var xmlData:XML;
var xmlLoader:URLLoader = new URLLoader();
var xmlRequest:URLRequest = new URLRequest("data.xml");
xmlLoader.load(xmlRequest);
xmlLoader.addEventListener(Event.COMPLETE, onComplete);

function onComplete(event:Event):void
{
    var loader:URLLoader = event.target as URLLoader;
    if (loader != null)
    {
        xmlData = new XML(loader.data);
        trace(xmlData.toXMLString());
    }
    else
    {
        trace("loader is not a URLLoader!");
    }
}

trace(xmlData == null);