How do you install a cat door which goes down steps?

Question

Our cat's food and litter is in the basement and we have to leave the door open for her to go down and up. But we are losing air conditioning. How do we build a cat door which has to go down stairs. Traditional doors won't work because they require the cat to step over a ledge and that would cause her to fall down the steps. Help Please!

Answer 1

Honestly short of moving the stairs forward or the door back i don't think you can. Maybe you should move her litter and food upstairs somewhere. If your worried about litter box smell then put a thin layer of baking soda along the bottom of the litter box before you put the litter in.  

Answer 2

what about putting a pet door in and building a  little ledge for her to jump on to when she goes through it.  all you would need is a piece of wood to nail in the top of the stair.

hopefully you get a picture of what i am describing...