Today the emissions of CO2 and other pollutants have become a central theme for the development of solutions related to sustainable mobility. In this sense, in recent years, a lot of research has been conducted with the aim of promoting ever greater electrification of means of transport, in order to reduce the use of internal combustion engines, favoring the spread of hybrid or fully electric solutions. These innovations are noticeable in the field of the automotive industry; however, similar research is also being carried out in the aerospace field. This master's thesis arises from a collaboration between the Polytechnic of Turin and the Leonardo Labs, with the aim of studying the mechanical transmission system of a regional aircraft equipped with a hybrid propulsion system.