Start animation when objects have stop problem

Hi

I am having a little problem getting an animation to start when an object reaches the end of it's path.

What i have is a ship which is static with an animated propeller (animating), and two platforms which scroll onto the screen and stops when under ship.

Now what is supposed to happen is that a ladder extends down between the platforms when platforms have reached the end of thier path.

The ladder is hidden and should reapear and extend down but the problem is that it is not working, the propeller stops animating ok (as it should) and i just did the same to the ladder as i did with the propeller.

Also, the ladders animate before the platforms reach the end of thier path.

What am i doing wrong please.

Many Thanks

Worf