Assistance in navigation with increased vertical integrity

The device has a global positioning system (GPS) receiver (20) to receive signals and navigation messages from satellites. A memory unit (30) memorizes a measure of altitude of an aircraft. A calibration device (40) estimates variation of the altitude and associated confidence interval (DPV) of the aircraft. The receiver, memory unit, and the device (40) co-operate to provide information of absolute altitude and the DPV. Independent claims are also included for the following: (a) a process of navigation aid of an aircraft; (b) an aircraft navigation aiding system having a navigation aiding device; and (c) an aircraft having a navigation aiding system.