In aircraft navigation, civil or military, it is certainly a prime requisite to be able to detect system failures quickly and alert the flight crew accordingly. There has been much interest in using the Global Positioning System (or GPS) for air navigation although the overall integrity of this new system has not yet been thoroughly proven;This study is part of a larger effort aimed at answering this question by looking specifically at the problem of the detection of subtle system clock failures. Several detection models, all patterned after the Magill adaptive filter, were developed and studied. One of these was chosen over the others to demonstrate failure detection in various flight environments and under different failure conditions;The Magill scheme calls for a parallel testing of several composite hypotheses, each identifying a measurement (pseudorange from a satellite in the case of GPS) to detect the failure. There can, of course, be as many hypotheses as there are measurement sources available. A null hypothesis covers the no-failure situation. Conditional probability calculations uniquely associated with each hypothesis provide the proper indication as to which of the hypotheses is the \u22correct\u22 one after accumulating enough information from the observed measurements;In the Monte Carlo simulations carried out to test this detection scheme, favorable results were obtained. The enroute scenario for an aircraft involves very modest dynamics which, when taken advantage of, showed clearly the feasibility of prompt detection and identification in this situation. In the dynamically noisier nonprecision approach environment, the results obtained were somewhat marginal, though encouraging nonetheless.
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