A Bayesian Analysis of Avionic Subsystem Built-in Test

A major development in test philosophy of aircraft being built today and those being designed for the immediate future is the incorporation of on-board, computer-controlled "built-in" testing (BIT) into the airplane as part of the avionic subsystem. A requirement being imposed by today's specifications is a probability of 0.95 or better that the BIT function will detect a failure. The discussion presented in this paper will show that a single specification of BIT capability is insufficient to completely define the requirements for BIT. The proof of this conclusion is offered in the form of an analysis of the conditional probabilities involved in the occurrence and reporting of subsystem failures. As a result of this analysis it is imperative that the customer be cognizant of the significance of the BIT requirements levied on the contractor and that the designer be allowed more latitude in his BIT requirements so that an optimum product will be obtained.