100
rrr ' . * MIL-STD-7566 NOTICE 1 31 August 1982 MILITARY STANDARD RELIABILITY MODELING AND PREDICTION TO ALL HOLDERS OF MIL-STD-7566: 1. THE FOLLOWlNG PAGES OF MIL-STD-756B HAVE BEEN REVISED AND SUPERSEDE THE PAGES LISTED: New Page - Date Superseded Page Date V 31 August 1982 V vi 31 August 1982 vi 18 November 1981 18 November 1981 2. MAKE THE FOLLOkING PEN AND I N K CHANGES: (a) (b) (c) Page 1001- 7 add 'I=" between PA , P6 =P6 , and Pc =Pc. Page 1001- 4 add "(11)" to the right of Ps = PAPBP1P2. Page 1001- 6 add "(15)" to the right of Ps = PAPB PC . 22 2 2 (d) Page 1002- 3 add "(2)" to the right of PS = 61E$1C2A+... .......+B162CiC2A. (e) Page 1002- 3 add "(3)" to the right of PS = 61C1+ ........ +61E'2C1 C2A. (f) Page 1003- 4 add "(1)" to the right of Ps = A[C1+C1c2]+ .... . . . .+61C,B2C2]. 3. RETAIN THIS NOTICE AND INSERT BEFORE TABLE OF CONTENTS. 4. indicated above have been entered. check sheet. This issuance, together with appended pages, i s a separate publication. Each notice i s to be retained by stocking points until the military standard i s completely revised or canceled. Holders of MIL-STD-7566 will verify that page changes and additions This notice page will be retained as a Custodi ans : Army - CR Navy - AS Air Force - 17 Review Activities: Army - EA, AR Navy - SH, US Users : Army - AM Navy - EC National Security Agency - NS Defense Mapping Agency - DMA Prepari ng Activity: NAVY - AS (Project No. RELI - 0038) RELI

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  • rrr '.*

    MIL-STD-7566 NOTICE 1 31 August 1982

    MILITARY STANDARD

    RELIABILITY MODELING AND PREDICTION

    TO ALL HOLDERS OF MIL-STD-7566:

    1. THE FOLLOWlNG PAGES OF MIL-STD-756B HAVE BEEN REVISED AND SUPERSEDE THE PAGES LISTED:

    New Page - Date Superseded Page Date V 31 August 1982 V v i 31 August 1982 v i

    18 November 1981 18 November 1981

    2 . MAKE THE FOLLOkING PEN AND I N K CHANGES:

    (a )

    ( b )

    ( c ) Page 1001-7 add 'I=" between PA , P6 =P6 , and P c =Pc.

    Page 1001-4 add " ( 1 1 ) " t o t h e r i g h t o f P s = PAPBP1P2.

    Page 1001-6 add " ( 1 5 ) " t o t h e r i g h t o f P s = PAPB PC . 2 2 2 2

    ( d ) Page 1002-3 add " ( 2 ) " t o t h e r i g h t o f PS = 61E$1C2A+... .......+B162CiC2A.

    ( e ) Page 1002-3 add " ( 3 ) " t o t h e r i g h t o f PS = 61C1+ ........ +61E'2C1 C2A.

    ( f ) Page 1003-4 add " ( 1 ) " t o t h e r i g h t o f Ps = A[C1+C1c2]+ .... . . . .+61C,B2C2]. 3. RETA IN T H I S NOTICE AND INSERT BEFORE TABLE OF CONTENTS.

    4. i n d i c a t e d above have been entered. check sheet. Th is issuance, t oge the r w i t h appended pages, i s a separate p u b l i c a t i o n . Each n o t i c e i s t o be r e t a i n e d by s tock ing p o i n t s u n t i l t h e m i l i t a r y s tandard i s complete ly r e v i s e d o r canceled.

    Holders of MIL-STD-7566 w i l l v e r i f y t h a t page changes and a d d i t i o n s Th i s n o t i c e page w i l l be r e t a i n e d as a

    Custodi ans : Army - CR Navy - AS A i r Force - 17

    Review A c t i v i t i e s : Army - EA, AR Navy - SH, US

    Users : A r m y - AM Navy - EC Nat iona l S e c u r i t y Agency - NS Defense Mapping Agency - DMA

    Prepar i ng A c t i v i t y : NAVY - AS

    ( P r o j e c t No. RELI-0038)

    RELI

  • CONTENTS (Continued)

    Page

    FIGURES

    Figure 1. Service use events in the logistic and operational cycles . . . . . . . . . . . . . 8 criteria . . . . . . . . . . . . . . . . . . 102-3 analog function. . . . . . . . . . . . . . . 2003-3 electronics functions. . . . . . . . . . . . . 2003-5 devices. . . . . . . . . . . . . . . . . . . 2003-7

    102.1 Performance parameters, limits and failure

    2003.1 Failure-rate estimating chart for electronic

    2003.2 Failure-rate estimation chart for digital

    2003.3 Failure-rate estimation chart for mechanical

    TABLES

    Table 1002-1 Truth table calculation for the mission reliability diagram. . . . . . . . . . . .

    1002-11 Reduction tabulation . . . . . . . . . . . . 1003-1 Logic diagram examples . . . . . . . . . . . 1004-1

    reliability diagram. . . . . . . . . . . . 1004-11

    reliability diagram. . . . . . . . . . . . 200-1 Environmental symbol identification and

    2003-1

    Success/Failure array for the mission

    Success/Failure array for the mission

    description. . . . . . . . . . . . . . . . electronic AEGs used in estimating analog

    Weighting factors for different classes of

    complexity for Figure 2003.1 . . . . . . .

    Figure 2003.2. . . . . . . . . . . . . . . elements for use in conjunction with Figure 2003.3. . . . . . . . . . . . . . .

    2003-11 Weighting factors for estimating digital electronics AEG complexity for use with

    2003-111 Weighting factors for shipboard mechanical

    1002-2 1002-4 1003-2

    1004-3

    1004-5

    200-5

    2003-2

    2003-5

    2003-6

    V 31 August 1982

  • TASK SECTIONS

    Task Section 100 Reliability modeling . . . . . . . . . . . . . 100-1

    200 Reliability prediction . . . . . . . . . . . . 200-1 TASKS

    Task 101 Basic reliability model . . . . . . . . . . . . 101-1 102 Mission reliability model . . . . . . . . . . . 102-1 20 1 Basic reliability prediction . . . . . . . . . 201-1 202 Mission reliability prediction . . . . . . . . 202-1

    METHODS

    Method 1001 1002 1003 1004 200 1 2002 2003 2004 2005

    Conventional probability . . . . . . . . . . . Boolean truth table . . . . . . . . . . . . . . Logic diagram . . . . . . . . . . . . . . . . . . Monte carlo simulation . . . . . . . . . . . . Similar item method . . . . . . . . . . . . . . Similar circuit method . . . . . . . . . . . . Active element group method . . . . . . . . . . Parts count method . . . . . . . . . . . . . . Parts stress analysis method . . . . . . . . .

    1001-1 1002-1 1003-1 1004-1 2001-1 2002-1 2003-1 2004- 1 2005-1

    APPENDIX A . APPLICATION AND TAILORING GUIDE Paragraph 10 . GENERAL . . . . . . . . . . . . . . . . . . . . A-1 10.1 Scope . . . . . . . . . . . . . . . . . . . . . A-1 10.2 Tailoring requirements . . . . . . . . . . . . A-1 10.3 Duplication of effort . . . . . . . . . . . . . A-1 10.4 Limitations . . . . . . . . . . . . . . . . . . A-1 20 . REFERENCED DOCUMENTS . . . . . . . . . . . . . A-1 30 . DEFINITIONS . . . . . . . . . . . . . . . . . . A-1 40 . 40.1 40.2

    GENERAL . . . . . . . . . . . . . . . . . . . . A-2 Ordering data . . . . . . . . . . . . . . . . . A-2 Data item descriptions . . . . . . . . . . . . A-2

    50 . APPLICATION CRITERIA . . . . . . . . . . . . . A-2 50.1 General considerations . . . . . . . . . . . . A-2 50.1.1 Level of detail . . . . . . . . . . . . . . . . A-2 50.1.2 . Timing . . . . . . . . . . . . . . . . . . . . A-2 50.1.3 Intended use . . . . . . . . . . . . . . . . . A-3

    *U.S. GOVERNMENT PRINTING OFFICE: 1982.50 5.022/4443

    31 August 1982 vi

  • MIL-STD-756B I8 NOVEMBER 1981

    SUPERSEDING MIL-STD-756A 15 MAY 1963

    MILITARY STANDARD

    RELIABILITY MODELING AND PREDICTION

    AMSC N3125 FSC RELl

  • MIL-STD-756B

    DEPARTMENT OF DEFENSE Washington, DC 20301

    RELIABILITY MODELING AND PREDICTION

    MIL-S TD- 7 56B

    1. This Military Standard is approved for use by all Departments and Agencies of the Department of Defense.

    2. Beneficial comments (recommendations, additions, deletions) and any pertinent data which may be of use in improving this document should be addressed to: Commanding Officer, Engineering Specifications

    Lakehurst, New Jersey 08733, by using the self-addressed Standardization - Document Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter.

    and Standards Department (Code 93), Naval Air Engineering Center, r

    a

  • MIL-STD-756B

    FOREWORD

    R e l i a b i l i t y p r e d i c t i o n i s an e s s e n t i a l func t ion i n eva lua t ing a des ign from concept through development and i n c o n t r o l l i n g changes dur ing product ion. P r e d i c t i o n provides a r a t i o n a l b a s i s f o r des ign dec i s ions such as t h e choice between a l t e r n a t i v e concepts , choice of p a r t q u a l i t y levels, d e r a t i n g t o be appl ied , use of proven ve r sus s tate- of- the- art techniques, and o the r f a c t o r s .

    It i s e s s e n t i a l t h a t common ground r u l e s be e s t a b l i s h e d f o r techniques and d a t a sources used i n t h e formulat ion of r e l i a b i l i t y models and p r e d i c t i o n s s o t h a t they may be appl ied and i n t e r p r e t e d uniformly. s tandard e s t a b l i s h e s procedures and ground r u l e s intended t o achieve t h i s purpose.

    It must be recognized t h a t r e l i a b i l i t y p r e d i c t i o n is a b e s t estimate of t h e r e l i a b i l i t y a n t i c i p a t e d from a given design w i t h i n d a t a l i m i t a t i o n s and t h e ex t en t of i t e m d e f i n i t i o n . A proper ly performed r e l i a b i l i t y p r e d i c t i o n i s inva luab le t o those r e spons ib l e f o r making program dec i s ions regard ing t h e f e a s i b i l i t y and adequacy of a des ign approach.

    This

    R e l i a b i l i t y p r e d i c t i o n s are gene ra l ly based on experience d a t a from similar i t e m s , o r t h e i r components, used i n a s a m e o r similar manner. Extreme cau t ion must be exerc ised i n a s c e r t a i n i n g t h e s i m i l a r i t y of o t h e r i t e m s and t h e degree of s i m i l a r i t y i n t h e cond i t i ons of use. s tandard emphasizes v e r i f i c a t i o n and j u s t i f i c a t i o n of t h e v a l i d i t y and a p p l i c a b i l i t y of d a t a sources t o t h e p repa ra t ion of p r e d i c t i o n s .

    This

    The n e c e s s i t y f o r determining t h e c o s t s of achiev ing and s u s t a i n i n g t h e r e l i a b i l i t y of an i t e m r e q u i r e s t h a t r e l i a b i l i t y be considered from two pe r spec t ives , r e l i a b i l i t y as a measure of ope ra t iona l e f f e c t i v e n e s s (Mission R e l i a b i l i t y ) and r e l i a b i l i t y as a measure of ownership c o s t (Basic R e l i a b i l i t y ) . modes of ope ra t ion t o improve Mission R e l i a b i l i t y i nva r i ab ly decreases Basic R e l i a b i l i t y and inc reases procurement and l o g i s t i c support c o s t s . This s tandard addresses Mission R e l i a b i l i t y p r e d i c t i o n and Basic R e l i a b i l i t y p r e d i c t i o n as s e p a r a t e but companion p r e d i c t i o n s both of which are e s s e n t i a l t o adequately quan t i fy t h e r e l i a b i l i t y of an i t e m .

    The inco rpora t ion of redundancies and a l t e r n a t e

    The need f o r updat ing a given p r e d i c t i o n w i l l vary from program t o program and cannot be p r e c i s e l y e s t a b l i s h e d i n a genera l s tandard . Updating w i l l depend p r imar i ly on t h e degree t o which t h e i t e m has been def ined , and t h e a v a i l a b i l i t y of p e r t i n e n t d a t a . Provis ions should be made f o r r e l i a b i l i t y p r e d i c t i o n updates a t a l l des ign review p o i n t s and o t h e r major program mi les tones .

    iii

  • P a r agr ap h

    MIL-STD-756B

    CONTENTS

    Page

    1 . 1.1 1.2 1.3 1.4 1.4.1

    1.5 1 .5 .1 1.5.2 1.6

    2 . 2.1 2.2

    3 . 3.1

    4 . 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.8.1 4.8.2 4.8.2.1 4.8.2.2 4.8.2.2.1 4.8.2.3 4.9 4.9.1 4.9.2

    5 . 5.1 5.1.1

    SCOPE . . . . . . . . . . . . . . . . . . . . . . 1 Scope . . . . . . . . . . . . . . . . . . . . . . 1 Applicat ion . . . . . . . . . . . . . . . . . . . 1 Purpose . . . . . . . . . . . . . . . . . . . . . 1 Numbering system . . . . . . . . . . . . . . . . 1 C l a s s i f i c a t i o n of t a s k sec t ions . t a s k s and

    Revisions . . . . . . . . . . . . . . . . . . . . 2 Standard . . . . . . . . . . . . . . . . . . . . 2 Task sec t ions . tasks . and methods . . . . . . . . 2 Method of reference . . . . . . . . . . . . . . . 2 _ a REFERENCED DOCUMENTS . . . . . . . . . . . . . . 2 I s sues of documents . . . . . . . . . . . . . . . 2 Other publ ica t ions . . . . . . . . . . . . . . . 3

    methods . . . . . . . . . . . . . . . . . . . . 1

    3

    DEFINITIONS . . . . . . . . . . . . . . . . . . . 4 Terms . . . . . . . . . . . . . . . . . . . . . . 4 GENERAL REQUIREMENTS . . . . . . . . . . . . . . 4 General . . . . . . . . . . . . . . . . . . . . . 4 Implementation . . . . . . . . . . . . . . . . . 4 . Ground rules and assumptions . . . . . . . . . . 5 Indenture l e v e l . . . . . . . . . . . . . . . . . 5 Coding system . . . . . . . . . . . . . . . . . 5 Mission success d e f i n i t i o n . . . . . . . . . . . 5 Coordination of e f f o r t . . . . . . . . . . . . . 5 General procedures . . . . . . . . . . . . . . . 5 I t e m d e f i n i t i o n . . . . . . . . . . . . . . . . . 6 Service use p r o f i l e . . . . . . . . . . . . . . . 6 Logis t i c cycle . . . . . . . . . . . . . . . . . 7 Operational cycle . . . . . . . . . . . . . . . . 7 Mission p r o f i l e . . . . . . . . . . . . . . . . . 7 Environmental p r o f i l e . . . . . . . . . . . . . . 7 R e l i a b i l i t y modeling and p red ic t ion r epor t . . . 7 Summary . . . . . . . . . . . . . . . . . . . . . 7 R e l i a b i l i t y cr i t ical element l is ts . . . . . . . 9 DETAILED REQUIREMENTS . . . . . . . . . . . . . . 9 Task desc r ip t ion and methods . . . . . . . . . . 9 Details t o be spec i f i ed . . . . . . . . . . . . . 9

    . \

    i v

    ... I ... - __ -.___ --. . . ...... ......_....I.I ._I--. ......

  • MIL-STD-756B

    CONTENTS (Continued)

    Page

    FIGURES

    Figure 1 . Figure 102.1 Performance parameters. l i m i t s and f a i l u r e

    Serv ice use events i n t h e l o g i s t i c and ope ra t iona l cyc l e s . . . . . . . . . . . . . . a cr i ter ia . . . . . . . . . . . . . . . . . . . 102-3

    Figure 2003.1 Fa i lu re- ra t e es t imat ing c h a r t f o r e l e c t r o n i c analog func t ion . . . . . . . . . . . . . . . 2003-3

    Figure 2003.2 Fa i lu re- ra t e e s t ima t ion c h a r t f o r d i g i t a l e l e c t r o n i c s func t ions . . . . . . . . . . . . 2003-5

    Figure 2003.3 F a i l u r e- r a t e es t imat ion c h a r t f o r mechanical devices . . . . . . . . . . . . . . . . . . . 2003-7

    TASK SECTIONS

    Task Sec t ion 100 R e l i a b i l i t y modeling . . . . . . . . . . . . . . 100-1

    200 R e l i a b i l i t y p r e d i c t i o n . . . . . . . . . . . . . 200-1 TASKS

    Task 101 Basic r e l i a b i l i t y model . . . . . . . . . . . . 101-1

    202 Mission r e l i a b i l i t y p r e d i c t i o n . . . . . . . . . 202-1 102 Mission r e l i a b i l i t y model . . . . . . . . . . . 102-1 201 Basic r e l i a b i l i t y p r e d i c t i o n . . . . . . . . . . 201-1

    METHODS

    Method 1001 1002 1003 1004 2001 2002 2003 2004 2005

    Conventional p r o b a b i l i t y . . . . . . . . . . . . Boolean t r u t h t a b l e . . . . . . . . . . . . . . Logic diagram . . . . . . . . . . . . . . . . . Monte c a r l o s imula t ion . . . . . . . . . . . . . Simi lar i t e m method . . . . . . . . . . . . . . Simi l a r c i r c u i t method . . . . . . . . . . . . . Active element group method . . . . . . . . . . P a r t s count method . . . . . . . . . . . . . . P a r t s stress a n a l y s i s method . . . . . . . . . .

    1001-1 1002-1 1003-1 1004-1 2001-1 2002-1 2003-1 2004-1 2005-1

    V

  • MIL-STD-756B

    Paragraph 10 . 10.1 10.2 10.3 10.4

    20 . 30 . 40 . 40.1 40.2

    50 . 50.1 50.1.1 50.1.2 50.1.3

    CONTENTS (Continued)

    APPENDIX A . APPLICATION AND TAILORING GUIDE GENERAL . . . . . . . . . . . . . . . . . . . . Scope . . . . . . . . . . . . . . . . . . . . . Ta i lo r ing requirements . . . . . . . . . . . . . Duplicat ion of e f f o r t . . . . . . . . . . . . . Limi ta t ions . . . . . . . . . . . . . . . . . . REFERENCED DOCUMENTS . . . . . . . . . . . . . . DEFINITIONS

    GENEWL . . . . . . . . . . . . . . . . . . . . Ordering d a t a . . . . . . . . . . . . . . . . . Data i t e m d e s c r i p t i o n s . . . . . . . . . . . . APPLICATION CRITERIA . . . . . . . . . . . . . General cons ide ra t ions . . . . . . . . . . . . Level of de t a i l . . . . . . . . . . . . . . . . Timing . . . . . . . . . . . . . . . . . . . . . Intended use . . . . . . . . . . . . . . . . .

    vi

    .... ._

    A- 1 A- 1 A-1 A-1 A- 1

    A-1

    A- 1

    A-2 A-2 A-2

    A-2 A- 2 A-2 A-2 A-3

    .

  • MIL-STD-756B

    1. SCOPE

    1.1 Scope. This standard establishes uniform procedures and ground rules for the preparation of Mission Reliability and Basic Reliability models and predictions for electronic, electrical, electro- mechanical, mechanical, and ordnance systems and equipments, hereinafter referred to as items. Item complexity may range from a complete weapon system to the simplest subdivision of a system. Reliability Prediction is as a design tool to provide relative measures of item reliability to design decisions. when applying and translating the absolute value of the Reliability Prediction to measures of Field Reliability.

    The primary value of

    Great caution must be used

    1.2 Application. The requirements and procedures established by this standard may be applied to any Department of Defense procurement for item development and production. requirements herein will need to be applied to every program or program phase. Procuring activities shall tailor the requirements. of this standard to the minimum needs of each procurement and shall encourage contractors to submit cost effective tailoring recommendations.

    It is not intended that all the

    1.3 Purpose. Reliability modeling and prediction is a methodology for estimating an item's ability to meet specified reliability requirements. that an item will perform its required functions during the mission. Basic Reliability prediction estimates the demand for maintenance and logistic support caused by an item's unreliability. the two predictions provide a basis for identifying areas wherein special emphasis or attention is needed, and for comparing the ownership cost- effectiveness of various design configurations. The two predictions may also be used as a basis for the apportionment (allocation) of ownership cost and operational effectiveness requirements to various subdivisions.

    A Mission Reliability prediction estimates the probability A

    When used in combination,

    1.4 Numbering system. Task sections, tasks, and methods are numbered sequentially as they are introduced into this standard in accordance with the following classification system.

    1 .4 .1 Classification of task sections, tasks, and methods.

    100 - Reliability modeling task section 101 to 199 - Reliability modeling tasks

    1001 to 1999 - Reliability modeling methods 200 201 to 299 - Reliability prediction tasks

    2001 to 2999 - Reliability prediction methods - Reliability prediction task section

    1

  • MIL-STD-75 6B

    1.5 Revisions.

    1.5.1 Standard. Any gene ra l r e v i s i o n of t h i s s tandard which r e s u l t s i n a r e v i s i o n of s e c t i o n s 1, 2, 3 or 4 w i l l b e i nd ica t ed by a r e v i s i o n le t ter a f t e r t h i s s tandard number, toge ther w i th t h e d a t e of r ev i s ion .

    1.5.2 Task s e c t i o n s , t a sks , and methods. Revisions are numbered consecut ive ly ind ica t ed by a le t ter fol lowing t h e number. For example; f o r t a s k 101, t h e f i r s t r e v i s i o n is 101A, t h e second r e v i s i o n i s 101B. When t h e Basic Document is rev i sed , those requirements n o t a f f ec t ed by change r e t a i n t h e i r e x i s t i n g da te .

    1.6 Method of re ference . The t a sks and methods contained h e r e i n s h a l l be referenced by spec i fy ing:

    a. This s tandard number b. Task number(s) c. Method number(s) d. Other d a t a as c a l l e d f o r i n t h e i n d i v i d u a l

    t a sk o r method

    2. REFERENCED DOCUMENTS

    2 . 1 I s sues of documents. The fol lowing documents of t h e i s s u e i n e f f e c t on d a t e of i n v i t a t i o n f o r b i d s o r r eques t f o r proposal , are referenced i n t h i s s tandard f o r information and guidance.

    STANDARDS

    M i l i t a r y

    MIL-STD-280 Def in i t i ons of I t e m Levels , I t e m Exchangeabi l i ty , Models and Related T e r m s

    MIL-STD-470 Main ta inab i l i t y Program Requirements

    MIL-STD-721 Def in i t i ons of Terms f o r R e l i a b i l i t y and Main ta inab i l i t y

    MIL-STD-780 Work Unit Codes f o r Aeronaut ical Equipment; Uniform Numbering System

    MIL-STD-785 R e l i a b i l i t y Program f o r Systems and Equipment Development and Product ion

    MIL-STD-881 Work Breakdown S t r u c t u r e s f o r Defense Material I t e m s

    MIL-STD-882 System Sa fe ty Program Requirements

  • MIL-STD-756B

    STANDARDS (Cont inued)

    M i l i t a r y (Continued)

    MIL-S TD- 1 388 Log i s t i c s Support Analysis

    MIL-STD-1591 On A i r c r a f t , Fau l t Diagnosis, Subsystems, Analysis /Synthesis of

    MIL-STD-1670 Environmental Criteria and Guidel ines f o r A i r - Launched Weapons

    MIL-STD-2072 S u r v i v a b i l i t y , A i r c r a f t ; Establishment and Conduct of Programs For

    MIL-STD-2080 Maintenance P lan Analysis f o r A i r c r a f t and Ground Support Equipments

    HANDBOOKS

    Mil i tarv

    MIL-HDBK-2 17 R e l i a b i l i t y P red ic t ion of E lec t ron ic Equipment

    MIL-HDBK-251 Re l i ab i l i t y /Des ign Thermal Applicat ions

    (Copies of s p e c i f i c a t i o n s , s tandards , drawings, and pub l i ca t ions requi red by con t r ac to r s i n connection wi th s p e c i f i c procurement func t ions should be obtained from t h e procuring a c t i v i t y o r as d i r e c t e d by t h e con t r ac t ing o f f i c e r . )

    PUBLICATIONS

    Naval Sea Systems Command

    NAVORD OD 44622 R e l i a b i l i t y Data Analysis and I n t e r p r e t a t i o n Volume 4

    % (Applicat ion f o r copies should be addressed t o : Commanding Of f i ce r ,

    Naval Ship Weapon Systems Engineering S t a t i o n (Code 5743), Po r t Hueneme, CA 93043.)

    I

    2.2 Other pub l i ca t ions . The fol lowing documents are

    S p e c i f i c requirements f o r use of t h e s e o r o t h e r p o t e n t i a l sources of r e l i a b i l i t y d a t a t h a t may be used i n conjunct ion wi th t h i s s tandard. d a t a sources must be spec i f i ed by t h e procuring a c t i v i t y .

    3

  • MIL-STD-7 5 6B

    RADC-TR- 7 3-248 (AD- 7 68 61 9)

    Dormancy and Power On-Off Cycling Effects on Electronic Equipment and Part Reliability

    RADC-TR-74-269 Effects of Dormancy on Nonelectronic (AD/A-O02838) Components and Materials

    LC- 7 8- 1 Storage Reliability of Missile Material Program, Missile Material Reliability Handbook Parts Count Prediction

    (AD/A-053403)

    (.Application for copies should be addressed to the National Technical Information Service, U.S. Department of Commerce, 5385 Port Royal Road, Springfield , VA 22161. )

    GIDEP Government Industry Data Exchange Program, Summaries of Failure Rates

    (Application for copies should be addressed to the Fleet Analysis Center, GIDEP Operations Center, Naval Weapons Station, Seal Beach, Corona Annex, Corona, CA 91720.)

    NPRD-1 Nonelectronic Parts Reliability Data, 1978

    (Application for copies should be addressed to the Reliability Analysis Center, RADC/RBRAC, Griffiss AFB, NY 13441.)

    3. DEFINITIONS

    3.1 Terms, Terms used in this document are as defined in MIL-STD-280 and MIL-STD-721.

    4 . GENERAL REQUIREMJINTS

    4.1 General. Reliability modeling and prediction shall be planned and performed in accordance with the general requirements of this standard and the task(s) and method(s) specified by the procuring activity .

    4.2 Implementation. Reliability modeling and prediction shall be initiated early in the configuration definition stage to aid in the evaluation of the design and to provide a basis for item reliability allocation (apportionment) and establishing corrective action priorities. Reliability models and predictions shall be updated when there is a significant change in the item design, availability of design details, environmental requirements, stress data, failure rate data, or service use profile. A planned schedule for updates shall be specified by the procuring activity.

  • MIL-S TD- 7 56B

    4.3 Ground r u l e s and assumptions. The con t r ac to r s h a l l develop ground r u l e s and a n a l y s i s assumptions. The ground r u l e s s h a l l i d e n t i f y t h e r e l i a b i l i t y modeling and p r e d i c t i o n approach, t h e lowest i nden tu re level t o be analyzed, and inc lude a d e f i n i t i o n of mission success f o r t h e i t e m f n terms of performance c r i t e r i a and al lowable l i m i t s . Ground r u l e s and a n a l y s i s assumptions are not i n f l e x i b l e and may be added, modified, o r de l e t ed i f requfrements change. Ground r u l e s and a n a l y s i s assumptions s h a l l be documented and included i n t h e r e l i a b i l i t y modeling and p r e d i c t i o n r e p o r t .

    4.4 Indenture l e v e l . The indenture level a p p l i e s t o t h e i t e m hardware o r func t iona l l e v e l a t which t h e i t e m conf igura t ion i s defined. Unless o therwise s p e c i f i e d , t h e con t r ac to r s h a l l e s t a b l i s h t h e lowest i nden tu re level of a n a l y s i s us ing t h e fol lowing gufde l ines :

    a . The lowest level spec i f i ed f o r t h e F a i l u r e Mode, E f fec t s , and C r i t i c a l f t y Analysis (FMECA) t o ensure cons is tency and al low cross re ferenc ing .

    b. The s p e c i f i e d o r fntended maintenance and r e p a i r level f o r hardware elements of t h e i t e m .

    4.5 Coding system. For c o n s i s t e n t i d e n t i f i c a t i o n of i t e m func t fons and hardware elements, t h e con t r ac to r s h a l l adhere t o a coding system based upon t h e hardware breakdown s t r u c t u r e , work u n i t code numbering system o f MIZ-STD-780, o r o t h e r similar uniform numbering system. and func t iona l b lock diagram numbering system t o provide complete v i s i b i l i t y of each modeled element and i t s r e l a t i o n s h i p to t h e i t e m .

    The coding system s h a l l be c o n s i s t e n t wi th t h e FMECA ( i f requi red)

    4 . 6 Mission success d e f i n i t i o n . The con t r ac to r s h a l l develop genera l s tatements of i t e m mission success i n terms of performance and al lowable l i m f t s f o r each s p e c i f i e d output . Mission success d e f i n i t i o n s s h a l l be included i n t h e ground r u l e s d iscussed i n 4.3.

    4 .7 Coordination of e f f o r t . R e l i a b i l i t y and o t h e r o rgan iza t iona l elements s h a l l make coimcident performance and u s e of t h e r e i e a b i l i t y models and p red ic t ions . requirements t o perform and use t h e r e l i a b i l i t y models and p r e d i c t i o n s i n support o f a r e l i a b i l i t y program i n accordance wi th MIL-STD-785, m a i n t a i n a b i l f t y program i n accordance wi th MIL-STD-470, s a f e t y program i n accordance w i t h MIL-STD-882, s u r v i v a b i l i t y and v u l n e r a b i l i t y program i n accordance wi th MIL-STD-2072, l o g i s t i c s support a n a l y s i s i n accordance wi th MIL-STD-1388, maintenance plan a n a l y s i s (MPA) i n accordance wi th MIL-STD-2080, f a u l t diagrams a n a l y s i s en general accordance wi th MIL- STD-1591, and o t h e r con t r ac tua l provis ions .

    Considerat ion s h a l l be given t o t h e

    4.8 General procedure. The s t e p s set f o r t h below d e f i n e t h e procedure f o r developing a r e l 2 a b i l i t y model and performing a r e l i a b i l i t y pred ic t fon . E f f o r t t o develop t h e information f o r t h e s t e p s below s h a l l be c l o s e l y c o o r d h a t e d wi th r e l a t e d program a c t i v i t i e s (such as des ign engineer ing , system engineer ing , ma in t a inab i l i t y , and l o g i s t i c s ) t o minbqize d u p l i c a t i o n s and t o a s s u r e cons is tency and co r rec tnes s .

    5

  • MIL-STD-756B

    a .

    b.

    C .

    d.

    e.

    f .

    g *

    h.

    i.

    j.

    Define t h e i t e m f o r which t h e p r e d i c t i o n is app l i cab le (see 4.8.1).

    Define t h e service use ( l i f e cyc le) f o r which i t e m r e l i a b i l i t y w i l l be modeled and p red ic t ed ( see 4.8.2).

    Define t h e i t e m r e l i a b i l i t y block diagrams ( see 2.3 of Task Sec t ion 100).

    Define t h e mathematical models f o r computing i t e m r e l i a b i l i t y (see 2.4 of Task Sec t ion 100).

    Define t h e p a r t s of t h e i t e m ( s ee 2.2 of Task Sec t ion 200).

    Define t h e environmental d a t a ( s ee 2.3 of Task Sec t ion 200).

    Define t h e stress d a t a ( see 2.4 of Task Sec t ion 200).

    Define t h e f a i l u r e d i s t r i b u t i o n (see 2.5 of Task Sec t ion 200).

    Define t h e f a i l u r e rates (see 2.6 of Task Sec t ion 200).

    Compute t h e i t e m r e l i a b i l i t y ( s ee 2 . 7 of Task Sec t ion 200).

    4.8.1 I t e m d e f i n i t i o n . I t e m d e f i n i t i o n s h a l l inc lude performance requirements and hardware concept t o t h e ex t en t known a t t h e t i m e t h e model and p r e d i c t i o n are prepared. C h a r a c t e r i s t i c s of t h e i t e m s h a l l b e s t a t e d i n terms of range, a l t i t u d e , speed, maneuverabi l i ty , environmental condi t ions , power, o r such o t h e r parameters as may be app l i cab le . The manner i n which t h e i t e m and i t s subdiv is ion ope ra t e i s usua l ly expressed by means of func t iona l diagrams whech can become t h e b a s i s f o r t h e r e l e a b e l i t y block dlagrams (see 2.3 of Task Sec t ion 100). Normally, t h e i m i t i a l i t e m def%ni t+on used f o r t h e f e a s i b i l i t y p r e d i c t i o n w i l l be l ack ing several d e t a i l s and w i l l r e q u i r e c e r t a i n assumptions as t o environmental condi t ions , design conf igu ra t ion , etc. The i t e m d e f i n i t i o n s h a l l be r e f i n e d and updated as more information becomes a v a i l a b l e t o support t h e pre l iminary design p red ic t ion , and subsequently, t h e d e t a i l e d des ign p red ic t ion . A s t h e i t e m d e s c r i p t i o n i s p rog res s ive ly updated, h igher l e v e l s of accuracy w i l l b e a t t a i n e d f o r p r e d i c t i o n r e s u l t s .

    4.8.2 Service u s e p r o f i l e . The service use ( l i f e cyc le) p r o f i l e o r po r t ion thereof t o be used f o r r e l i a b i l i t y modeling and p red ic t ron s h a l l e i t h e r be proveded by t h e procuring a c t i v i t y o r s p e c i f i e d f o r c o n t r a c t o r prepara t ion . The service use p r o f i l e is a thorough d e s c r i p t i o n of a i l events and environments assoc ia ted wi th an i t e m from

  • MIL-STD-756B

    f inal factory acceptance through i t s terminal expenditure or removal from inventory. storage, test and checkout, operational deployment, etc., is addressed.

    U e 1 i l lu s t r a t e s the major service use events to be considered i n the logis t ic and operational cycles. The profi le depicts expected time spans, environments, operating modes (including standby and ready modes), e tc . , for each event. cycles, mission profiles, and environmental profiles i s used t o develop the service use proffle.

    Each s ignif icant servtce use event, such as transportation,

    Information from logis t ic cycles, operational

    4.8.2.1 Logistic cycle. The logis t ic cycle shall describe the expected duration and sequence of events which maintain, transport, and s tore an item t o assure operational availabili ty.

    4.8.2.2 Operational cycle. The operational cycle shall describe the expected duration and sequence of events of the period from an item's assignment to an operational user through expenditure or return to some phase of the logis t ic cycle.

    4.8.2.2.1 Mission profile. The mission profi le shall describe events and conditions associated w i t h a specific operational usage of an item. profi le shall depict the time spans of the events and operational conditions t o be anticipated. Multiple mission profiles may be required t o adequately describe an item's multimission capabili t ies.

    A mission profi le i s one segment o f the operational cycle: The

    4.8.2.3 Environmental profile. The environmental profi le sha l l describe the specif ic natural and induced environments (nominal and worst case) w i t h the operations, events, and functions described by the logis t ic and operational cycles. associated environmental profile.

    Each mission profi le shall have an

    4.9 Re1 iabi 1 i t y model i ng and prediction report. The r e l i ab i l i t y models and r e l i a b i l i t y Dredictions shall be documented i n a report that ident i f ies the level of' analysis, summarizes the results, documents the data sources and techniques used i n performing the analysis, and includes the item definit ion narrative, resultant analysis data, worksheets, ground rules and assumptions. Interim reports shall be available a t each design review to provide comparisons of a1 ternative designs and t o highlight h i g h fa i lure rate elements of the item design, potential mission r e l i ab i l i t y single fa i lure points, and proposed design corrections or improvements. The final report shall re f lec t the final design and provide identification of high fa i lure ra te elements, overstressed parts, and mission r e l i a b i l i t y single fa i lure points which could not be eliminated from the design. EIhen submitting a report applicable for an Expl oratory/Advanced Devel opment Model , and prediction report i s required.

    a simp1 i f i ed re1 i abi 1 i ty model i ng

    4.9.1 Summary. The report shall contain a summary which provides the contractor 's conclusions and recommendations based upon the analysis. Contractor interpretation and comments concerning the analysis and the in i t ia ted as recomnended actions for the elimination or reduction

    7

  • MIL-STD-756B

    TRANSPORT U

    LOGISTIC CYCLE

    .

    PROCUREMENT- U PACKAGING

    TRANSPORT

    MAINTENANCE r,

    I I I I I I I I I

    REPETITIVE CYCLES I FOR VARIOUS TYPES I OF STORAGE AND VARIOUS GEOGRAPHIC I AREAS OF STORAGE I

    I I

    STORAGE

    TRANSPORT

    OPERATIONAL CYCLE

    - - p q

    * TRANSPORT 5 DISPOSAL

    Figure 1. Service Use Events in the Logistic and Operational Cycles.

    8

    . . ~ - x- I- . . . .._-._.._I- ... .-

  • MIL-STD-756B

    of f a i l u r e r i s k s s h a l l be included. major problems de tec ted during t h e a n a l y s i s s h a l l be provided i n t h e f i n a l r epo r t . A l i s t of hardware o r func t iona l elements of t h e i t e m omitted from t h e r e l i a b i l i t y models and r e l i a b i l i t y p r e d i c t i o n s s h a l l be included wi th r a t i o n a l e f o r each element 's exclusion.

    A des ign eva lua t ion summary of

    4.9.2 R e l i a b i l i t y c r i t i ca l element l ists. R e l i a b i l i t y c r i t i c a l elements of t h e i t e m ex t r ac t ed from t h e r e l i a b i l i t y modeling and r e l i a b i l i t y p r e d i c t i o n e f f o r t s h a l l be l i s t e d and included i n t h e summary. R e l i a b i l i t y c r i t i ca l elements inc lude h igh f a i l u r e ra te elements , ove r s t r e s sed p a r t s (i .e. , exceed e s t ab l i shed p a r t s d e r a t i n g c r i t e r i a ) , and mission r e l i a b i l i t y s i n g l e f a i l u r e po in t s .

    5. DETAIL REQUIREMENTS

    5 .1 Task d e s c r i p t i o n and methods. The d e t a i l t a s k s and methods f o r prepar ing r e l i a b i l i t y models and performing r e l i a b i l i t y p r e d i c t i o n s follow. The t a s k d e s c r i p t i o n s and methods are d iv ided i n t o two genera l s ec t ions : Sec t ion 100, R e l i a b i l i t y Modeling; and Sec t ion 200, R e l i a b i l i t y P red ic t ion .

    5.1.1 Details t o be s p e c i f i e d . The "Details t o be Specif ied" paragraph under each Task Sec t ion i s intended f o r l i s t i n g t h e s p e c i f i c d e t a i l s , add i t i ons , modif icat ions, d e l e t i o n s , o r op t ions t o t h e requirements of t h e t a s k s covered by t h e s e c t i o n t h a t should be considered by t h e Prepar ing A c t i v i t y (PA) when t a i l o r i n g t h e t a s k d e s c r i p t i o n t o f i t program needs. be provided t h e c o n t r a c t o r f o r proper implementation of t h e t a sk .

    "Details" annotated by an "(R)" ARE ESSENTIAL and s h a l l

    Custodians:

    Navy - AS A i r Force - 1 7 Army - CR

    Review Act iv i t i es : Army - EA, AR Navy - SHY 0s

    Users : Army - AM Navy - EC National Secu r i ty Agency - NS Defense Mapping Agency - DMA

    Prepar ing Ac t iv i ty : Navy - AS

    P r o j e c t No. RELI-0001

    9

  • MIL-STD-756B

    TASK SECTION 100

    RELIABILITY MODELING

    1. DOCUMENTS REFERENCED I N TASK SECTION 100:

    STANDARDS

    MILITARY

    MIL-STD-780 Work Unit Codes f o r Aeronaut ical Equipment; Uniform Numbering System

    MIL-STD-881 Work Breakdown S t r u c t u r e s f o r Defense Material I t e m s

    2. REQUIREMENTS

    2 . 1 Basic R e l i a b i l i t y model. The Basic R e l i a b i l i t y model s h a l l c o n s i s t of a r e l i a b i l i t y block diagram and an a s soc i a t ed mathematical model. model which inc ludes elements of t h e i t e m intended s o l e l y f o r redundancy and a l t e r n a t e modes of opera t ion .

    By d e f i n i t i o n , t h e Basic R e l i a b i l i t y model is an a l l series

    2.2 Mission R e l i a b i l i t y model. The Mission R e l i a b i l i t y model s h a l l c o n s i s t of a r e l i a b i l i t y block diagram and an a s soc i a t ed mathematical model. intended u t i l i z a t i o n of t h e elements of t h e i t e m t o achieve mission success . Elements of t h e item intended f o r redundancy o r a l t e r n a t e modes of ope ra t ion s h a l l be modeled i n a p a r a l l e l con f igu ra t ion o r similar cons t ruc t app ropr i a t e t o t h e mission phase and mission a p p l i c a t i o n .

    2.3 R e l i a b i l i t y block diagrams. R e l i a b i l i t y block diagram s h a l l be prepared t o show interdependencies among a l l elements (subsystems, equipments, etc.) o r func t iona l groups of t h e i t e m f o r i t e m success i n each service use event. t o show by concise visual shorthand t h e va r ious s e r i e s- p a r a l l e l block pornbinations (paths) t h a t resu l t 5n i t e m success . of t h e $tern's miss5on d e f i n i t i o n , and service use p r o f i l e is requi red t o produce t h e r e l i a b i l i t y diagram.

    The Mission R e l i a b i l i t y model s h a l l be cons t ruc ted t o d e p i c t t h e

    The purpose of t h e r e l s a b i l i t y block diagram i s

    A complete understanding

    2.3.1 Block diagram t i t l e . Each r e l i a b i l i t y block diagram s h a l l have a t i t l e inc luding i d e n t i f i c a t i o n of t h e i t e m , t h e mission i d e n t i f i c a t i o n o r po r t ion of t h e service use p r o f i l e addressed, and a d e s c r i p t i o n of t h e mode of ope ra t ion f o r which t h e p r e d i c t i o n is t o be performed.

    2 . 3 . 2 Statement of condi t ions . Each r e l i a b i l i t y block diagram s h a l l inc lude a s tatement of condi t ions l i s t i n g a l l c o n s t r a i n t s which in f luence t h e choice of block p re sen ta t ion , t h e r e l i a b i l i t y parameters o r r e l i a b i l i t y v a r i a b l e s u t i l i z e d i n t h e a n a l y s i s , and t h e assumptions o r s i m p l i f i c a t i o n s u t i l i z e d t o develop t h e diagram. Once e s t a b l i s h e d , t h e s e cond i t i ons s h a l l be observed throughout t h e a n a l y s i s .

    100- 1 TASK SECTION 100 18 November 1981

  • MIL- S TD- 75 6B

    2.3.3 i n s p e c i f i c terms s t a t i n g exac t ly what t h e ca l cu la t ed r e l i a b i l i t y r ep re sen t s f o r t h e i t e m s as d i ag ramed and performing under t h e criteria presented i n t h e s tatement of condi t ions .

    Statement of success . A statement of success s h a l l be def ined

    2.3.4 a l o g i c a l o rde r which relates t h e sequence of events dur ing t h e prescr ibed ope ra t ion of t h e i t e m .

    Order of t he diagram. The blocks i n t h e diagram s h a l l fol low

    2.3.5 Block r ep resen ta t ion . The r e l i a b i l i t y block diagram s h a l l be drawn s o t h a t each element o r func t ion employed i n t h e i t e m can be i d e n t i f i e d . one element of func t ion contained i n t h e i t e m . b lock diagram s h a l l be configured i n series, p a r a l l e l , standby, o r combinations thereof as appropr ia te .

    Each block of t h e r e l i a b i l i t y block diagram s h a l l r ep re sen t A l l b locks of t h e r e l i a b i l i t y

    2.3.6 I d e n t i f i c a t i o n of blocks. Each block of t h e r e l i a b i l i t y block diagram s h a l l be i d e n t i f i e d . Diagrams conta in ing few blocks may have t h e f u l l i d e n t i f i c a t i o n w r i t t e n i n t h e block. blocks s h a l l use a c o n s i s t e n t and l o g i c a l code i d e n t i f i c a t i o n w r i t t e n f o r each block. The coding system s h a l l be based upon t h e work breakdown s t r u c t u r e of MIL-STD-881, work u n i t code numbering system of MIL-STD-780, o r o the r similar uniform i d e n t i f i c a t i o n system t h a t w i l l permit unambiguous t r a c e a b i l i t y of t h e r e l i a b i l i t y block t o i t s hardware (o r func t iona l ) equiva len t as def ined i n program documentation. The code s h a l l be i d e n t i f i e d i n a s e p a r a t e l i s t i n g .

    Diagrams conta in ing many

    2.3.6.1 Non-modeled elements. Hardware o r func t iona l elements of t h e i t e m which are not included i n t h e r e l i a b i l i t y model s h a l l be i d e n t i f i e d i n a sepa ra t e l i s t i n g u t i l i z i n g t h e coding system employed i n 2.3.6 of Task Sec t ion 100. Rat iona le f o r each element 's exc lus ion from t h e r e l i a b i l i t y model s h a l l be provided.

    2.3.7 R e l i a b i l i t y v a r i a b l e . R e l i a b i l i t y v a r i a b l e s s h a l l be determined f o r each block and presented i n such a manner t h a t t h e a s s o c i a t i o n between t h e block and i ts v a r i a b l e is apparent . i s a number ( t ime, cyc les , events , e t c . ) used t o desc r ibe t h e du ra t ion of opera t ion requi red by each block t o perform i ts s t a t e d func t ion . This v a r i a b l e shall be used i n c a l c u l a t i n g t h e r e l i a b i l i t y of t h e block.

    The r e l i a b i l i t y v a r i a b l e

    2.3.8 Block diagram assumptions. Two types of assumptions s h a l l be used i n prepar ing r e l i a b i l i t y block diagrams: (1) t e c h n i c a l and (2) genera l . Technical assumptions may be d i f f e r e n t f o r each i t e m and f o r each mode of opera t ion . The t e c h n i c a l assumptions s h a l l be set f o r t h under t h e s tatement of condi t ions . The genera l assumptions are those app l i cab le t o a l l r e l i a b i l i t y block diagrams. It is no t necessary t o l i s t t h e genera l assumptions s t a t e d i n t h i s s tandard on t h e r e l i a b i l i t y block diagrams, provided re ference has been made t o t h i s paragraph. The fol lowing genera l assumptions s h a l l apply t o r e l i a b i l i t y block diagrams:

    TASK SECTION 100 100-2 18 November 1981

    ___ ____ __- --I--- --- - - -

  • a.

    b.

    C .

    d.

    e.

    2.3.8.1 sof tware

    MIL-STD-756B

    The blocks denote elements o r func t ions of t h e i t e m s t h a t are considered when eva lua t ing r e l i a b i l i t y and which have r e l i a b i l i t y v a l u e s a s soc i a t ed wi th them.

    All l i n e s connect ing blocks have no r e l i a b i l i t y va lues . The l i n e s serve only t o g i v e order and d i r e c t i o n t o t h e diagram and do not r ep re sen t t h e wir ing c a b l e s and connectors a s soc i a t ed wi th t h e i t e m . s i n g l e block o r included as p a r t of t h e block f o r an element o r funct ion.

    Cabling and connectors are incorpora ted i n t o a

    A l l i n p u t s t o t h e i t e m are wi th in s p e c i f i c a t i o n l i m i t s .

    F a i l u r e of any element o r func t ion denoted by a block i n t h e diagram w i l l cause f a i l u r e of t h e en t i re i t e m , except where a l t e r n a t i v e modes of ope ra t ion may be present .

    Each element o r func t ion denoted by a block i n t h e diagram i s independent, wi th regard t o p r o b a b i l i t y of f a i l u r e , from a l l o t h e r blocks.

    Software r e l i a b i l i t y assumption. The assumption t h a t a l l is completely r e l i a b l e s h a l l be s t a t e d i n i n s t ances when sof tware

    r e l i a b i l i t y i s not incorporated i n t h e i t e m r e l i a b i l i t y p red ic t ion .

    2.3.8.2 Human r e l i a b i l i t y assumption. The assumption t h a t a l l human elements are completely r e l i a b l e and t h a t no i n t e r f a c e problems occur between human elements and t h e item s h a l l be s t a t e d i n i n s t ances when human r e l i a b i l i t y i s not incorporated i n t h e i t e m r e l i a b i l i t y p red ic t ion .

    2.4 Mathematical models. Models s h a l l be derived t o mathematical ly relate r e l i a b i l i t y block diagrams t o time-event r e l a t i o n s h i p s and f a i l u r e rate d a t a . The mathematical model s h a l l be capable of being r e a d i l y updated wi th iqfarmat ion r e s u l t i n g from r e l i a b i l i t y and o t h e r r e l e v a n t tests as w e l l as changes i n i t e m conf igura t ion , mission parameters and ope ra t iona l c o n s t r a i n t s .

    The s o l u t i o n of t h e models will be t h e item pred ic t ed r e l i a b i l i t y .

    3. 5.1.1).

    Details t o be s p e c i f i e d by t h e Prepar ing Acf iv i ty (PA) (See The fol lowing are app l i cab le when Task 101 o r 102 are invoked:

    a. Indenture level (4.4)

    b. Software R e l i a b i l i t y App l i cab i l i t y (2.3.8.1 of Task Sec t ion 100).

    c. Human R e l i a b i l i t y App l i cab i l i t y (2.3.8.2 of Task Sec t ion 100).

    100-3 TASK SECTION 100 18 November 1981

  • MIL-STD-756B

    (R) d. Modeling Method(s). An option is to allow contractor selection of the appropriate modeling method(s). methods may be applicable to different system components.

    Different prediction

    e. DI-R-7094 Reliability Mathematical Models should be specified when deliverable data is desired in conjunction with this task.

    (R) f. Item definition (4.8.1).

    (R) g. Service use profile (4.8.2).

    TASK SECTION 100 18 November 1981 100-4

    ----- ---- - _. - ~

  • MIL-STD- 7 5 6B

    TASK 101

    BASIC RELIABILITY MODEL

    1. PURPOSE/RATIONALE

    1.1 the demand for maintenance and logistic support caused by an item and its component parts. redundancy or alternate modes of operation are modeled in series. Except for those instances in which there is neither redundancy nor alternate modes of operation provided f o r the item, the Basic Reliability model cannot be used to estimate Mission Reliability. However, both the Basic Reliability model and the Mission Reliability model are used in combination to compare the ownership cost-effectiveness of various design configurations and as a basis for apportionment (allocation) of ownership cost and operational effectiveness requirements to various subdivisions of an item.

    A Basic Reliability model is a series model used for estimating

    Accordingly, all elements of the item provided for

    1.2 The basic information for the Basic Reliability model is derived from documentation identifying all equipments and associated quantities that comprise the item. As the proposed item design is firmed and comes under configuration control, the established configuration baseline should be the basis for the Basic Reliability model.

    1 . 3 The Basic Reliability model should be developed to the level of detail (equipment, subassembly, or part level) for which information is available and for which failure rate, (or equivalent), data can be applied to evaluate the maintenance and logistic support impact of the item design.

    1.4 the Basic Reliability model is used to develop mathematical expressions or computer programs which, with appropriate failure rate data, can provide apportionment, estimates and assessments of Basic Reliability.

    Together with duty cycle and mission duration, information,

    REQUIREMENT

    2,l The contractor shall develop and maintain a Basic Reliability model based upon a defined item configuration. All equipments and associated quantities comprising the item shall be included in the model. All equipments, including those intended solely for item redundancy and alternate modes of operation, shall be modeled in series. A Basic Reliability block diagram shall be developed and maintained for the item with associated allocations and predictions in each reliability block. The Basic Reliability block diagram shall be keyed and traceable to the Mission Reliability model, functional block diagrams, schematics and drawings, and shall provide the basis for accurate mathematical representation of Basic Reliability. Nomenclature of elements o f the item used in the Basic Reliability block diagrams shall be consistent with that used in the Mission Reliability model, functional block diagrams, drawings and schematics, weight statements, power budgets and specifications.

    101-1 TASK 101 18 November 1981

  • MIL-STD-756B

    TASK 102

    MISSION RELIABILITY MODEL

    1. PURPOSE / RATIONALE

    1.1 A Mission R e l i a b i l i t y model i s used f o r eva lua t ing complex s e r i e s- p a r a l l e l equipment arrangements which usua l ly e x i s t i n weapon systems.

    2. MISSION RELIABILITY MODELING

    2 .1 developing Mission R e l i a b i l i t y models is understanding t h e d e f i n i t i o n of

    How t o Define t h e I t e m f o r Modeling. A p r e r e q u i s i t e f o r

    t h e i t e m as r e l a t e d t o t he d e f i n i t i o n of r e l i a b i l i t y . For Basic R e l i a b i l i t y modeling, t h e i t e m d e f i n i t i o n i s simple - a l l equipments comprising t h e item are modeled i n series. "All" equipments i nc ludes any equipments provided s o l e l y f o r redundancy o r f o r a l t e r n a t e modes of opera t ion . However, f o r Mission R e l i a b i l t y modeling, t h e i t e m r e l i a b i l i t y model and mission success d e f i n i t i o n can become e l u s i v e problems e s p e c i a l l y f o r complex multimodel systems incorpora t ing redundancies and a l t e r n a t e modes of opera t ion . spec i fy ing r e l i a b i l i t y w i th in t h e context of a l l o t h e r p re s s ing requirements and r e s t r a i n t s t h a t comprise a func t ioning i t e m . A proper d e f i n i t i o n is important i n order t o e s t a b l i s h meaningful requirements and goa ls . adequate i t e m d e f i n i t i o n a i d s i n determining when t h e i t e m is being used as intended, when i t sees i t s a n t i c i p a t e d environment, when i t s conf igu ra t ion has been changed beyond i t s o r i g i n a l concept , as w e l l as when it i s performing i t s s p e c i f i e d func t ion . I t e m r e l i a b i l i t y i s defined as t h e p r o b a b i l i t y of performing a s p e c i f i e d func t ion o r mission under s p e c i f i e d condi t ions f o r a spec i f i ed t i m e . Therefore, a r e l i a b i l i t y requirement f o r func t ion o r mission success must inc lude :

    I n i tem d e f i n i t i o n , emphasis i s placed on proper ly

    An

    a. A d e f i n i t i o n of i t e m performance such t h a t every cond i t i on i s def ined as acceptab le (success) o r unacceptable ( f a i l u r e ) . Obviously, i t e m modes of ope ra t ion must be known t o d e f i n e success and f a i l u r e . For example, simultaneous t ransmiss ion of rea l t i m e and s to red d a t a might be defined as success f o r one i t e m , whi le another i t e m may not r e q u i r e simultaneous t ransmiss ion of real t i m e and s to red da t a . I f t h e la t ter i t e m had two t r a n s m i t t e r s f o r sending d a t a they would be considered redundant, o r provide an a l t e r n a t e mode of opera t ion . I n t h e former i t e m , however, t h e requirement r u l e s ou t t h i s a l t e r n a t e mode of opera t ion . Another i t e m requirement might be t h a t a c e r t a i n d a t a ra te o r amount of d a t a be t ransmi t ted from a sa te l l i t e t o e a r t h . Analysis of t he i t e m may show t h a t i f some channels i n a mul t ip lexer f a i l , t h e requi red d a t a rate o r amount of d a t a is s t i l l achieved. This cond i t i on would be def ined as success .

    102-1 TASK 102 18 November 1981

  • MIL-STD-756B

    b.

    C.

    d.

    2.2

    A definition of the conditions. environmental conditions which prevail on the various equipments of the item throughout the mission. In addition, duty cycle or periods of operation for the various equipments must be defined.

    This involves defining the

    ,

    A definition of mission time. of the time during which the item must function is important. In complex items which operate in different functional modes at different stages of the mission or which use certain subsystems only if conditions require, the functioning-time requirements for each subordinate group should be established. If the time requirements cannot be specified definitely, it may be necessary to determine probabilities of successful functioning during a range of mission times.

    A careful quantitative statement

    A definition of the reliability variable of the item elements. The reliability variable is a number (time, cycles, events, etc.) used to describe the duration required by each item element (and included in the Mission Reliability block diagram) to perform its stated function.

    Developing the Item Definition. A complete definition of the item covers the use, performance, restraints, and failure definitions. Thus, it is necessary to define:

    a. Purpose, intended use, or mission.

    b. .

    Performance parameters and allowable limits.

    c. Physical and functional boundaries.

    d. Conditions which constitute mission failure.

    e. Service use profile.

    Step 1 - Define the purpose and intended use or mission of the item.

    This includes:

    a. Defining mission functions and modes of operation. A particular item can be utilized for more than one type mission. example, an aircraft may be used on a military reconnaissance mission, a bombing mission, an intercept mission, or a strafing mission. If separate aircraft were used for these missions, they would be treated independently, with a separate Mission Reliability model for each mission or aircraft. If the same aircraft were used to perform all these missions, they could be treated as functions and one item reliability model could be generated to cover all functions. It is also possible to have separate reliability requirements and models for each mission.

    For

    TASK 102 18 November 1981

    102-2

  • MIL-STD-756B

    b. Defining the mission in terms of performing functions. For purpose of clarity, functional and alternate modes of operation have

    1.

    2.

    Before a model word statement

    been defined- below.

    Functional Mode of Operation - Some versatile items perform multiple functions with different equipment or groups of equipment being required for each function. function is a task to be performed by the hardware and therefore, a functional mode of operation consists of performing a specific function. For example, in a radar system, searching and tracking would be two functional modes of operation.

    A

    Alternative Modes of Operation - When an item has more than one method of performing a particular function, it has alternative modes of operation. For example, a UHF transmitter may be used as an alternative method of com- municating data sent normally via a 'VHF transmitter.

    can be developed, requirements must be formulated. A of what is required for mission success or a Mission

    Reliability block diagram must be generated. block diagram is a pictorial f o m of a statement of what is required for mission success. When requirements are not firm, it is possible to develop several Mission Reliability models assuming different requirements. In other words, a family of item reliability diagrams can be generated for various requirements for mission success.

    Step 2 - Establish and specify the item and subsystem performance parameters and allowable limits.

    It is desirable to construct a list or chart for convenience. The list of parameters should be all inclusive, completely defining the entire item under consideration. The allowable upper and lower limits for these parameters should be developed. Columns (1) , (2) , and (3) of .. Figure 1 0 2 . 1 illustrate a list of performance parameters and allowable limits.

    The Mission Reliability

    performance Parameter

    (1)

    1. Power output (PO)

    2. Channel capacity (n)

    3. Voltage pain (A)

    4 . Detection range (HI

    5. Miss distance (d,J

    Units of Measure

    ( 2 )

    Horsepower, Kilowatts, etc.

    Number of channels

    Decibels

    Nautical miles

    Meters

    Specified Requirement

    (3)

    PO=500f20%

    n=48+0

    A-40t3db

    H - 3 0 M -50

    d=WlO - 0

    Failure Classification in Terms of

    Performance Limits ( 4 )

    Major: 200

  • MIL-STD-756B

    Step 3 - Determine t h e phys i ca l and func t iona l boundaries of t h e i t e m .

    Phys ica l boundaries:

    a. Maximum dimensions.

    b. Maximum weight.

    c. Sa fe ty provis ions .

    d. Human f a c t o r s r e s t r a i n t s .

    e. Materials c a p a b i l i t i e s .

    f . etc.

    Funct ional boundaries:

    a. Whenever t h e i t e m under cons idera t ion is contained i n o r depends upon another i t e m , i t e m i n t e r f a c e s must be coordinated f o r compat ib i l i ty . i n t e r f a c e wi th s h i p s c e n t r a l c o n t r o l , power sources , d a t a requirements, etc.

    Examples i nc lude man-machine i n t e r f a c e s ,

    Step 4 - Determine t h e condi t ions which c o n s t i t u t e mission f a i l u r e . A f a i l u r e i s an i n a b i l i t y t o complete a s t a t e d mission w i t h i n s p e c i f i c l i m i t s . would c o n s t i t u t e mission f a i l u r e . For example, one cond i t i on of succes s fu l mission completion may be a requirement of a minimum 200 k i lowa t t s (KW) f o r t h e power output of a t r ansmi t t e r . Hence, any s i n g l e o r combination of i t e m hardware and software f a i l u r e ( s ) t h a t would r e s u l t i n less than 200 KW of t r a n s m i t t e r power output would c o n s t i t u t e a mission f a i l u r e . Column (4) of F igure 102.1 i l l u s t r a t e s a d e f i n i t i o n of f a i l u r e cr i ter ia .

    I n c e r t a i n i n s t ances where a f a i l u r e cond i t i on e x i s t s , a mission can s t i l l be completed i n a somewhat l imi t ed manner. I n t h e s e in s t ances it i s usua l ly worthwhile t o i d e n t i f y t h e mission opt ions a v a i l a b l e as a r e s u l t of a prime mission f a i l u r e condi t ion .

    Using t h e previous s t e p s , i d e n t i f y and l ist t h e condi t ions t h a t

    d ?

    Step 5 - Define t h e service use p r o f i l e .

    The service use p r o f i l e is a thorough d e s c r i p t i o n of a l l events and environments assoc ia ted wi th an i t e m from f i n a l acceptance through i t s t e rmina l expenditure o r removal from inventory. The p r o f i l e d e p i c t s expected t i m e spans, environments, ope ra t ing modes ( inc luding standby and ready modes), etc. , f o r each event. Although t h e Mission R e l i a b i l i t y model should, and o f t e n does, cons ider t h e complete l o g i s t i c and ope ra t iona l c y c l e s assoc ia ted wi th t h e service use p r o f i l e i t is t h e mission p r o f i l e and environmental p r o f i l e t h a t receives t h e most a t t e n t i o n .

    TASK 102 18 November 1981

    102-4

  • MIL-STD-7 5 6B

    a. The mission p r o f i l e desc r ibes events and cond i t i ons a s soc i a t ed wi th a s p e c i f i c ope ra t iona l usage of an i t e m . p r o f i l e s may be requi red t o adequately desc r ibe an item's mul t imiss ion c a p a b i l i t i e s . The mission p r o f i l e ( s ) needs t o address t h e i t e m duty cyc l e s o r per iods of opera t ion . The i t e m should be subdivided i n t o components o r equipments and a p l o t of t h e intended use through t i m e f o r each component o r equipment should be developed. Duty c y c l e is t h e r a t i o of ope ra t ing t i m e t o t o t a l t i m e . i n c a l c u l a t i o n s i s as fol lows:

    Mul t ip l e mission

    The method t o handle duty c y c l e

    1. I f t h e component i s considered t o have a n e g l i g i b l e f a i l u r e rate during a non-operation per iod , t h e f a i l u r e rate can be modified by a duty c y c l e f a c t o r . t h e equat ion P, = e-Xtd can be used f o r a cons tan t f a i l u r e rate component where d , t h e duty c y c l e f a c t o r , is t h e r a t i o of ope ra t ing t i m e t o t o t a l mission t i m e , t .

    For example

    2. When a component has a f a i l u r e rate dur ing non-operating per iods d i f f e r e n t from t h a t experienced during opera t ing per iods , t h e fol lowing equat ion can be used:

    Ps = Ps (opera t ing) *Ps (nonoperating)

    For t h e cons tan t f i g u r e ra te component, t h i s equat ion y i e l d s

    -[Xltd + X,t(l-d>] Ps = e Where

    X1 = f a i l u r e ra te during ope ra t ion

    x2 = f a i l u r e rate during non-operation b. An environmental p r o f i l e desc r ibes t h e s p e c i f i c n a t u r a l and

    induced environments (nominal and worst case) a s soc i a t ed wi th t h e opera t ions , events , and func t ions descr ibed by t h e ope ra t iona l cyc l e . Items can be u t i l i z e d i n more than one environment. For example, a given i t e m might be used a t a ground s i te , on shipboard, and i n an a i rbo rne environment. I n a d d i t i o n , a given mission may c o n s i s t of several phases of opera t ion . phase of opera t ion is a per iod of t i m e during which a given environment p r e v a i l s . For example, i n a sa te l l i t e , boos t , o r b i t , r e e n t r y , and recovery wi th t h e i r a s soc i a t ed environments are phases of opera t ion .

    A

    102-5 TASK 102 18 November 1981

  • MIL-STD-756B

    These environmental cons ide ra t ions a r e handled as fol lows i n Mission R e l i a b i l i t y models.

    1. For i t e m s having more than one end use , each wi th a d i f f e r e n t environment, t h e Mission R e l i a b i l i t y model would be t h e same f o r a l l environments except t h a t t h e f a i l u r e rates f o r t h e va r ious equipments of t h e i t e m would be d i f f e r e n t f o r t h e va r ious environments.

    2. For i t e m s having s e v e r a l phases of ope ra t ion , s epa ra t e Mission R e l i a b i l i t y models can be generated and p r e d i c t i o n s made f o r each phase of opera t ion . The r e s u l t s can then be combined i n t o an o v e r a l l i t e m model and i t e m p red ic t ion .

    2.3 How To Construct a Mission R e l i a b i l i t y Model

    2.3.1 Fundamental r u l e s f o r p r o b a b i l i t y computations. This s e c t i o n d i scusses t h e fundamental r u l e s f o r p r o b a b i l i t y computations t h a t provide t h e b a s i s f o r t h e d e r i v a t i o n of t he p r o b a b i l i t y of s u r v i v a l (P,) equat ions developed i n Method 1001.

    2.3.1.1 The a d d i t i o n r u l e (exc lus ive c a s e ) . I f A and B are two mutual ly exc lus ive events , i .e . , occurrence of e i t h e r event excludes t h e o t h e r , t h e p r o b a b i l i t y of e i t h e r of them happening i s t h e sum of t h e i r r e spec t ive p r o b a b i l i t i e s :

    P(A o r B) = P(A + B) = P(A) + P(B) (1) This r u l e can apply t o any number of mutually exc lus ive events :

    P(A + B...+ N) = P(A) + P(B) ...+ P(N) (2) 2.3.1.2 The a d d i t i o n r u l e (non-exclusive c a s e ) . I f A and B are two events no t mutually exc lus ive , i . e . , e i t h e r o r both can occur , t h e p r o b a b i l i t y of a t least one of them occurr ing i s :

    P(A o r B) = P(A + B) = P(A) + P(B) - P(AB) (3) The equat ion f o r t h r e e events becomes:

    P(A + B + C) = P(A) + P(B) + P(C) - P(AB) - P(AC) - P(BC) + P(ABC)

    Th i s r u l e can be extended t o any number of events .

    TASK 102 18 November 1981

    102-6

    ( 4 )

  • MIL-STD-756B

    2 . 3 . 1 . 3 i .e., t h e occurrence of one does not a f f e c t t h e p r o b a b i l i t y of occurrence of t h e o the r , t h e p r o b a b i l i t y t h a t both w i l l occur i s equal t o t h e product of t h e i r r e s p e c t i v e p r o b a b i l i t i e s .

    The m u l t i p l i c a t i o n r u l e . I f events A and B are independent,

    P(A and B) = P(AB) = P(A) P(B) ( 5 )

    Equation ( 5 ) may be extended t o any number of independent events:

    P(AB.. .N) = P(A) P(B) . . .P(N) ( 6 ) 2 . 3 . 1 . 4 i .e . , t h e occurrence of one a f f e c t s t h e p r o b a b i l i t y of occurrence of t h e o t h e r , a c o n d i t i o n a l p r o b a b i l i t y exists. B has occurred i s denoted by P(A B ) , and s i m i l a r l y B given A is denoted by P(B A). Thus, i f A and B are not independent, t hen t h e p r o b a b i l i t y of both occurr ing is:

    Condit ional p r o b a b i l i t i e s . If events A and B are not independent,

    The p r o b a b i l i t y of A given t h a t

    P(AB) = P(A) P(B,/A) = P(B) P(A/B) ( 7 )

    I f A and B are independent, P(A B) = P(A) and P(B A) = P(B) and Equation ( 7 ) reduces t o Equation ( 5 ) .

    For t h r e e events , A, B and C

    P(ABC) = P(A) P(B/A) P(C/AB) (8)

    2 . 3 . 2 Procedure f o r developing i t e m models.

    S tep 1 - Define what is requi red f o r mission success and t r ans- la te t h i s i n t o a mission success diagram.

    S tep 2 - Write t h e p r o b a b i l i t y of success , Ps, equat ion f o r t h e i t e m .

    Step 3 - Calcula te Ps f o r each of t h e equipments of t h e i t e m . This i s done by u t i l i z i n g one of t h e va r ious relia- b i l i t y p r e d i c t i o n techniques.

    S tep 4 - The p r o b a b i l i t y of success numbers f o r t h e va r ious equipments der ived i n S tep 3 are i n s e r t e d i n t h e formula derived i n S tep 2 f o r t h e i t e m p r o b a b i l i t y of success .

    S tep 5 - A p r o b a b i l i t y of success curve ve r sus t i m e can be p l o t t e d by t ak ing several va lues of t i m e f o r mission t i m e , and eva lua t ing t h e p r o b a b i l i t y of i t e m success by t h e above procedure f o r t h e several va lues of t i m e chosen.

    S tep 6 - Addi t iona l s t e p s i n t h e a n a i y s i s w i l l depend upon t h e dec i s ions t h a t t h e a n a l y s i s is intended t o opt imize .

    102-7 Y TASK 102

    18 November 1 981

  • MIL-STD-756B

    2.4 Discussion of procedure. A s descr ibed i n 1 .2 of Task 102 i t i s necessary t o d e f i n e t h e s p e c i f i c mission of i n t e r e s t ( i f more than one exists), t h e phases of opera t ion , t h e func t ions and a l t e r n a t e modes of ope ra t ion t o perform these func t ions .

    Defining mission success is tantamount t o w r i t i n g a word s tatement which d e s c r i b e s what equipments o r combinations of equipments are requi red f o r mission success and drawing a r e l i a b i l i t y block diagram f o r t h e s tatement . Seve ra l methods of going from a r e l i a b i l i t y block diagram t o a p r o b a b i l i t y of s u r v i v a l formula are shown i n t h i s s ec t ion .

    For example, a word s tatement might be:

    Equipments A, B , and C , o r D and E , and equipment F must work f o r mission success . The Mission R e l i a b i l i t y block diagram would be as fo l lows:

    SUCCESS

    It i s no t convenient t o go d i r e c t l y from t h i s Mission R e l i a b i l i t y diagram t o a p r o b a b i l i t y of success equat ion f o r t h e system. of s u r v i v a l equat ion is:

    The c o r r e c t p r o b a b i l i t y

    - ps - PAPBPCPF + PDPEPF - PAPBPCPDPEPF

    A t f i r s t i t might appear t h a t t h e p r o b a b i l i t y of success equat ion could be w r i t t e n as

    where PA = p r o b a b i l i t y of equipment A working.

    The event t h a t A , B , C , and F works ( represented by ABCF) and t h a t t h e event D, E , and F works ( represented by DEF) are not mutually exc lus ive . Consequently, adding t h e p r o b a b i l i t i e s of t h e s e two even t s , PAPBPcPF +- PDPEPF does not y i e l d t h e c o r r e c t r e s u l t .

    Another word s tatement could be t h a t any two of t h r e e genera tors A , B , and C must work f o r success . I n o t h e r words, t h e genera tors are phys i ca l ly ope ra t ing i n p a r a l l e l and any two have t h e c a p a b i l i t y t o supply t h e needs of t h e system. Its mission success diagram may be shown i n one of two ways:

    I

    102-8 TASK 102 18 November 1981

    - -__ . -- - - - _ _ " _I____ --

  • MIL-STD-756B

    or

    The "(2/3)" of diagram (a) denotes that two of the three equipments must operate for success. success criteria of parallel equipments. Diagram (b) is the equivalent of diagram (a) but becomes a cumbersome technique when expanded beyond three parallel equipments.

    Diagram (a) is the easiest technique to model

    3. REQUIREMENT

    3.1 The contractor shall develop and maintain a Mission Reliability model for each configured item required to perform the mission functions. A Mission Reliability block diagram shall be developed and maintained for the item with associated allocations and predictions in each reliabilty block. to the Basic Reliability model, functional block diagram, schematics and drawings, and shall provide the basis for accurate mathematical representation of Mission Reliability. the Mission Reliability diagrams shall be consistent with that used in the Basic Reliability model, functional block diagram, drawings and schematics, weight statements, power budgets and specifications.

    The Mission Reliability block diagram shall be keyed and traceable

    Nomenclature of elements of the item used in

    3.2 Hardware or functional elements of the item which are not included in the Mission Reliability model shall be identified. Rationale for each element's exclusion from the Mission Reliability model shall be provided.

    3.3 being readily updated with information resulting from reliability and other relevant tests as well as changes in item configuration, mission parameters and operational constraints.

    The Mission Reliability mathematical model shall be capable of

    3.4 If a Failure Mode, Effects and Criticality Analysis (FMECA) is required, the Mission Reliability model and the FMECA shall be consistent in the definition of mission success and utilization of elements of the item in redundant and alternate modes of operation in specific mission phases.

    102-9 TASK 102 18 November 1981

  • MIL-S TD- 75 6 B

    TASK SECTION 200

    RELIABILITY PREDICTION

    1. DOCUMENTS REFERENCED I N TASK SECTION 200:

    STANDARDS

    M i l i t a r y

    MIL-STD-1670 Environmental Criteria and Guidel ines f o r A i r - Launched Weapons

    HANDBOOKS

    M i l i t a r y

    MIL-HDBK-217 R e l i a b i l i t y P r e d i c t i o n of E lec t ron ic Equipment

    MIL-HDBK-251 Re l i ab i l i t y /Des ign Thermal Applicat ions

    OTHER PUBLICATIONS

    RADC-TR-73-248 Dormancy and Power On-Off Cycling E f f e c t s on E lec t ron ic Equipment and P a r t R e l i a b i l i t y

    RADC-TR- 7 4- 2 6 9 E f f e c t s of Dormancy on Nonelectronic Components and Materials

    LC- 7 8-1 Storage R e l i a b i l i t y of Missile Material Program, Missile Material R e l i a b i l i t y Handbook P a r t Count P r e d i c t i o n

    GIDEP Government Indus t ry Data Exchange Program, Summaries of F a i l u r e Rates

    NPRD-1 Nonelectronic P a r t s R e l i a b i l i t y Data, 1978

    2. GENERAL REQUIREMENTS

    2 . 1 C l a s s i f i c a t i o n . R e l i a b i l i t y p r e d i c t i o n s , as defined he re in , are c l a s s i f i e d as fol lows:

    Type I - F e a s i b i l i t y p r e d i c t i o n

    Type I1 - Prel iminary design p red ic t ion Type I11 - Detai led des ign p r e d i c t i o n

    200-1 TASK SECTION 200 18 November 1981

  • MIL-STD-756B

    Generalized d e s c r i p t i o n s of p r e d i c t i o n s s p e c i f i e d by t h i s s tandard w i l l be found i n t h e fol lowing paragraphs. Examples of r e l i a b i l i t y p r e d i c t i o n methods appropr i a t e f o r t h e t h r e e types of p r e d i c t i o n s are provided by Methods 2001 through 2005. The a p p l i c a b i l i t y of i n d i v i d u a l requirements of Sec t ion 200 he re in i s a func t ion of t h e type of p r e d i c t i o n t o be performed; t h e s t e p s de l inea ted w i l l be performed t o t h e ex t en t permit ted by t h e level of des ign conf igura t ion d a t a a v a i l a b l e . Unless o therwise s p e c i f i e d , t h e r e l i a b i l i t y p r e d i c t i o n s h a l l be f o r worst case ope ra t ing and environmental condi t ions .

    2 .1 .1 F e a s i b i l i t y p r e d i c t i o n (Type I) . F e a s i b i l i t y p r e d i c t i o n is intended f o r use i n t h e conceptual phase of i t e m development. During t h i s phase t h e level of d e t a i l e d des ign information i s gene ra l ly r e s t r i c t e d t o o v e r a l l a s p e c t s of t h e i t e m . Detai led conf igu ra t ion d a t a gene ra l ly are l imi t ed t o t h a t which may be der ived from e x i s t i n g i t e m s having func t iona l and ope ra t iona l requirements s i m i l a r t o those of t h e i t e m being developed. Methods 2001, 2002, and 2003 desc r ibe f e a s i b i l i t y p r e d i c t i on methods.

    2.1.2 Pre l iminary design p r e d i c t i o n (Type 11). Prel iminary design p r e d i c t i o n i s intended f o r use i n t h e e a r l y d e t a i l e d des ign phase. During t h i s phase des ign conf igu ra t ion d a t a are documented by engineering ske tches and pre l iminary drawings. The level of d e t a i l e d information a v a i l a b l e may be r e s t r i c t e d t o p a r t l i s t i n g s . S t r e s s a n a l y s i s d a t a are not gene ra l ly a v a i l a b l e . Method 2004 desc r ibes a pre l iminary des ign p r e d i c t i o n method.

    2.1.3 Detai led des ign p r e d i c t i o n (Type 111). Detai led des ign p r e d i c t i o n i s intended f o r use i n and subsequent t o t h e d e t a i l e d des ign phase. -~ This phase is cha rac t e r i zed by drawings which i d e n t i f y a l l p a r t s , materials, and processes needed t o produce t h e i t e m . Operating stress and temperature a n a l y s i s d a t a are necessary f o r each p a r t i n t h e i t e m . The a n a l y s i s d a t a s h a l l be based on design a n a l y s i s and measurement techniques accep tab le t o t h e procuring a c t i v i t y . Method 2005 desc r ibes a d e t a i l e d design p r e d i c t i o n method.

    2.2 P a r t d e s c r i p t i o n . P a r t and a p p l i c a t i o n d e s c r i p t i o n s s h a l l be provided f o r any p r e d i c t i o n based upon p a r t f a i l u r e rates. 'The p a r t i d e n t i f i c a t i o n number from t h e schematic diagram, t h e app l i cab le s p e c i f i c a t i o n and t h e s p e c i f i c a t i o n type number s h a l l be included.

    2.3 Environmental da ta . Environmental d a t a a f f e c t i n g p a r t f a i l u r e rates must be defined. These d a t a i nc lude t h e s p e c i f i c n a t u r a l and induced environments (nominal and worst ca se ) a s soc i a t ed wi th t h e opera t ions , events , and func t ions descr ibed by t h e l o g i s t i c and ope ra t iona l cyc les . Guidel ines f o r determining t h e environmental cond i t i ons of use f o r air- launched weapons are found i n MIL-STD-1670.

    TASK SECTION 200 200-2 18 November 1981

    .. I _I___ --..__I_____ _--_ -I-_-_Ix .-.-

  • MIL-STD-756B

    2.3 .1 Environmental ca t egor i e s . Environmental c a t e g o r i e s s h a l l be def ined f o r each service use event using Table 700-Las a guide of t y p i c a l ca t egor i e s . Data sources, such as MIL-HDBK-217 and WRD-1 which u t i l i z e environmental f a c t o r s t o a d j u s t f a i l u r e rates, s h a l l apply t h e environmental f a c t o r which most c l o s e l y matches t h e intended environment. Fac to r s u t i l i z e d s h a l l be c i t e d and s u b s t a n t i a t e d .

    2.3.2 P a r t ope ra t ing temperature. P a r t temperatures used f o r p r e d i c t i o n purposes s h a l l inc lude t h e i t e m i n t e r n a l temperature rise as determined by thermal a n a l y s i s o r test da t a . thermal a n a l y s i s procedures, r e f e r t o MIL-HDBK-251.

    For gene ra l guidance and d e t a i l e d

    2.4 S t r e s s ana lys i s . Analyses s h a l l be performed t o determine t h e ope ra t ing stresses t o be experienced by each p a r t commensurate wi th t h e p r e d i c t i o n c l a s s i f i c a t i o n and t h e des ign d e t a i l a v a i l a b l e . These ana lyses s h a l l be based on techniques acceptab le t o t h e procuring a c t i v i t y . F a i l u r e rates s h a l l be modified by appropr i a t e f a c t o r s t o account f o r t h e e f f e c t of appl ied stress. S t r e s s r a t i o s c i t e d i n t h e p r e d i c t i o n r e p o r t s h a l l be i n d i v i d u a l l y i d e n t i f i e d as Estimated (E) , Calculated (C) , o r Measured (M) . 2.5 F a i l u r e d i s t r i b u t i o n s . The f a i l u r e d i s t r i b u t i o n appropr i a t e t o t h e s p e c i f i c e l e c t r o n i c , e lectr ical , e lectromechanical , mechanical, and ordnance i t e m s h a l l be used i n computation. I n i n s t ances where t h e f a i l u r e d i s t r i b u t i o n f o r t he item i s not known, t h e exponent ia l , binominal, weibul l , o r o the r f a i l u r e d i s t r i b u t i o n may be assumed. The f a i l u r e d i s t r i b u t i o n s u t i l i z e d s h a l l be c i t e d and any assumptions subs t an t i a t ed in t h e p r e d i c t i o n r epor t .

    2.6 F a i l u r e rates. Fa i lu re rates f o r a l l e l e c t r o n i c , e lectr ical , e lectromechanical , mechanical, and ordnance items are requi red f o r each s i g n i f i c a n t event and environment def ined by t h e service use p r o f i l e . All sources of f a i l u r e d a t a s h a l l be approved by t h e procuring a c t i v i t y p r i o r t o use. Basic f a i l u r e rates from most d a t a sources must be modified w i t h app ropr i a t e f a c t o r s t o account f o r t h e s p e c i f i c i t e m a p p l i c a t i o n under cons idera t ion . Fac to r s used s h a l l be c i t e d and s u b s t a n t i a t e d i n t h e p r e d i c t i o n r epor t .

    2.6.1 Funct iona l group f a i l u r e rates . Funct ional group f a i l u r e rates may be derived from f a i l u r e rate d a t a f o r f u n c t i o n a l l y s i m i l a r groups o r i t e m s . The GIDEP F a i l u r e R a t e Summaries are an a v a i l a b l e source f o r l o c a t i n g group and i t e m f a i l u r e rates.

    2.6.2 Operating f a i l u r e rates. Operating f a i l u r e rates f o r e l e c t r o n i c and electromechanical p a r t s may be found i n MIL-HDBK-217. F a i l u r e rates f o r o the r p a r t s may be found i n NPRD-1, t h e GIDEP F a i l u r e R a t e Summaries, and o t h e r sources.

    200-3 TASK SECTION 200 18 November 1981

  • MIL-STD-756B

    2.6.3 Nonoperating f a i l u r e rates. Nonoperating f a i l u r e rates f o r p a r t s t a k e i n t o cons ide ra t ion p e r t i n e n t environmental i n f luences o r o t h e r stresses of t h e app l i ca t ion . RADC-TR-74-269, and LC-78-1 provide nonoperating f a i l u r e rates.

    Data sources such as RADC-TR-73-248,

    2.6.4 found i n d a t a sources such as WC-TR-73-248, WC-TR-74-269, and LC-

    S torage f a i l u r e rates. S torage f a i l u r e rates f o r p a r t s may be

    78-1.

    2.7 Item r e l i a b i l i t y . I t e m r e l i a b i l i t y s h a l l be computed us ing mathematical models and app l i cab le f a i l u r e rate da t a . The p r e d i c t i o n r e s u l t s s h a l l be expressed i n t e r m s c o n s i s t e n t w i th t h e s p e c i f i e d r e l i a b i l i t y requirements.

    3. DETAILS TO BE SPECIFIED BY THE PA (SEE 5.1.1). The fol lowing are app l i cab le when Tasks 201 o r 202 are involved:

    a.

    (R) b*

    C.

    d.

    e.

    f .

    g *

    h.

    (R) i.

    Since r e l i a b i l i t y modeling t a s k s are normally p r e r e q u i s i t e t a s k s t o p r e d i c t i o n t a sks , elements i n 3 of Task Sec t ion 100 apply.

    P r e d i c t i o n Type (See 2.1 of Task Sec t ion 200).

    Worst Case A p p l i c a b i l i t y (See 2.1 of Task Sec t ion 200).

    Environmental Categories (See 2.3.1 of Task Sec t ion 200).

    S t r e s s Analysis A p p l i c a b i l i t y (See 2.4 of Task Sec t ion 200).

    F a i l u r e R a t e Data Sources (See 2.6 of Task Sec t ion 200).

    I t e m R e l i a b i l i t y Requirements (See 2.7 of Task Sec t ion 200).

    DI-R-7095 ( R e l i a b i l i t y P r e d i c t i o n and Documentation of Supporting Data) should be s p e c i f i e d when d e l i v e r a b l e d a t a i s des i r ed i n conjunct ion wi th t h i s t a sk .

    P r e d i c t i o n Method(s). An op t ion i s t o al low con t r ac to r s e l e c t i o n of t h e app ropr i a t e p r e d i c t i o n method(s). methods may be app l i cab le t o d i f f e r e n t system components.

    D i f f e ren t p r e d i c t i o n

    TASK SEC I O N 2 18 Novem t er 19 !4! 200-4

  • MIL-STD-756B

    Table 200-1. Environmental Symbol Identification and Description.

    Ground, Benign

    Space, Flight

    Ground, Fixed

    Ground, Mobile

    Naval, Sheltered

    Naval, Unsheltered

    Airborne, Inhabited, Transport

    Airborne, Inhabited, Fighter

    Airborne, Inhabited, Helicopter

    Airborne, Uninhabited, Transport

    Airborne, Uninhabited, Fighter

    Airborne, Uninhabited. Helicopter

    Missile, Launch

    Missile, Captive Carry

    Missile, Free Flight

    Symbol

    GB

    SF

    GF

    GM

    NS

    NU

    AIT

    AIF

    AIH

    %T

    %F

    %H

    Y,

    MC

    MF

    Nominal Environmental Conditions

    Nearly zero environmental stress.

    Earth orbital. Approaches Ground, Benign conditions. Vehicle neither under powered flight nor in atmos- pheric reentry.

    Conditions less than ideal to include installation in permanent racks with adequate cooling air and possible installation in unheated buildings.

    Conditions more severe than those h r GF, mostly for vibration and shock. Cooling air supply may also be more limited.

    Surface ship conditions similar to GF but subject to occasional high shock and vibration.

    Nominal surface shipborne conditions but with repetitive high levels of shock and vibration.

    Typical conditions in transport or bomber compartments occupied by aircrew without environmental extremes of pressure, temperature, shock and vibration, and installed on long mission aircraft such as transports and bombers.

    Same as AIT but installed on high performance aircraft such as fighters and interceptors.

    Same as AI as helicopTers.

    but installed on rotary wing aircraft such

    Bomb bay, equipment bay, tail, or wing installations where extreme pressure, vibration and temperature cycling may be aggravated by contamination from oil, hydraulic fluid and engine exhaust. mission aircraft such as transports and bombers.

    Same as A but installed on high performance aircraft such as fyihters and interceptors.

    Installed on long

    installed on rotary wing aircraft such

    Severe conditions of noise, vibration, and other environments related to missile launch, and space vehicle boost into orbit, vehicle re-entry and landing by parachute. tion near main rocket engines during launch operations.

    Same as A,, , % aircraft pTatfoFm.

    Typical conditions of pressure, vibration and tempera- ture experienced in atmospheric flight to target.

    Conditions may also apply to installa-

    or AVH depending on the applicable

    200-5 TASK SECTION 200 18 November 1981

  • MIL-STD-756B

    TASK 201

    BASIC RELIABILITY PREDICTION

    1 . PURP 0 SE / RAT IONALE

    1.1 estimating the demand for maintenance and logistic support caused by an item and its component parts.

    A Basic Reliability prediction utilizes a series model for

    1.2 Mission Reliability prediction. Whereas the Mission Reliability prediction indi