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MIL-STD-1629A Appendix A §50.7: failure mode and item criticality numbers
| Tool | FMEA |
| Source | U.S. Department of Defense (1980). Procedures for Performing a Failure Mode, Effects and Criticality Analysis. MIL-STD-1629A, 24 November 1980. Appendix A, Section 50.7, and Task 102. |
| Level | Professional |
Problem
A part has a failure rate λ_p = 0.10 × 1.5 × 40 × 1.2 = 7.2 failures per million hours. Two of its failure modes cause mission loss (severity Category II) with mode ratios α = 0.3 and 0.2 and a conditional probability of loss β = 0.5; a third mode (α = 0.5) only causes unscheduled maintenance (Category IV). For a one-hour mission compute the failure-mode criticality numbers and the item criticality number for Category II.
Inputs to Enter
- Example select: MIL-STD-1629A Appendix A criticality example (loads the worksheet)
- Worksheet columns item | failure mode | effect | cause | class | beta | alpha | lambda_p | t: Part, Mode 1, II, 0.5, 0.3, 7.2, 1.0; Mode 2, II, 0.5, 0.2, 7.2, 1.0; Mode 3, IV, no beta, 0.5, 7.2, 1.0
Answers
- C_m = β α λ_p t: mode 1 = 0.5 × 0.3 × 7.2 × 1 = 1.08, mode 2 = 0.5 × 0.2 × 7.2 × 1 = 0.72 (per million hours); mode 3 has no β and no C_m
- Item criticality C_r (Category II) = 1.08 + 0.72 = 1.80; the highest C_m is listed first on the criticality matrix
- No RPN section is printed because the worksheet has no S, O, D ratings
Notes
Choose the MIL-STD-1629A example in the Example select; the default pump-skid worksheet is illustrative, not a published case.