A quick look at the manual on the Airstream webpage indicates it was potentially just an option... so the first question may be, does it have a levelling system.
A google search for "2005 airstream land yacht leveling system" returned several pictures and listings of 2005 models for sale that show the control panel and system being a "Power Gear" controller from Lippert.
Hopefully that helps a bit, or someone with an actual 2005 chimes in. There are also a few posts for land yachts in the late 90's through early 00's discussing Power Gear leveling systems. This sub-forum may worth a look or search: