In AS3 only, you can now abort a loading operation, before it has completed.
Senocular has written a post about it here.

in summary:

var loader:Loader = new Loader();
var request:URLRequest = new URLRequest(“image.jpg”);
loader.load(request);
addChild(loader);

// abort loading if not done in 3 seconds
var abortID:uint = setTimeout(abortLoader, 3000);

// abort the abort when loaded
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, abortAbort);

function abortLoader(){
    try {
        loader.close();
    }catch(error:Error) {}
}
function abortAbort(event:Event){
    clearTimeout(abortID);
}