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Avionics equipment, especially for safety-critical systems, is developed by means of a series of design steps, propagating and refining requirements through a number of hierarchical levels, from the aircraft level, through system and sub-system levels, down to equipment, subassemblies and individual components (see SAE ARP4754A [11]). At each development level, accompanying safety assessments (e.g. per SAE ARP4761 [12]) are performed to derive safety requirements which ensure compliance to the overall safety requirements determined by the aircraft and systems functional hazard assessments (FHAs). The safety related requirements of all development levels flow through the process down into the individual equipment specifications and are ultimately implemented in the equipment design where the design data is approved for the certificated aircraft (or engine) type. The equipment production process builds the equipment according to this approved design data.

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.