Mine

private function onResizeHandler(){
	var stageAspectRatio:Number = Stage.width / Stage.height;
	if(stageAspectRatio > _aspectRatio){
		this._width = Stage.width;
		this._height = Stage.width / _aspectRatio;		
		this._x = 0;			
		this._y = - (this._height - Stage.height) / 2
	} else {
		this._height = Stage.height;
		this._width = Stage.height * _aspectRatio;
		this._x = - (this._width - Stage.width) / 2
		this._y = 0;
	}
}