I had a landing leg fail when I jacked up one side of my 5th wheel to do a brake adjustment. The trailer was not hitched to my truck, and by jacking one side of the trailer, a lot of weight was transferred to the landing leg on the opposite side. The failure occurred at the bracket where the fixed leg was attached to the trailer frame. Depending on how your landing jacks are attached to the trailer, it might not be a problem, but based on my experience I would never jack up any part of my 5er unless it is hitched to my truck.