loader unload event not calling

hi friends

my code is

try {
    if (MovieClip(this.parent)!=null) {
        if (MovieClip(this.parent).imagename!=null) {
            var t=MovieClip(this.parent).imagename;
            var url:URLRequest=new URLRequest(t);
            var ldr:Loader = new Loader();
            ldr.load(url);
            ldr.contentLoaderInfo.addEventListener(Event.COMPLETE,onLoadingComplete);
            ldr.contentLoaderInfo.addEventListener(Event.UNLOAD, unloadimages);
            imgholder.addChild(ldr)

            function onLoadingComplete(e:Event):void {
                var targetLoader:Loader=Loader(e.target.loader);
                targetLoader.content.height=140;
                targetLoader.content.width=180;
                dispatchEvent(e);
            }
            function unloadimages(event:Event):void {
                for (var childcounter:uint = 0; childcounter < imgholder.numChildren; childcounter++) {
                    var object:Object=imgholder.getChildAt(childcounter);
                    imgholder.removeChildAt(childcounter);
                }
                //while (imgholder.numChildren > 0){ imgholder.removeChildAt(0);}
                ldr.contentLoaderInfo.removeEventListener(Event.UNLOAD, unloadimages);
                imgholder.removeChild(ldr);
                ldr.unload();
                ldr=null;
            }
        }

    }
} catch (e:Error) {
    trace(" Load Big Image " + e);
}

my loder unload event not calling>>??