This thesis, developed within the field of aerospace engineering, is focused on the study of fretting fatigue in spline teeth of aeronautical power transmissions. After a theoretical overview of the problem, a numerical modelling approach was employed to investigate the initiation mechanisms of fatigue cracks under cyclic micro-movements between contacting surfaces. The study represents an extension of previous research that primarily addressed fretting wear, which in this work is considered as an influencing factor on fatigue behaviour. The main objective is to analyse and predict the reduction of component service life. The results highlight the impact of contact parameters and operating conditions on fatigue damage, providing useful tools for fatigue life prediction and for improving the reliability of aeronautical transmission systems..