To protect a worst-case user, Satellite-Based Augmentation System (SBAS) transmits inflated integrity information for protection level computation. In this work, a novel user-based technique for autonomous protection level computation is proposed. Its quality is examined over Key Performance Indicators tests for integrity and availability using real European Geostationary Navigation Overlay Service (EGNOS) data. The accomplished experiments confirm that this technique allows significant availability improvement without breaches of the integrity.