The advent of the Global Positioning System (GPS) provides an alternative source of approach guidance for aircraft. In the US, the Wide Area Augmentation System (WAAS) has been available in many regions to provide precision guidance to Category I standards since 2007. The equivalent European Geostationary Navigation Overlay Service (EGNOS) was certified for use in safety of life applications in March 2011.[27] As such, the number of Cat I ILS systems may be reduced, however there are no plans in the United States to phase out any Cat II or Cat III systems.[28]