MIL-STD-1629-RevA - Barringer and Associates, Inc.

MTl,-STD-lf)2(l A3.2.1.4 Part failure rate (an). The part failure rate (~p) fromthe appropriate reliability prediction or as (calculated using the proceduredescribed in MIL-HDBK-217, shall be listed. Where appropriate, applicationfactors (n ), environmental factors (TE), and other n-factors as may berequired stall be applied to the base failure rates (~b) obtained fromhandbooks or other reference material to adjust for differences inoperating stresses. Values of n-factors utilized in computing ~p shallbe listed.--,,3.2.1.5 Operating time (t). The operating time in hours or thenumber. of operating cycles of the item per mission shall be derived fromthe system definition and listed on the worksheet.3.2.1.6 Failure mode criticality number (~) . The value of thefailure mode criticality number (Cm) shall be calculated and listed on~he worksheet. Cm is the portion of the criticality number for the iLemdue to one of its failure modes under a particular severity classification.For a particular severity classification and operational phase, the Cmfor a failure mode may be calculated with the following formula:,where:cm = Criticality number for failure mode.~, = Conditional probability of mission loss(3. 201.2 of Task 102).a = Failure mode ration {3.2. 1.3 of Task 102).Ap = Part failure rate (3.2. 1.4 of Task 102).t = Duration of applicable mission phase usuallyexpress in hours or number of operatingcycles (3.2. 1.5 of Task 102).3.2.1.7 Item criticality numbers (c,.). The seconu criticalitynumber calculation is for the item under analysis. Criticality numbers(Cr) for the items of the system shall be calculated and listed onthe worksheet. A criticality number for an item is tl]enumber ofsystem failures of a specific typ~ expected duc to the item’s failuremodes. The specific type of system failure is txpr(sse(i h!’ ~1)(’severity classification for the item’s f~ilur(~ modes. For a pnrrjcul:rseverity classification and mission phase, tt]c Cr for an item is Ll~esum of the failure mode critiralitv numbers. (-’r., under LI)Gs~’vcri~~c]a~~ificc~ti~n t][ldm~~v ;~qsU }W c:]lc:{l. .]~f,(~ ~;,sj! :1 L/.[If[l?l(~\\~~~’i’, [[’~l;llj~,-~ :JCr = ];(f?dpt)n n = 1,2, ’3,...jn–lTASKJ02—24 November 1980— — —.