Mission Failure Probability Calculations for Critical Function Mechanizations in the Automated Highway System

Reliability analysis is an important part of the Automated Highway System (AHS) research and development. In 1994, Honeywell released the “Malfunction Management Activity Area Report for AHS Health Management Precursor System Analysis” which showed a reliability analysis of the AHS vehicle system. However, the Honeywell report does not describe in detail how they arrived at their answers. In this paper, we will be providing a more detailed analysis of how Honeywell arrived at the probability of failure vs. time plots for both the different subsystems in an AHS vehicle and the overall system. Matlab programs were written to calculate system reliabilities for series and parallel systems. In performing the analysis, there were several places as stated in the paper where our answers differed from Honeywell’s answers. Because of these differences, our results and conclusions are different from Honeywell’s results and conclusions. Based on a 95% test coverage and a system failure rate limit of 1 x 10-6 failures per mission, Honeywell determined that triplex redundancy for all subsystems is necessary to meet these requirements. However, for the purposes of our study, and assuming 100% test coverage and also a system failure rate limit of 1 x 10-6 failures per mission, we determined that duplex redundancy will result in a mission time of 3.5 hours, which is still satisfactory.