The well-known bearing characteristic frequencies (BPFO,BPFI,...etc.) reflect the complex kinematic of oper- ating bearings. Far from the idealised perfect rolling assumptions, the experimental frequencies deviate from their theoretical values. The deterioration of the bearing health is likely to induce changes in the kinematics, materialising by a shift in the characteristic frequencies. However, non-stationary operating conditions are also known to influence these frequencies. In this work, the effect of loading and angular acceleration is assessed to measure the feasibility of a bearing degradation indicator using characteristic frequencies for non-stationary operating machines. The method is applied to the monitoring of industrial wind turbines.