Q: How can the AccordioPanel communicate a loader to load a new image when a new panel is expanded ?

A: You need to add a new attribute to each of the items in the xml file, representing the path to the corresponding image. Next, listen for the "onExpand" event to know when an item has expanded and check the attribute containing the path to the image for the loader component. Finally, associate that path to the loader.

You'll need to have an AS3 accordion panel component on the stage, with an instance name of "accPanel" and a LoaderProV3AS3 component, with the instance name of "ldr". Here is the code to do it:
import com.jumpeye.Events.AccordionPanelEvents;

// We need to listen for the "onExpand" event, so when one of the items
// is selected, the corresponding image loads into the loader object.
accPanel.addEventListener(AccordionPanelEvents.EXPAND, expandHandler);

function expandHandler(evtObj:AccordionPanelEvents):void {
    // evtObj.item - is the item that has just been expanded
    // the "largeImage" attribute from the xml file is added as property on the item
    ldr.source = evtObj.item.largeImage;
}