Because the quantitative criticality calculations defined within MIL-STD-1629A cannot be compared across severity classes, they are not good metrics for determining a “hit-list” of critical failures—that is, a sorted list of critical failures that takes into consideration both frequency of failure and severity.
MIL-STD-1629A, however, does provide for a qualitative criticality analysis in which possible failures are mapped into a “criticality matrix” (Task 102, paragraph 4 and figure 102.2). The example matrix from the standard has been recreated below.
In this matrix, the horizontal axis consists of the MIL-STD-1629A severity classes
(in ascending order of severity).
The vertical access consists of the five probability of occurrence levels from paragraph 3.1 (“Qualitative approach”) in Task 102 of MIL-STD-1629A:
· A – Frequent
· B – Reasonably Probable
· C – Occasional
· D – Remove
· E – Extremely Unlikely
Frequent, catastrophic failures appear in the upper-right section of the matrix; whereas extremely unlikely, minor failures appear in the lower-left section. Qualitative criticality thus increases as you move diagonally from the lower-left to the upper-right area of the matrix, taking into account both severity and likelihood of occurrence.
