Benefit of GNSS multiconstellation in position and velocity domain Global Navigation Satellite Systems has a key role in current and future Communication, Navigation and Surveillance infrastructure for aviation application. In air navigation the use of GPS as support to the equipped navigation systems is in use only during less restrictive flight phase (i.e. en-route phase over oceanic areas). In other kind of operations, augmentation systems are required, with a consequent increasing of the architecture complexity. The purpose of this paper is to analyze the performance of multi GNSS (GPS, GLONASS, Galileo) in position and velocity domain. In order to improve the accuracy of the considered multi GNSS, which not always overcomes the GPS-only case, a smoothing filter on measurements is considered. A PVT (Position, Velocity, Time) algorithm based on the Carrier Smoothing Code observables is implemented and the perfomanance of this method are compared with classical Single Point Positioning tecnique.