Variable problem (Example .fla/swf inside)

Question

I have a plane movieclip which chooses a plane sprite randomly. When you drop a bomb the bomb should choose the sprite fitting the plane that it was dropped by. (Plane 1 drops bomb 1, plane 2 drops bomb 2)
This works if I have one plane already on the stage, and no others. However, if I attach more plane movieclips it drops only bombs with the same sprite. (plane 1 and plane 2 only drop bomb 1)
Here is an example fla/swf:
http://dl.dropbox.com/u/6414392/plane%20example.zip
I commented the code a little, its not much. If you delete the controller movie clip and put the plane on the stage then it will work. Use it like it is and it doesn't.
This is driving me nuts, but I am probably only missing one little thing that makes it not work when attaching movieclips.

Answer 1

Now only the first appearing plane drops a bomb, the others don't drop anything at all.
Couldn't you take a look at the .fla? Or simply the .as files I attached? Because right now, I'm not sure if I just put it there wrong. Its probably harder to see whats wrong without taking a look at it too.
The code now looks like this:
var bomb = _root.attachMovie("Bomb","bomb"+_root.getNextHightestDepth(),_root.getNextHightestDepth() ,{bombType:plane_type});
I don't know what to do. I don't get how to tell the bomb from which plane it came. All the other problems I encountered so far, I could wrap my head around and learned from it. But this is a tough nut to crack.
Edit: I'm really sorry to be so thick and daft. I hope you don't give up on me, I really want to get this!
Edit2: Ok I tried around with it, and now this happens: (its the .swf, no need to download)
http://dl.dropbox.com/u/6414392/Plane_Example.swf
This is the code I used:
Plane.as:
class Plane extends MovieClip
     var plane_type;
     function onLoad()
     //choose random frame (plane image)
     plane_type = Math.floor(Math.random()*2+1);
     //Go to the frame
     gotoAndStop(plane_type)
          function onEnterFrame()
               _x-=4;
               if (Key.isDown(Key.DOWN))
          var bomb = _root.attachMovie("Bomb","bomb"+_root.getNextHightestDepth(),_root.getNextHightestDepth() ,{bombType:plane_type});
          bomb._x = _x-20;
          bomb._y = _y+20;         
Bomb.as
class bomb extends MovieClip
     var gravity;
      var bombType
     function onLoad()
     //Change bomb picture to the same number that is bomb_type (which is set in the Plane Movieclip)
     gotoAndStop(bombType);
     gravity = Math.random()* 4+ 2;
     function onEnterFrame()
     _y+=gravity
     _x-=2
     _rotation-=gravity
This is so frustrating, I've wasted hours on this.