The stairs are coming from AES, which can be bought from another company

The AES software itself is free and the airport needs to be in the list which is available at another company.

To get full AES on the airports supported, you need to buy credits, which cost around 15 euro's for 10 credits.

All details are here:
http://en.shop.another company.com/eshop.php?action=article_detail&s_supplier_aid=10333&s_design=DEFAULT&shopfilter_category=Flight%20Simulation&s_language=english

I use AES on all my addon airports i bought from another company/FlyTampa, and it really gives the finishing touch when you taxi to a gate and that when you come to stop and shutdown your engines, the gate actually docks onto your aircraft  8-)