

ActionScript 3