stairway does not work - conus will appear instead of stairway

I have a curios problem.
In my ground handling control panel there is no stairway.
So I click on "build aircraft set" and click "add" on the stairway entry.
Then I choose again my control panel and click on "+" at the stairway.
But the conus will appear instead of a stairway.
When I click on conus (+) the conus will appear too.
Also I wonder how I can save my aircraft set that I do not have to choose stairway add in the build aircraft set menu again and again ... if i find out how to show the stairs. I am confused :-(