Advanced Receiver Autonomous Integrity Monitoring (ARAIM) is a concept that extends RAIM to other constellations beyond GPS. ARAIM will enable the integration in the position solution of the newer GNSS core constellations that may have different properties (in particular with higher failure rates than GPS). This inclusion will provide better levels of performance of horizontal guidance than RAIM with GPS alone. In addition, when sufficient satellites have dual frequency (L1-L5) signals, ARAIM could enable aviation safety of life operations, including approaches with vertical guidance. The European Union (EU) and the United States (US) have an agreement establishing cooperation between GPS and Europe's Galileo system. As part of this cooperative agreement a technical subgroup was formed to investigate the benefits of Advanced Receiver Autonomous Integrity Monitoring (ARAIM) , This EU-US ARAIM subgroup has developed a reference airborne algorithm  and two potential ARAIM architectures [3,4, 5].