- Slope Stability Software: Plane Failure Analysis: Version 1: (November 1998) I have put together a package to calculate the factor of safety for plane failures in rock and soil slopes where defined discontinuity planes exist. It is fairly intuitive to use, but you must be consistent with the input units. This is the first release and works with Win95 and WinNT 4 (with service pack 3 installed).www.engr.siu.edu/mining/kroeger/index.html