In this sample <doulbe-click> handler is added to deal with additional file loads:

 		public function mouseDblClick(event: MouseEvent): void
		{
			if ( this.loader  || loadcount == 0 || loadcount > 2) return;
			if ( loadcount == 1)
			{			
				this.loader = new Xc3Loader("/demos/models/walkload/pawn.zc3");
				this.loader.resourcePath = "/demos/models/walkload";
	        	        this.loaded = false;				
			}
			else if ( loadcount == 2)
		    {				
				this.loader = new Xc3Loader("/demos/models/walkload/bunny.zc3");
				this.loader.resourcePath = "/demos/models/walkload";
	        	        this.loaded = false;				
		    }
			this.loader.useCurrentScene = true;
 
			statusText.visible = true;
			statusText.text = "loading file: " + loader.sourceURL; 
			statusTimer = new Timer(1000, 0.2);
			// designates listeners for the interval and completion events
			statusTimer.addEventListener(TimerEvent.TIMER_COMPLETE, onTimerComplete);				 
			statusTimer.start();			
 
			this.loader.addEventListener(LoadEvent.LOAD_COMPLETE, this.cast3dLoadComplete);
			this.loader.addEventListener(LoadEvent.LOAD_ERROR, this.cast3dLoadError);
			this.loader.addEventListener(LoadEvent.LOAD_PROGRESS, this.cast3dLoadProgress);
			this.loader.load(this.animator.source);				
		}

An important thing to remember after you created loader with

this.loader = new Xc3Loader("/demos/models/walkload/pawn.zc3");

is to set 'current Scene' flag

this.loader.useCurrentScene = true;

such that loader will not create a new scene but load into current.

Other things to consider:

• Node IDs should be unique across all loaded models otherwise collision producers unpredictable result.

• if loaded on fly model has a camera, it will override setting for current camera in a scene.

After you loaded a model you may want to position it in scene in a certain place and angle, which can be done with Positioner class as shown below:

		private function cast3dLoadComplete(event: LoadEvent): void
		{
 
			if ( this.loader.sourceURL == "/demos/models/walkload/pawn.zc3" )
			{				
				positionNode("Circle", {x: 0, y:4, z:17}, null);
			}
               }
		/**
		 * sets node position / orientation in 3D scene
		 */		
 		public function positionNode(nodeId:String, position:Object, rotation:Object): Boolean
		{
      	               var nodename:String = nodeId;
	               var node:Node3d = this.animator.source.find(nodeId) as Node3d;
			if (!node) return false;
 
			var p:Positioner = new Positioner(node);
			if (position) p.updatePosition(position.x, position.y,position.z);
			if (rotation) p.upadetRotation(rotation.x, rotation.y ,rotation.z , rotation.w);
 
			return true;
		}

Complete source code for this sample

You can also look at Subload sample in distribution package.