Navigation System and Method

An aircraft, a system, and a method. The aircraft may include a computing device. The computing device may include a processor. The processor may be configured to utilize inertial navigation data, global navigation satellite system (GNSS) measurements, and flight trajectory data to compute navigation data and a predicted horizontal integrity level (HIL). The processor may be further configured to output the navigation data and the predicted HIL to be used for performance of a required navigation performance (RNP) procedure or a preflight planning procedure.