Accessing a Movie Clip on the stage from a class

I have a Flash file with Movice Clips that are placed on the stage at author time. Let’s say one of the clips is called “stageClipMC”.

Say I have a main class file with the following code:

 
package 
{
 import flash.display.MovieClip;
 import flash.events.*;
 import src.MainNav;
 public class main extends MovieClip
 { 
  
  public function main() 
  {
   var mainNav:MainNav = new MainNav();
  }
 }
}

Now… from this class, I can directly access “stageClipMC” just fine.

The code for the MainNav class is:

 
package src 
{
 import flash.display.MovieClip;
 public class MainNav extends MovieClip
 {
  public function MainNav():void {
   trace("stageClipMC: " + stageClipMC);
  }   
 }
}

Tracing “stageClipMC” return “undefined”. From this class, how would I access the clip on the stage? I have tried different variations on “MovieClip(root)” and “MovieClip(stage)” to no avail.

Thanks for your help!