This paper presents a methodology to calculate the contact pressures on the rolling elements and other significant parameters applicable to raceway bearings used in aeronautical helicopter gearboxes. The mechanism is modelled by a hybrid method where the parts are decomposed in finite elements and the bearings are described by substitution features. This hybrid method accounts for the flexibility of the parts as well as geometrical defects. In this method, the contacts between rolling element and raceways are solved analytically. The Hertz contact theory is used to calculate the contact behaviour. The geometrical defects are included in the model thus changing the value of local displacements. Our paper shows the impact of the flexibility of the different mechanical parts and its geometrical defects, on the behaviour of the bearing raceways. Three most important conclusions are brought to the fore. First the load distribution in the bearing is modified by the flexibility of the parts and the bearing raceways. Second, positioning defects in our assemblies have insignificant effect on the bearing service life. Third orientation defects increase the pressure in roller bearings and the balls orbital speed variation in ball bearings.