Appreciating the effectiveness of single event effect mitigation techniques

The increased usage of electronic components in avionics have highlighted their sensitivity to atmospheric radiations, such that their impacts on systems need to be analyzed within the safety assessment process. There are numerous challenges associated with the determination of guidelines and recommendations to support the justification that single event effects have been adequately addressed. To verify that the design complies with its failure rate objectives while considering single event effects (SEE), the preliminary system safety assessment (PSSA) and the system safety assessment (SSA) need to include a safety analysis of SEE-induced faults. This analysis should consider all types of SEE impacts on any SEE-sensitive component in the system. The effects can be destructive, nondestructive and permanent, or non-destructive and temporary; they can be limited to one component or propagate to the integrated circuit board, and beyond, to the system. Since SEE are akin to random failures, the associated safety analysis is performed at the equipment level for comparison against the failure mode and effect analysis (FMEA), for all equipment involved in prescribed failure conditions as determined by the functional hazard assessment (FHA). The SEE analysis is centered on the determination of quantitative SEE error rates. These rates depend on the mission profile, the atmospheric neutron flux, and the sensitivity to SEE of the components in the system. Several sources exist for the approximation of a relevant neutron flux, such that their selection should be substantiated with regards to the system's criticality. The sensitivity to SEE can also be determined by various means, with various accuracies. The measure of the effectiveness of the SEE mitigation techniques is a direct result of this assessment. It is therefore important to appreciate the effectiveness using means commensurate with the applicable types of SEE, and the level of exactness required by the associated failure condition.