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AOTHOR Wha)en, Gary V.; Askr'ei., 1il1iajn B. ., .
TTLE Inpact Qf Dsign Trade Stirdi.es\oS-yteInB,umnsbure5s
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INSTTUTION Air Poce Human Resources Lab.,'Wright-pattrson F43,Ohio A'v.aced S'stems Div.; Mconne1l Douqras t / (
AstonauticsEat, St. Louis; .REPORT NO AFHRL-TR748 7
PUB DATE Dec 734 .
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'.his study focused on two.obJectives. The firt,objctive was to ;dent1Lyand. classify the, char er.stics of JT (.onceptua1 desigt.r-s-tudr t!t lav htigh pcertial impact'n1hxman resourc guiremeits4 of ir Fore 7wea.ion stems. heuse..'was a case history reyiew and ana1yztf 129dep'igrde st4di.es,. The- analysis indig M-h.e av.3pJz ,ystn4 I .&êmonratedthe greatest poteutiaiac 'n aii ?6uwe, zf. -crè1so that trade u-di s. eikst I
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IMPACT OF DESIGNTRADE STUDIESON SYSTEM HUMAN RESOURCES
By
Gary V. Whalen ,
McDonnell Douglas CorporationSt. Louis, Missouri 63166
William B. Askren
ADVANCED SYSTEMS DIVISIONWright - Patterson Air Force Base, Ohio 45433
December 1(40
Final Report-for Period May 197 July19741/
.
Approved for public release; distribution unlimifed:
LABOR TORY
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SYSTOWOOMMANDfOkCE(4i!Xj3i1TEXAS 78235-
FORCE-BROOKS MR
"..;.. 1.4. 14 IN"..1. ,
When 'OS Governinm,drawings, specifications, or other data are usedfor any purpose other tliag a definitely related Governmentprpcurement operation, the Government. thereby incurs noresponsibility nor any obligation whatsoever, and the fact that theGovernment may haVe formulated, furnished, or in any way suppliedthe said drawing specifications, Or other data is not to be regarded byimplication or otherwise, as in any manner licensing the bolder' or anyother person or corporation, or conveying any rights or permission tomanufacture, use or sell any patented invention that may in any waybe related thereto.
This final report was submitted by McDonnell Douglas C oration, St.Louis; Missouri 63166, under contract. F33615-73-C-4150, project1424, with Advanced Systems Division, Air Force Human ResourcesLabOratory (FSC), Wright-Pitterson Air Force Base, Ohio 45433. Dr.William I Askren, Advanced Systems Division, was the task scieptist.
This report has been reviewed and cleared for open publication and/orpublic releaSe by the appropriate Office of Information (Op inaccordance.with AFR 190-17 and DoDD 5230.9. There is no objectiontotiniimited distribution of this report to the public at large, or byDDC to the National Technical Information Service (NTIS),
This technical report has been reviewed and is approved.
GORDON A. ECKSIRAND, DirectorAdvanced Systems Division 4
V N
Appros;ed for publication.
HAROLD E. FISCHER, Colonel, USAFCommander
1,
UnclassifiedSECURITY CLASSIFICATION OF THIS PAGE (When DataEntered)
REPORT DOCUMENTATION PAGEREAD INSTRUCTIONS
BEFORE COMPLETING FORMI REPORT NUMBER .
AFHRL-TR-74-89
2. GOVT ACCESSION NO
,
3 RECIPIENT'S CATALOG NUMBER
. TITLE (and Subtitle)
IMPACT OF DESIGN TRADE STUDIESON SYSTEM HUMAN RESOURCES
\
5 TYPE OF REPORT & PERIOD COVERED
FinalMay 1973 July 1974
6 PERFORMING ORG. REPORT NUMBER
.,
7. AUTHOR(t)0
GarS, V. WhalenWilliam B. Askren .
8 CONTRACT OR GRANT NUMBER(s)
F33615.73-'C-4150
9 PERFORMING ORGANIZATION .NAME AND ADDRESSMCDonnell Douglas CorporationMcDonnell Douglas Astronautics CompanyEastLife Sciences DivisionSt. Louis, Missouri 63166
,
10 ' PROGRAM ELEMENT, PROJECT, TASKAREA & WORK UNIT NUMBERS
62703F1124005
i Pr.ti. CONTROLLING OFFICE NAME AND ADDRESS
Hq Air Force Human Resources Laboratory (AFSC)Brooks Air Force Base, Texas 78235
,
12 REPORT DATE 1Deceiver 1974 1
13 NUMBER OF PAGES66
14 MONITORING AGENCY NAME 6 ADDRESS(1( different from Controlling Office)i
Advanced Systems Division .
Air Force Human Resources LaboratoryWright-Patterson Air Force Base, Ohio 45433 ,
15 SECURITY q.ASS. (of this report)
Unclassified
isa. DECLASSIFICATION/DOWNGRADINGSCHEDULE
-16. DISTRIBUTION STATEMENT (of this Report) ..
..
Approved for public release; distribution unlimited.A .
17. DISTRIBUTION STATEMENT (of the abstract entered in Block 20. if different from Report)
c .
1 .
0 C.
.18. SUPPLEMENTARY NOTES
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19 KEY WORDS (Continue on reverse stdrit necessary end Identity by,btock:;number)
. design trade studies aircraft design- .system design ,. avionics systems
.
subjective estimations ,o
conceptual phase .
human resource requirements maintenance personnelhuman resource data (HRD)
20; ABSTRACT (Continue on reverse side if frecessery and identity by block number)
This study was 'undertaken to accomplish two objectives.The first ,q,,hjective was to identify andclassify the characteristics of conceptual design trade studs that have high potential impact on humanresource requirements of Air .Forte,weApon systems. The approach used was a case history review andanalysis of 129 F-15 aircraft design trade studies. Th analysis indicated that the 'avionics systemdemonstrated the greatest potential impact,on human resoMtes. It was also found that trade studies dealingwith design alternatives th-at,encompass widely different technologies have substantial impact on humanresources. The types" of human resources data (URD) most influenced by alternktive design options were
, .
DD ,FJACr73 1473 EDITION OF r NOV 65 a0BSOLETE1
Unclassified
SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered)
ti
s
SUMMARY.y
'Problem.
Human resources (HR) refer to the man-related variables of a system. ,
Such considerations as manpowet quantities, skills, occupational categories,::
and training requirements are included in the term. Although HR account for
a major portion of system costs and effeCtiveness, they are not incjuded
early in major system design decissions: This study sought to define the
categories and characteristics of trade studies that,havepotentiarmpacton huTan resources. If HR information is to be wed in early design deci-sions, accurate data must be made available to the-design engineer. One
source of such data is the subjective estimates of experienced`maintenance
technicians. The accuracy of subjective estimates of the impact of design-alternatives on human resources was investigated using conceptual phasedesign packages as stimulus materials..
Approach and Results
A case history approach for identifying trade studies with HR implica-
tions was qmployed. One hundred twenty-nine F-15 aircraft design trade -
studies were analyzed and fitted into five system categories. The HR .
influence of trade studies assigned to each category was evaluated. The
"Avionics System" was found to have.the greatest effect on -IR; the "BasicAircraft System" was found to have the least influence. Further analysis
revealed that maintenance task times and personnel costs were the components
of HR judged to be most influenced by conceptual design decision options.
HR items of maintenance loCation (flight line or shop), methods of instruct-
ing technicians and career fields wereleast effected. A cluster analysis
of trade studies showed that a wide technological disparity between design
alternatives was associated with high impact on HR.
I
The accuracy of subjective estimates of HR was eval,Uated using four
groups of expetlenced Air Force technicians and conceptual design engineer..
ing packages of,avionicsabtopilot andfire control systems: 'Checking their
Subjective HR estimates with criteria data obtained from field supervisors
,
resulted im,accurate predictions of crzew- size, sti1,1 level, career field and
task completi n times for flight line maintenance actions.
Concl sions
Trade studies with potential HR impact can be tdentified. Avionics, as
an ircra t subsystem, was foundto offer the most fruitfucarea for intro-
du -mg the FIR considerations. ,Maintenance,task time and personnel cost dif-
f ences emerged as HRjtems most sensitive to'impact by design alternatives.
f
'Experienced Air Fotce technicians were found to be able to respond to
imited descriptions of avionicss with accurate estimates of mainte:
dnce task completion times, skill levels, career fields and crew sizes."'
The results'terve asa preliminary indication that technicians can and will.
make.reasonably accurate estimatef of important HR items using conceptual'
design phase information.
s
SUMMARY.y
'Problem.
Human resources (HR) refer to the man-related variables of a system. ,
Such considerations as manpowet quantities, skills, occupational categories,::
and training requirements are included in the term. Although HR account for
a major portion of system costs and effeCtiveness, they are not incjuded
early in major system design decissions: This study sought to define the
categories and characteristics of trade studies that,havepotentiarmpacton huTan resources. If HR information is to be wed in early design deci-sions, accurate data must be made available to the-design engineer. One
source of such data is the subjective estimates of experienced`maintenance
technicians. The accuracy of subjective estimates of the impact of design-alternatives on human resources was investigated using conceptual phasedesign packages as stimulus materials..
Approach and Results
A case history approach for identifying trade studies with HR implica-
tions was qmployed. One hundred twenty-nine F-15 aircraft design trade -
studies were analyzed and fitted into five system categories. The HR .
influence of trade studies assigned to each category was evaluated. The
"Avionics System" was found to have.the greatest effect on -IR; the "BasicAircraft System" was found to have the least influence. Further analysis
revealed that maintenance task times and personnel costs were the components
of HR judged to be most influenced by conceptual design decision options.
HR items of maintenance loCation (flight line or shop), methods of instruct-
ing technicians and career fields wereleast effected. A cluster analysis
of trade studies showed that a wide technological disparity between design
alternatives was associated with high impact on HR.
I
The accuracy of subjective estimates of HR was eval,Uated using four
groups of expetlenced Air Force technicians and conceptual design engineer..
ing packages of,avionicsabtopilot andfire control systems: 'Checking their
Subjective HR estimates with criteria data obtained from field supervisors
,
resulted im,accurate predictions of crzew- size, sti1,1 level, career field and
task completi n times for flight line maintenance actions.
Concl sions
Trade studies with potential HR impact can be tdentified. Avionics, as
an ircra t subsystem, was foundto offer the most fruitfucarea for intro-
du -mg the FIR considerations. ,Maintenance,task time and personnel cost dif-
f ences emerged as HRjtems most sensitive to'impact by design alternatives.
f
'Experienced Air Fotce technicians were found to be able to respond to
imited descriptions of avionicss with accurate estimates of mainte:
dnce task completion times, skill levels, career fields and crew sizes."'
The results'terve asa preliminary indication that technicians can and will.
make.reasonably accurate estimatef of important HR items using conceptual'
design phase information.
PREFACE
This study ,was initiated by the Advanced Systems Division, Air ForcdH man Resources Laboratory, Wright-Patterson Air Force Base, Ohio, udderPr ject 1124, Human Resources in Aerospace System Development and Operations,Ma or Duncan L. Dieterly; Project Scientist, and Task 112401, PArsonnel,'Training and Manning Factor& in the Conception and Development of AerospaceSystems, William B. 7\skren, Task Scientist.
.
Appreciatibn is extended to Mr. Howard K. Geritzen of the DeputS, forDevelopment Planning, Aeronautical Systems Division, ;for his support in theuse of engineering data for-the Advanced Tactical FighterAircraft. ,Appre-ciation 4s also' extended, to McDonnell Douglas Corporation personnel whosupported the research effort, especially Herb A. Chase.forgassistanceregarding manpower estimation, William J. Edens, Jr: fior statistical consul-tation, and Edward R: Jones for advice and direction in conducting the study.The authors also gratefully acknowledge, the cooperation and considerableassistance movided.by operational Air Force ip,tallations.. Tactical AirCommand pers6nnel from the 27th Tactical Fight8r Wing, Cannon Air Force Base,NdW Mexico; and the 4th Tactical FighterAinv SeMour-Johnson Air PorceBase, Noi-th Carolinaprovided,informatjpn on flight line maintenance require-ments. Air Training Command persognel,frbm Chanute Air Force Base, Illinois,.and L6wry Air Force BoSe, Colorado, provided the subjective estimations of-flight line_ requirements for aviDnics sys'tems. Authorized manpower 'surmarieswere supplfe0,by,Hqadquarters Tactical Air Command, Langley Air Force Base,.Virginia. .t. ,
Th'e conteptul design engineering pa[kages . were prepared under thedirection of Wiald R. Kozlowski by McDonnell Aircraft Company, St. Louis,Missouri :---/Thp conceptual phase data for the F-111D aircraft was supplied byGeneral Dynaleics Corporation', ,Fort Worth; Texas.4 This study was conductedduring the period May,1973 through July 1974. . Hi.
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TABLE OF CONTENTS
Title
INTRODUCTION
,CHARACTERISTICS OF DESIGN TRADE STUDIES WHICH
IMPACT SYSTEM HUMAN RESOURCE REQUIREMENTS . . . .
-
Appnach
Procedures and Results
Categories of design trade,studieS, Trade studies which influence hUman resources
Relationship between system areas and tradestudy influence on HRD
Impact of trade studies on individual human. ,
resource data itemsMister analysis' of trade studiesAnalysis and evaluation of trade studies in .
high and low clusters ,
A Comparison of human resources for twooperItional systems
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10
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18
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Summary and.Discussion
ACCURACY OF SUBJECTIVE'ESTIMATES OF .THE4IMPACT OF'DESIGN ALTERNATIVES, ON SELECTED HUMANRESOURCE DATA ITEMS
26
27
Appraach ,27
ProceAdures 4 28
Engineering data packages used as stimulus ..
"material.for subjective estimates. 28 4,
Description of personnel making human resource
data predictions 28
Type of human-resource data predicted 28
Criteria for evaluating the accuracy of thehuman resource data predictions . , . . ,,,,, ......... 28
" Results 32
Accuracy of predicted maintenance task'times 32
Accuracy of predidted career'field, skilllevel, and crew size '. 34
Critiques of engineering data packages 35
Development of future data packages for use
as stimulus materials 38
Qualifications of personnel making humanresource data predictions 38
Summary and Discussion 38
SUMMARY AND CONCLUSIONS 41
TABLE OF CONTENTS
(continued)
:itl-e Pagg i
REFERENCES . . 42
APPENDIX A - 43,..
APPENDIX B 46
APPENDIX C 50
LIST OF PAGES
1 through 64
4
UST OF ICSTRATIONS
1Ei.gLlre . Titre
1 FREQUENCY GROUPING OF F-15 CONCEPTUAL PHASE TRADESTUDIES BY POTENTIAL INFLUENCE ON HUMAN RESOURCES
,
REQUIREMENTS 14
Page
2 FORM -USED BY TECHNICIANS TO RECORD PREDICTIONSOF HUMAN RESOURCES DATA 31
3 COMP ISON OF PREDICTS AND ACTUAL TIMES TOPERF M FLIGHT-LINE MAI ENANC TASKS ON AUTOPILOTSYST MS
COMPARISON OF PREDICTED AND ACTUAL TIMES TO PE FORMFLIGHT-LINE MAINTENANCE TASKS ON,FIRE CONTROLSUBSYSTEMS
5' COMPONENT LOCATION
No.
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33,
33
39
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LIST OF 'TABLES
Table
1 DESIGN TRADE STUDIES INVOLVING THE BASIC AIRCRAFT,AVIONICS, PROPULSION, UTILITIES AND ALL
,SYSTEMS, 11.
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Page
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2 CHARACTERISTICS OF TRADE STUDY REVIEWERS (n = 5) 12
3 FREQUENCY' DISTRIBUTIONS OF HRD CATEGORIES ACROSSTRADE STUDY SYSTEM st:1/4REAS
OBSERVED AND EXPECTED VALUES OF THE CHI 'SQUARESUMMARY MATRIX
5 S-IX POINT RATING SCALE USED TO EVALUATE THE POTENCYOF TRADE 'OFF STUDIES ACROSS HRD ITEMS
6 CHARACTERISTICS OF tiRD IMPACT EVALUATORS (n = 6) ....7. IMPACT OF TRADE STUDIES ON HRD ITEMS
,8 , 'BINARY PROFILES OF HRD ITEMS FOR TRADE OFF- STUDIESFOUND TO HAVE IMPACT ON PERSONNEL REQUIREMENTS
9.- BINARY PROFILES AND ,THE FREQUENCY OF. Tk--.IR OCCURRENCE
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16
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.... . . 20
21
FOR TRADE STUDIES WITH IMPACT OK HUMAN, RESOURCES ....
1'O TITLES OF DESIGN TRADESTUDIES IN HIGH AND 'LOW HUMAN,-- RESOURCES IM CT CLUSTERS
11 CHARACTERISTICS OF NOLOGY EVALUAtORS:(n = 5) -.1-
12 SUMMARY OF t-TEST STATISTIC
DIFFERENCES BETWEEN DESIGN ALTSTUDIES WITCHIGH IMPACT AND LOW I
OR COMPARING ,TECHNOLOGICALTIVES FOR TRADE.
CT
13 QUANTITIES OF MAINTENANCE MANPO
. 22
23
14 DIFFERENCES N SKILL LEV-EL ALLOCATIOt OF AVIO CSTECHNICIANS ASSIGNED TO E-111 AND F-4 AIRCRAFT
15 CHARACTERISTICS OF TECHNICIANS 4k STIMATEO THE IMPACOF CONCEPTUAL AUTOPILOT DESIGNS :, HUMAN RESOURCESDATA
.16 . CHARACTERISTICS OF TECH GIA S WHO ESTIMATED THEIMPACT OF CONCEPTUAL FIR Ci TROL DESIGNS ON HUMANRESOURCES DATA
6.41
25'
29
30
Tabl e
. LIST OF .TABLES(Continued)
4
a n Page
17 PERCENT DEVIATION OF MEAN PREDICTED TIMES FROM: ACTUAL-
TIMES. TO PERFORM FLIGHT LINE MAINTENANCE , .... .. . .
18 COMPARISON OF PREDICTED AND ACTUAL RIGHT LINLCREWSIZES AND SKILL LEVELS FOR SELECTED F-4E, and F-11-1D
MAIWENANCE, TASKS
419 SUMMARY OF CRITIQUES OF ENGINEER41G DATA PACKAGES
' FOR AUTOPILOT SYSTEMS
20 S121MARY 'OF ENGINEERING DATA PACKAGE CRITIQU,ES' FOR;
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INTRODUCTION
,HuMan resourcesare a major determinant of an Air Force weapon system'soperational effectiveness and life-cycle costs. Askren (1969) has estimatedthat Yb Arcent of system performance-and cost may be accounted for by humanresource considerations.' In spite of the importance of man - .related factors,data on human resources usually are not introduced into the system develop-ment proCess until after film design decisions have been reached. The designengineer tends toga ens simplicity, compatibility, and ayailabilityat the expense of increased manpower, the need for neWipecialty areas, vari-ation in-skill levels and dfMinished feelings of job satisfaction. Whenhuman resources are examined, their implications are often identified toolate to have major impacts on system design.
Recent research has demonstrated thatiluman resou(/data (HRD) canbeneficially influence design if personnel manning, skill constraints, andthe supporting, task information are givin to the design engineer at thebeginning of his assignment (Meister, Sullivan, and Askren, 1968; Meister,Sullivan, Finley, and Askren, 19696). Design engineers consistently trans-late personnel skill constraints into certain system characteristics such astest points, troubleshooting. procedures, and types of test equipment (Meister,Sullivan, Finley and pskren, 1969b). Askren and Korkan (1971) found that -7system design choices can be predeterMined and des54bed, in decision-treeschematic form, providing a means for relating HRD/to Ypecific design options.Lintz, Askren, and Lott (1971) demonstrated that design engineers can and willinclude HRD in engineering design trade studies, and that ,the trade off,prbcessis very much dependent on the personal style a'nd judgmentsof the engineer..All of the research results point to one conclus*:- HRD.can be introducedinto the system -design process, and can be expected to enhance the designproduct.
Equipment selections and designs are made continuously throughout*thedevelopment of every major system., HoWever, the-most significant decisionsin terms of hardware and software are typically arrived at during the initialand early phases of development, often referred to as conceptual and defini-tion phases. Once. a'system progresses toward full scale production, majordesign changes must be held to a minimum because.such changes would jeOpar-dize prOgrammed Completion schedules as well as,a.,dd to the procurement costsof the system.
ConseqUently, two questions were addreMti bx this study.
(1) Are there categories .o types of trade studies performed duringthe early phases of design which have particularly significantimpact on subsequent personnel requirements anIshould, therefore,includhuman resources data as a design parameter?, If thesetrade'studies can be categorized, then attention may be irectedat obtaining the necessary quantitative data that enginetrs need.to make trade off decisions.
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( 2) What i g the accuraoysvjea-41te'':.e-s-tViates 157f ,t,faejuipa.o-t: PY:_ife-s-i-gfc- ---;:;-alternatives s on -tiunia,reres,oucce---__regirtreble,nts,1-81/4---A fharbill resource, ..effects data are not 0-pg.1441:,1-y.:..aratT..aliaelt du-rittne- -Conceptual ; designphase, an accurate. ,slitu,r,e,v.-jpred,i ct.in ,Miniati.ir.*ilitie'- impl icafiliris.. . .....
. must be developed.`.. ,ikficitetiti ,017.-so.ki.r4-7'.. '-alifeipliiiKce::f.tiit4 .:t....t......::L.-'-',::*-i""is the b p i n i on _0j.-....igedifbcid.;.teGttn-i.Otins ;-.I-F-- :Sci.ini-tY 1:1.f. -1*Anj:- , -,.::fibtechnicians as, i'qd-re.,#)-17:fltifet` bl ,Of, 6zitj.czeiTt01' ;tles.:igri.s' ott 1 -'4.... _.:.-.
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This s report i g divided. inio tWO 5.ecti ons .- v;.,--.111-k-'.fil. list , secti.otr*Ats, wi th"..
question 1 , ,and involves Tli.cdetafl-ed, -analygis -of earTy.t!!ke7_:.gt4-die41,.91",*;a7 ---,AyrForce,Ii9pter ai-rc raft ,- KEhe Fr 15. sy4e7i . : -Th.t.-sosorid___- -----,
secti on--aidigesses qupti on, 2 , anal concerns.red.ttig,,a;ccaCy of -usrr --!-----
maintenance echpiOiang, to foifecast human rge" requi rements,-or,-th.k::-.-2---'electronic suSsYs'teins or twccr fighter- .ai-rcra.f :.'.; :--' '
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1
I.1-;--afrbraft des i gri formulati on ah ef initillt Was , mos t acti ve dunpg -the 1967 to' .'
_;.f.-,,:-7----7;--.-1969'7. vibe frabie. It was du-ring' thl--seiMent ,o f -ty-item deveroliment that,. num- , --' '`, "- verolis -MI,j16-3-1-degligh2.--ttta0- studieS_.Weteilerformed and consequently Ova -liable ,-......: ., .
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sourcei 1.The task statement was found,,to '16e Itnei best source far ;descriptions of the .-: -,i.-
u overall trade study reqUiremO:t§, ainsl: the a,3 ernative !designs Considered ,-formeeting system requirements
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a
Cateioties 1)-IF VeSIgn trade studies. One'hundred twehty:-nine trade?
studies, wereillittated during the early, conCeOUWdefinition phases o-tthe
.F-15 (Appendi)X B).- The' task statement .foreach'w4,reVie0ed by the senior
author and An F-15- personnel. subsystem OeeialiAt; an*ItS. relevance- tcf-cne
or more of the aircraftls systems was determined; : In- thls'i40, a iistri-
7,,.____ ution of trade, studies was' asseObled under,th.iOloWing headings":,.basjc.-,._ _
a i rtriftlavioni cs.,., ripiroptat MO ti 1 i ties , and, 01 a i rcraft_systemS": .;
-/-', ,
_ , .
, : -,- - _, -... Tab 1 e- 1 cwlta,,i ns 04', c0A-ibu t i on of thEz- trac* studies across system '---
. ,-., . \ ___
_ Laren.- Ihs,classAficof-poilf%,all systems" contairi. four trade,studies that _
)wereAf sycti a: b rOacC sCoO,p01, they influenced the ',des tign' charitteriscs
of the entire 'aircraft,: ../,,
7 '. X; .' -. .:.TABLE:_l . ..\ ,
: 1 j. ,.:, -;. _ : .
,Q
r.
/ TRADE1STUdItS INVOLVING THE BASIC AIRCRAFT,
:AVIONICS, AlROPULSION,JITILITIE§ AND ALL SYSTEMS
,TRADE -'--4/1/PrgS
BAS-IC,
AIRCRAFT
1
AVIONICS PROPULSION UTILITIES
AllSYSTEOS
..
TOTAL
........'
Total%..
-"gii1.-t,entage-r-
,--...43
k:-...........
.. 34
26.4
25
19.4 .
23
17.8
4
,
,3.1,4.
129
, 100
"*, '..\
. ,... ,\
is ,*-ihe: majority .o-f,trade studies, 43, dealt with design issues involving- _ ,
,-..thebasic,aircrafty.Viith the design qUestions primarily focused on airframe
-)AndAlight.: control, u'llace, configurations. A considerable ,number of trade
--.. 'silidiil; 134, ciere.7dfirgAted -at ;t1ie avionics systems ; i .e.. , the electronic
4PV.i.t0-.psed for *plation aricrontrol of the aircraft and associated weal
plvis:;/All additional,,,fi:Aditng iiaS;,,that only ,2 of the 129 trade studie, con-
tacned..lcuman fact6i-i adliiation-paj.aMeters except for flight crew considera-,
tioAv.,,J, ,..i, , N , .
d I ...' \ '.
' ? t ' #.% N
.-TrAde studies 1 .ch'ihtlilence hlidiall resources. Next, the trade studies
werelY41.-uated for thei level,,-9f inflmew the engineer's choice of a design
alternatIe would have! theYlumaniresources that would eventually be
needed td4flaintain the system' the tys_tentin this study refers to F=15 -
aircraftLttrrdware and _s,dftwarh. dOMponedsk HUman resources may be viewed
as an entity \comprising tile. liscill0 reql.al'ements associated with a system.
Human resoUrtes in- this ease wee 'specifiO4s personnel attributes and
'maintenance 4aracteristicS Tens itebr5\04pre identified as follows:\
,.. , !..,. \;,S\
(a) nuilib0.1of technicia s ne§lekto mait-tO\ n a system\ ;':.
(b) occupatOnal special of4tig techni*fis ,
-,..:,\.'0.i .
,. :;,A v. 'i,V
-).r--''
fl
(c) ski11 level within an occ.upational specialty
( d ) time that would be required to perform typical maintenance tasks
(e) probability of errors ip task performance
(f) location of maintenanceactivities (flight-line'or shop)
_..kgr-tralning time needed to teach technicians to perform required-.,:2mdintenance. _
T- - -----
tr4 1ping content ...
methods of instruction
.6v, overall personnel' cost.
Jhe task statement for each design trade study' was submitted for reviewfive McDonnell ,Dou§l'aS.Corporation (MDC) engineering psychologists famil-, ,'fariith human resource requirements. The psychologists (Table 2) Were-
;indepe4dently asked to -make a judgment as to the .potential influence the-.:;:---velection-of trade study al ternatives.contatned in each of the 129 taskstateMepts,ewould, have on the above 10 human resource items. If the designalternatives- appeared too be choices that would influence significantly -thecharacteristics anNorprocedures of the personnel that would beneeded forsystem maintenance;' -tke trade study was categorized as having "Human ResourceData (HRD). Influence---0n _the other hand, if the design alternatives of a.trade study offered little or no potential impact on field personnel charac-teristics, it was pieced' In the "No HRD Influence" group. The dichotomize-ti-on -was based solely upon an individual reviewer's subjective appraisal of.the trade study's apparent effect on field maintenance personnel requirements,
-,TABLE 2
CHARACTERISTICS OF TRADE STUDYREVIEWERS (n = 5)
.
-
E', .YEARS,/,
e
-,HUMAN;FACTORS
'EXPERIENCE, YEARS GRADE' LEVEL*'R.
RA4GE-J., ..U1EAlli.:,q . RAISE
, vMEAN RANGE MEAN
3.1;.6 t
-:!,41;a?
y:..:
/6,1 10.2 4-13 9.3
*MDC01,PYclieo st Grade! evel : t= Assooiate Psychologist,7 =iP4thol* gist, 10 =/Senio sychologist, ell = Group Psychologist,13 Sevitol'e4ro4p,004'hologist '
:!...%, // / /ft"'..,'.,7/
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0
r //711170
i',./11,; :57 .t /'I .1
4/14/ .: $1.1/ '
r i. '
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it 9'
When four of the five reviewers were found to hakie independently con-curred with the amount of HRD in'flUence for a given trade study, it wasassigned to the agreed Upon category; i.e "HRD Influence" or "No HRDInfluence." ,I$-. agreement was tiot.reached with regard to the trade
study's teal effect-on HRD;_it'Was classified into the "Influence on
HRD Not Clear" category. Figure 1 summarizes the results of the evaluationof the impatt of the 129 trade studies on human resource factors in general!,
and shows that 39 trade studies were judged to influence HRD and°36 trade'studies would not, effect HRD. ,For 54 trade studies, it was unclear whether
or not there would be any effect.
Relationship between system areas end trade study influence on HRD. The
relationship between the assigned HRD category and the five aircraft systemareas (basic aircraft; propulsion; utilities; avionics; and, all systems) was
examined. Table 3 summarizes the frequency distributions of trade studies byHRD category and aircraft syStem.
TABLE 3-----
FREQUENCY DISTRIBUTIONS OF HRD'CATEGORIESACROSS TRADE STUDY SYSTEM AREAS t
SYSTEM INVOLVED WITHTRADE STUDY '-'
HRD CATEGORY
TOTALINFLUENCE NO INFLUENCE NOT CLEAR
Basit Aircraft 6 19 '18 43,
Avionics' 16 6 12 34
Propulsion 8 4 13 25
Utilities. 6 6 1123
All Aircraft Systems 3 1 0 4
.,',
'` TOTAL '. 39 36 tt--
'
4.'..v 129
A chi square analysis was performed on this frequency disteibutiop. For
--.:.....purposes of the chi square analysis, the,fifth system category of all aircraft
...,:..:-,systems was omitted because of the low cell frequencies. Table 4 presents the
44).served (0) and expected (E) values. The,chi square statistic (x2 = 15.08)
-''-;was` significant 'beyond the .05 level. L'-
--Tile greatest differences between observed and expected frequency values t.
occurred in the basic aircraft and avionics rows. Fewer trade studies were
judged to have HRD influence in the basic aircraft area than would be, expected.In the avionics area, a greater nuMber of trade studies were found to have HRD
13
.;.
..
;'
ifFIGURE I FREQUENCY GROUPING OF F-15 CONCEPTUAL PHASE.TRADE STUDIES
BY POTENTIAL INFLUENCE OF HUMAN RESOURCES REQUIREMENTS
TRADE
STUDIES WHICH,
INFLUENCE HRD
= 39)
z
129
TRADE STUDIES
V
EVALUATION OF
?OTENTIAL INFLUENCEON HUMAN RESOURCES
REQUIREMENTS
INFLOEtiCE ON HRD-
NOT CLEAR
(LESSTHAN 80%-
AGREEMENT)tn 54)
Ia SELECTED FROM
DEFINITION PHASES
F-15 CONCEPTUA Any
EVALUATED BY5 ENGINEERING
PSYCHOLOGISTS
TRADE
STUDIES WHICH DO NOT
INFLUENCE HP1)1
(n =6)
/
TABLE 4
OBSERVED AND EXPECTED VALUES OF THE CHI. SQUARE* SUMMARY MATRIX.
.
SYSTEM AREA
HRD CATg RY
INFLUENCE NO INF UENCE NOT CLEAR
.0 E'
.0 E 0 E
BASIC AIRCRAFT "6 12.4 "--19:::: ,:. i: 1.0 :::: 18 A 18.6
AVIONICS
-....
: :::...I 9.ii.:-:.
9.5 12 vg,
PROPULSION : = 8 7.2 4 7.0 . 13 10.8
UTILITIES 6 6.6 6 1 6:4 11 9.1
*X = 15.08; df = 6; a < .0 5
0 = OBSERVED FREQUENCY; E EXPECTED FREQUENCY .
\-1
in, uence than would be expected. These results indicate that for the F-15
sys em, trade studies in the avionics area.have the greatest potential effect
on uman resource requirements.
Impact of trade studies on individual, human resource data items. The
research was also aimed at identifying the individual items of -Ewan resourcedata which are effected by trade.sAdy,decisions. Toward this end, particular
attention was directed at the 39 trade studies that were identified as havingan influence on HRD. The task statements'for these 39 trade studies wereevaluated for impactOn individual hutan resource items by using a six point
rating scale (Table= 5).
Ratings of impact were obtained from six MDC engineering psychologists.Table 6 contains biographical information on the evaluating psychologists. Four
of the six psychologists had also participated in the initial trade studyreview described in the previous section. An average and a measure of vari-
ance was computed for each of the'ten HRD items across:5i 39 trade studies.These results are presented in Table 7., .
Based upon.
th average ratings, "Time to Complete Maintenance" and:Overall Personnel Costs" were the items most heavily influenced by the" 4 `
design, trade studies. The items "Maintenance Location," "Methods of Instruc-.tion,?' and "Air Force Specialty" were the'least influenced. Based upon the
standard deviation values, there is best agreement on ratings for "MaintenanceLocatfon," and poorest agreement on "Number of Technicians.'.
TABLE 5; I.
SIX POINT RATING SCALE USED TO EVALUATE THEPOTENCY OF TRADE OFF ST'UDIE'S ACROSS HRD ITEMS #."
'Indicate your appraisal of the nature of the trade study's impact on operational '
unit maintenance personnel requirements.
The trade study involves alternatives thatwould vary the number of maintenance tech-nicians assigned to the operational unit.
Personnel occupational specialtigl or careerfields vary with the design alternatives,.
The trade study decision involves alterna-tives that would require different skill_levels or degrees of technical competency.
The amount of.tirpe needed to perforM typicalmaintenance tasks (Such.as-inspections,
checkout, or troubleshooting). would be .
different for each alternativajesign.
Thg probability or likelihood of etechniciancoMmitting maintenance error appearS as a'
' factor in the alternative degign choices.
The maintenance location field, sh6p,or depot) differs with ilternative designs.
,fie design alternatives differ from each other( ) ( ) (
with regard to technical trainino Iimg formaintenance personnel, i.e., the duration ofcourses, OJT, or field training would be,.affected by the final design selection.
ad 11) >1
4..)C Qf 0) .0 CY)C;) RS rn
In r- Eino
( ) ) ( )
( ) ( ) ( )
>1
rn4.1 ' C aJ
.E0 11JS.. S-e- Qf 0) 17)N< < N<
O. ( ) ( )
The training content or course subject matter( ) ( ) ( ) ( ) ( ) ( )
Would'be quite different for each alternative.
The methods of instructing technicians to( ) ( ) ( ) ( ) ( ) ( )
perform maintenance tasks appear to differacross the alternative design options.
The design decision involves options that) ( ) ( ) ( ) ( ) )
influence overall 'personnel costs due totraining considerations, technical profi-ciency, number of technicians and/or theease of performing maintenance.
16
9
TABLE 6
-- .CHARACTERISTICS OF HRD IMPACT EVALUATORS
0
= 6)
cAGE yEARS0 .
HUMAN FACTORSEXPERIENCE, YEARS
.
GRADE LEVEL*
RANGE , MEAN° 1 RANGEt
AEAN RANGE MEAN0 0
31-62 - .43.6 ; 7-32 14.8. 4-13 10.0
*MDC PsythoTqgist Grade Levels: 4 = Associate Psychologist,7 = PsycholOgist, 10 = Senior Psychologist'.-11 = Group Psychol-
., ogist,.13 = Senior Group Psychologist
TABLE 7
IMPACT Of TRADE STUDIES QN HRD ITEMS**
,-HRD ITEM.
MEAN RATING** STANDARD DEVIATION.
lime to ComPleteMaintenande 4.59 .86
.
Overall Personnel Costs ,.' 4.46.
.77
Cbntent of Training Courses '1.98 ..78
Number of Technicians 3.98. .95
Training Time RequirementsIP
3.94 . .74
Maintenance,'Erf63rs .
.3.94 -
M.80
Skill Level 3.47 .82
AFAecialty,10. 3.12 .88
i-
Method of Instruction 3.06 ,75
Maintenance Location.
,2.75''' .67
*Based on 39 trade,studies,judged as having an'effect on humanresource
'**Rating form used a six point scale,:
6 = Stron,ply%A.Vee that HRD item influenced by trade Study:1 =, Strongly Disagree that HRD item influenced by trade study.
,
2t,
O
,
of
-179.1\
22
os
Cluster analysis of trade studies. A'cluster analytis was_performed onthe 39 trade-studies with potential HRD influence. The intent of this analy-sis was to identify those trade studies that received similar ratings acrossthe ten HRD items. The assumption was made that trade studies with identicalor very similar profiles might have some common traits or characteristics.
The average rating given each of the te. HRD, elements for each tradestudy was compared with the overall mean obtained for the respective HRD item'.across all 39 trade studies. If the HRD item mean for a trade study wasgreater than the overall mean for the HRD item, It was ossigned a value of 1.If the HRD item mean has less than the overall mean for that item, it wasassigned a value of 0. In this way, the impact of each trade study on the.ten HRD items was reduced to a series of, ten binary notations. A ten itemprofile was` computed for all 39 trade studies (Table 8).
r*.
The binary profiles were then examined for similar4tY. When trade studyprofiles were found to share a comMomOroffle on 8 or mare of the 10 HRDitems, the studies were establishecraS a cluster or group,. 'Trade studieswith 8 or more values of "1" were considered to be "high impact" HRD profiles;8 or more values of "0" were considered to be "low impact" HRD profiles.Table 9 presents the results of the profile examination. Twelvd trade studiesmade up the high impact cluster; eight trade studies made up the low impactcluster. The titles of the trade studies in these two clusters are given inTable 10.
A,
(
Ana:lysis and evaluation of trade studies in high and low clusters. The12 trade studies in the high cluster and the 8 trade studies in the lowimpact cluster were reviewed by the Senior author and one other engineeringpsychologist familiar with personnel requirements and, aircraft hardware.From a content analysis of fhe trade study task statements it was hypothe-Ozed that the high HRD impact trade studies were dealing with alternativedesign choices that involved wide departures from one another in technical
, characteristics. For example, a trade study dealing with the flight controlsystem design received a very high HRD profile rating (10 values of 1). Thedesign evaluation considered alternatives ranging from a baseline manualflight control system to a fly -by -wire system i which the pilot would actuateflight control systems via electrical impulses.1, By contrast, the designalternatives in the low HRD rating cluster dealt with alternatives not nearlyas diverse. For example, the low profile group includes a study of the eval-uation of-navigation equipment. The study involves,a baseline tactical airnavigation (TACAN) system with range and bearing as opposed to a TACAN withbearing only. The degree oirtechnological disparity between the TACAN alter-natives appears to be minim29. Based upon the content review of the high'andlow HRD impact groups, the fq) owing hypothesis was generated: The greaterthe technological disparity be ween trade study design alteenatives, the1greater will be the potential impact of the design decision on human resourcesrequirements.
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4
TABLE 9.
BINARY PROFILES AND-THE FREQUENCY OF THEIR OCCURRENCE FOR TRADE
STUDIES WITH IMPACT ON HUMAN RESOURCES
HIGH
IMPACT
CLUSTER*
1
0
1
1
0 1
0 0
O. 0
0 0
0 0
0 1
0 . 1
0 1
1 0
1 0
1 0
1 0
1 0
1 1
1 1
LOW
IMPACT
CLUSTER**
1.11 1
1 1
1 1
0
1
1
-.0
HRD PROFILENUMBER tiF TRADE
STUDIES WITH PROFILE
1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 2
1 1 )1 1 0 1 1 0 1
1 1 1 0 1 30 1 1 1
.1 1 1 1 1 1 1 0
0 0 0 1 1 ' 1 1 1 1
1 0 1 0 1 0 0 0 1
1 0 1 1 0 , 0 1 1 1: .
1 1 1 1 1 0 0 0 1a* 0
0 0 0 1 0 1 0 0 , 1 A.0 1 1 1:1 0. 0 0 0 1
0 1 1. 1 0 1 1 1 1
1 0 1 0 1 1 0 1
1 0 1 0,1 0 2'1 0 1 0 1 1 0 0 1
1 1 1 0 1 0 1, o 1
1 1 1 1 1 o 1 0 1
0 i 0 1 1 0
0 1 1 0 1-1 0, 1 1
1 0 0 1 1 0 0 0 1.
1 0..1 0 0 1 1 0 1
1 0 1 0 71. 0 0 1
1 1 0 0 0 0 0 0
0 0 0 0 0 0 0 0 7.10 0 0 0 0 0 0 0
0 .0 0 0 0 0 6
*HIGH CLUSTER CONTAINS 8 OR MORE VALUES OF 1
**LOW CLUSTER CONTAINS 8 OR MORE VALUES OF 0
20
4
I
L.
.TABLE 10
Y.7 /TITLES OFDESIGN TRADE STUDIES IN HIGHAND LOW HUMAN RESOURCES.IMPACT'CLUSTERS
e
HIGH .IMPACT CLUSTER ,(n = 12)
Evaluation of Auxiliary Power Units
Evaluation of Flight Control System Design Concept-....-.., , ,
.
Evaluation of Quantitativeaiild Qua3itative AGE Determination
Evaluation of Escape System Ejection Seats vs.' Escape Capsule
Evaluation of Built-in-TeSt Equipment ..
Evaluation of Fire COn'trol System
Evaluation of Flight Control Actuator Configuration
'valuation,of Field Shop Automation control'
Evaluation of Oxygen. System
Evalulltion of Integrated CNI Control and Displays
Evaluation of Identification System. p
4Evaluation of Stability gSContrbl Requirements
LOW IMPACT CLUSTER (n = 8)
Evaluation of Crash Data -Recorder
val4tion of Avionics Interface pd Computational Analysis*- I :
Evaluation of Trailer and Training Equipment (Aircrew).
Evaluation of Navigation Subsystem 1
Evaluation of Elect6-optical Identification Tracking
Evaluation of Infl.ight Engine Restarting Methods
4Evaluation of. Electriaal.Generating System
Evaluation of Aircraft' Mounted Auxiliary Drive-
a4 .
oa_, 21
-c
:a
',In order to check the hypothesis, the trade studies contained in the twoClusters were randomly submitted to systems engineers for a technical evalua-tion of the degree of disparity among design alternatives. Five experiencedsystems engineer's (Table 11) reviewed each trade study. For a given tradestudy, they were first asked to identify the two design choices'that con,tained the greatest differences in technological content. Then the degreeof disparity was quantified by setting one of the two design choices at "and having the engineer express the extent.to which alternative deiign var edin-technology on a 100 point scale. If the disparity was larg4, it wasexpressed by a high number; a small difference in technalogY was reflected bya low number.
TABLE 11
CHARACTERISTICS OF TECHNOLOGY EVALUATORS (n = 5)
AE,' YEARS
.
ENGINEERINGEXPERIENCE, YEARS EDUCATION; YEARS .., -GRA6E'LEVEL*
Range Mean Range Mean Range .Mean.
Range Mean
41-55 47.0 21-27 23.4 - 16-20 18.0
.
13-16 14.4
*Engineering Grade Levels: 13 = Senidr Group Engineer; 15 = Project Engineer;16 = Section Manager
The five estimates of technological difference assigned to the alterna-dyes of each trade study were averaged. The average estimate of technolog-ical differences for the twelve trade studies in the high HRD impact dustywas 38.7. The average estimate of the technological difference for the 8trade studies in low HRD impact cluster was 17.7.. A t-test was performed'totest a null hypothesis regarding the significance of the difference betweenevaluations given the high and low cluster trade studies. The differencebetween clusters was significant at the « < .10 level. Table 12 summarizesthe, statistical results.
O
^s.'
;; ; 4
a.;4
( ,
SUMMARY OF t-TE.ST,STATISTICS FOR-COMPARING TECHNOLOGICAL DIFFiR64; '''., 1 .
BETWEEN-DESIGN VTERNATIVES FOR TRAbE STUDIESWITH HrGH IMPACT AND LOW IMPACT . ,-.1,. 1 ;,',,
Vigh Impacton HRD
,. .:
.- rJ'.7-1.0
. f -
......,,-)-.---- v: :i .
.,..,,-
, .
A 1,-, 1,_
1
\ " ;..1 :ti :.i . ,, 1 1
T. ,%%;,' - t 2i',
A compar\isonof human resources for tWo:::operational tystems. A compari-*
skbf two fi§hter aircraft systems from effbrent time perio4was performed
to\determine which subsystems showed the most change in manpow0 requireMents.
The\tiv system& chosen were the older F-4 and the more,recently developed
F-111. The applzoath used was to compare chaages in the manning assigned to
.the,4mmon,career-tields-used ..tz-$upport bpth aircraft. . Table 13 contains
the 0:stributionlof authorized mangbwer allocations for an F-4 and an F-111.
Aactfcal fighterlwing, as reported by the Air Force Manpdwer and Organtzi- .
tional\Directoraep, Tactical Air Command (as of June 1973):1, The Manpower
.
allocil'ii ons diffet quite.noticeably in the:avionics systems career-field., .
i ; i:
. ,
The.sea finding$ confirm the earTier resPlts that agonAtt-systems have
the greatest imItact on numan resmirce.consiiierattons. ,It is speculated thatA .
--this change is accopnted for by a silbstantth disparity'irlaviontcs equipment :
designs between theAwo aitcraft:( 'It is 'further speculated that the technol- :
pgical differ4Res-betwgen-the 'other subs.Sfsfems we not as great.,
.
Table 14 illustrates the skill level di$tribLitionS of personneleassigned
to the FA tnd 5-111 avionicS. career fields. It is interesting to note that
'although the number of technic*s assigned to F-111;avionics was greater ;
than.that assigned.to the r74, the average skill leveUof F-111 avionics , .
technicians was less. This factor has implications for otlier human resources
data such as training time, availability of personnel by aptitude level, and. .
Low Impact
$ on MRD
conseqyent costs associated with manning needs.
i
'Reference: 22.Jund 1973 letter to Air Force Human Resblirces Laboritory
Advanced Systems Division, Wright-Patterson Air Force Base, Qhio 45433,- :.
from Headquarters Tactical Air Command, Langley Air Force Base,"filirginia.
,?..,,- , ..- ,
23
s
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, .
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2 .,... , e ..' : V . ." 'f .., , I,,. ', t e'i ..' . ..._,-'s ; ' '' ,,-' f ,;:' r i ,: / '' ' ' LC,' t!!
. 4 't. .,t; ',,,,' i '' ::, ' .0 ti ' %'
', ; , , It 14 41100f I; C
..;,. ; . ., ';' , 1 '.. 1 , I C
. . C i .
i ''' : 1 .. , ' ,..14%; '' ..
t
:#-E
. , TABLIE 13?
. ,' ,, , 'QUANI71SD,;AINTEAhN'HC E ii A- NPL! Or.WEV
;i1I
,:I
CAREER FIELD , ,..- ') - 7:-.:-. .7.' 'l : ' \ .. +4 ',,- ,..,. '. ;,,, . F-111 '. CHANGE'.., ..:-..., ...-:.-....:..:....:...::.:-: ::.....:-...;;;.,
AVIONICS SYSTEMS.>.-
AIRCRAFT MAINTENAN,CC ,
MUNITIONS AND,WEA13010 , -, :__ MISSILE ELECTRONIC
.
- IN IELLIGENCE
'4METALWORKING : .- , ::
ADMINISTRATION ; . _. ., , ,'AIRCRAFT ACCESSORY .:. t.:
- ,, .
SUPPLY ; ..,, ... .
MAINTENANCE ANALYSIS ' : :;. :.
INTRICATE EQUIPMENT
EDUCATiON.AN6 TRAINING . -,'.1' '.` .'! ,
MEDICAL !. ...
.
. .. ..\-.
FABRIC' AND RUBBER PROTECTION : . ''COMMAND CONTROL . ,; ,
FIRST iERGEANT-/: 11 I . :. . :
:P. :::, -'.',''' '-:-:-.--..:':::::i::.7.4::\ '.,./ 202" ;
,....:.:-..:-:,,:--- . : ... :-..:-.::../..::::..:.
',,.' . ... 482 '.-
,i',, : 190; , .:: _
26.. .
: 11, -, . '.-
56 -: ,, 78 f
1185 -
,
' P:'
\ '..
'.. st...2'......,.-::
, ......
, li : , :
, , 16 -.'- ';- ,.., ..
,, .,4
s,' .'','- -.. -:. -, ./:
. ,.. '' -':'''; :''- 329
.:......... .. - . .
. . - SR a
___":._-_;.33.1: r-
2: ; -t , ....
.-. '-' 26.,'.
. ,:,.' . 11 ,
91 -LI
197
20:i----. ---.
,
0 ,
-. 11
, 22 ,
-'-.. II,'- ,16 ,
,.
. '. '" ...,...:.:-::127':: -'::.'
.... .- - .---...:-98'.
59
\ 24
17 '\.-;.,,...',7
'7 7 1-....`15'''s1
.. .:. ';'.13. . `
--- ' -- .,-12 '..
;3
2
-e----
0
0
0
0
-... --
' ,
: I . .. .....,: ; ,.-.,.
4 TOTAL,'..,
1,616 1,723 - : ....
-\ 207
. .! ' .... ' 41.. , K ' : .. . ,' I ..
*SUMNiAR Y : I '.BA,SEO UPON AUTil.O.BligOiANNINGTOR-TACTICA1., WINGS OF 72 A *CRAFT, IN 'A COMBATCON6IGU ION.!COMPLETEVrAFF p4IY-BASE SUPPORT FUNCTIONS ARE NOT NCLUDED. ,
..--!,:,.. . ./-: 1:1:,-... . t / .
,,'. ,,: 11 /-;;;l'i ..- .,./ : .. .... .., .';,
247
, .,
'1.
,,.1 ;r
\ ,̀.
.1 0TABLE 14
\ .:,\W, \\
DIFFERENCES IN SKILL LEVELVALLOCATIONS \\\.OF AVIONICS TECHNICIANS '4V,SSIGNED TO \\
F-111 AND F-4 AIRC Fts% .
;:.-?..
SKILL LEVEL F-111 F-4A.,
'.3
sHiJq:..'i,; !
,
.:1 :: :.
?'...'.1.1'..="..'4... ; ''17 ii76;1 ....., .........
.,,e...
1. ,
,
73,
184
65
\ ,, \
6
\A ''43
ss .109
N\\\ -,4
,v.,.....-.,-
...,...,
- TOTAL 329, 2kl
Mean skill valte 4.4 5.1
*AF Skill Levels: 3 = Apprentice
5 = Specialist.
7 = Technician
,9.F.7..Su.perintendent
)4-"'"%.(
s.,
t;
s
),st
Summary and 0iscu6n,\
This part of-th :#0dy uSed a case history approach to first identifyand then analyze trod studies that have significant impact on human resourcerequirements of an aircraft system. The approach was primarily descriptivein nature, and was intended to point out likely areas for including humanresources data as a parMeter in arriving at final design decisions.
.
The 129 trade studieS from the F-15 system were fitted into 5 categor-ies. Approximately 60%*Of the studies were categorized as "basic aircraft"and "avionics"'tradeoffs.. :The remaining 40% of the studies were "propulsion,""utilities" and "all systeMs!! investigations. Thirty nine (30%) of these 129trade studies were jUdged_is definitely having the potential to significantlyinfluence human resource requirements. Thirty six.(28%) were rated asdefinitely having no influehce.on human resources. For the remaining fiftyfour'(42%) it was uncertain:0 to their influence. The group of 39 tradestudies showing the greateSt'effect on human resources was (primarily concernedwith studies of avionicS :sygtems. The group of 36 with least influence wasprimarily concerned witKpa!1;4 aircraft studies. Further analysis of the 39trade studies with the greatest influence showed that human resources dataitems of maintenance tasOime\and personnel cost were the most severelyimpacted. Human resource'ltems%of maintenance location, method of instruc-tion, and career field weretheleast effected. TherFwas indium impact oritraining course contend qUaptity.of maintenance technician-training time,skill level, and task perforffiance'errors.
'The cluster analysis of the 39-trade studies with greatest potentialinfluence on humanresources resulted in two dominant clusters: one whichisolated 12 studies with'the most pOrerful effect on the individual humanresources data item and the second which isolated 8 trade studies that hadthe lesser effect on the indiyidital human resource items. It was found thatthe two clusters of trade studies, differed significantly in terms of theamount of technological difference that existed between design alternatives'for the trade studies. The cluster with,greatest impact on the individualhuman resources data items had the'greatest technological difference betweendesign options, viz, the avioniCs:systems: The analysis of manpower changesfrom an older to a newer fighter aircraft system showei the greatest quantitychange occurred for avionics systems..
.These results strongly suggest that subsystems with rapidly changingtechnologies, or subsystems with design alternatives involving distinctlydifferOnt technologies should be examined closely for HRD implications.-The avionics area appears to be an area of rapid change and a h'Pgh degreeof influence on the human resource requirements of new systems. The ten
,human resource data Items were-variously effected by trade studies. Mainte-nance task time and personnel costs should receive priority attention asdata to be provided to engineers for use in design trade studies..
26
ACCURACY OF',SUBJECTIVEESTIMATES OF THE IMPACT OF
DESIGN ALTERNATIVES ON SELECTEDHUMAN RESOURCE DATA ITEMS
Approachz.
If HRD is to be used as a parameter in the trade study process, it mustbe supplied to the engineer. Engineers have neither the time nor the back-ground to develop HRD. One potential source for.HRD is subjective estimatesby experienced maintenance technicians. As a specialist in the daily main-tenance and utilizatiOn of systems equipment, he appears to be in the posi-tion to offer predictions on the impact that alternative conceptual-designsmight have on personnel, training, and maintenance factors. Since mainte-nance task time emerged in the first part of the study as a top rated humanresource factor for design trade 'studies, it was decided to test the accur-acy of the subjective estimate method for predicting that dais of data.In addition, since data on Air Force specialty careers (AFSC), crew sizes, andskill levels are used to calculate personnel costs (the second most impor-tant HRD item in Table 8) an effort was made to determine,the accuracy ofsubjective estimates of these kinds of data. .1011hereas avio ics emerged as
the system technology area with th6 greatest impact.on'HRD, it was chosenas a test bed system for this phase of the study.
. MDC avionics engineers compiled engineering data package describing
the avionics systems for two aircraft at a conceptual phase o development%
Using the historical records fof the F-4E aircraft at McDonnel Aircraft
Company and the F-111D at General Dynamics Corporation, the engineeringpackages were assembled. Ta insure that only information that normallyexists during the conceptual design phase was included, avionics systemsfor a third aircraft, the advanced tactical fighter (ATF), were used asconceptual models: At the time of 'this study the advanced tactical fighterwas in the conceptual design phaseaneserved as an operation .al defnition.for what was,'and what was not, conceptual phaseengineering data (A pendix C).
The completed engineering packages were then reviewedfor consis ncy
and standardizatiot by technicians from the MDC Product' Support Depart ent.The conceptual data packages were-then ready'to serve as stimulus meter alfor HRD' predictions.
Air Force technicians, with training and field experience in avigpics
.maintenance, independently reviewed the conceptual packages and made subjective estimates of the maintenance task times, career fields, crew sizes andskill levels of personnel that would be required to support such a system
at an operational base. Their predictions were averaged and checked foraccuracy with the actual human resource requirements reported by shop super-visors who controlled the Oily maintenance for operational F-4E and F-111Davionics systems.
ka7
2
Procedures
Engineering data packages'used as stimulus,material for subjectiveestimates. Using the ATF system as the model, six packages were assembleddescribing the design data available during tire, conceptual phase of thefollowing avionics subsystems: (1) F-4E autopilot; (2) F-1110 autopilot;(3) ATF autopilot; (4) F-4E fire control; (5) 4P-1110 fire control; and (6)ATF fire control. The ATF data package is contained in Appendix C.
Description of personnel making, human resource data predictions. Sixgroups,of experienced Air Force technicians from the avionics maintenancecareer field served as sources for the human resource predictions (Tables15 and.16). Each group made estimates for one of the six avionics concep-tual designs. Special care was taken to insure that no technkian hadactual field experience with the subsystem for which he was to make tasktime predictions as would be, the case during a conceptual design effort.
Type of human resource data predict d. Utilizing only the informationcontained in the design data packages; t e technicians made predictions, op.the amount of elapsed time that would be required to perform the followingflight lihe maintenance tasks: prepare;troubleshoot; remove and replace;adjust; align; functional test; and, clos 40. These estimates were recordedon the form shown in Figure 2. Estimates were made for each component of thesubsystem. For exampl, for the F-4E autopilot*, predictions were made forthe following components: control amplifier; transducer; g-limit acceler-ometer; lateral accelerometer; pitch rate gyro roll rate gyro; yaw rategyro; and, controller. Estimates were also made ofthe career field, skilllevel and quantity of the personnel required to perform the maintenancetasks for each component.
Following their predictions, each technician was individually interviewedand asked to critiwie the infOrmation'contained in the engineering designpackage. He was asked to suggest changes to the data package which Wouldincrease his cenfidence in his human resource data estimates.
Criteria for evaluating the accuracy of the human resource datapredictions. Visits were made to operational Air Force Tactica.rAir Command 4,bates2 to collect criterion task completion times, crew-sizes, career fields,and skill levels required to perform flight line maintenance actions for boththe F-4E and F-1110 autopilot and fire control avionics systems. The cri-terion data was first sought from base-level Air Force Manual 66-1 timerecords, however, these data were expressed as manhours rather than totalelapsed times for maintenance. actions. Direct observation and timing ofmaintenance actions would have entailed resources and time expendituresbeyond the scope of the study. For these reasons, the information was
2Seymour Johnson AFB, NCCannon AFB, NM
28
TABLE 15
TSHERISTICS OF TECHNICIANS WHO ESTIMATED T'HE IMPACT
\OF CONCEPTUAL AUTOPILOT DESIGNS ONHUMAN RESOURCE'S DATA
Personnel Making F-4E Predictionsall
L.__
AGE (YRS) GRADE TITLE' AVIONICS EXPERIENCE (YRS)
AVERAGE RANGE AVERAGE RANGE AVERAGE RANGE
21.6 23 -33 i \ 5.4 5-6 1.0 3.1-12.b
Personnel' Making F-111D Predictions.
ri
..,AGE (YRS) 'GRADE T TLE* AVIONICS EXPERIENCE (YRS)
AVERAGE RANGE AVERAGE RANGE' AVERAGE RANGE
5
_30.8 25-38 5.5 \ 5-6 8.3, 6.0-12.0-
Personnel Making ATF Predictions
AGE (YRS) GRADE TITLE* - AVIONICS EXPERIENCE (YRS)
AVERAGE- , RANGE AVERAGE RANGE AVERAGE RANGE
29 24-36 5.2 ,
,5-6 9.8 415-18.0
*AIR FORCE GRADE TITLES:
1= AIRMAN BASIC
2 = AIRMAN
.3 = AIRMAN 1ST CLASS
4= SERGEANT
5 = STAFF SERGEANT
6 = TECHNICAL SERGEANT
1 = MASTER SERGEANT
8 = SENIOR MASTER SERGEANT
9 = CHIEF MASTER SERGEANT
29 L1
rim;
0
c
TABLE 16CHARACTERISTItS OF TECHNICIANS WHO ESTIMATED THE IMPACT
OF CONCEPTUAL FIRE CONTROL. DESIGNS ON
HUMAN RESOURCES DATA
Personnel Making F-:-4E PredictionsAGE (YRS) GRADE TITLE* AVIONICS EXPERIENCE (YRS)
AVERAGE RANGE AVERAGE ;RANGE AVERAGE RANGE
31.2 28-37 6.6 1 5-7 11.7 10.3-13.7
., t Personnel Making f;:.111D Predictions
n.AGE (YRS) GRADE TITLE* AVIONICS EXPERIENCE (YRS)
AVERAGE RANGE . AVERAGE RANGE AVERAGE RANGE33 25-39.
s5.6 5-7 13.3 5.5-21.2
b I Personnel Making ATF PredictionsAGE (YRS) GRADE TITLE* AVIONICS EXPERIENCE (YRS)
.AVERAGE RANGE AVERAGE RANGE , AVERAGE RANGE
30.6' 23-40 5.2 4-7 9.0 1.7 -20.Q
*AIR FORCE GRADE TITLES:
1= AIRMAN BASIC 5 = STAFF SERGEANT2 = AIRMAN 6 = TECHNICAL SERGEANT
3,.= AIRMAN 1ST CLASS 7 = MASTER SERGEANT
4 = SERGEANT 8 = SENIOR MASTER SERGEANT
9 = CHIEF MASTER SERGEANT
a
30
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obtained from thA shop supervisors responsible for scheduling, directing andadministering the activities of their maintenance work center. Their judg-ments were convidered to be highly accurate as the supervisors were seniorenlisted personnel who had frequently monitored and performed the maintenancetasks of interest., Each supervisor's HRD judgment wasifurther-reviewed bythe senior technician assigned to each F-4E and F-111D Chief of MaintenanceOffice.
,
Results'
Accuracy of predicted maintenance task times. A comparison of thepredicted times from design engineering data with actual times reported bysupervisors for the completion of flight line maintenance tasks is providedin Figures 3 and 4. Figure 3 compares predicted with actual times for the'autopilot subsystems. 'Figure 4 compares predicted with actual times forthe fire control subsystems. The accuracy of the average time predictionswas within 8.3% to 66.8% of the actual times required to perform the tasks(Table 17). Three of the stimates were less than the 'actual values. Theworst estimate occurred for' the F-111D autopilot system. With regard to allfour.avionits systems, the 'technicians made n overall underestimation ofactual task times by 29.4%.
One application of these results could be to apply an adjustment to theestimated task time values for a.conceptual phase design. Such an adjustmentin estimated values would serve to compensate for the tendency of techniciansto underestimate ual times. The correction equation would take the follow-ing WO:
Corrected Task Time Subjective Estimated Time1-Percent of Underestimation
CTTSET
SETCTT =
.700
For the ATF the corrected task time for the autopilot system1design wouldbe 1878 minutes and for the fire control system the corrected task 'time wouldbe 1356 minutes.
32
O
(FIGURE 3. COMPARISON OF PREDICTED AND ACTUAL TIMES TO PERFORM FLIGHT-
LINE MAINTENANCLTASKS ON AUTOPILOT SUBSYSTEMSw
2800
L7".1 2400
(,)
L.!
2000
1600
1200
a 800
LAJ
400
g-=CD
F-4E F-111D
FLIGHT CONTROL SYSTEM
FIGURE 4. COMPARISON OF PREDICTED AND ACTUAL TIMES TO PERFORM FLIGHT-
LINE MAINTENANCE TASKS ON FIRE CONTROL SUBSYSTEMSr,
AVERAGE BY
LAJ
AIR FORCE TECHNICIANS
AVERAGE PREDICTION BY
AIR FORCEJECHNICIANS
ACTUAL TIME
(NOT AVAILABLE FOR ATF)
ATF
200
S"2400
III 2000
LL, 1600 -
1200L
a- 800
w400
:F2
CD
ACTUAL TIME
(NOT AVAILABLE FOR ATF)
F-4E F-111D
FIRE CONTROL SYSTEM
33 ,
ATF
I
TABLE 17
PERCENT DEVIATION OF MEAN PREDICTED TIMES FROMACTUAL TIMES TO PERFORM FLIGHT LINE MAINTENANCE
SystemDeviation of Mean
Predicted from Actuals
OE Autopilot
F-1110,Autopilot
F-4E Fire Control
F-1110 Fire Control
8.3% Greater
66.8% Less
19.4% Less
14.3% s-
Mpan Deviation----
29.4% Less
Accuracy of predicted career field} skill level, and crew size. Littleoh variation within rating groups occurred with regard to prediction of Air Force-Specialty Cgde (career field), skill level or crew size. In all cases theavionics career field was listed. Skill levels were set at a mix of 3 and 5levels. Crew sizes for most flight line maintenance tasks were set at 2 men.These datamatchedalmost perfectlythe.actual flight line manning as reportedby the maintenance supervisors (Table 18) at the operational units. The AirForce's maintenance philosophy and safety program tends to set minimum crew
TABLE 18
COMPARISON:OF PREDICTED AND ACTUAL FLIGHT-LINE CREW SIZESAND SKILL LEVELS FOR SELECTED F-4E AND F-111D MAINTENANCE TASKS
'HRDITEM
AUTOPILOT SYSTEM FIRE CONTROL SYSTEM
F -4E ,F-111D- F=4E F-111p
Estimated Actual Estimated Actual ,Estimated Actual Estimated Actual
AverageSkill
Level4.2 4.5 4.0 3.8 4.0 4.6 4.5 4.2
Average
Number.
2.1 2.4 2.2 2.6 1.9 ,2.0 2.0' 2.1
14?
a
sizes for specific tasks at 2 men. The accuracy of the predictions, in this'area of human resource requirements may be interpreted as an awareness onthe part of the technicians of the way in which the Air Force provides'man-power for maintenance on avionics systems. This knowledge of the Air FOrcepolicy regarding assignment of career field, skill level and crew 'sizeresulted in high'q accurate predictions.of personnel requirements'for fieldmaintenance activities.
`Critiques of engineering data packages. The'stimulUs data9paCkages forthe autopilot and fire control subsystems for the F-4E, F-111D and ATF'air-craft contained data set to the conceptual phase of hardware design. AirForce technicians, who made human resource predictions were askeI to critiquethe completeness of the data package in a follow-on interview. They wereasked to make suggestions as to how the data package could be improved so asto improve their confidence in the human resourcessestimates they made.Tables 19 and 20 summarize, the number of times'a given category of informa- 0
tion was mentioned as needing more detail or needing to be more fullyexplained. Approximate y half the technicians mentioned that there was someinformation that was of little or no interest tcfthem when making theirpredictions. Data.on ircraft flight parameters, general fuselage and pro:.pulsion descriptions, and performance envelopes were considered "nice toknow" but not partic arly relevant to the prediction task.
,With regard to data packages on the autopilot syStems, the lack ofdetailed information on component locations and access requirements was'most,frequently mentioned as hampering the accuracy of task completion time fore-casts. This could be corrected by using a drawing of the fuselage and illus-trating the propoged location of system components.
Descriptions of type and need for aerospace ground equipment (AGE) suchas electrical and hydraulic power units, air conditioning units, and special'stands-was listed as too general or not describe0.The remaining deficiencies ofr
were related to lack of information on: shop level maintenance equipment;built-in-test equipment modes, operation and test time lengths;.component
. (
adjustment requirements; access panel location, number and design; fullerdescriptions of components; flight-line test equipment; and a more completeexplanation of system redundancy.
0 ,
For the fire control system data packages the rack of detailed descrip-tion of the built-in-test equipment was mentioned most frequently as loweringthe confidence of human resources data predictions. The technicians alsoreported that additional information on copponent adjustmen4 alignment and,pressurization requirements, shop level maintenance equipmene64. access panellocation, number and design, AGE requirements, radome opening, descriptionsof components, functional checkout and block-diagrams would have impro d
-their prediction of human resources requirements for the system..
S
354
rn
TA
BLE
19
SUMMARY OF CRITI9UES OF ENGINEERING DATA PACKAGES
-FOR AUTOPILOT SYSTEMS
.
Information not Detailed
,Enbugh with Regard to:
.
F-111D 4Flight
Control System
.F -4E Flight
Control System
ATF Flight!
Control System
'Total
Co4onent Locations and Access
52
613
Aerospace Ground Equipment
Requirements
.
'.
4-
.
29
Shop Level Maintenance Equipment
.,
4,
.
1
28
.
Builtin Test Equipment Modes
of Operation and Test Lengths
. .'
3a
47
Access Panel Location, Number
and Design
17- :
3.
3.
06
Component Adjustment Requiremehts
05
1,,
6
Flight Line Tet Wipment
.5
..0
Descriptions of Components
2.
,-
03'
5
Explanation of System Redundancy
2.
.0
.2
4
Vr
.1!
':.
..;
. ,
4!
-7 :
,#1/4.-
'?
'1"
.7.-1/4
..,,-
TABLE 20
-.7;----
,
i.,.
.
.
,.
,SUMMARY OF ENGINEERING DATA PACKAGE CRITIQUES
-FOR FIRE CONTROL SYSTEMS
`Idtormation not Detailed
/Enough with Regard to:
F-111D Fire .0
Control System '
f-4f- Fire
Control System
ATF Fire
.
Control 5ystem
Total
Built-in--Test Equipment Modes
of Opuatfon and Test Lengths
,
5.
44
13
-CompOnent AdjUttgents, Alignments
and PreSsuyization-Requirements
'
.
4.
,..,-
06
10
Si0Level Maintenance Equi0Ment
.2
53
10
'ACCess Panel Location, Number
,andDesign
-,
,;
3.
33
..
..,
I9
AeroSpace Grounk7Equipment
.
Requirements
_
.
1
..
15
_
7
Radome Operating
r.'
...,.
3.
1
.-e
26
Descriptions of Components
2,-.
.A
2.
-2.
---,
6
Scope and Duration of
.'
-Functional Checkout Procedure
...:-
-,
,--
,.
*2
4 5
Component LocatiOns-itid-AcCesi
.2
..
1.
25
A Functional Block Diagram
1/-
I .
1I
13
.- . ..
At4'Developmnt/Of future'ditajpackages for use as stimulus materials. The ,,
critiques obtained from the-technicians can be used to form a picture of what AP: a jopd data packale should in&lude. The items presented in Tables 19 and 20:pointOut specitk,subjects tilt should be addressed in detail by the data ,
package. The type 4f illustra 'on contained in Figure 5 would be a suitable.. forMat for presentN'informati&ii on component location.
'..IThe feasibilitf applying be guidelines for conceptual design"daia
packages remains to7he demonstrate., It is possible that the level of detail,......--'requested for test e461pment.oper'aMb, the exact location of a component,
and the relative locations ofother. system.hirdwarejsuch as hydraulic ltnes1_--.would not be KEW abl e-- it "-the _concepty-or_iterse .
. ...--- --- _, -Qualifications of personnel 'making human resourcedata-hreeetions:. "
Most of the technicians whQ.,Paqicipated in makang_the"timeistimetes-jelt..:....that the.approach was valid-arid:ZW1c1..be-_-expe-nded,...--Diirtng-the-Course.-9-f.--"the interviews several .5kigges7tions werejmAde-onjpq-.theiccjfraq,pf7.predic-_,-
P
'V
etions might' be improved, ATk§enei':it:iori-ef!.a'inare..65m0et jr.aakage of ,,..-.
'equipment characteristics vaAline.-spolv.aree-od,was ". ussed above. The/., , .
careful selection of experiender,tWarka-s-,:anollier. Based upon the"!/ experience gained in this studyklni followihg:Oalificationt, shguld he` -
applied to technicians'who mafe0i,Likra- resource Oredictions from/d.esign,engi-,neering data packages: (1) ree.elit:Jjeld experieq0n perforriling,maiqe-,
/
nance on subsystem equipment with,deMn Characteligics.timill4r to the ! // ccinceptual system being studied, :irld,i,. 2) high aptit4de,/techniiansiShouldbe utilized. The forecast proced6elnWvet formulating subjektUe assump-tions that appear easier for high aptisi0 technician's to make.i/A addit4pn, .
technicians should be motivated to partlOpate in the .predictive procewanpbeassured that their opinions will be given.serious consideration.
'1:'-:
.,3
Summary and Discussion' ... -.-
.\
This part of the study was chhcerned,with.ehecking the;lccuracy of ..
subjective predictions of human resource requireMents for aOpnics.equipmentstill in the conceptual phase of design. The intention was'tt.determine thevalidity of using experienced technicians as a source for human,resource datethat could then beA.' Used by a design engineer to form design trade -off.
.
decisions.
The approach used was to develop conceptual phase engineering packages'to serve as stimulus materials 'for subjective estimates of tipman resourcedata items. Experienced'Air Force avionics technicians' made the estimates,
' and were then interviewed for their op4nions'of the approaqh_as well as thecompleteness of the stimulus /us materials.', ..
1 ,
.
''x :'The subjective estimates were cheeked for accurgr* comparing themwith data reported by avionics shop supervisors. OT6ra11 'the technicians,underestimated flight line maintenance task times by 29.4%. In additionthe predictions of crew &ize,specialticode and skill levels were found
Ao be highly acturate..
38
_" ;
1
FIGURE 5 COMPAfg LOCATION
FC-8;® RATE GYROSCOPE (TYPICAL)
ROLL : AFT BULKHEAD RIGHT SIDEOF COCKPIT
YAW :ACCESS DOOR 89R*ITCH: ACCESS DOOR 89L
IFC-3
!.!
of,""-
..1.yAlfiCRAFT ACCELEROMETER (TYPICAL)G-PITIN:G:NOSE COMPARTMENTLATERAL :UNDER AFT SEAT.
1
,/V
7.
;1
FCC 4
,4;.
cy A OTOMATiC PIkOTENGAGING CONTROLLER,'FWD COCKPIT, LEFT CONSOLE.
FC-7
FC-12
&CONTROL AMPLIFIERART COCKPIT, UNDERLEFT CONSOLE.'
0 MOTIONAL PICKUP TRANSDUCERFWD COCKPIT, CONTROL STICK
39
4a
',t,
Fe-15
® ELECTRICAL EQUIPMENT RACKAFT COCKPIT UNDER LEFT CONSOLE
I-
' A.
0
It is most probable that the predictive accuracy of the human resourcesdata.codidlie improved still further by altering the procedure used to collectthe data; 'Some 'suggested procedural changes are: more thorough briefing oftechnicians on the subeystemC4iscussions between design engineers and theteCtInicians who do the.rating,p the subsystem of interest (especially withregard to airframe des* and:Oharacteristics of access point locations); and,cross-talk and time for detaiOd discussions among technicians. A majorconsideration that accounts f4r;di4arities.tetween predicted task times andactual times are the numerous!iacd: sometimes major alterations between concep-tual designs and full scale pttopUction models. This aspect probably cannot .
F be accounted for when using thqsj.lbjective estimation technique.
^ ;
The results should be interpreted as a preliminary indication thatexperienced technicians can and Will..make reasonably accurate estimates ofseveral human resource data items baied upon conceptual phase designinformation.
40
El
e
r.
SUMMARY AND'CONCLUSIONS
Two questions were addressed by the study: (1) C'n design trade studieswith potential limpact on human resource requirements be identified and cate-gorized? and, (2) What is the accuracy ofisubjective estimates of the impactoftdesign alternatives on human resource requirements?
In an attempt to identify and categorize traq studies that have bearing,,on the human resources of a weapon system, a descriptive case history approach'pas utilized. F-15 aircraft design trade studies were reviewed and analyzedfor potential influence on personnel variables. Those judged to have influ-ence were further analyzed to determine where commonality existed. Thedegree of technological disparity between design study alternatives emergedas am important factor in setting human resources impact. An independentevaluation of technological differences between trade study alternatives lentconfirmation'to the hypothesis that distinctive technologies should be closelyexamined for human resource implications. Prime human resource considera-tions were found to be maintenance task completion times and personnel costs.
At the present time in aerospace hardware development, the avionNcssystem emerged as the system area with the greatest concentration of designdecisions with impact on maintenanCe'task times and personnel costs. Thissystem repAsents a rapidly Dovi,ng technology, and should, more so than theother system areas examine d take into consideration the man-related impli-cations of equipment configuration and design.
The second question dealt with accurate forecasts of human resourceneeds based upon conceptual designs and engineering descriptions. Exper- ,
ienced technicians made estimates of maintenance task completion times,numbers of personnel, skill levels, and,career fields that would be requiredto support several avionics systems.
A compaHson of-the humaa/resourcepredictions with the criterion datashowed that experienced technicians could respond to conceptual descriptionsof avionics systems with sufficiently Accurate estimates of maintenance tasktimes, crew sizes, specialty codes and skill levels to justify use of thesedata in engineving design studies. The predictive accuracy of subjectiveestimates might be further enhanced by developing more detailed conceptualengineering packages, altering the procedures followed when making pre-dictiong,and be'tter controlling the characteristics of the techpicians(such as experience and ability) asked to make the forecasts..
41
i..
. REFERENCES
Askren,. W. B., Designing System's to Fit Personnel Manning and SkillCapabilities. Air Force Systems Command Research and Technology Briefs,May 1969.
A ren, W. B. and Korkan, K. D., Design Option Decision Trees. A Method forelating Human Resources Data to Design Alternatives. AFHRL-TR-71-52,ecember 1971.. AD-741 768.
Lintz,iL. M., Askren, W. B., and Lott, W. J., System Design Trade Studies:The Engineering Process and Use of Human Resources Data. AFHRL-TR-71-24,June 1971. AD-732 201.
Meister, IX, Sullivan, D. J.; and Askren, W. B., The Impact of ManpowerRequirements and Personnel Resources Data on System Design. .AMRL-TR-68-44,Septembe 1968. AD-678 864.
Meister, D., 41livan, D. J., Finley, D. L., and Askren, W. B., The Effectof Amount wit! Timing of Human Resources Data on Subsystem Design., AFHRL-TR-69-22, October 1969(a). AD-699 577.
Meister, D., Sullivan, D. J., Finley, D. L., and Askren, W. B., The DesignEngineer's Concept of the Relationship between System Design Characteris-tics and Technician Skill Level. AFHRL-TR-69-23, October 1969(b).AD-699 578.
42.
4
/
a
....1.4,
4
..,
APPENDIX A
SYSTEM ENGINEERING TASK STATEMENT
s
43
1
aA
../
/ I4
,..r
,
it
# t
COO. ENGR
. SYS,pIGR
APPROVED
APPROVED
REPORT
MODEL
DATE
SYSTEM ENGINEERING TASK STATEMENTTRADE-OFF. STUDY pa OC ED UllE
TITLE
PURPOSE rA brief statement defining the objective (the "what") of the study, i.e.,
feasibility study of--, evaluatemethods of--, define requirements for--,etc.; the reason (the "why") for condu^ting the study, i.e., satisfy re-quireme4ts for--, practical applications, determine the effect (or effect-iveness) of-2, provide improvements--, ..A.c.; and the affect of the study onW/S performance, i.e., mission definition/effectiveness, air vehicle perform-ance, crew effectiveness, subsystem interfaces/interrelationships, equipmentselection etc.
BREVITY and CONCISFJESS throughout this form are required to demonstrateyour understanding bf thz proposed study and provide management with justifi-dktion for allocating budget.BASEUNEALTERNATIVESOCUTIONS
- State the baseline configuration and the alternative solutions selected forstudy. Tabulate these for ease of identification and evaluation. Proposedsolutions must be briefly stated yet definitive. Two or more solutions mistbe identified to qualify as a trade study, i.e., baseline plus one ormorealternatives, or two or more.alternative solutions (baseline TBD).
-10
t;
FUNOONMSTEf.IVOATAINVOLVEDINTHISSTUDY
Functions: a. Tabulate all applicable functions from rysten Engineering'sfunctional block diagrams.
b." In the absence of inputs from functional block diagrams, de-fine the function(0 of the subject of ,thg study. (Use theverb.- adjective (if required) - noun form for functionaldefinition, example: drop torpedo, provide altitude data.)
SysteMs; Tabulate the systems/subsystems which interface with this study' or will be affected by the results of this study.
Data: Tabulate in outline heading form, (1) the data inputs required774:173771liporting organizations, customer, and/or suppliers tocomplete this study. These data include analyses, parametricplots; layouts, inputs,for weight, aintainability, safety, re-liability, cost, etc.; supplier propoials/data and so on, and (2)applicable existing documents, i.e., MIL Specs, drawings, reports,etc.
Enter the date that the decision resultinc from this study is reouired by the
REQUIRED STUDY CO!.:PLETION DATE coLnizant(requesting)eFineer to meet his schCottintrnentr .
STUDY SUPPORT REQUIRED FROM:
0 STRENGTH0 LOADSO WEIGHTS0 STRUCTURAL DYNA%liCScfnuiDAr:CE 1. oom-not. mECH0 A ERODYNALIIC S0 HUMAN FACT ORSco LAM LABORATORIES
44.
§A?"lgISA;.:4:t1FAIYSISAINTAINAFALITY ENGG.OGISTCCS ENGG
AGE ,ERGGENGG RELIABILITYFLIGHT TESTELECTRICAL ERGO
44
0ELECTRONIC SYSTE7.'S ENGGSTRUCTURAL ENG:,
0 MECHANICAL ENGG0 PROPULSION
FLUID SYSTE'.5 ENGGAUTO:.1ATIO1 CO.SAFETY ENGG
A ..., -
e
e .
FACTORS INFLUENCING EVALUATION
Tabulate the factors which will become pertinent in evaluating the merits
of the alternatives Onder study. Typical factors include mission effective-
ness, performance factors, cost, safety, weight, installed volume, schedule
fabrication/procurement problcms, testing, logistics,'-crew interface
problems, reliability) mailitaitability,support requirements, etc.
1
-
EXPECTED RESULTS'
-Summarize briefly the expected results or gain from the study for the
NS(X) program. 'Results" include as applicable, (1) the probable superiority
of the baseline or of alteinative solution "n", (2) the influence the de-
cision may have on interfacing subsystems, (3) the nature of the impact on
performances M & R, revisions to customer data requirements, cost, etc.,.
(4) the possible need for associated trade studies, and (5) .procureent/
design specification requirements. "Gain" includes the negationaf theestimated consequences-of' making the wrong selection.
TASK FINITION
Task finit n consists of two parts as ollows:
1. Statement of Ground Rules: List all of'the constraints, factors heldconstant, common denominators, etc., which form the premise for con-
ducting this study.
2 . 'Statement of Work: B.riefly state in outline form the tasks of the
Aupporting organizations. Enter them as separate line items to facili-
..take project evaluation and,scheduling. -
1
TOTAIMA6HOURSREQUIRED. STUDY START DATE
Enter manhours required for your discipline to support the study.
171
45 sa
- _.j
r.
APPENDIX B
. TITLES OF TRADE STUDIES
116
O
N .
A
TITLES OF F-15°TRADE STUDIES(1968)
ro Evaluation of Arresting Hook ConfigurationEvaluation of Trailing -Edge Flap ActuationEvaluation of Wing Fuel Tank Drainage ProVisionsEvaluation of Leading Edge Flap Actuation MethodsEvaluation.of Brake Heat Sink MaterialEvaluation of Wing-to-Fuselage SpliceEvaluation of Nuclear Survivability /VulnerabilityEvaluation of Structural Strength LevelEvaluation of Maneuver Load FactorEvaluation of Field Shop Automation ControlEvaluation of Trainer and Training Equipment - Maintenance Training EquipmentEvaluation of Trainer and Training Equipment - Aircrew Training EquipmentEvaluation of Additional Hard Points - Aftament SuspensionEvaluation of Auxiliary Power Units\(APU)Evaluation of;Cockpit Noise ReductionEvaluation of Lubrication and Qb4))1ingWstem fdr the Airframe Mounted
Accessory Drive System (AMADS)Evaluation of Oxygen SystemEvaluation of Canopy Transparent Enclosure .Evaluation of Canopy Actuator ConceptiEvaluation of Canopy Motion Concepts'Evaluation of Windshield Transparent EnclosureEvaluation of Gun PlacementEvaluation of Flight Control SystemCDesign ConceptEvaluation of Optimal Allocation of,Subsystem MTBFs
1
Evaluation of Quantitative and Qualitative AGE DeterminationEvaluation of.Hydraulic Reservoir Design .
Evaluation of Hydraulic FiltersEvaluation of Hydraulic,System Cooling MethodsEvaluation of- Hydraulic Tubing and FittingsEvaluation of Hydraulic System ConfigurationEvaluation of Leading Edge Flap Mechanization
1
Evaluation of'Rudder Pedal Adjust System 4
Evaluation of;Low Stage Bleed 'Air vs. Low and High Stage Bledd AirEvaluation of Flight Vehicle Power.Extraction MethodEvaluation of Engine Combat Damage Protection MethodsEvaluation of Flight Control System Precision FlyingEvaluation of Tactical Nuclear Weapon Delivery CapabilityEvaluation of Voice,Warning Hazard Alerting SystemEvaluation of integrated CNI Control and DisplaysEvaluation of Cockpit LightingEvaluation of. ed Line DisplayEvaluation Of 1 Resistant Hydraulic FluidEvaluation of Emerge SystemsEvaluation of Engine Con 'ration and EnvelopeEvaluation of Foreign. Object amage ProtectionEvaluation of Fuel System Conf r rattK
147
.. .
Evaluation of Aircraft Oil Cooling System Hydraulic art LubricatjonEvaluation of In-Flight Refueling Receptacle Location'Evaluation of Use of Bleed Air from APU for Ground 061Ping ChartEvaluation of Design, Construction and Materials .. .
Evaluation of In-Flight Monitoring (IFM) of Non-Avionic SystemsEvaluation of Environmental Control Systems -,Use of 'Hot Air vs. ElectricalCoAductive Coating for Defogging the Windshield
Evaluation of Environmental Control System - Use of Compressor DischargeAir vs. Iriterstage Bleed and Compressor Discharge Air for the Environmental.Control System
Evaluation of Environmental Control System - Simple, Air Cycle'vs. Bootstrap
...00EValuation of Envir4mental Control System - Area Modulation and Thi.uSt
Air Cycle
Recovery Outlets vs. Fixed Simple Outlet in the Ram Circuit!Of the AirCycle System 4
Evaluation of Environmental Control System - Use of Bleed Air for APU, forGround Cooling vs. Use of Ground Cooling Cart vs. Use of Internal Blowers
Selection of Test Bed Airplane for F-15 Avionics DevelopmentEvaluation of Escape System - Ejection Seats vs. Escape CapsuleEvaluation of Fuel Booster PumpsEvaluation,of Fuel Quantity Gaging MethodsEvaluation of Fuel Tank InertingSysteM,Evaluation of Smoke Detection Methods
,.,
Evaluation,of Thrust ReVerser/ContrOler vs. Speed Brake. Evaluation of Optimum Aerodynamic Systems Concept
Evaluation,of Stabilitp2nd Control Requirements. .
Evaluation of Back-Up Starting MethodsEvaluation of Modular Gun System Consopt g
,Tactical Electronic Warfare System laaIntegrated CNI Antenna Analysis
'Evaluation of Integrated-CNI Controls and DisplaysEvaluation of Build-In Test. Equipment (BITE)
r
Evaluation of Navigation Subsystem
Evaluation of Electro-Optical Identification 'racking (EOIAT)Evaluation of IFF (APX 81 Type)Evaluation of Helmet Mounted Sight.Evaluation of Crash Data RecorderEvaluation of Fire Control SystemEvaluation of Engine Oil Tank LocationEvaluation of Communication Systems ______,, -
Evaluation of Identification SysterrEvaluation of Avionics Interfaces
Additional. Longitudinal and Lateral Control Trade -OffEvaluation of Radar Dish Diameter ,
Avionics Interface and Computational Analysis'.Supersonic Tank Trade.Study
Co figuration Trade -Offa2?luation of Gun Sight Camera/Video Recorder
Evaluation of Flight Control Seryo Actuator ConfigurationPitot Boom Location
48
A
,
A
Supplemental Heat Sink-Water vs. Regenerative Air vs. Fuel-" 1
Boresight Technique SelectionEvaluation of.Iinflight Engine Restarting MethodsElectric Generating SystemIR Suppression Trade-OffExhaust Nozzle Configuration Trade-Off
, t
Air Induction Configuration Trade StudyEngine Evaluation Studies -
Base Drag Reduction StudiesInlet Aspect Ratio Trade Study .
, ,
.
Nozzle Jet Impingement/Expansion Ratio Study.
Cascade vs. Alternate Type Thrust ReversersBypass, Spill, Bleed Trade -OffBypass vs. No Bypass SystemInlet/Engine Anti-Icing Study .
0Inlet Ramp Scheduling Trade StudyEngine Scaling EffectsEngine FlexibilityManufacturing Test Equipment TradeEvaluation of AMAD'Configuration
OttEvaluation of Wing SplicesEvaluation of Engine Installation/Removal/Transportation AGEMethods of Providing Avionics Ground CoolingAircraft Weight Penalties vs. AdlOnics Cooling CapacityWindshield Washer Requirements f6r Removal of Insects and SaltEngine Build-Up/Q.E.C. Kits -
Evaluation of Torque Box Joint Design and Skin Fabrication, Methods - InbdendEvaluation of Aileron Actuation -
Evaluation of F-15 Canopy Jettison System;Evaluation of APU Inlet and AMAD Ventilation
9Evaluationv)f, Windshield Support StructureCanopy Normal Actuation System Trade StudyForward Fuselage to Center Fuselage SpliceInlet First RaMp ActuationtStiogyCenter and Aft Fuselage Splice,Stabilator Hinge Line Location Trade StudyEscape System Initiation Trade StudyEMergency Stabilator PowerEfficiency, Cost, and .Time Reduction of Engine InstallationTrOdsionsAlternate Emergency Hydraulic Power Schemes
49'
It." A"
1:es
e If
a
APPENDIX C
ENGINEERING DATA PACKAGE WHICH
DESCRIBES THE CONCEPTUAL DESIGN
OF THE
FIRE CONTROL SYSTEM FOR THE
,ADVANCED TACTICAL' FIGHTER
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McDonnell Douglas corporation is under contact with Air Force SystemsCommand to identify and evaluate approaches that maybe used to better esti..rmate.manpower requirements associated with avionics subsystem hardWare'.L^,',designs., One approach under consideration is to have experienced avioniCsy'technicians review an avionics subsystem and then ,comment on the probable, '-number and types of personnel thatwillbe needed to maintain it:
The. information contained in this booklet describes an avionis-sub4.system. Based upon the equipment design, func ions and physical chais-acter-
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istics, you will be asked to estimate the proba e'time that will be requiredto perform common maintenancwsipasks. We would a so,apprecite having youropinion of:the AISC, skill level-and training that would be needed-to-matchmaintenance personnel with equipmentcharacteristics.
- Please read the technical description. When you feel that yOu have afair understanding Of the equipment,lndicate to the Study Investigator thatyou are ready to comment on the subsystem., For purposes of this study, we_would prefer to have you form your opinions independently, without the-bene-
r fit of discussion with other technicians. ,
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Finally, we wint to thank you for your cooperation. If you have-anyquestions on the,procedure to be followed or the intention of the study,please direct,tflem to the Study Investigator at this time. .
. .NOTE
This information isbased on concep al design
actual system performance in the fiel .
phase data and it snot intended to re ect the
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1:0 GENERAL DESCRIPTION -: , .
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':I ! The -aircraft is a single iflaCe twin engine, supersonic, all- weather,'tactical ,.'fighter-bOmber. Prime mission weapons are: two 2000 lb Raided
r i: Weapons; two short range miiSqes; and one 25mm internal gun with 700 rounds.1.1 f, Of ammunition. The:propulsibrrSystqm cliMists of two mixed-flow. turbofanzf engines with afterburners. he'apprximate overall dimensions of the air'
craft are: ' \ :
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. \ISpan: ', 37 ieet,: 7 41-#es. i r!
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!Length: '72 leet ; .'1:.::: ;,:
i Height: 17. -feet , : 4: trXIws . /'''. 1
The ,approximate weiiti pi...ttiCairdif.aft are:
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: : empty operating welglif'7,gp,8l0 pound's--. ';'1. L'_ = operating weight - 56: 540.:.;p9f.fpds .
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.-.:7:. =4"hp-.;alrcraft perforMS offenSW,tactical issions in a chal enging .
51' defense avironment, The aircraft's stability characteristics rely upon litre.
---: -.flight control_pystem to provide artificial dynamic stability dtg:sialirvt:".7 = :eontrol of the..-airplane. As%a control configured vehicle (CCU1÷ .traft,relies heatily upon the aVionic computer for the system is analysis----- an synthesis-teChniqyes demanded 6/.' the multi-variable syste . The computer'
'%%: I AIRI*1* optimal and- stIbp.Otimal gain calculations and p rov id S the control;'i.!:- i .1,putiAlts to-the fl ight Cantrol stem. -.tem. A CCV:reSUlts in 'rel ed static sta
-..blrliply- requirements for the- eirtraft and offe/m the follow} g benefits..,
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.-a, reduced control surface sije;
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-O;.: trim" requirements and
\o improved maneuverability.
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INTRODUCTION
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The ATF radar is a compact, highly reliable coherent air-to-ground radarwith additional, capability for air-to-air search and target track. Physi:cally, the radar incorporates proven, advanced high density packaging tech-niques resulting in a basic radar configuration in the 350 ground category.Excellent reliability is achieved through Aximum,utilization of digitalcircuitry in the form of full wafer LSI, conventional hybrids and integratedcircuit designs. The system incorporates a Built -In -Test (BIT) system whichprovides a continuous measure of system performance as well as fault isola-tion capability.
The system provides the following air-to-ground capabilities:
(I) Real Beam Ground Map
.(2) Air -to- Ground Ranging
(8) Navigation System Update
(4) Synthetic Aperture Map
(5) Ground Moving farget Indication/Track'
(6) Terrain Clearance
(7) Terrain Avoidance.,;
Ground Map - A real beam, BO, 40, 20 or 10 mile ground map is included in thebaseline design; 'Improved range resolution is provided in the system throughpulse compression means.
Air -to- Ground Ranging - In this mode, the radar is slaved to the target t.
designator/ symbol which appears on the VHUD. The position of the symbol canbe contro led by the force controller throughout the VHUD field ofThe radar measures thE),-range along the boresight to the target utilizing theelevati monopulse difference sigpal'as a range\discriminant. The rangeome ement is-entered into the weapon delivery computer by depressing 06/action switch.
Navigation System Update - Angle and range information utilized by the naljga-tion computer can be updated by using cursor displacement signals and theground map. The cursor is positioned initially by the navigation compute' toa reference point on the display: the error as measured by the radar Oh be:,reducedloy manually positioning the cursor to.the radar detected referencepoint. The'newsrange and azimuth coordinates are entered into the navigation
'system by depressing the radar action switch.
153
Synthetic Aperture Map - Synthet aperture radar (SAR) utilizes coherentdoppler gradient processing ac s the antennakbeamwidth to achieve azimuthresolution significantly improved over that whfth could be achieved fromconventional brute force processing across the real beam. Two differentsynthetic aperture modes are provided; a doppler beam sharpened (DBS) modeand a squinted spotlight mode.
The DBS mode provides 10:1 improvement in the azimuth resolution overthe fo'ward sector tO° to 45° off the velocity vector either side in a for-ward sector scanning mode. This is illustrated in Figure 1. The DBS modeprocessed video would be displayed on a sector-scanned PPI type displayformat.
The squinted spotlight SAR mode provides constant azimuth resolutionindependent of range and fixed range resolution resulting from pulse/compres-sion. This mode can be used for passing scene mapping where the antenna isheld. at constant squint angle or map a fixed ground sector by scanning theantenna. This SAR mode could be used over squint angles from 30° to 900.The number of looks refers to the number of map images which are non-coherentlysummed to alleviate target scintillation and homogenous AArain intensityvariation.
Ground oving Target Indication/Track - Ground moving target detection andtrackin is provided by this mode.
Terrain Clearance - A method of sensing a terrain profile in a vertical cor-ridor, the computation and display of maneuver templates that can be superim-posed upon the radar data as a visual warning and the generation of verticalsteering commands to the pilot is provided. ;64'
Terrain Avoidance - A manually selected mode including radar sensing anddisplay to aid the pilot in manually controlling the aircraft so as to avoid:terrain features projecting above the clearance plane.
The following air-to-air modes are provided:
Air-to-Air Search - The radar is mechanized to search a wide volume (+ 90° x"---+ 60°) with 1, 2 or 4 bar Itan. The operator may select the scan width and
iiumUer of bars and position the search pattern anywhere within the antennagimbal limits. During search, unambiguous range and angle are presented tothe.pilot on a clean (clutter free) 4isplay by,processing programmed multiplePRFs during the timer-on-target throughout the entire search volume.
Acquisition and Track - Target acquisition (or radar'lock-onris initiated.through use of a range and azimuth_cursor and a computer controlled auto-
; lacquisition scan. After the cursor is manually positioned to the approximatew.,range and azimuth of the target, a depression of the acquisition switch causes
the radar to acquire automatically the designated.target. Angle, range, and
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SQUINTED SAR
SPOTLIGHT MODE
FIGURE 1
GROUND MAPPING MODES
CONVENTIONAL
GROUND MAP
4t,
velocity tracks are achieved within two seconds. Target illumination, pre-launch timing signals, and tracking data needed for employment of the Sparrowmissile is incorporated into the system.
Do fight - The dogfight mode is designed to provide a head-up acquisition andattack capability. Depressing the dogfight switch causes the antenna toautomatically scan a 20° x 20°,volume centered along armament boresight. Asymbol is presented on the HUD at the target look angle, permitting the pilot .
to verify visually that thAradar is locked on to the desired target.
INSTALLATION (/
The system consists of six Line Replaceable Units (LRUs) as given inTable I. The radar antenna installation is shown in Figure 2. The trans-mitter and receiver/exciter are installed directly behind the antenna and theremaining. LRUs are installed in the avionics compartment below the cockpit.ladar parameters are contained on,Table.II.
TABLE I
LRU-NN
WEIGHT
Antenna 55 Lbs
'Trinsmitter 165 Lbs
Radar SignaloProcessor 40 Lbs
Radar Data Processor 23 Lbs
Receiver/Exciter 41 Lbs
Low Voltage Power.SuOply 26 Lbs
350 Lbs
li-..itPrime power is estimated to be13600 watts. Liquid cooling-will be
required for'the transmitter. Forced air cooling will bd. required for allother units except for the antenna which will be free connection cooled.
ANTENNA
porating a sum and difference network to provide a monopulse capability and*six dipole elements to vide an IFF capability.
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The antenna is a 24 inch diameter circular k;band,plapar array incor-.
TABLE II
FIGURE 2
ANTENNA
RADAR PARAMETERS
RF Frequency :X-Band
Antenna
Type'DiameterGainBeamwidthScan Limits
Average Transmitter Power
PRF.
Planar Array24 Inch33.8 db3.8°
90° (AZ) x ± 60° (EL)
800 Watts
s,Low 0.8- 4 KHz'Medium 8 - 17 KHz
Noise Figure 2.5 db ,
111057
1 )The function of the planar array is to receive a high-power X-band RF
,signal from the radar transmitter and to radiate a narrow beam for targetillumination. Raddr echoes are received and routed through the microwaveprocessijig circuitry of the antenna. Three signals (a sum, an elevationdifferenoe, and an azimuth difference) are obtainable from the planar arraysum-and-difference network on receive; so that two-plane monopulse capabilityis provided. These signals are combined within the microwave processingcircuitry to provide a signal,from which angular tracking information isavailable.
TRANSMITTER
The primary function of the transmitter is to amplify and modulate theX-band signals suitable for transmission'through the antenna for the prin7cipal radar functions. A gridded traveling wave tube (GTWT) is utilized asthe final amplifier for the pulsed radar signals. A CW traveling wave tubeprovides continuous wave RF signals for AIM-7E and F Sparrow Missile illum-ination. TWT power supplies and protection circuitry,, modulators, transmittercontrol circuitry and various related microwave components are.located inthis unit. Both the GTWT final amplifier and the CW TWT are liquid cooled.Thd high power portions of the waveguide, up to the:multipactor, are pressur-ized.
TrtCAt rairlaUlelONC 0,SCO.ftla
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TRANSMITTER
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RADAR SIGNAL PROCESSOR
, The radar signal processor Provides range gatitig, doppler f4ltering,post-detection processing, and timing and control functions. The syntheticaperture processing oft-1.* digital signals for the high resolution ground
-se map mode, and the GMTI° processing are performed within this LRU.' The\rangegated doppler filtering required for the medium PRF air-to-air modes isincluded in this unit. In addition, the digital pro'cessor provides low PRFoutputs for air-to-air pulse operation, air -to-ground mapping, and air-to-'ground.ranging operation. During tracking and air-to-ground ranging, themonopulse signals are.processed and gated to the ROP where -angle, rangeivanddoppler errors are derived. The digital processor includes timing andcontrol, function that 'provides"the basic rad4r clock for range gating,processor timing, and medium PRF generation; in addition, it provides syn-,chronization for changes in RF frequencies.,
RADAR SIGNAL PROCESSOR
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RECEIVER/EXCITH4
The ReCeiver/Exciter,LRU performs-the low noise amplification and condi-tioning of the received signals and provides the coherent local oscillatorsignals and RF drive signals for the transmitter.
The radar receiver portion performs loW hoise amplification and signalconditioning on low level X-band energy reflected,from the target and receivedby the antenna group. The receiver configuration is primarily governed by therequirement for a pa.rametYic amplifier and two-channel itionopulse capability.By various combinations of microwave and IF switching, the.receiver,providesthree distinct operational capabilities: (1) lbw noise parametric amplifierand two-channel monQpulse receiver. The low noise parametric amplifieroperation is providedin the sum (E) channel only. To ensure wideband Mono-pulse performance, identical components are used, where possible; i4 the twochannels.
The exciter provides phase coherent, few noise, RF drive for the griddedtraveling wave tube (GTWT) and CW RF drive for. the CW TWT the transmitterunit. This unit also generates and proVides a local oscillator (L0)signalto the receiver unit. The RF oscillator is capable of tuning the. transmitterdrive and LO signal to any one of six radar channels in'the RF tend whileMaintaining a highly accurate frequency offset between the two signals. SixCW channel frequencies are also provided... The RF,oscillator unit also provf&s(1) the fiequency modulation ranging (FMR) for the GTWT drive, (2) codingoscillators for the AIM ;7E and F missile frequencies, (3) binary phase shifter'for coding the GTWT RF drive during pulse compression modes and (4) RF blankingof the GTWT drive output when commanded by the transmitter unit &prevent GTdrive leakage during receiver listening time. Basically, this consists of ix
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RECEIVER/EXCITER
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plug-fp-modules and a filter assembly. The modules are: (1) PD RF generatorcontrol, (2) radar 0. generator, (3 LO reference generator,.(4) *age regu-lator and channel control, (5) CWI RF generator control and (6) C F gener- '
ator All input and outpu signals, except those supplied through coaxconnectors, are filtereCRY individual filters located within the filterassembly.
LOW VOLTAGEPOWER SUPPLY
The low miltage power supply and antenna servo electronics are combinedwithin this ,LRU.
The function of the low voltage power subsystem is to convert and condi-tion aircraft p.rime power to the voltage forms required by the applicableunits of the radar set. This subsystem consists of.three modules in the lowvoltage power supply unit, the power conditioner in the digital processorand thirty linear regulators located throughout the radar. The power supplyprocesses the aircraft 115 Vac three-phase, 400 Hz power and provides eightsemiregulated, two regulated, and one special dc voltage output. Linearregulators are located in the LRUs. The linear regulators provide the finalregulation and ripple reduction required, as well as current limiting.
The antenna servo system is composed of a number of rotating components, .
mounted on the antenna gimbals, and the servo electronics, which are locatedin the low voltage power supply. The gimbal servos (elevation and azimuth) (
can be-operated in either a space-stabilized or an aircraft-referenced mode.The space-stabilized mode is mechanized through the use of rateintegratinggyros. The aircraft- referenced mode is provided through the use of tachome-ters. Azimuth and elevation positions are controlled by dc analog rate com-mands from the radar, data processor.
LOW VOLTAGE POWER SUPPLY
a'BUILT IN TEST
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BIT tests are deSigned to exercise and analyze the 'radar set as it 'nor-mally would be used., BIT, uses system functions agd BIT monitors in an inter-woven test design consisting of continuous monitoring by on-line 'devices,continuous (at the end.of antenna bar and/or-frame) monitoring of the selectedmode and initiated testing at operator discretion. Tests are mechanized whichprovide the maximum test capability without weight° or volume penalty or oper-ational perfoimance degradation.
The BIT provisiOns accomplish testing in all modes of operation whetherin flight or on the ground. The tests ar organied into software sequenceswhich continuously test the mode of operation selected at the radar set con- .
trol. Additional tests which are either .on line continuously or can'be inter-mittently initiated provideoJault'detection of critical element failures whichwould not otherwise be obvious. Operator initiated. BIT tests are provided forthose functional tests which would disrupt normal system operation were theyautomatically commanded. -
.The in-flight tests are designed to detect failures within the radar set,commanicate the failure indication to the operator, store the test result inthe RDP memory and set a latching annunciator if the failure can be isolatedto a specific line replaceable unit (LRU). Failures detected in flight whichcannot readily be isolated to a single LRU are fault isolated after completionof the mission. this fault isolation test makes use of additional softwareroutines after the weight on wheels indication is received. The added testsare required only for failures which occur in difficult ipterfacesluch as thetarget acquisition checks, RDP input/output interfaces or Radar Set /externalavionics interfaces. Most common failures (> 80 percent of'total failures)will be isolated to an LRU automatically; therefore, ground fault isolationwill not be required in most cases of radar set organizational level. mainte-nance. Fault isolation consists of special software data reduction routines'which search the test result matrix for logical fault assignments by deductivereasoning.
RELIABILITY
Attl`
The radar is,designed to have a system reliability in excess of 63.4hours. Experience in modern radar design and production plus advances inmicrocircuit technology, improved thermal designand'packaging techniques,provide the basic guidelines to be, employed in achieving high reliability:Standardization of-parts selection is*being achieved through close coordina-tion between'component specialists and responsible design activities; particu-lar emphasis is being placed on dodumenting ceMponent application and deratingcriteria for refinement of standard parts lists. Specific MTBFs for the LRUsand system are given in Table III. '
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TABLE III
RELIABILITY AND MAINTAIgABILITY DATA
MTBF
(Hrs)
A
Organizational
Intermediate
TTR
A x
TTR
TTR
A x TTR
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Antenna
296
338
0.682
'230:52
0.683
230.85
Transmitter
345
290
0.682.
197.78
0.956
277.24
Radar Signal Processor
.347
288
0.516
148.61
0.342
101.38
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Radar Data Processor
380
2,63
'0.516
135.71
0.441
115.98
Receiver/Exciter
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485
206
0.682
140.49
0.956
196.94
LowVoltage Power Supply
525
191#
0.516
98.56
0.405
77.36:
63.4
951.67
)'1000.36.
.1576,.
MTTR =
.MTTR =
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AAP
,0.60 Hrs
400.63 Hrs
'*Failure rate - percent per 1000 hrs.
TTR.7 Total time to repair
MTTR - Mean time to repair
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1MAINTAINABILITY
./Maintainability design features incorp on the radar simplify main-,
tenance procedures as evidenced by the minimum s requirement ofpersognel and the'low system mean time to repair (MTTR) at the Organizatiorteand Intermediate levels of maintenance. The prediction for MTTR at- aircraftis less than 40 minutes where usually only one apprentice mechanic perforAs °
the 'maintenance tasks of replacing the faulty .RU and verify system repair.LRU maintenance in the shop is performed by Mechanic level personnel 00. ,
accomplish fault isolation to the shOp repla9eable assembly (SRA),, replacethe faulty item and verify repair in a mean time of less than 40 'lid/mites.Bit and piece repair of faulty SRAs is accomplished.at the Depot level ofmaintenance. Organizational and Intermediate level MTTRs are*ven in Tpl3WIII /
The most significant` contributor to the ease of maintenante,and,low MTTRat-aircraft is the built-in-test (BIT) design of the radar. Th4 ,BIT:mechani-zation enables both airborne and ground evaluation of the functgonal charac-teristics of the radar and indicates'the go-no-go, status to UTE pilot or.maintenance personnel.. BIT detects 95% of radar catastrophic ,failures andreasumed At of tolerances conditions, and provides fault isolation to,theWRA. BIT thuieliminates,.the usual lengthy fault isolation proceOres assbciated'with at-aircraft maintenance and the need for any at-airpra:ft.testequipment. The proposed mechanization is a proven design similar to that, nbwincorporated in current production radars.
-,
y ORGANIZATIONAL LEVEL TEST EQUIPMENTZi 1
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Built-In Test (BIT) is used almost. exclusively for Organizational 1:1i7-(flight line) level support. With an absolute minimum of additiona:i eq0134.-ment, BIT is fully capable of detecting'and isolating faults to thereplaceable LRU and verifying repairs. No external equipment, exceptcraft services, is required to,operate BIT. It features both airbome.aiitiground continuous monitoring and initiated test sequences. All failureinformation is preserved in computer'memory for use by maintenance perssoWnWOnly a few items, in addition to BIT, are needed to support the ARS at 0 \IOrganizational level. These include hanrng equipment, means ofmeaSurihaircraft cabling integrity and a wa'vegui e pressure leak detector. Failed%LRUS are returned to the Intermediate level shop for repair`. NO harmonlial'tion or other adjustMents are required when replacing an LRU at the aircraftIn many cases, the stored BIT data (BV matrix)., provides enough informatioVto isolate below the LRU .level - inffrmation that could be vital fOr.emer-4.gency repairs or to assist shop personnel in reducing shop maintenance time.\
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