Run remote SWF in AIR Security Sandbox

I am trying to load an external SWF and run it in the AIR sandbox.

this is the AIR application code:

public class Downloader extends Sprite
{

    private static const REMOTE_FILE:URLRequest = new URLRequest("http://myserver.com/downloadable.swf");
    private var _main:NativeWindow;

    public function Downloader()
    {
        var loader:URLLoader = new URLLoader(REMOTE_FILE);
        loader.dataFormat = URLLoaderDataFormat.BINARY;
        loader.addEventListener(Event.COMPLETE, downloadComplete);
    }

    private function downloadComplete(e:Event):void{
        var ba:ByteArray = e.target.data;
        var stream:FileStream = new FileStream();
        var file:File = File.applicationStorageDirectory.resolvePath("downloadable.swf");
        stream.open(file, FileMode.WRITE);
        stream.writeBytes(ba);
        stream.close();

        loadAndRunSwf();
    }

    private function loadAndRunSwf(){       
        this._main = new NativeWindow();
        this._main.width = 1024;
        this._main.height = 768;

                    ////obsolete?
        //var context:LoaderContext = new LoaderContext();
        //context.allowLoadBytesCodeExecution = true;
        //context.applicationDomain = ApplicationDomain.currentDomain;  

        var file:File = File.applicationStorageDirectory.resolvePath("downloadable.swf");
        var loader:Loader = new Loader();
        loader.load(new URLRequest(file.url)/*,context*/);

        this._main.stage.addChild(loader);
        this._main.activate();
    }
}

Downloadable .swf Code:

public class Downloadable extends Sprite
{
    private var _btn:Button = new Button();
    private var _baseFolder:File = new File("app-storage:/");

    public function downloadable_test()
    {
        this.addChild(_btn);
        _btn.label = "access Harddisk";
                    ...
    }
}

so now, if I run Downloader, it will load swf and try to run it, but I will get an exception in Downloadable in the line

    private var _baseFolder:File = new File("app-storage:/");

error:

SecurityError: file
at runtime::SecurityManager$/checkPrivilegeForCaller()

So - what do I need to do to prevent such security errors? I want my remote SWF to be treated as native code running in the same security sandbox as the AIR code.