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Fault tree analyses and the associated safety assessment process plays an essential role in demonstrating acceptable avionic system compliance to the system safety requirements derived from safety related regulations associated with the civil aircraft certification process (e.g. 14CFR/CS §25.1309). SAE ARP4754A and SAE ARP4761 are established industry guidelines for the safety process and fault tree methodology applicable to civil aircraft certification based on techniques which have now been in use for decades. System model-based techniques, used for some time in system and software development, are now being applied in the safety assessment process. These system behavior models of functions with their associated dependencies and assignments have been supplemented with failure modes and effects to “automatically” generate fault tree like outputs. These system model-based fault trees are intended to become integral to the safety assessment process.

Many of the certification regulations in 14 CFR Part 25 are by design, broad and as such, can be subject to large differences in the interpretation of what constitutes adequate compliance. Advisory Circulars (AC's) were developed for many of the regulations to assist industry, as well as certification personnel, with what is considered an acceptable, but not the only means, of compliance. However, there are many regulations where no advisory material is available. In these cases, the “acceptable means” of compliance can vary to a greater degree among the various aircraft certification offices. This difficulty is aggravated as new applicants and regulatory personnel enter the certification field. Recent discussions and interpretations on the usage of an avionic unit's mean time between failure or MTBF for its detectable faults as the basic repair rate for undetected or latent faults, is a subject area where no significant advisory material exists.