For a navigation system to be declared as usable for civil aviation purposes, it must fulfil some normalized requirements in a given phase of flight. To date, no current satellite navigation system alone can satisfy the demanding civil aviation requirements. This lack of performance makes the hybridization necessary between the satellite system and another (other) system(s). The aim of this paper is to evaluate the contribution of hybridization to the performance of the main navigation systems, and in particular satellite systems such as GPS and GNSS. The interesting case of INS hybridization will be emphasized.