GPS Failure Detection by Autonomous Means Within the Cockpit

In civil aviation, it is desirable to be able to detect navigation system failures quickly and alert the pilot and crew accordingly. Also, while not absolutely necessary, it certainly would be simpler in the GPS case if the detection could be done autonomously within the cockpit rather than via a communication link with a network of monitoring stations on the ground. There is some redundancy in the GPS system, even if only four satellites are in view. This can be further enhanced with the addition of baro-altitude information, and it is the system redundancy that makes autonomous failure detection possible. The scheme used for failure detection in this investigation is the Magill adaptive filter, which is also known as the Multiple Model Estimation Algorithm (MMEA) in control theory. Preliminary results indicate that soft ramp-type satellite clock failures can be detected and identified in a relatively short time for the low dynamic environment that might be encountered in the high-altitude enroute situation. Failure detection is more difficult in the low-altitude nonprecision approach scenario, but preliminary results indicate that this can also be done.