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ratio%, when the true MTBF is much greater than (@O)O, much less Ihe” (81] f. The all.eqwpment test plan maybe selected when all units of the production.
Typology: Study Guides, Projects, Research
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14 July 1987
Reliability Test
Methods, Plans,
and Environments for
Engineering Development,
Qualification, and Production
No deliverable data required by thk document.
Approved for public release: distribution is unlimited.
Department OF DEFENSE Washington. Or 20363 .s Reliability Tesl Methods Plan% And Environments For Engineering Oevelopmenl, Qualification, And Production I Thi$ Military Handbook is approved for use by all Departments and Agencie$ of the DeparImenl of Oefen$e
be of use in improving thi$ document should be addressed 10: Commander, Space and Naval Warfare Sptem$ Command, AlTN: SPAWAR 003-121. Wa$hmglon, DC 20363-5100. by u~ing the self -addressed Standardization Document Improvement Propmal (OD Form 1426) appearing al the lnd of lhIS document or by letter
t!
Paragraph
a .,:; 3:? 3.! 3.1. 3.1. 3.1. 3.1. 3.1. 3.1.
4.!. 4.1. 4.1. 4.1,
&2. i 4.2.
4.3. 4.3,
4.4.! 4.4. 4.4.
4.5. 4.s.
Purpose................. Applicability....... Application of handbook. Taiioring. h~e;h,cdci!refe:eeoce Equipmentcategori=
REFERENCE DOCUMENTS Government documents........ specificaliGns, Siafidard$, and %m%ak.$ Olher Government documents
DEFINITIONS......... Term%......... Contractor........ Corrective maintenance (repair) Decision risk~ Failures......... Independent chargeable failure categories Measures oirei!abiiity...... Mis$ion profile.............. Life-cycle profile Procuring activity......
Purpos e................ c..--p -...... Applicatiomm atria............ Te%t methods............... Te\t plans.................. Test method and test plan selection factors Test melhti and test pliir, $ekder, Tes! method and%! plan pararnew$ebc!icm Reliability DevelopmenVGrowth Evaluation Methods The Duane Method................. The AMSAAMethod.................. E.SmOnilOringm etho6s Ccmpti:ed CA time irotewa! m.et%d Graphical me!h~ Standard EMS........ .;;;;;;.~; MTBFaswrance test.... Derivation of equation. Procedure........ Sequen:ia! :enp!an:.......
iv
Page
1 1 1 1 i 1 1 4 Q ~ 4 4 A 4 5 s 5 5 6 6 6 6 6 6 6 6 7 8 8
Is 16 16 17 18 19 19
cONTENTS(Continued) Page . Symbols.......................... j:
6.2. 6.2. 6.2.
TABLE 1 2 3 4 5 6 7 8 9A 96 10A 108 11 12 13 14 15 16 17
20 21 22 MIL-HDBK-
CONTENTS IContinuedl Cdibrmiona nd. ccumcv...................................... Tes!ing the:est focilky........................... Installation oftietest tiamintk test facilii..................... Sub;ect WJm{Keywordlfk iW................................ REFERENCES.....................................
Apdicntion mmri x.......................................... Summarv olvariables forthe AMSAA model....................... Summarv ofeauations, AMSAA model........ Equalion 6election guide, AMSAA model......... Critical va!ues of C: mvamettic form of the Cramm.Von M,sesstatintic.................................... Confidence intervals for MTOF. Iailure.terminmed test Confidence intervals for MTBF, time.terminated tesl........ AMSAAmodel eaamole................................... ( 1 .>1 100 oercem standard confidence limits on MTBF atiet Bccenldecision llowet. OL”l>.i)l........................ (1 II 100 oe.rcent acertdare (^) ,,Canf idence limits on MTBF aher accepldec,s#on luvper.0u17,all...................... ( 1 .>1 1Od percent standard Conf idnnce limits on MTBF after reiectdecicion llowe, -R,”l>.1))...................... 11 .,1 100 percent mnndard confidence Iimim on MTeF after rejec!decision (upper .O~lv........................... Summarv oftixed4wntion te.l plans............................ Summary of high risk freed-duration test plans................. Demonstrnled MTBF confidence limit multipliers. for failure calculatmn Dnmonstcnted MT9F confidence limit mu ftipliefs, for time cnlculalion Accept times of fixedduralion test plans, Proeram Manager’s Assessment !............................................. Compari80n of risks. standard fixed. duration tests versus PrOQ,Bm Mamwer’sAs sessmant..................................... Test times, .Wmdafd fixad-dumtion tes! plans versus Program ManaQer.a Assessmanl................................... Failure times fofthe numerical example.......................... Example of correct ordering in the AO bound calculation.... Example of incorrect ordering in the AO bound calculation Example data for computer program............................. Exnmple computer run fordatain TA8LE 21....................... vii I—.
Page 73 74 75 76 77 78 79 80
CONTENTS (Continued)
TASLE Page
so
Thermal stress environments for marine crab Environmental profile data (example) Test profile data (example) HOI day temperatures ~C) for Cla$s I equipment in air- conditioned compartments HOI day ambient temperature (“C) for Class II equipment inair<ond, tioned companments Hot day ambient temperatures ~C) for lquipment in ram air-cooled companmems Cold day arnb, enl temperatures ~C) for equipment ir? ram air-cooled compartments Temperatures ~C) for Clasi I and Class II equipmenl ,n air-conditioned companments Jet aircrafi random vibration lest. Tabulation of temperature values Summary of temperature values Tabula; ,onof wbrallon Ievel$ Summary of vi brat$on levels Composite test prof,le t,mel, ne Temperature level Iab”lat, on hot day(example) Temperature summary - hot day (example) Temperature level labulation - cold day (e,ample) Temperature summary cold day (example) V, bral,on level Iabulal,on (e,ample) V, bral, on level wmmary (example) Temperaw,e rate of change (example) Composite test prof,le timeli,>e (example) Random vibration test for Vf5TOLaircratl Env8r0nmenlal pro f,lesequence Stores hosl a,rcrati m,ssion utlllzat, on ratei for enwronmental testing Random wbratmn. 9,-, [OVL), level adluslmenl fanors for the max, mum predicted environment (951h percentile with 50 percent confidence based on one+ide tolerance limO1)
lt
117
118 119 120 120 121 121 122 123 123 124 124 125 125 126 127 128 129
Method of calculating the acceleration power spectral den!ily u spectrum to produce ~ A, lqual 10a unit - g,m, (OVL) 132 ,. Preliminary operational des,gn requirements (expected lifeof5years)......... 135 Life cycle environments 140 Assumed typ!cal a!tack mission profiles 158 A method for calculating test profde ttmes for a specific number of test cycles 159 Attack a!rcran caplive-carriage mission profole data (e~ample) 161
CONTENTS (Continued)
FIGuRE
27 28 29 30 31 32 33 34 3s 36 37 38 39 40 41 42 43 44 45 41!
s?
58
Te$t Plan ”Xlli-D...... Test Plan XIV-D....... Test Plan XV-D Test Plan XVI-D.............. Test Plan XV1l-D............... Test Plan XIX-D....... ‘lest Plan XX-D Tes\Plan XXI-D Test Plan XVllI-D..... Bounda~line cri!eriun for rejet~ -accept decision. All Equipment lestplan derived from Tesl Plan I-D All Equipment teslplan derived from Test Plan II-D AIIEquipment leslplan dertved frOm Tes:Plan 111.D All Equipment lest plan derived from Test Plan IV. D All Equipment leslplan derived from Test Plan V-D All Equipment te>lplan deri.ed from Test Plan W-D All Equipmenl!est planderived frOm Tes3Plan Vii-D All Equipment testplan der, vedf<om Tesl Plan Vlll-D Time truncauon( lypelcen%or, ng) Combnned envlronmenta( lest profkle for fixed.ground equipment Combined env, ronmenlal Ie$t prof,le for mobile ground equipment...... Naval Wrfa<e Crak, mtssion enwronmenlal profde $or externally mounled equipmenl(cold cycle). Naval surface craft, mwion enwronmental profile for externally mounted equipment (hot cycle) Naval surface CfafI, M#SiOrT efWi10nr_IW71a1 profile for imernally mounted equ!pmenl (cold cycle) Naval surface crab, miwon env, ronmenl~l profile for i nterna!ly mounted equipment (hot cycle) Naval surface Craft, miss, on enwronmental profile for internally mounted temperature controlled Naval surface craft, m,s%ion environmental profile for internally mounted temperature comrolled Surface craft and submarine vibration spectrum Submarine pro file............... Combined environmental test profile, for marine craft equipment................. General mission profile and characteristic for six aircraft types and twelve m,wons General mismon profile and characteristic! for six a!rcrafl typei and Iwelve mt$~!ons Genera! miwon prof,le and characteristics for four aircraft types and seven m,s%ions General mts%ion profole and characteristics for an attach aircraft ona high.low.low-h,ghmtsslon
Page
22a 230 232 234 236/ 238 240 242 244 246 248 250 252 254
255
26s
x
Page
61 62 63 64 65 66 67 66 59 70 71 72 73
-te 75 76 77 78 79 80 81 82 83 M 85 06 87 88 89 90 91 92 93 94 95 % 97 98 99 100 101 ,Q 103 106 10s General mission profile and characteristics for a fighter air~rafl cm an intercept mission General mission profile and characteri$ticf fOr a ,econna; y=r,:e cr=f~ ofi a hiqh+upemonic mis5i0n Mis$ion profile for temperature rate of cha~e calculaliOn Dynamic ~rewre (q) as function of Mach number and altitude Ra”dOm vibration tesl envelope. for jet aircrafi Environmental profile (example) Missionpi6f;:=f?~~~cPJe) Teap:Ofite(=amPle! Attack aircrafl test priflte ( 10w-lOw-lOw) Attack a,rcra~tesl prOfile (clOse$up~n) Attack aircrah test prOfile (hi9h-10w”hlgh) Attack aircraft test pro~tle (h.=.;+.h!gh.high) ~t:ack ~,rc:ep. !eg p,ofile (h, gh-low40w. hi9h) Af!ack atrcrafl iestorOfile(ferry) : ASW al,craft teSI profile (contact investigation - h19h) ASW ~,rcrah IeSI profile (contacl investigation intermediate). Asw a,rcrahlesl prOfile(mln?lafi@ *YVV ~ircrap, ;eil ~:cf{!e (h:gh.high. high!. ASW Z,r<ratl tesl profile (search and attack). ASW aircrah te$l Profile (surface ‘Surveillance) ASW alrCtaf LteSt PrOflle(ferry). EcM alrcra~t e~tpfOfiie( penefrat;or~ ECM alrcraf~ ~e~,Pr~!;l@ @tJnd-Of~ EC~wl~ir::afe$~pfQf!lP(f@rr~) Flghler aircrafi test PrOfile (high-hi9h-high). F,ghter aircraft lest pro flh?(escoti). flghler air<ratlte$t profile (a, r deiense and capiive ti~gfi,i). FighWr afircrati 1e51PrOiiie @;er~eWL). ;ighter aircrak :EW wfile (high-[ ow-low”high) F,ghler aircrafi tes~ PrOfile (Iow-lOw-lOw) Fighter aircfati test prOfile (10w.10w-hi9h) Fighler a,~crah te$t PrOfile (cl~e $“pWn) Fighter airc,af! te$t proiiie (ferry). Reco””aistii,ce aircratt W%. p.-. ..,.-.fila ..-.^ /high-l@w-high! Reconnaissance air~rafi test prOfile [lOw-10w’h’gh) Reconnaissance aircrafi test PrOfile (low-lOw-lOw) : Reconnaissance airc~afi test prOfile (high-$ uper$On’cJ ‘ Reconnaissance aircrah tes1 PrOiiie (hi9h.QJb@ic; ReC0nna15SanCe aircrafi tes: FJr6fi:~ ffe:w) Ta”ke, ai,craft Iest profile (high-low.high refuel). Tanker a,rcraft {low-low-low refuel). Tanke, aircrafl le$lprofile (%trikerefuel) COmpOsilelesl prOfi@(example) Compos,lelesl pro file(example) Type A VfiTOL airborne early warnln9 miS~lOn PrOfile
2s 201 282 283 2& ~g~ 286 287 288 -@ 290 291 292 293 294 295 296 297 298 299 366 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315
xi
cONTENTS (Continued)
Page
I
FIGuRE
14s
1b?
Equipment installed in amembled lxternal stores and air-launched weapons - vibrational refponae acceleration noversus frquencyspectra Induced buffet maneuver random vibration response spectrum...................... Low- low free-flight mimion profile (example) Environmental engineering program Khemalic Logistics functional schematic diagram European scenario assumed maintenance $chedule and po$$ible operational utilization rate for environmental analfie} (example) Target movement timeline for lnvironmental design criteria (European scenario) - large quantities (example).......... Estimated percentage of time distribution for lranspoflalion, holdldelay, and handling, for nominal .probable factory-to-theater movement beeline.............. Assumed typical attack aircrafi operating envelope [standard day) showing the a~$umed high. medium.low mlmonprofile Assumed typical attack aircrafi operating lnvelope (standard day) showing the assumed h,gh.low-h,gh mis~ion profile Vibrauon faclor (g,”, (OVL))~ flight missiofl profile high-medium-low use with FIGu RE5 130 and 143 except(”), verw$minimum g,~, (OVL)~(elample) Vibration factor (g, ~$ (OVL))~ fhght mission profile high-low-high use with FIGURES 130 and 144 except (“), versus MiniI’IWm (g,,m (OVL))? (example) Store free. fitght vibration facwr (g,~, (OVL))2 flight mis~iOn PrOflle IOW-IOW USe with FIGURES 131 thru 134 and TABLE 4B(example) Unit-grm, (OVL)-acceleration P5D verws frequency spectra.. Vibration profile$ for rail transportation Rail transpofiationtest profile Program listing for FORTMN program Program listing for FORTWN program
xiiifiiv
1.1 -. Thi$ handbook provides test methods, test plans, and test enwronmenlal pro f,les which can be used ,n reliabtltty Iest, ng dur#ng the development, qualification. and producuon of systems and equipment
1,2 Acml,cabilitf Th,s handbook lxplaim techniques for use in reliability test% performed during Ihe imegraled lest programs $pecil,ed in MI L-STO-785. Procedures. plans, and environments which can be used m Reliability DevelopmentiGrowth Tests (RD/GT), Reliability Qualification Tesls (RC)T), and Pfoduclion Reliability Acceptance Tests (PRAT) arediscus$ed. In addition, Environmental Stress Screening (ESSI methods are provided.
1.2,1 APII Iicatmn^ of^ handbook.^ Data^ provided^ inthk^ handbook^ can^ ba u$ed^ $eIeclively^ on reliability te$t program~ and can be \pecifted m Depanmem o! Defense contracted prctcutements, reques!s for propo~al$. statement$ of work. and Government in-houw development wh,ch reqwre reliability testing
1.2.2 Tailorinq. The data provided herein can be selected for use on tailored reliability test programs as reQu# red by govern, ng regulauons and as appropriate 10 the particular system or equtpmenl, tintended aPPl, Cation, Pr09ram lYPe, magnitude, and funding,
1.3 Method of refeten<e When referencing the lest methods, test plans. and environmental lest conditions of thts hand booh, the handbook and the fpecific paragraph number(s) are 10 be rated
1.4 Equ, preen\ ca!eqornes The methods in this handbook are apPhcable 10 SIXbroad calegones of equipment, dlst, ngufshee accord, ng to each equipment’s field $arvice applicatmn:
Calegory 1
Category 2
Category 3
Category 4.
Calegory 5
Calegory 6.
F,,ed.grcwnd equipmenl
Mobile ground equipmem A Wheeled vehicle B Tracked .eh, cle C. Sheller con f,gurat, on D. Manpack
Shipboard equipmenl A. Naval surface craft B Naval submarine C Mar!ne crafi D Underwater vefwcle
Eqwpment for jet aircrati A. Ft,ed-wing B vertical and Shorl Takeoff and Landing (v/5TOL)
Turboprop aircrah and helicopter lquipment A Twboprop E Hel Kop:er
Ml$sile$ and assembled external $mres A A,r.launched miwles B Assembled elternal stores C. Ground.launched mmiles
2.1.2 Other Governme~t documents The following other Government documents form a part of Ih,i handbook m the ealent spec, f#ed here, n
PuBLICATIONS
NAVAL AIR SYSTEMS COMMAND (NAVAIR)
AR70.38 Reiearch.^ Development,^ lest^ And^ Evaluation^ Of Material^ Far E.lreme Chmatic Conditions AD.lll S Electromagnetic Compatibility Design Guide For Avionic$ And Related Ground SuppcIrt
(Copies of specifications. standard$. handbooks, and publications required by contractors in connection with specific procurement functions should be obtained from the procuring activity or a! directed by the contracting of ficer.)
3 \ ~ Term> used herein arein accordance with l&wdef, nitlons in MI L.5TD.2Lf0, MI L. ST D.721, iv:,, ,. TO.785. MI L- ST D-81O. and MI L- HDSK-189, w,lh the Pxcept, on andadd, uon of Ihetermsspecafoed O. ~ I! through3 1,9.
3.1. \ Contractor. Contraaor includes Governmental or ,ndustnal acthwl,es developing or producang {nliitary sys!ems and equipment.
3.1.2 Corrective n,aintenance (reoair]. The acciom performed, as a result o{ failure. to reslore an ,Iem to a specified cendiuon
3.1.3 Decision r,$k$ Deci!ion ri$ks shall be as fpecified in 3.1.3.1 through 3.1.3.3.
3.1.3.1 Consumer’s risk @. (^) Consumer”% risk (&) i$ the probability of accepting equipment which he! a true n!ean-lime.&lween-fa,lure (MTBF) equal 10 the lower te$I MT8F (01 ), The p,obab(l,ty of accepting equipment which ha~ a lrue MTBF less than the lower ?%1 h4TklF (o, ) will be Ie!$ than @)
3.1.3.2 Producer”$rtsk (~ Producer’s risk (CY) IS the probabllltyof refecungequipment which ha> a true MTBF equal to the upper lest MTBF (8D ) The probability of rejecl, ng eqtopmenl wh, ch has a lrue MTSF greater than the upper test MT8F (L90 ) w,II be less than (a)
3.1.3,3 C%<riminaiion ratm (d!. The dmcrimmation ral,o (d) usone of the standard lest plan parameters; it osthe ratio of the upper tesl MTBF (80) 10 Ihe Iowertesl MTBF fe, ): lhat is, d. C?UI 0..
3.1.4 _ Failure iypesand clas$ii!ca(ion$ arespec, iled In MIL.5TD.721, wtththe ezcepl)onoi multiple, paltern, and chargeable fa,lureswhnchare $per,l, ed ,$. : ~ 4 1 through 3 1.
3.1.4.1 Multiple failure% Mull,ple fa,lu!es are !he wmultaneous occurrence of IWO or more independent fatlures When two or more faded parts ale found durtng lrouble$hoollflg and Iaolure$ csnn6: be \hown 10 be dependefll. mul!lple fa!lures are prmumed to have occurred,
3 ~.d.2 Pattern fa,lures The occurrence of IWO or more Ia,lure%of the%ame pan #n ,dent, cal o. equ$valenl applucatoons when Ihe fa,lures are cau%ed by the same bawc failure mechanwm ano the teIlu#es occur M a rale wh,ch n tnconsislenl wnh the pan”% predlcled fa!lure ra!e
3 1 4.3 Chargeable failure Arelevanl, Independent failure of equ,pment under test and any Cfependent failure$cau%ed lhereby wh, chareclasmi, eo a%one ia,lure and used todelermine contractual compfaance with acceptance and reject, on criteria
3 1.5 Independent! chargeable fa,lure caleaorte$ Fa,luresdef, ned, n 3.1 5.1 lhrough 3 1 55 are categorized as independent chargeable Ia$lures
3 1.S 1 Eauipment des,qn fa,lure Any Ia,lure wh,ch can be traced dmectly 10 the des$gn of the equspmenl; that ,s. the des#gn of the equtpment caused lhe part tn questoon to degrade or fall. rewlttcg tn anequ, pmenl failure
3.1.5.2 Eau,pmenl manufaclunno failure A failure wh,ch i$caused by poor workmanship or finadequ ale ma”ufactur,”g process conl, ol d“r, ng equipment construction. Iestlng, Or ,epalr Prl Or 10 Ihe slar! of testing: for example, the failure of an ai$embly d“e to cold solder jmnls
3.1.5.3 PandeS!Qn fa,lure The fajlureof pans wh!ch can be traced d,reclly loonadequatedes,gn
3.1.54 pan Manufaclurtna failure Parl fa,lureswh+<h are the rewllof poor workmanship or inadequate manufacturing process control dur, ng par{ assembly, tinad equate nnspecl, on, or Improper te51tng
3 1 55 So flwa~e erro, fa,lure k fa, ture caused by an error inlhe computer pro$~am a%so<$ated wtn the hardware
4.1 -. Section 4 provides information and gwdance tor Y?lecIing the Iesl melhods and Ies.. plans required 10 implemeni the left program~ specif}ed in MIL.STD-7E
4.1.1 ~. Section 4 provides test method% and test plans which can be used when performing the reliability test programs $pecified tn Task\ 200.300, and 400 of MI L-ST D.7E1. Methods are provided for e.aluatincl data Drocfuced durina RDIGT and ESSDroaram$. lest Dlans are Drovided for MTBF assurance and fixed-d ur;!ion aid sequential re;iabili!y demons~ral;on and awe;srnent le~ts and all-equipment reliability iestk Thaw test plain can ba selected for u$e in ROT and PWT. .. 4.1.2 Agolications matrix, The interrelation$hip~ between the test methods and test plans described herein and the tasks $pacified in MIL-STD-7BI are provided in TABLE 1.
4.1.3 Test methods Methods for evaluating reliability growth during RD/GT and for evaluating ESS programs are provided in4.1.3.l and 4.1.3.2.
4.1.3.1 Growlh monitor!na method Two growth momloring (data evaluation) methods are described: the Duane Method and the Army Material Systemf Analysis Agency (AMSMJ Method The Duane Method is a graphical and nonstatistical technique which can be used 10 graphically plot changes in reliability. The AMSAA Melhod is based on Ihe a}wmphcm that the time> between successive failures ca” be modeled as the intensity funct, on of a nonimmogeneow Poisson process. Th!$ ,mensity f“ncuon is expre;%ed a$ a Mult!ple of the cumula18ve Ie$t tame raised 10 wme power. The Ouane and AMSm methods are described in MIL-HDBK.1B
4.1.32 ESS evaluation methods Two ESSevaluat#on melhods are described which prowde a meam to determine when the ESS procetiure should be terminated One of the methods provides a techn,que for calculating a required ESS time Interval (which must be $au$f,ed 10 $IOP screening) prior to the slarf of Ihe ESS The second method make% use of arbitrary Inmes based on hmlor,cal data.
4.1.4.2 Stzmdmd test olans The standard lesl plans conta, n slalist!cal criteria for deIerm8nung C0mp18a~Ce w,th spectif,ed rehabillty requtremenl$ and are based on the assumption that the underlying distribution of tnme+belween-fail ures ISexponential The exponential assumption impltes a constant fa)lure rate; therefore, thew test plans cannot be used for the purpose of el)minat$ng design defects or infant mortality failures The standard tell plans are as categorized In a through d:
a. Probability Ratio Sequential Test plans (PRST) (Test Plain I-O through VI-D) b. Shon-run h!gh.r!sk PRST plans (Test Plans VII-O and VIII-D) c. Ftxed-duratmn lest plans (Test Plain IX-O through XVII-D and XIX-O through XXI. D) d. Ail-equipment reliab!hcy te$l plan (Test Plan XVIII-O)
These statistical test plans are to be used to determine contractual compliance with pre-e$tabl!shed accep!. reject criteraa and should not be used m project equ$pme”t MTa F
4.2 lest method and tesI elan selectnon factor% The rnOSI important factors to be c.anmdetee when selecl, ng an approprna!e lest plan or method are prowded tin 42.1 through 422 S
I
4.2 1 Tesl method and te%! elan selection Thelejl rnethod%and te%: plans to be uwd in RD:GT, RQ7, PRA?, and ESS shall be selected from lrw malerml prowded m a Ih,ough f The test melhom or lest plans
$hould be specified fin the contracl and Ihe equlpmenl specification and described. an delatl, ,n the reliability test plan document. a. The rel!abil!ty grotih monitoring method should be selected under condtuom where parameters of the ume-to-failure d,stributmn are lxpected 10 be changing with t#me. b. The ESSmethods are 10 ba wed to eliminate larly defecu (infant morcalily). The Standard Environmental Streis Screen i$ a form of ESSused when ic muff be verifkd that equipn%en!, which has passed previous reliability testing, has not been degraded by the production process c. The MTBf as$urance I-I can be used to provide assurance that a minimum specifwd MTBF has been achieved and that early defect failure$ have been llaminated. d. A flaed-duration lest plan must ba aelecced when it i$ necc.fmry to obtain an estimate of the true MTBF demonstrated by the lest, as well a%an accept-reject decision, or when total test lime must be known in advance. e. A sequential lest plan maybe aelectad when it is desired toaccepl or reject predetermined MTBF values (eO. @!) with predetermined risks of error (ca~). and when uncertainty in total test ome is relatively unimportant. Tht$ lest will fave test lime, as compared 10 fJxed-du ration le$t plan$ having iimilar risks and doscr, m,naticm ratio%, when the true MTBF is much greater than (@O) O, much less Ihe” (81] f. The all.eqwpment test plan maybe selected when all units of the production run must undergo a reliability lot acceptance test. These Stau$tical lest plans are 10 be used to determine conlracluat compliance with pre. e$labtished accept-
4.2.2 Tesl me:hod and te$l plan paramelerwlecoon. Themoslimponant pa~ametersmbe considered when select, ng test methods and test plain are discussed in 4.2.2.1 through 4.22. 4.22 1 Ectu,oment performance. The parameter! to be measured during reliability le%:i and the applicable acceptance I!mtl% should be delermmed by the performance requirements of the equipment destgn control specif,cat,on ana should be included in the test procedures. A.2 2.2 Equipment auamity lhe number of equipmenl 10 be \ested, not necessarily $,mullaneousby, shall be aelerm$ned as described herein or as specified in the carnracl. a Sample s,ze [reliab,l,ty growth andqualificat,on). The$ample vzerequired for the growlh and qua! tf,cat,on pha!e lest plain should be as spec!f,ed on the contractor as agreed to by Ihe conwactor and the procur, ng acu., ty b. Sample $ize (production reliability acceptance). Unles$ olherw45e specif,ed by the procuring acttwty, the mmimum o{ samples ta be tested per [ott% three p,eces al eqwpmenl. The recommendeci Jample s;ze #s 10 pewent of the equipment per 101. up 10a maximum of 20pieces of eqwpment per lot c. All-equipment praductian reliability acceptance test. Under this Iesl plan. all producuon equopment is subjecled to the rel!abtlity acceptance le5t. All-equipment acceptance Iesung (100 percent sample) should only be specif ted under exceptional circumstances. as determined by the requ, remenls af ~fety or mosston success d Sample $ize (ESS) Unless otherwise $pecif,ed by the procuring aCli.itY. ielected development equipment and all equ,pment in production Iats should be wb]ected to ESS In h!gh volume production runs, the sample sflze from each lot shauld be selected by the procuring activity. In,taal 101$ should be 5creened al lhe 100 percent level. Sample size on later lot> may be reduced by the procurtng acttw:y baaed on the screening results. e $ampiesize (opltonal nonstatistical te$l). The sample stze far1h#5 Iesl isal! equlpmenl tin a lal whase ver,l, ed reliabil,ly charac(er!$ticj may be degraded by m.inufaclur, ng and qu.31f1ydefeC!>
1’””
