Normal mode force appropriation is a method of physically exciting and measuring the undamped natural frequencies and normal mode shapes of a structure. Traditionally used in the aerospace industry for ground vibration testing, it is capable of accurate normal mode estimates. The method attempts to determine multi-point force vectors that will induce single mode behaviour, thus allowing each mode to be viewed in isolation. However it fails to tackle changing dynamic response with forcing level of excitation in nonlinear systems. The method of Force Appropriation for Nonlinear Systems or FANS, produces a special appropriated force vector resulting in nonlinear response. The structure responds dominantly in the target linear mode shape permitting the direct nonlinear characteristics of that mode to be identified in the absence of cross coupling effects.