The design requirements cover both cases, vertical and horizontal overlod.
The landing gear system must be designed
so that when it fails due to overloads during takeoff
and landing, the failure mode is not likely to
cause spillage of enough fuel to constitute a fire
hazard. The overloads must be assumed to act in the
upward and aft directions in combination with side
loads acting inboard and outboard. In the absence
of a more rational analysis, the side loads must be
assumed to be up to 20% of the vertical load or
20% of the drag load, whichever is greater.