Actionscript 3 :: Access A Public Property From AvEniroments Class Through The Player Class?

I have the following inheritance structure:

var environment:AvEnvironment = new AvEnvironment(...);
addChild(environment);
environment.addChild(new Terrain());
environment.addChild(new Player());

I am trying to access a public property from AvEniroments class through the Player class, however I'm getting an undefined property error (#119). I've tried the following:

this.x = AvEnvironment.xs // public property in this class
this.x = parent.xs

I've also tried something like this:

var ev:AvEnvironment = AvEnvironment(parent);
this.x = ev.xs

but I get a TypeError. Error #1009: Cannot access a property or method of a null object reference.