Display Multiple Layers Using PortlandTiledMapServiceLayer Example

[GlennKirbo]

I am trying to get a Custom Tiled Map Service layer to display with a base map layer below it.
The PortlandTiledMapServiceLayer Example works fine until I try to add a base layer of imagery by changing 1 line of mxml. (code below).  When I run the app I get no errors but only one layer appears.  If I list the base layer first I just get it and if I list the portland layer first I just get it. What am I missing?

<esri:Map id="myMap">
  <esri:ArcGISTiledMapServiceLayer url="http://services.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer" />
  <samples:PortlandTiledMapServiceLayer id="virtualTiles" fadeInFrameCount="12"  alpha=".5" opaqueBackground="false" />
 </esri:Map>

[GlennKirbo]

Robert,

Thanks for your help.
I have finished a first draft of the port to ArcGIS.
It has most of the same features as our JS API.
http://maplarge.com/ArcGIS/basic.html

Glenn