This contribution is part of analysis and research in field of unmanned vehicles navigation developed at Faculty of Aeronautics, Technical University in Kosice. The content of this contribution is an issue of the INS and GNSS integration. Loosely coupled integration architecture was in this case chosen as the basic for simple explanation of the integration issue. Within this contribution the emphasis is focused on suitable Kalman filtering and mathematical background. In the last part of the contribution is given short review on actualization of the basic discrete equations of inertial navigation. I. , , ∆ , 4