fileReference multiple download and preloader

programming flash
1

this is a part of my code which i use for downloading files.
this works fine when i download one file at a time.
the problem is when i start downloading another file while previous is still downloading, my proloader freaks out and start showing both download percentages at once.
how could i write a preloader to add multiple values together?

public function download( url:String, fileName:String = null ):void {
            
            _URLRequest = new URLRequest(url);
             addListeners();
             
            try {
                _fileRef.download(_URLRequest, fileName);
            } catch (er:Error) {
                trace(er.message);
            }
        }

private function addListeners():void {
            _fileRef.addEventListener(Event.CANCEL, cancelHandler, false, 0, true);
            _fileRef.addEventListener(Event.COMPLETE, completeHandler, false, 0, true);
            _fileRef.addEventListener(IOErrorEvent.IO_ERROR, ioErrorHandler, false, 0, true);
            _fileRef.addEventListener(ProgressEvent.PROGRESS, progressHandler, false, 0, true);
            _fileRef.addEventListener(SecurityErrorEvent.SECURITY_ERROR, securityErrorHandler, false, 0, true);
            _fileRef.addEventListener(Event.SELECT, selectHandler, false, 0, true);
        }


private function progressHandler(e:ProgressEvent):void {
_percent = e.bytesLoaded / e.bytesTotal;
_loaded = _percent;
_txt.text = _loaded + "%";
 }

i can post more code if neccessary.