Failure rate calculation with priority FTA method for functional safety of complex automotive subsystems

ISO26262 is going to be officially released as international standard in this year and interest of functional safety for all over safety related industries is increasing. To get compliance with functional safety standards, safety risk analysis is required and failure rates calculation with diagnosis coverage is important and mandatory. Especially for automotive safety-related systems, complex safety systems with new leading edge technologies are getting common and safety risk analysis is getting more complicated. New functional safety has to have consideration of complicated safe states because a simple power-off/shutdown function is not acceptable for the safe states in many cases. This paper provides one of calculation solutions for the hazard/failure rate of such a complex system. Basically, in lots of cases the conventional FTA/FMEDA approach works but for some specific conditions the conventional approach is not suitable. This paper describes the comparison between those approaches of conventional and priority FTA, considering proof-test timing and other specific conditions.