Navigation system integrity is a quality and safety parameter, which alerts SBAS (Satellite Based Augmentation System) users when the system exceeds tolerance limits. The environmental effects could cause position errors that exceed the computed protection level, i.e. system non-integrity events. In this work a novel error filtering algorithm for additional SBAS performance improvement is presented. It is simple to implement within the user receiver. The algorithm takes into consideration the kinematics of the individual user, which is equipped with Inertial Navigation System (INS) as well. Important relations between position error probability characteristics before and after filtering are delivered. These relations are used for new Vertical Protection Level (VPL) determination. Using the proposed filtering algorithm and related to it VPL, system availability improvement without integrity sacrifice can be achieved.