Integrity monitoring and failure identification within an integrated satellite/inertial navigation system

Global Navigation Satellite Systems (GNSS) provide highest accuracy navigation capabilities when using differential techniques. Although the accuracy performance can comply with the tight limits as defined by ICAO or RTCA for precision approaches and taxi guidance, under real environment several effects onboard the aircraft degrade the quality of GNSS to an unacceptable level, so that GNSS would not be capable for sole means navigation. For system integrity checks, different approaches like Receiver Autonomous Integrity Monitoring (RAIM) or ground based overlay techniques are in discussion so far, but none is able to compensate insufficiencies of the satellite systems concerning dynamic environment and reliability. Therefore a combination of satellite information with inertial sensors suggests itself, because the latter are an ideal complement to GNSS due to their good dynamic behaviour, although they are characterized by long-term drift as a result of misalignment, accelerometer and gyro errors. Their budget varies with dynamic manoeuvres so that a preflight error determination and system calibration is insufficient. A complementary navigation system based on Kalman-filter techniques enables the estimation and compensation of different sensor errors of the inertial as well as the satellite part. In the paper the potential of quality control, i.e. failure detection, identification as well as failure repair, exclusively with means of onboard information for integrity monitoring is discussed. In consequence this approach is called Aircraft Autonomous Integrity Monitoring (AAIM)