MIL-STD-1798C
5.2.12.3 Design Criteria for in-direct failure mode effects.
The subsystem design and mitigations implemented shall reduce the predicted rate of Class A mishaps resulting for indirect failure mode effects to less than 1x10-7 per flight hour. Indirect failure mode effects are those in which the failed part is not directly involved in delivering a lost safety-critical function, but a collateral effect of failure interferes with a safety-critical function.
An example is: An Auxiliary Power Unit experiences an uncontained failure sending hot turbine material into a fuel tank, resulting in a fire which causes loss of aircraft. The HA is a critical tool available to the MECSIP engineer to identify the hazards associated with each subsystem and define mitigations for those hazards. A list of indirect failure modes and the appropriate design criteria to control those hazards are listed in 5.2.12.3.1 through 5.2.12.3.5 and shown on
figure 3.
FIGURE 3. Indirect failure modes.
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