GPS by itself is unsatisfactory as a sole means of navigation for civil aviation users even with a conventional Receiver Autonomous Integrity Monitoring (RAIM). The principal limitation of RAIM is its availability. Indeed, even in differential mode (DGPS) or with the Selective Availability turned off, there are periods when the five satellites with sufficiently good geometry required for fault detect-ion are not available. These periods can last, several minutes and this is even worse with the fault detection and exclusion function. New sequential algorithms can make up the insufficiency of currently used snapshot methods.