Reliability analysis of a single-engine aircraft FADEC

This paper presents a reliability analysis of two options to a fault-tolerant full authority digital electronic control system (FADEC) intended for control of an aircraft gas turbine engine. The study concentrates on an application for an aircraft equipped with a single engine, thus placing very hard constraints on the reliability of the FADEC. The analysis is based on Markov modeling and a method of mapping state probabilities. Using this method, the influence of varying criticality among the flight mission phases can be investigated, as can the influence of not using the common assumption of "perfect from start". The study shows that latent faults together with incomplete repair between flights (i.e. the system is not perfect from start) have a clear influence on the assessed reliability. How important these faults are depends to a great extent on the probability of repair. The study also indicates that phase modeling is of less importance, mainly because the phases are quite similar in the specific model and the assumed flight mission time is fairly short compared to MTTF for the components of the FADEC.