Moviecliploader target timeline

For some reason I can’t access the timeline of the movie i’m loading.

currently, I have a swf (we’ll call it “loadME”) to be loaded. it sets a _global variable for the timeline like so:

_global.mainTimeline = this

So then in another movie I load the aforementioned clip like so:

var mc:MovieClip = this.createEmptyMovieClip('holder',0);
var loa:MovieClipLoader = new MovieClipLoader();

function onLoadInit(mc:MovieClip){
trace('initialized'); //traces 'initialized'
trace(mc); //traces the instance
trace(mainTimeline); //traces undefined
trace(_global.mainTimeline); //traces undefined

the actual content loads, but I just can’t seem to access its timeline. I should mention that the _global.mainTimeline is a movieclip on the stage of the clip to be loaded.