t 

• 

I 

, I 

t 

I ., . 

Doc 

FAA 

AM 

89/09 

DOT/F AA/AAM-89/9 

Office of Aviation Medicine 

Washington, D.C. 20591 

.. 

\ 

I 

• Human Factors Issues in 

Aircraft Maintenance and 

Inspection 

William T. Shepherd, Ph.D., Editor 

James F. Parker, Jr., Ph.D., Co-Editor 

October 1989 

Final Repon 

This document is available to the publii: 

through the National Technica'l. Information 

Service, Springfield, Virginia 22161. 

U.S. Depanment 

of Transponation 

Federal A vi at ion 

Administration 

E.R.A.U. URR4Rl:-
NOTICE 

This document is disseminated under the sponsorship of 

the U.S. Department of Transportation in the interest of 

information exchange. The United States Government 

assumes no liability for the contents or use thereof 

, 

., 
t 

Technical Report Documentation Pagt 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

DOT/FAA/AAM-89/9 

4. Title and Subtitle 5. Report Date 

October 1989 

HUMAN FACTORS ISSUES IN AIRCRAFT 6. Performing Organization Code 

MAINTENANCE AND INSPECTION 

B. Performing Organization Report No. 

7. Author~ s) 

Williaru T. Shepherd, Ph.D., Editor 89-RR-18 T .., P. •• .Tr. Ph. n . C:o-F.cli !:or 

9. Performing Organization Nome and Address 10. Work Unit No. (TRAIS) 

Systems Control Technology, Inc. 

1611 North Kent Street, Suite 910 11. Contract or Grant No, 

Arlington, Virginia 22209 D'l'l<'AO 1-R7-<0-0001 6. 

13. Type of Report and Period Covered 

f 12. Sponsoring Agency Name and Address 

u.s. Department of Transportation Final Report Federal Aviation Administration 

800 Independence Avenue, s. w. 14. Sponsoring Agency Code 

Washington, D.C. 20591 ADS-22Q, AAM-2~Q 

15. Supplementary Notes 

AAM-240 Biomedical and Behavorial Sciences Branch 

ADS-220 Rotorcraft Technology Branch, System Technology Division 

16. Abstract 

The Federal Aviation Administration sponsored a two-day meeting in October 

1988 to address issues of human factors and inspection. Presentations were 

given by some 13 individuals representing the full spectrum of interests in 

I 

commercial aviation. Presentations also were given by three human factors 

scientists with backgrounds in vigilance and industrial inspection technology. 

Each presentation, as well as the following question and answer period, was 

recorded for transcription and study. 

The objective of the meeting was to identify human issues of importance, 

particularly as such issues might contribute to inspection or maintenance error. 

The desired outcome. was to be: 

(l) an improved understanding of personnel performance in 

aviation maintenance, and 

(2) recommendations, as appropriate, to the FAA concerning 

needed research efforts and/or possible new or revised 

regulatory actions. 

Several recommendations were presented to the FAA in the areas of communications, training, management, regulatory review, and research and development. 

17. Key Words 18. Distribution Statement 

Human Factors This document is available to the U.S. 

Aircraft Maintenance public through the National Technical 

Aircraft Inspection Information Service, Springfield, 

Virginia 22161. 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 120 

I Form DOT F 1700.7 <B-72) Reproduction of completed page authorized 

J 
Foreword 

The Federal Aviation Administration (FAA) is mandated to 

ensure the highest level of safety in American aviation. A 

matter of concern recently has been the increasing age of jet 

aircraft in the air carrier fleet. Many of these aircraft 

now are entering their second and third decade of use. 

In June of this year, the FAA sponsored a meeting of 

representatives of the aviation industry to review problems 

associated with aging aircraft. While much of this meeting 

addressed issues of hardware, metal fatigue, and corrosion, 

there was a discussion of human factors in maintenance. 

Today•s meeting reflects a growing interest in human factors 

and its potential contribution to continuing aviation 

safety. 

I hope that the perspective of today's meeting will 

extend beyond just the aging aircraft problem. We should 

consider new technologies such as use of composite materials, 

for example. The effect of automation, advanced electronics, 

new aircraft design techniques, and training innovations also 

should be reviewed. Any issue that bears on the performance 

of maintenance personnel should be included. 

All segments of the aviation industry concerned with 

maintenance are in attendance today. We have representatives 

from the Federal Aviation Administration, the National 

Transportation Safety Board, aircraft manufacturers, airline 

operators, regional airlines, helicopter operators, the 

maintenance training establishment, those concerned with new 

technologies, and, in particular, several human factors 

scientists with impressive research credentials relating to 

inspection and maintenance. With the skill and expertise 

represented here, I am certain we will develop positive 

recommendations of real value to the FAA and to aviation as 

we consider ways to ensure optimum use and support of 

maintenance personnel. 

William T. Shepherd, Ph.D. 

Federal Aviation Administration 

iii 
p 

Executive Summary 

The Federal Aviation Administration sponsored a two-day 

meeting in October 1988 to address issues of human factors 

and personnel performance in aviation maintenance and 

inspection. Presentations were given by some 13 individuals 

representing the full spectrum of interests in commercial 

aviation. Presentations also were given by three human 

factors scientists with backgrounds in vigilance and 

industrial inspection technology. Each presentation, as well 

as the following question and answer period, was recorded for 

transcription and study. 

The objective of the meeting was to identify human 

factors issues of importance, particularly as such issues 

might contribute to inspection or maintenance error. The 

desired outcome was to be (1) an improved understanding of 

personnel performance in aviation maintenance and (2) 

recommendations, as appropriate, to the FAA concerning needed 

research efforts and/or possible new or revised regulatory 

actions. 

Recommendations presented to the Federal Aviation 

Administration are summarized as: 

1. More recommendations centered on communication than 

for any other topic discussed. Apparently the changing 

structure of the airline industry has disrupted communication 

networks which existed in earlier years. These networks 

were quite useful in disseminating maintenance information. 

Accordingly, it is recommended that the FAA foster at least 

one additional meeting of this kind to review specific topics 

noted in subsequent recommendations. · 

2. The FAA should consider means for encouraging or 

developing a data base of industry information concerning 

maintenance technologies, procedures, and problems. Many 

individual data bases exist. These should be consolidated 

and expanded. 

3. The current review of Part 147 should be expedited as 

feasible. Results should include provision for 

specialization training as an advanced part of the 

curriculum of approved schools. Licensing procedures for 

avionics technicians also should be reviewed. 

4. The supply of trained maintenance personnel is 

inadequate. The FAA should encourage or develop promotional 

materials regarding maintenance as a career. 

v 
5. "Advances in Training Technology" should be addressed 

extensively in any future FAA-sponsored meeting. 

6. The pressure of "gate time" is an ongoing problem. 

All parties should consider ways to insulate inspectors from 

production and from the rest of maintenance. 

7. Consideration should be given by the FAA to the 

conduct of a task analysis, or some modified version, of both 

mechanic performance and inspector performance. This 

provides critical information for any job redesign and 

improvement. 

8. A research center, or program, where maintenance 

concepts could be studied in detail would be of great value. 

This could exist either at the FAA Technical Center or the 

civil Aeromedical Institute. 

9. Effective maintenance requires appropriate maintenance 

information. The FAA should review the preparation and 

delivery of maintenance manuals to ensure that the latest and 

most appropriate maintenance data are available to 

maintenance personnel as rapidly as possible. Particular 

attention should be given to information concerning wear 

limits, damage limits, repair schemes, and aircraft wiring 

diagrams. 

10. A number of organizations are conducting research 

activities relating to maintenance performance. Channels 

should be established so that details of these activities can 

routinely feed into the data base noted in Recommendation 

Number 2. In addition, any future meeting should include a 

full session devoted to "Requirements and Improvements in the 

Preparation and Delivery of Maintenance Information." 

vi 

-
p 

h 

e 

d 

1 

Table of Contents 

Foreword ..........•................................................. iii 

Executive Summary. . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . • . . . . v 

Meeting Welcome. . . . . . • . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . • . . . . . . • . . • . . . . . 1 

Introduction........................................................ 4 

Aviation Maintenance Parameters. . . . . . . . • • . . . . . • . . . . • . . . . . . . . . • . . . . . . 5 

Conclusions and Reconunendations ..........•........•..•.........•.... 11 

Appendix A: Meeting Presentations 

FAA Regulatory Requirements for Aircraft Maintenance and 

Inspection, Raymond E. Ramakis ....••.....•.••..........••.•.... A-3 

Maintenance and Inspection Issues in Aircraft Accidents/ 

Incidents, Part I - Barry Trotter .........••..........•..•..... A-6 

Maintenance and Inspection Issues in Aircraft Accidents/ 

Incidents, Part II- James W. Danaher .......•...........•...... A-9 

.~ Day-to-Day Problems in Air Carrier Maintenance and 

Inspection Operations, Robert T. Lutzinger .•.............•.•.. A-12 

~·Maintenance and Inspection from the Manufacturer's Point 

of View, Robert L. Oldani. .....................••............. A-17 

-Human Performance in Aircraft Maintenance: The Role of 

Aircraft Design, Anthony E. Majoros, Ph.D ..................... A-25 

~ Maintenance and Inspection Issues in Air Carrier Operations, 

Robert Doll. .•.....................•....•............•........ A-33 

Conunuter Air Carrier Maintenance and Inspection, 

....... Norman s. Grubb .•...............................•............• A-3 7 

Human Factors in Aircraft Maintenance and Inspection, 

Rotorcraft Maintenance and Inspection, James T. Moran ......... A-42 ~~ 

Nondestructive Inspection Equipment and Procedures, 

George Ansley •.........•..•.....•..•........•................. A-45 

Improved Information for Maintenance Personnel, 

Robert c. Johnson ..........................•.................. A-55 

Strengths and Problems in Maintenance Training Programs, 

Richard Hlavenka .....•.••.......•.••......•..............•.•.. A-61 

vii 
i . . ~.,- The Human Operator as an Inspector: Aided and Unaided, 

Colin G. Drury, Ph.D .......................................... A-65 

Vigilance and Inspection Performance, EarlL. Wiener, Ph.D .... A-72 

Human Performance Issues in Nondestructive Testing, 

Douglas H. Harris, Ph.D ....................................... A-77 

Appendix B: Meeting Agenda....................................... B-1 

Appendix C: Meeting Attendees.................................... C-1 

viii 
f 

Meeting Welcome 

Anthony J. Broderick 

Associate Administrator for Regulation and Certification 

Federal Aviation Administration 

There is considerable interest today at the FAA in the subject of 

aircraft maintenance and inspection. I personally am very excited about 

the fact that people are willing to spend their valuable time to get 

together and talk about something which, it is fair to say, we know 

little about. We in the FAA are not sure where this interest and this 

meeting will take us. I am confident, however, that the results will 

take us somewhere that we would rather be compared to where we are 

today. Because of the lack of maturity of the subject matter, as some 

might say, we are in a position where we might be able to make 

significant contributions to aircraft maintenance and aviation safety 

with a fairly modest investment of time and resources. It will be 

exciting to be a part of this activity. 

I am impressed with the cross section of professionals brought 

together to address today's topic - people from academia, the airlines, 

the manufacturers, the FAA, and a number of other fields with activities 

relating to aircraft maintenance. Only a collective effort and 

cooperation of this type, in a nice quiet room, will result in the 

progress we need. 

What we are really talking about today is human performance in 

aircraft maintenance, including everything from training of maintenance 

personnel to development of procedures for. maintenance of complex digital 

flight equipment. We are particularly concerned with the human's role in 

the inspection of older aircraft which have been in the fleet for twenty 

or more years. We begin, of course, with the full realization that a 

large measure of professionalism exists in the maintenance business 

today. TburoblP..m is complex and will not be solved simpl.LJ!L urging 

th~ indYU.rr_!& .. b£ing_I!!Qt"e_pr0fessionals- ~bQ!I!:!LQ.t: __ r;:~cQI!ll!lending ·.,: nice 

warmroom in which to perform maintenance. -·--··----- ------ ---- ---·-- ------

~roblelll.!__~l!.-~..l!~e i t.._is that we_ do not h.~ye an. ()t]~aniz~'!-bod.):_O_f 

information. -that-we -Gan.app ly _ f!lh~n. an .eng.ineer . determines .. tha.L an . / 

i.nspection is need~d for cracks in a particular section .of an airplane. ~::/ 

How doyou do that itl.spection? What: should-the ·ensineer-kn~bout 

principles of human performance that wHl ensure that-theinspection. is 

performed with best accyracy? -------- --------- ~ -~-· ·----

The FAA at this time is preparing an Airworthiness Directive for 

release which will require additional inspections for certain older 

aircraft. For illustrative purposes, and these may not be quite the 

correct numbers, these inspections use a 40,000 landing cycle threshold 

to begin inspections, followed by a 4,000 landing cycle for repeat 

inspections. In this case, we are applying the same inspection criteria 

to an aircraft with 70,000 cycles as we are to one with 30,000 cycles. 

This bothers me because the process for deriving the threshold for 

inspection and repetition assumes that the development of cracks may be 

detectable at 40,000 cycles and that, if cracks are not found, the 

aircraft may be flown safely for another 4,000 cycles before new cracks 
; 

J 

i 

j 

\ 

/ 

can develop to a hazardous extent. When this process is applied to an 

aircraft with 60,000 or 70,000 cycles, we are saying that if the aircraft 

is inspected in the next 500 cycles and then 4,000 cycles later, it will 

be safe. We now have evidence from two recent instances, well known to 

most of you, in which we found that this may not be true. 

In the well-publicized Aloha Airlines incident, the airplane was 

inspected and an air-worthiness action performed just a few months before 

it had the tragic inflight episode. Then, just recently we found another 

airplane, with another airline, which had about 50,000 to 55,000 cycles 

and had developed a major crack and a number of smaller ones. This 

airplane also had been inspected earlier, with its cracks discovered only 

as it was going in for repainting. So here we have two airplanes, with 

all the attention focused recently on 737's, for which somehow the system 

did not work. We have professionals involved in engineering and 

professionals involved in maintenance and yet cracks developed undetected. 

We must develop an improved approach to the inspection process and, 

more important, it must be an organized approach. We need to take a 

technological approach, break the process into its components, and then 

examine each component to see if we can build a body of knowledge that 

will apply. 

Is vigilance the issue? The job of performing these inspections can 

be terribly boring and the job frequently must be performed under adverse 

conditions. Is vigilance simply the answer? Or are we expecting too 

much of people at any level of vigilance? 

What about training? Aircraft of today are more complex and employ a 

variety of materials and construction techniques. New systems are 

available for the inspector. Has our training establishment kept pace 

with these changing technologies? While I suspect that it has at least 

to a certain extent, I do not know whether additional attention 

is required on training. 

Another issue is communications. How do engineers at a manufacturing 

facility, where a Service Bulletin is written, and FAA engineers, who 

approve the Bulletin, communicate with engineers at an airline and with 

airline maintenance personnel? How do we communicate what we expect and 

what we want done? Are we doing a good job in this communication? I 

suspect we do a heart-felt job but I do not believe we have good 

guidelines to follow. This is a part of the system that has never been 

critically analyzed. 

·~. Then there is the work environment. Chicago in the winter can be a 

cold place to be. Tasks that normally are routine and that must be 

performed hundreds of times can be quite difficult under these 

conditions. When you look toward some of the more subtle inspections we 

are talking about, there is a question as to whether we are realistic in 

expecting quality performance under adverse working conditions. 

So, how have we gotten away with it? Well, I am not sure we have 

gotten away with it. We have seen some significant maintenance-related / 

accidents in the last decade. Al_~_,tl'le average age of the fleet is 

increasing. As a result,greater.<!emands and greater reliance are going 

to be jil_aced on the: 1118intenance and inspection functioqs. We must know 

the good and bad points of these functions and how to deal with them. 

2 
r 

t 

.y 

;e 

a 

1 

One avenue for consideration, and a favorite topic of mine, is the 

use of robots. When I visit Boeing, I see huge wings being automatically 

drilled and riveted. Excellent use is being made of robotics 

technology. But when I go to an airplane on the line or in a maintenance 

operation for heavy checks, I do not see a lot of automation being 

applied. Why not? Possibly because it is expensive and not readily 

available. But shouldn't this be something we look to as a basis for 

improvement? Shouldn't we encourage industry to develop effective ways 

to use robotics? While this might not provide an ultimate answer, it 

could contribute significantly. 

In the future, we will be relying not so much on the genius of the 

designer and the production staff but, with the aging fleets, on the 

genius and the dependability of the maintenance staff. In other FAA 

programs related to the aging aircraft fleet, we are looking at the 

structural aspects of aircraft design, our database requirements, and 

actions to be taken. But no matter what.w_EUJ!Llflit.h_r~_!,q d~ign, 

i~rovement.IL.Q!'_Pro_duc~J:On imp.t:.C>~et!I~I!!-1'..__'!'_~!!\UJ!.t_r;..!lcognize that "!~111 

rely more and more heavily on maintenance in the coming years. -- -·-- ---------- ·-------- -------- ____ , __ ,_, .. ---· -·· ···-·- --~ ·---- '"'' ----

Let me close by again thanking you for coming. We are here to 

exchange infot~tion and listen to ideas. Even if, as a result of all 

the thinking and talking we do here, not a single FAA Directive is 

written, I am confident that the exchange of information among leaders in 

this part of the aviation industry will be worthwhile and, in itself, 

will result in safety improvements. Thank you. · 

3 

., 
' '. 

"'· 

Introduction 

The Federal Aviation Administration sponsored a two-day meeting in 

October 1988 to address issues of human factors and personnel performance 

in aviation maintenance and inspection. Presentations were given by some 

13 individuals representing the full spectrum of interests in commercial 

aviation. Presentations also were given by three human factors 

scientists with backgrounds in vigilance and industrial inspection 

technology. Each presentation, as well as the following 

question-and-answer period, was recorded for transcription and study. 

The objective of the meeting was to identify human factors issues of 

importance, particularly as such issues might contribute to inspection or 

maintenance error. The desired outcome was to be (1) an ii!\I\.tg_ll.ed 

understanding of personnel performance in aviation maintenance and (2) 

. recommendatl.ons, as appropri.atii; f.o . the FAA. coricerrling needed research 

efforts--and/or possible new or revised regulatory actions. 

The following section presents recommendations developed through a 

synthesis of comments and suggestions made by attendees both in their 

formal presentations and during subsequent discussions. The 

recommendations have been reviewed for intent and for accuracy by each of 

the presenters. Following the recommendations, an edited version of each 

presentation is included as Appendix A. 
e 

,e 

r 

f 

h 

Aviation Maintenance Parameters 

Aviation maintenance operates as an indispensable element in supper~ 

of the larger U.S. aviation industry. A review of human factors issues 

affecting the quality and efficiency of aviation maintenance personnel 

should be conducted with an understanding of industry parameters. An 

overview of the industry will illustrate the scope and diversity of 

maintenance requirements faced by the industry. 

The mix of aircraft in the air carrier and general aviation fleets is 

shown in Table 1. The data for air carriers in Table 1 include 

scheduled, supplemental, commuter, air taxi, and air cargo carriers. 

These data illustrate why primary attention is being given to air carrier 

operations today. The carrier fleet c~nstitutes aliii2SLJlXB.C.tly two 

perc~e~nl;. ofj;he .entir-e m.1mb~~ of aj.rcraft~~op~r~tj,ng_~~!:!_in~_t;_l)~ l}nited 

States ... However, this fleet ~'"'1'KF_i~.s _l'Q\1~ .Ume.s~ -~~~enger .loadOr 

OU\er-classes of aircraft. In terms of safety of the generai .. pubTic;-air 

carrier operations wa:r1·ant the first look. However, no one should be 

insensitive to the fact that over 100 million passengers also are carried 

annually in general aviation operations. 

Table 2 shows the projected growth of the u.s. aircraft fleet over 

the next ten years. This shows that growth as foreseen will take place 

in air carrier operations and in commuter airlines. No growth is 

projected for general aviation over this ten year period. New general 

aviation aircraft will enter the fleet but certainly not at the rate seen 

in 1978, the peak production year. Other aircraft will retire during 

this period, and as a result there will be no growth for general aviation. 

TABLE 1 

U.S. AIRCRAFT FLEET 

(1986) 

Aircraft Air Carrier General Aviation 

Turbine 

Piston 

Rotorcraft 

Passengers Carried 

4,063 

364 

4 

419 

Air Transport Association (ATA) 

million 

5 

' 1 

. 10,500 

195,700 

6,900 

119 million 
-

Air Carrier 

Commuter 

General Aviation 

Domestic Passenger Load 

TABLE 2 

PROJECTED GROWTH OF 

U.S. AIRCRAFT FLEET 

(1987 - 1999) 

Forecast 

Annual Growth 

2.6'l'. 

2.9 

0.0 

4.6 

Note: In past two years, 759 large jet aircraft were delivered. Very 

few older aircraft were retired. 

Federal Aviation Administration (FAA) (1988) 

Table 2 also shows that during the past two years, 759 large jet 

aircraft have been delivered to the airlines. Over that same time 

period, very few older aircraft - the DC-9s and early 727s - have been 

retired. This illustrates the changing dynamics in fleet 

characteristics. 

An important charag_t..!!J;:isU.c-of.. both the air carrier~leet and the 

general-aviation fleet is that each is growing older. Table 3 shows the 

average age for a group of selecte<f-aircraft "C.iirrently in use in the u.s. 

air carrier fleet. While these aircraft obviously were selected to 

demonstrate the aging characteristic, nonetheless they are representative of aircraft used in current operations. Note that four of these 

aircraft have an average age in excess of 20 years. Also, considering 

that these data are current as of the end of 1987, the average age of the 

aircraft shown is now somewhat greater than indicated. 

Aircraft 

DC-8-50 

727-100 

BAC-1-11 

DC-9-10 

707 

737-100 

DC-8-70 

747 

~Ve!Jl&e.a&.e of 

as of year-end 

ATA (1988) 

TABLE 3 

AGE OF SELECTED AIRCRAFT 

IN U.S. AIR CARRIER FLEET 

Number Average 

16 23.1 

344 21.7 

38 21.6 

91 21.0 

35 19.8 

20 19.2 

85 19.2 

167 13.9 

all aircraf;t in u.s. a~r c~r_r~_~r fleet = 

1987. 

6 

Ase 

12.1 years. Data 
LA 

s. 

:he 

ota 

"' _/ The age of the U.S. general aviation fleet is depicted in Figure 1. 

It is obvious that general aviation ha~_the same problem_w~tb aging 

aircraft as ~ir carr~. Considering that these data now are 

probably two-years old and thus are shifted to the right slightly, the 

average age for the entire general aviation fleet is in the order of 20 

years, with some aircraft more than 35 years old. It is also interesting 

to note that every year the data in Figure 1 are being pushed to the 

right slightly because of the fact that aircraft are not being retired 

from the general aviation fleet as had been initially anticipated and 

very few new aircraft are being introduced. 

0-4 10-14 20-24 30-34 

5-8 15-18 25-28 35+ 

Age (Yeare) 

Figure 1. Age of U.S. general aviation aircraft. (FAA, 1987) 

"------· ' 

-. --:::,, ~ile the ll&e of an aicylane is important, ma,ini;~fl_ance reguiremwts 

for air. _c.arrier::...aircraft. ar.e...dete£!!1j,ned _ms>re cffr'!ct~_ the_-!],umber_ of. 

l_anding cycles and pressurization cycles. Table 4 shows the "economic 

design life objective" establishetfbY Boeing for four of its widely used 

con~ercial aircraft. Note that for each airplane a twenty-year 

set·vice-use objective is set. Objectives for landing cycles vary, 

however, depending on anticipated use patterns (short flights-many 

landings vs. long flights-few landings). 

7 
r r 

TABLE 4 

ECONOMIC DESIGN LIFE OBJECTIVES 

FOR FOUR AIRCRAFT 

Landing 

Aircraft Cycles Hours Years 

707 20,000 60,000 20 

727 60,000 50,000 20 

737 75,000 51,000 20 

747 20,000 60,000 20 

Boeing Commercial Airplanes, 1989. 

Figure 2 shows for nine·aircraft types the number of landing cycles 

made by the high-time airplane compared with the economic design life 

objective for that aircraft type. In many instances, the landing c~ 

for the high-time airplane exceeds by a consii1er811e amount-thi c¥~1~ 

established iilitialiy as an objective. This does not mean, of course, 

that-"these-ati:"C.raft are in danger of falling apart at any moment. Each 

of these aircraft has been periodically inspected and· maintained, with 

worn parts and systems replaced, as these landing cycles were 

accumulated. "Economic life objective" is simply a concept established 

during the design of the airplane. The objective is not set as a 

limitation on the airplane. 

100 

~ Deelgn Objective 

- High Time Airplane 

78 

J_ 

:I eo 

-g~ 

~- .= 

28 

0....._~ 

707 7:S7 IIAC 1-1 1 D0-8 DO-1 0 

727 747 L-101 1 Do-• 

Figure 2. Landing cycles for selected active air carrier aircraft. (FAA, 1988; Boeing 

Commercial Airplanes, 1989) 

As the commercial aircraft fleet in the United States 

landing cycles increase, the burden on maintenance grows. 

maintenance industry today is large and continues to grow 

8 

ages , and ___ as 

The 

in parallel 
with the expansion of airline operations. Table 5 shows that over 50,000 

mechanics are employed today, with a total cost for maintenance operations which exceeds $6 billion per year. At the present time, about 

eleven percent (11~) of maintenance activities are contracted, with the 

major part of maintenance being accomplished by the airlines themselves. 

The $6 billion cost for maintenance shown in Table 5 represents an outlay 

of some eleven percent (11~) of airline operating revenues. Maintenance 

is expensive. 

Mechanics employed 

TABLE 5 

MAINTENANCE PARAMETERS 

FOR U.S. SCHEDULED AIRLINES 

= 51,233 

Maintenance expenses = Over six billion dollars 

Major carriers contract 11~ of maintenance work 

ATA (1988); Office of Technology Assessment (OTA) (1988) 

Maintenance costs as a percentage of total operating costs is 

important but it may not be the best indicator of maintenance expense. 

The percentage will be influenced by the contribution to operating costs 

made by fuel costs and non-maintenance labor, both of which are known to 

have wide fluctuations. Therefore, maintenance expense trends for 

specific aircraft are considered more meaningful. Figure 3 shows the 

average flight equipment maintenance expense for the B727-200 fleet. 

Thi.s shows that for each revenue aircraft departure since 1982, there has 

c;t·'·~" an almost steady iw~rease in maintenance ex·pense. 

780 

700 

"il' eeo 

en 

--

! 

~ 

I 

eoo 

eeo 

eoo 

4150 

-400 

7e 77 78 78 eo e1 e2 83 e4 ee ee 

Year 

F gure 3. Average flight equipment maintenance expense for 8727-200 fleet (Dollars. 

revenue departure). (OTA, 1988) 
In summary, data describing the U.S. aviation industry and its 

supporting maintenance base show an expanding industry in which the 

average age of aircraft used both by commercial airlines and by general 

aviation increases each year. There is a corresponding increase in 

maintenance costs. Both of these trends point to a need to ensure that 

aircraft maintenance, and the use of maintenance personnel, is conducted 

as efficiently as possible. The safety of the public and the economies 

of air transportation support programs to optimize maintenance operations. 

References 

Federal Aviation Administration. General aviation activity and avionics 

survey. FAA Report No. FAA-MS-87-5. Washington, DC. Decmeber 1987. 

U.S. Congress, Office of Technology Assessment. Safe skies for 

tomorrow: Aviation safety in a competitive environment. 

OTA-SET-381. Washington, DC: U.S. Government Printing Office, 

July 1988. 

Air Transport Association of America. Air transport 1988 - the annual 

report of the U.S. scheduled airline industry. Washington, DC, 

June 1988. 

Federal Aviation Administration. Briefing by Western Region. 1988. 

Federal Aviation Administration. FAA aviation forecasts - Fiscal years 

1988 - 1999. FAA Report No. FAA-AP0-88-1. Washington, DC, February 

1988. 

10 I I . 
>ns. 

:.§.._ 

7 • 

Conclusions and Recommendations 

The attendees at this two-day meeting had diverse allegiances, some 

being from the Federal Aviation Administration and the National 

Transportation Safety Board, some from aircraft manufacturers, others 

from the airlines, and others from remaining segments of the industry. 

As a result, many of the suggestions and recommendations which were 

offered were specific to that part of the industry represented by the 

attendee. However, some themes are apparent. The following 

recommendations represent a grouping of attendee suggestions according to 

these themes, with specific recommendations included within each major 

topic. Some of the recommendations are directed to the FAA; others 

toward the industry itself. 

Communications 

"Communication" formed some part of more recommendations than for any 

other topic addressed during the meeting. Comments were made by several 

members that even if the meeting accomplished nothing else, it served a 

very useful purpose by allowing representatives from all parts of the 

industry to get together and exchange views. Credit was given to the FAA 

for providing the forum in which this exchange could take place. ~/~~ 

Apparently the changing structure of the airline industry as it proceeds ( ;~/~ through deregulation has seriously disrupted industry networking. In (/// ) 

earlier days. there existed a more effective communication network anio~g "E::::::_~// airhne operators, -8;!etwQn.~Wt1I~aiso.inc:it!ded".iiiiiiii,[!l.ct_~rs. ~ .. TilTs ____ _ 

network does not seem to exist today, at least not to the same extent, 

and attendees voiced a real need either to rejuvenate the network or 

replace it in some manner. At the conclusion of the meeting, several 

attendees expressed a~ desire that the FAA not let this meeting be a 

one-of-a-kind affair. They wished to see some comparable get-together 

occur at least once a year. 

The purpose of a periodic meeting would be to review maintenance 

problems and to spread word through the industry concerning new 

procedures and new technologies. One attendee stated, "If we have a 

safety situation and have options to resolve the problem, everyone should 

know about it." 

Aflother expressed need, as part of the _coll)l!l!ln_i~l!-t;Aon~-~Titreaty, was 

(.Q.[ __ a Ciata base_ of- maintenance-frlfo-riiiati.On.~t;o b!!.~-ed...thr!lughout ·uie··-

industri:- There does not exist at this-time-aRy central repository 

containing assembled knowledge concerning maintenance procedures, 

technologies, equipment capabilities and limitations, unique aircraft 

problems, personnel variables, and so on. This need is supported by the 

circumstances surrounding the loss of an engine by a DC-10 during 

take-off several years ago. In this case, apparently one operator had 

learned that removing the engine and pylon together for maintenance could 

cause cracking of part of the structure at the attach point between the 

pylon and the wing. While this airline obviously stopped using the 

procedure, word of their experience did not become immediately available 

to the rest of the industry. 

~oi,ffi; was made that manufacturers n~__1p_j:_e_!!!!_withJ..i.~~~All.. 

Operator~p.- _!:._!le collection of necessa-ry-data for an_!f!.dUs_try~ jl,lli;a..ll_as_e...._ 

By so _doJ_ng,_ both-partieswouTifllave heft"er-Tnsignt into the kinds of 

11 
' 

I 

"l_,, 

m!lintenance errors be in& !!lade,~ the~ most fre9.uent types, and aircraft 

qe~Ign features relating~J;o increased !'rrgr. 

The importance of continually striving to ensure good~ communications 

between airline management and the labor force was noted. Morale of th~ 

" workforce can be iJlfJul'.riced positively by let.tlng worker~i know whiin-a-Job 

h'S.s been weiCd:one. Also, the workforce should have some insiglit 1nto --

the~-prol:>Teins being faced by management. For example, one airline had 

numerous occurrences of engine oil leaks, some involving inflight 

shut-downs and unscheduled landings. While airline management was quite 

concerned over these occurrences, it apparently viewed them as a series 

of unrelated mechanic discrepancies instead of a systemic problem. As a 

result, appropriate management corrective action was not taken, and 

appropriate information and concern was not passed to the workforce. 

Consequently, maintenance personnel did not give this issue the full 

attention it should have received. 

Finally, note was taken of the fact that not all airline operators 

attend industry meetings, such as those sponsored by the Air Transport 

Association. In fact, the point was made that operators who do not 

attend industry meetings are the same ones who are not achieving the same 

level of maintenance quality as other operators. The communication value 

of such meetings is undeniable. Some means must be found to encourage 

all operators to attend these meetings. 

Recommendations 

1. The FAA should sponsor at least one more meeting addressing human 

factors and personnel problems in aircraft maintenance and inspection. 

All airline operators, including regional carriers, should be invited. 

One topic would be to assess the desirability and appropriate means for 

institutionalizing this industry meeting. While there might be some 

invited speakers to discuss new technologies or comparable matters, a 

good part of the meeting should be set aside for panel discussions led by 

an industry member and open to all other members. 

2. The FAA should consider means for encouraging or developing a 

data base of industry information concerning maintenance technologies, 

procedures, and problems. An FAA-sponsored Clearinghouse for Maintenance 

Information would be of great value to the industry. Apparently over the 

last several years the Electric Power Research Institute (EPRI) has been 

developing a comparable data base addressing maintenance issues in 

nuclear power plants. Possibly a representative of EPRI could describe 

this data base, and methods for developing a similar one, as one item in 

the FAA/industry meeting described in Recommendation 1. 

Personnel 

Recruitment/Availability. ·The airline industry has expanded rapidly 

in recent years with a consequent need for larger numbers of qualified 

maintenance and inspection personnel. Resources to meet these new 

staffing requirements have not always been there. This is true both for 

trunk carriers and for regional airlines. In fact, regional airlines may 

be even harder hit as some of their personne'l move to major carriers. 

Commuters then must fill their ranks from maintenance schools, the 

military, and from fixed-based operators. The result is that, both for 

12 
ns 

he 

}ob 

te 

,s 

a 

:ame 

•lue 

1man 

•r 

I by 

tnce 

the 

•e 

in 

lly 

I 

'or 

may 

•r 

major carriers and for regional carriers, the workload is expanding and 

the experience level of maintenance personnel is decreasing. To 

illustrate, the following statistics apply to Inspectors for one major 

carrier. 

46~ have less than three years 

22~ have less than two years 

12~ have less than one year 

This is in an operation in which the Manager of the Inspection Department 

estimates that it takes an inspector two years to become effective; six 

years to become efficient. 

The result of the lowered level of experience for inspectors and 

mechanics is that work is done more slowly and more mistakes are made 

that must be corrected. An additional burden is placed on the inspector 

force. / 

'/ f// 

V Traininr.. Much discussion during thEU.tl~~i_!\g c,e.n!;~red on .a.II.!~!U!l!..c;L.of •vtr.!lj.ning f.or .maintenance pei'!2!1nel. Much of the problem was attributed 

to requirements for training established by the FAA in Part 147 of the 

Federal Aviation Regulations. Some parts of the initial training covered 

b:,c ParL 14 LdeaLwit:.b_ woodwork, _WE<_ld_illS, XiiDric---st<fti. repair, ...a.nd....r.a.~Jlll_ 

engines, all topics of.. .little ~o.rg•o;>'l!'_~n!ie forthe c.!!rrier jet fleet. The 

A&P curriculum .. was generally viewed as inadequate. - ---·-··-··--

Another problem is that avionics technicians who have completed an 

FAA-approved avionics school are treated differently than those who have 

completed an airframe and power plant school. For example, an Avionics 

Manager cannot be Director of Maintenance without acquiring an A&P 

license. However, an A&P license alone qualifies one to become Director 

of Maintenance, while understanding little about the microprocessors, 

integrated circuits, and sophisticated avionics which are critical to 

modern aircraft. 

The general dissatisfaction with Part 147 should be tempered by the 

k!!.2wl edge -tbat.-.the.FAA. currenuy::.U ·wlelrlin&.. t.hil3 .. document forchange-:--

One member of the training establishment offered the-si.igge!it.ion tnilt 

during this period of change consideration be given to expanding coverage 

to include topics covering professional ethics, professional 

communications, and personal commitment to one's job. He felt that such 

training could be of considerable value in expanding the professionalism 

of maintenance personnel in the next decade. 

~e suggestion for improvement was that training be expanded tp 

include certai~ post-graduate~cialty programs. Such programs would be 

added to the existing curriculum and would be elective. This would be 

one way of dealing with such issues as the fact that at this .time no 

training is required for helicopter maintenance. Also, advances in 

nondestructive testing (NOT) technology and procedures have exceeded the 

number of qualified NOT personnel. One of the graduate courses might 

include use of such advanced test systems. 

Training for maintenance personnel is ongoing, extending to some 

extent throughout their career. For example, one operator has five 

percent (5~) of the inspector force in formal training at all times. 

During such training, maximum use· should be made of new training 

technologies. For instance, videotapes produced in-house are now being 

13 
used by one carrier to illustrate compliance with latest Airworthiness 

Directives. This carrier is quite pleased with results of its video 

program. This and other technologies should be used industry-wide. 

Licensing/Certification. The issue of "type rating" mechanics in 

different aircraft was raised as a means of ensuring that a mechanic's 

qualifications are appropriate for the aircraft-on which he works. 

Aircraft are becoming more sophisticated; helicopters are extremely 

complex; and avionics systems represent the very latest in technology. 

At this time, airline operators, in keeping with their insurance 

coverage, limit the duties of certain mechanics to their experience 

level. However, no regulation covers this. A suggestion was made that 

current licensing procedures, particularly with respect to avionics 

technicians, be reviewed and that consideration be given to the 

establishment of new levels of licensing and certification. The Canadian 

Aviation Regulations, which require licensing by aircraft type for 

mechanics, was cited as a possible model. 

Discussions among all attendees brought forth pros and cons 

concerning increased licensing or certification. Concern was expressed 

over additional layers of regulation. However, if new licensing 

techniques would add to the quality of maintenance, they would meet with 

approval. 

Reconuuendations 

1. The current review of Part 147 should be expedited as feasible. 

Results should include provision for specialization training as a formal 

and advanced part of the curriculum of approved schools. As part of this 

effort, consideration should be given to current licensing procedures for 

avionics technicians. These procedures should be revised consistent with 

the growing role of avionics personnel in aircraft maintenance. The 

result of all of this will be a better entry product into airline 

operations and the resolution of some current job problems. 

2. Consideration should be given to ways of promoting aviation 

maintenance as a career. The FAA can play a useful role by encouraging 

or actually developing some promotional materials. Are brochures 

describing aviation maintenance available for distribution at the high 

school level? Is there an up-to-date video which describes the 

profession and its rewards? 

3. Should there be another meeting of this type, as recommended 

earlier, "training technology" should be a key topic. The FAA should 

invite some expert who is familiar with all of the latest training 

systems to conduct this session. 

J Job Pressures 

'" Tim~r.eli.Sllre_._,also_..J<n_q_wn_.!l!L "r,ate time," is. considered_by many: _to_be 

the most important fa.cto:r affecting_p~rf.oruw.nce 9Cmecliali:ics and ··· 

inspectors. Management and the mechanic force have the pressure-of 

getting the airplane to the gate on time. Inspectors have the pressure 

of being certain the aircraft is air-worthy. The conflict between these 

two driving pressures can produce an adversarial relationship Which does 

not benefit either side. 

14 
t 

ian 

d 

.th 

'· tal 

chis 

for 

rith 

lg 

> be 

>es 

Ground time available for maintenance also can produce job 

pressures. Striving for higher aircraft utilization means that more 

maintenance must be accomplished in fewer hours, with these hours 

frequently being at night. Under these conditions, the need to meet an 

early a.m. departure time can again cause friction between the 

maintenance and inspection groups. 

The consensus is that inspectors must be insulated from production 

and from all the rest of maintenance, yet these groups must complement 

one another. In some operations, this insulation is expressed in writing 

and supported verbally. Yet the pressure for on-time service inevitably 

will cause some group dissonance. The objective is to insure that such 

dissonance does not seriously impact the perfot~nce of either group. 

One way, of course, is to have inspectors and mechanics report to 

management through different organizational chains. Even here, however, 

the pressures remain. 

Another factor impacting job performanc~ is fatigue Young mechanics 

just out of school who may-lU!starting a family find it difficult to do 

so on entry wages. As a result, they take a second job and are quite / 

fatigued by the end of their maintenance shift, particularly if it is the .:Lc" 

night shift. In other instances, the shorta~e of mechanics requires 

overtime. work which itself contributes to fatTgue: .. ATioCEhl.s tends to 

make ~in~e!'aric_e_j>~~s(in_n~_! mar~- error-prone. ---- -------- . . - ' - ·-- ---·-- ··---- Recommendations 

1. All parties should consider ways to insulate inspectors from 

management and from the rest of the Maintenance Department. Inspectors 

should not feel the "gate time" pressure. With older aircraft, it is 

particularly important that inspector performance be of the highest 

quality. This might mean a review of inspection tasks to see how many, 

if any, might be shifted from ongoing maintenance activities to the 

longer scheduled maintenance visits, where gate time is a more distant 

concept. Supervisory personnel should be given some training in the 

detection of fatigue and its insidious effect on work performance. If 

fatigue appears to be a constant problem, some rescheduling of 

maintenance activities might be considered. The first step, of course, 

is to detet~ine whether fatigue is or is not a problem. 

JPerfot~nce Improvement/Job Design 

Many individual variables can be considered in a program to improve 

performance for maintenance personnel. A human factors scientist in 

attendance indicated that, for inspector performance, such variables 

include conspicuity of the signal (flaw), signal-to-noise ratio, length 

of inspection periods, social atmosphere, and others. Pursuing this 

list, in effect, constitutes job redesign, which has high potential for 

performance improvement. A proper job redesign, however, would not 

consider each of these variables separately. 

A full job design, or redesign, would begin with a specification of 

overall system objectives and the contribution of the human. The human 

would be considered as one system component with the designer's job then 

being one of matching other system elements to the human. This is done 

on the basis of a task analysis of operator activities. The task 

15 
" " 

analysis points to man/machine mismatches, workloading of the human, and 

many other variables related to performance. A meaningful job redesign 

requires a task analysis as a starting point. 

An important product of a task analysis is a description of the kind 

of performance feedback required and the manner in which it should be 

presented. Human factors scientists noted that feedback must be 

complete, relevant, and timely to be effective. However, the requirement 

for feedback is highly dependent on the nature of the task. In one study 

cited, performance in a visual inspection task was markedly improved 

simply by providing feedback concerning the inspector's performance more 

rapidly. The importance of feedback to job design was very apparent. 

One attendee noted the need for a research center, or at least a 

coordinated research effort, which might be dedicated to studies of job 

design and aircraft design and the contribution of each to maintenance 

error. He noted that there is no place where regulatory agencies, 

operators, and manufacturers can team together to examine concepts and 

other variables assumed to play a part in maintenance effectiveness. 

Recommendations 

1. Consideration should be given by the FAA to an effort in which a 

task analysis could be conducted both of maintenance performance and 

inspection performance. To be useful, such an analysis need not describe 

performance on a second-by-second basis. It should be done in sufficient 

detail, however, that the physical, perceptual, and mental aspects of the 

task can be reviewed. Input/output requirements and task loading must be 

defined. A description of relevant environmental factors also will be 

needed. In all, the task analysis should be conducted in sufficient 

detail that results can feed directly into computer-based efforts to 

model maintenance and inspection performance. 

2. The suggestion concerning development of a research center where 

maintenance concepts might be studied in detail warrants careful review. 

Inasmuch as either the FAA Technical Center or the Civil Aeromedical 

Institute could undertake such a program, no new facilities would be 

needed. An additional task element to either facility, with appropriate 

guidance and funding, could initiate this research center. 

Maintenance Information 

Effective maintenance is predicated on a continuing flow of 

'· information. Th~ !nformation suy~ortin&_l\lai_nten!if!<;_e_ IIIUSt b~.,!,~~~l)'_,_ 

a~curate, appropri.at;~_tQ,l,!,!ler _ _r_eq!!ire~ents, and in .1! fOI11! readily · 

und_~?§ltood~- ·;. number of comments indicated concern over the adequacy of 

mainte~nce information today. 

The demand for new generation aircraft apparently has resulted in 

aircraft being placed in service before a full technical support program 

can be developed. one consequence, according to regional air carriers, 

is that maintenance manuals are inadequate. They leave much to be 

desired in terms of wear limits, damage limits, repair schemes, and 

adequate or accurate wiring diagrams. As a result, operators must 

frequently make requests of manufacturers for repair limits, repair 

16 
1nd 

.nd 

1ent 

.udy 

b 

a 

ibe 

ent 

the 

be 

<"e 

... 

te 

lf 

IDI 

schemes, and other relief. This information is only forthcoming after it 

has been developed by enginee<"s and app<"oved by FAA representatives. 

This causes delays in the provision of good technical info,-mation and is 

a so~rce of frustration. Maintenance personnel are precluded from 

proceeding with subjective repair judgments which might conflict with 

later maintenance documentation. 

Where a number of individuals are doing the same work, 

standardization of info,-mation is essential. Although there is an ATA 

system which specifies a standard format fo<" finding material in a 

maintenance manual, the mate,-ial itself differs among manufacturers. 

Maintenance and inspection manuals themselves are not standard in te,-ms 

of shape, size, or format. Standa,-dization of language requires 

additional work. For example, turbine temperatures fo,- different 

ai,-craft are expressed as: EGT, T4, TS, TIT, and TOT. Although areas of 

pickup on the engine may differ, all of the figures p<"oduce the same 

information. Standardization of format and language would be of value. 

The aviation industt·y well recognizes the need fo<" prope<" maintenance 

infot~ation. In an effort to imp,-ove the situation, several years ago 

the Douglas Aircraft Company developed an "Advanced Maintenance Infot~ation Packet." In this, maintenance tasks were presented in 

sequence, with accompanying graphic presentations, with cautions and 

warnings fit into the sequence, and with tools and special equipment 

identified p<"io<" to the task. Tests showed a considerable reduction in 

errors when this packet was used. 

The Boeing Company, in another program to improve the situation, 

developed an Automated Customized.Task Card. In this system, material 

from the maintenance manual is computerized, thus eliminating the task 

card reader and the microfilm reader/printer. Material now is accessed 

directly from the computer and is more readily available. Errors 

encountered previously in preparing data for the mechanic have now been 

eliminated. 

Many attendees noted issues with Service Bulletins. These bulletins, 

prepared by the manufacturer and reviewed by the FAA, are used to 

identify airct·aft problems and maintenance needs after the airplane has 

entered service. They are prepared by engineers and can be complex, 

often using language more meaningful to engineers than mechanics. The 

Boeing Company is attempting to improve these bulletins by using 

"simplified English." Apparently, however, much remains to be done by 

the industry at large with respect to Service Bulletins. 

In an effort to extend the state-of-the-art of information 

presentation, the Air Force has been working for some years on an 

Integrated Maintenance Information System in which needed information is 

provided to a mechanic directly at the flight line through use of a video 

display. Through this display, the technician can access a number of 

different data bases to support his immediate requirements. In the 

preparation of this system, scheduled for field testing within the next 

few years, the Air Force has addressed many of the human factors issues 

involved in preparation and delivery of maintenance information. 

Recommendations 

1. Any program to improve maintenance performance must address the 

issue of adequacy of maintenance info,-mation. Technical documentation to 

17 
support maintenance must be accurate and timely, must meet the needs of 

the user, and must be presented in a completely intelligible format. The 

FAA should review its surveillance of maintenance manual preparation to 

ensure that proper technical data are supplied to operators, particularly 

concerning wear limits, damage limits, and repair schemes. 

2. The FAA should sponsor a program to collect and categorize 

infot~tion on research activities pertaining to maintenance data. We 

know of work being done by Douglas, Boeing, and the Air Force. We do not 

know of other industry initiatives or of relevant research outside the 

aviation industry. Should there be another meeting addressing human 

performance in aviation maintenance, one session should be devoted 

entirely to "Requirements and Advances in the Improvement of Maintenance 

Information." 

18 
,f 

The 

:o 

trly 

not 

ICe 

APPENDIX A 
FAA Regulatory Requirements 

For Aircraft Maintenance and Inspection 

Raymond E. Ramakis 

Manager, Aircraft Maintenance Division 

Federal Aviation Administration 

The attention of this meeting is on the human factors of aircraft 

maintenance and inspection. Rightfully so, since this is where the 

problems are. If we find some failure in aircraft design, we can issue 

an Airworthiness Directive and thus correct the situation. Procedures 

for dealing with design issues and aircraft faults are clearly specified 

by the FAA. It is the area of human factors that has not been touched. 

I would like at this time to review in very general terms the 

regulatory requirements established by the FAA for aircraft maintenance 

and inspection and note the human factors implications of these 

regulations. 

In the certification process for a new aircraft, regulations require 

the manufacturer to develop an appropriate maintenance program. 

Basically, he is required to provide an airplane manual and a continued 

airworthiness program for his airplane. 

The basic maintenance and inspection program, for large 

transport-category airplanes, is developed through a Maintenance Review 

Board and a failure-fault analysis system. This system allows the 

manufacturer, the Federal Aviation Administration, and the airlines to 

work together in shaping a maintenance plan. The result is the initial 

program for maintaining an airplane. The process offers the manufacturer 

an excellent method for establishing a program that is acceptable both to 

the airlines and to the FAA. 

As the aircraft enters revenue service, it comes under Part 121 of 

the Federal Aviation Regulations. Within Part 121 is Subpart L, 

"Maintenance Requirements," which contains the federal regulation that 

governs, in a broad sense, what airlines can and cannot do with that 

aircraft. These regulations are adopted and reviewed by the FAA through 

what we call Operations Specifications. This allows the development of a 

complete and comprehensive maintenance program which has been put 

together and agreed to by all parties. 

The final document resulting from the above process is called a 

Continuous Airworthiness Maintenance Program. It covers every aspect of 

maintaining that airplane from A to z - not a stone is left unturned; but 

it does not address the human process. The document describes the 

intervals between maintenance cheeks; that is, when an "A" cheek is 

required, when a "B" cheek is required, etc. It describes all 

programs that the airline must comply with in order to be in accordance 

with the regulations. But, again, it does not address the human process. 

F.elieral-~irworthinelu! ... ~~~lation Part 121 does speak, in broad terms, 

of the requirement for a certificate holder to ensure that competent 

p~e~ adequate facilities and equiprnenr-ilre provided for the 

performance of maintenance. This is th~-~~t;~mt..J;.o ~hJ&b .hUJ!\!lJLfaetors 

ar~- Ideally, 1nterp_~et!ng ~l!~s ... bro~c1 _ _t.~J::!II~_illlly_l!l_eajls t_?at 

A-3 
wben~;;~.n aic-cc-aft comes in_foca~.c~hec.k+ J;h!rr~LWJ.il_b~LJln abundance of 

w.el:L-trainea mechanics-and inspectoc-s, al(ailable in well_:_lighted, -

.- well-heated iiil.a-cOoled hangac-s- with__p_l_e_l}_ty:~(,f~zc-.£':!~1! _ti!l\_e~to-ac~omplish 

therequtt"ed- ma1.~_!!!'~nc::,. _ anci_Jn!>P~_c_t_ians. ~ - -- ~- ---

Unfoc-tunately, the woc-ld descc-ibed above does not exist in c-eality. 

Aircc-aft typically fly all day, with utilization c-ates of 8 to 12 houc-s 

pec- day, and ac-e scheduled foc- maintenance late at night. Maintenance 

pec-sonnel, in tuc-n, face a demanding schedule to ensuc-e that the aic-plane 

is available to meet the next schedule. The natuc-e of the flight leg, 

since dec-egulation, in which "hub and spoke opec-ations" ac-e used, adds to 

the pc-oblems of the mechanic. 

+ The -~a_I!t:._p_c-_ess~c-e of ensMt"t:ng_J:.]la.t_ fl.i&htlL.maintain --"'n-~n-time schedule, pac-tially caUJ'_l!g _b_y __ the_ Deparlment . .o.f. Tra.JlSl!lU:tation, has the 

inevitable ··result -of _l>lacin&..heav~ pressuc-e on maintenance oparati9J).s----.md 

iilc~~~ifng the lfkel-ih~od that maintenance will be huc-ded and ~ossibiY"-' ift..:dequate. - ~- ----- ~-------·-A 

-\ Tc-r>Jni!l_g__p!__m"i!ltem>_n_<:~~~n~J __ j.§ __ JlnOt_l!~c-_ matt!l'_L~ 

cons_ic:ley_a_ti,op. _ The quality of tnining vades~ t.bc-ougb the industc-y. 

sonle aic-lines have training pc-ogc-ams that would c-ival a university, with 

considec-able time and c-esouc-ces invested. In othec- instances, tc-aining 

is not neac-ly as good, although it will meet minimum standac-ds 

established by the FAA. 

~~lities built foc- aic-cc-aft maintenancebd!llL.tb~ir__g~ j>fOblems. 

These structures- are lac-ge simply because th;y have to hold lac-ge~---­

aic-craft, test stands, and oth.er maintenance equipment~ They do--not lend 

themselves to- good environmental controL Even the newest hangars used -

by-some orthii largest airlines are very cold dudng the winter and very 

hot during the summer. In addition, the lighting may or may not be 

optimum for the kind of maintenance being performed. However, all of 

these facilities are completely in compliance with FAA c-egulations. 

)( T~inal ~f~ctoc- foc- consi_d_era_tion_ is that of economics. Aircnft ---- ____ .. -------- "~ __ "70 _____ ------. --·--

maintenance definitely is affected by the financial condi~-~n of an 

airline. -~Facilities, tools, and the woc-k envic-onment are negatively 

a(fected in an airline with financial difficulty. This is unfoc-tunate, 

but it is true. All too frequently, financial attention is given first 

to operations, next to marketing, and finally to maintenance. Yet, even 

with an austec-e maintenance activity, an aic-line can remain in compliance. 

Considering that all airlines essentially are in compliance with FAA 

regulations, do we have a pc-oblem? Unfoc-tunately, there are indications 

that we do. Thec-e is, of course, the well known Aloha Airlines 

accident. There also are _ins-tance>~, in which human factors definitely 

played a role, that coUld have resulted in an accident but f-ortunate!~ 

did not. ~--In'one case, discussed eac-liec-, a 737 was found to have a ~ 

numbec- of cc-acks, one of which was 55 inches long. This was covec-ed by -, 

thc-ee layec-s of paint. A c-elated Aic-woc-thiness Dic-ective said, "do a 

lfisual inspection." The visual inspection, of couc-se, was not adequate 

.. to c-eveal these cracks even though thec-e was a slight bulge (3/64") undecthe thc-ee layec-s of paint. The pc-oblem was only noted when the paint_was 

stdpped. -

A-4 
f 

lish 

ity. 

ours 

nee 

~plane 

eg, 

dds to 

with 

ning 

ems. 

t lend 

~sed 

ve~y 

of 

aft 

y 

ate, 

i~st 

even 

Hance. 

hFAA 

tions 

ely 

ely 

"' ' d by 

a 

~ate 

under 

nt,was 

' ' / 

In the case of a DC-9 accident at Minneapolis some time ago, there 

were spacers in the engine that were to be replaced if cracked. The 

results of the accident's investigation by the National Transportation 

Safety Board indicated that, although this could not be proved without 

doubt, there were cracks in the spacers and the spacers were not 

replaced. The investigation determined that there were no training 

records for the person doing the inspection. There also were no records 

indicating whether his eyesight was good or bad. 

When maintenance programs fail in some manner, as we have discussed 

above, the FAA must assume a measure of responsibility. Airworthiness 

Directives and other FAA messages to industry are perhaps not as 

practical as they could be or as well written as they should be. 

FAA regulations also deal somewhat superficially with training 

requirements for maintenance personnel. For example, consider the 

training for "required inspection personnel." These are the individuals 

Who inspect an aircraft area where maintenance, 'if done improperly, could 

lead to a catastrophic result. In effect, these inspectors provide a 

double set of eyes to ensure adequacy of maintenance. While this 

position is of obvious importance, the regulation simply states that 

"each certificate holder must ensure that persons who perform required 

inspections are appropriately certificated, properly trained, qualified, 

and authorized to do so." 

Finally, keep in mind the inspector who may be on top of an airplane 

at 3:00a.m., under cold conditions, and working his way down lines of 

rivets that in all might be 1,000 feet long. This is the individual who 

must perform his job with complete precision if the aircraft is to be 

totally safe. We must consider these human factors issues and not build 

potential errors into the system through neglect of them. 

A-5 
" ' v 

Maintenance and Inspection Issues in 

Aircraft Accidents/Incidents, Part I 

Barry Trotter 

Aviation Safety Investigator 

National Transportation Safety Board 

The data bases maintained by the National Transportation Safety Board 

include listings of aircraft accidents and incidents related to 

maintenance and inspection factors. For Part 135 operators, those 

offering air taxi and charter services, approximately 200 such events 

have been recorded for over the past ten years. This includes those 

offering both scheduled and unscheduled services. For Part 121 

operators, the commercial air carriers, the number is 49. 

In terms of any statistical assessment, the above numbers are quite 

small. However, these numbers must be approached cautiously since they 

may represent only the tip of the iceberg. In the sequence of events 

leading to any aircraft accident, one may find that a maintenance or 

inspection lapse played some part, even though the lapse might not 

represent a primary cause of the accident. 

An example of an event in which inspection lapses played an important 

part is provided by the account of a commercial 727 which lost an engine, 

in the literal sense, while approaching San Diego several years ago. In 

this case, water from a leaking toilet caused a block of blue ice to form 

on the exterior of the aircraft which then broke loose and was ingested 

by the engine, causing the engine to break loose from the airplane. In a 

review of the circumstances leading to this accident, it was found that 

the toilet had been leaking for some time and no one had picked it up 

during any of a number of inspections of the aircraft. These included 

routine inspections as well as the customary preflight walk-around by the 

flight crew. Why the leak was not discovered is not easy to explain 

since the blue lavatory water had caused a blue streak back over the 

aircraft and over the wing. On examination of the aircraft it was found 

that the stain had been there for some time. 

Some inspection problems arise as a result of complexities in the 

regulatory process which overlies aircraft maintenance. An example is 

pt·ovided by a 737 airplane which was delivered to a commercial airline in 

1969. Subsequently it was acquired by another airline, which completed 

the mandatory Airworthiness Directive inspection of exterior rivets in 

May of 1988, about five months ago, and was given a clean bill of 

health. This Airworthiness Directive did not require inspection down to 

Stringer 14 below the window line. However, there are Service Bulletins, 

which are not mandatory in the regulatory sense, covering that area of 

the aircraft. Obviously, the new operator was not informed concerning 

whatever compliance the previous operator had made with these Service 

Bulletins. 

When the aircraft was stripped for repainting recently, a 12-inch 

crack was discovered in the Stringer 14 area. This crack had nicotine 

stains and other buildup indicating it had been there for some time. 

Along the line trailing this crack were multiple smaller cracks, adding 

up to approximately a 55-inch area with a potential for a serious rupture 

A-6 
ard 

e 

y 

ant 

ne, 

In 

orm 

d 

n a 

t 

the 

nd 

in 

d 

to 

ns, 

g 

ure 

of the aircraft's structure. We do not believe that these cracks 

appeared between May and the time the aircraft was stripped for 

painting. In order to learn more about this, the NTSB has had that part 

of the aircraft cut out and brought to our laboratory for in-depth study. 

Other inspection issues arise from procedures established by 

operators to conduct specific maintenance activities. In some cases the 

procedure may be entirely adequate, but the next higher procedure - the 

one designed to ensure that maintenance personnel comply with the basic 

procedure - is inadequate. In a classic example, an L-1011 airplane was 

proceeding from Nassau to Miami when it suffered multiple engine failures 

due to loss of oil. Chip detectors had been replaced in the engines 

without the required 0-rings, and the oil simply ran out. 

In the procedures used-for replacing chip detectors, a maintenance 

supervisor would remove the 0-rings from a sealed packet, put them on the 

chip detector, and hand it to the mechanic in exchange for the chip 

detectors removed from the aircraft. In the case at hand, the supervisor 

was not present, so the mechanic simply picked up a set of chip detectors 

having no 0-rings in place and installed the detectors in the engine. 

While the usual practice of the airline precluded such an occurrence, 

there was no specific procedure designed to prevent this from happening. 

In the case of the mechanic, one can only surmise that perhaps boredom 

and the repetitive nature of this process might have played a role. 

The use of Service Bulletins to define maintenance requirements 

deserves a special comment here. Service Bulletins, prepared by the 

manufacturer and reviewed by the FAA, are used to identify aircraft 

problems and maintenance needs after an airplane has entered commercial 

service. Service Bulletins often advise compliance if an operator is 

engaged in a particular type of operation and also suggest a schedule for 

compliance. Service Bulletins are not mandatory. 

A problem arises when an airline is not large enough to have an 

engineering staff capable of evaluating the many Service Bulletins that 

arrive to select those which address particularly the type of flight 

activities in which the operator is engaged. There may also be issues of 

economy. In any event, many Service Bulletins may not get proper 

attention and thus, when the airline is acquired by another operator at 

some later date, the new owner has only a hazy idea of the maintenance 

condition of his new aircraft. He may not have specific information 

concerning which Service Bulletins were done and which were not done. 

On one occasion, one cargo airline acquired an aircraft from another 

carrier and received all maintenance records in a cardboard box. In the 

changeover, records were not systematically reviewed and some procedures, 

including the mandatory Airworthiness Directives, were not followed. One 

Airworthiness Directive required trailing edge flap spindles to be 

replaced after 18,000 hours of service. While making an approach in this 

airplane, two of these spindles broke due to stress corrosion, causing 

serious flight control difficulties. In the investigation it was found 

that the operator, unaware of the 18,000 hour requirement, had scheduled 

replacement on their not~l schedule to occur at 28,000 hours. They were 

running approximately 10,000 hours past the time for replacement required 

by the Airworthiness Directive. 

A-7 
r 

 

The above examples illust~ate some of the aviation accidents and 

incidents ~eviewed by the National T~anspo~tation Safety Boa~d which have 

been caused, at least in pa~t, by p~oblems in maintenance and 

inspection. In gene~al, howeve~, one must conclude that the system, as 

it now exists, wo~ks p~etty well. Millions of hou~s a~e flown each yea~ 

with ve~y few accidents. Nonetheless, the~e a~e two exceptions to this 

system which I think should be noted. One is the individual, whethe~ it 

be an ai~line ope~ato~ o~ a single mechanic, who is not pe~fo~ing to the 

standa~ds of the ~est of the indust~y. In this case, I believe it is 

incumbent upon the FAA su~veillance system to be able to spot this 

individual and implement a p~og~am to ensu~e that his wo~k imp~oves. 

This is especially t~e fo~ the ai~line ope~ato~. Fo~ the individual 

mechanic, the ~esponsibility falls mo~e upon the ai~line management. 

Howeve~ it is done, we must have consistency of maintenance and 

inspection th~ough all of aviation. In gene~al, this will involve mo~e 

than simply ''complying with minimum FAA standa~ds." 

The second exception conce~s the phased maintenance program in Which 

a full maintenance activity, such as aD check, is spread across 52 

blocks over eight years. This means that the airline operator does not 

get a complete look at any one time at any of the aircraft's systems. It 

also means that seven years in a high cycle operation may pass before the 

operator looks again at a critical portion of the aircraft. This may 

simply be too long to ensure adequate surveillance of developing aircraft 

problems. 

The Wational Transportation Safety Board conducts extensive 

inveBtigations of aircraft accidents and incidents of the type I have 

just described. Some of these events can be traced to the performance o£ 

personnel conducting maintenance and inspection operations. Although 

aircraft accidents directly traceable to lapses in maintenance and 

inspection are rare, they warrant continuing attention by the aviation 

industry. 

A-8 
re 

.ch 

tft 

of 

Maintenance and Inspection Issues in 

Aircraft Accidents/Incidents, Part II 

James W. Danaher 

Chief, Human Performance Division 

National Transportation Safety Board 

We at the National Transportation Safety Board are visited frequently 

by persons wishing to use our data systems as they seek answers for a 

variety of questions in aviation. Usually the visitors come away 

somewhat disillusioned and with considerably less than they had hoped for 

in the way of answers. The statistics we maintain, while they can be 

very useful, just do not always offer complete answers for aviation 

questions. This is particularly true concerning maintenance and 

inspection. The number of accidents and incidents in which maintenance 

and inspection errors are cited as causal or contributory factors is 

quite small. This small number of recorded events does not mean that 

such occurrences are not significant and pervasive. Rather, it merely 

indicates that accidents and incidents are not a sensitive measure of the 

significance of the maintenance and inspection problem. 

From a philosophical standpoint, we must realize that an accident or 

incident is at the end of a sequence of events which, in some respects, 

could be thought of as a complete breakdown of our aviation system. In 

such case, all of the measures and safety margins which have been 

contrived to prevent accidents have broken down; in that same sense, a 

mid-air collision represents the ultimate breakdown in the traffic 

control separation system. In the chain of events leading to an 

accident, maintenance errors generally happen way upstream, with nmny 

opportunities to interrupt the chain and prevent the accident. Accidents 

thus can be seen to be a very poor indicator of the real frequency of 

maintenance and inspection errors. 

Earlier during this meeting, the comment was made that the aviation 

community has barely scratched the surface in looking at the human 

element in maintenance and inspection. This certainly appears to be 

true. A look at the Safety Board's categorization of errors in its 

aviation accident and incident data system indicates there is only 

limited coding capability to realistically tally the errors that occur in 

maintenance and inspection tasks and which might have contributed to 

mishaps. 

Quite a bit has been said about the environmental aspects of 

maintenance, i.e., the excesses of tempet:atUr~-.--~-Vibraf.TOn;noise, 

illumination, precipitation - all those workplace environmental factors 

that can adversely affect human performance and could contribute to 

errors of omission and commission. These undoubtedly are important 

factors influencing performance. However, I submit that we should not 

focus solely on these environmental factors in our study. One of our 

investigators returned from the Aloha Airlines accident and stated 

informally that "the problem isn't so much a coveralls problem as it is a 

coat and tie problem." It was his belief that the mechanic and inspector, who at times work under adverse conditions, often bring a high level 

of motivation and professionalism to the job which helps them cope with 

such conditions and sustain good performance. What is required is a more 

A-9 
r 

 

i 

comprehensive approach to providing the maintenance team with the full 

Wherewithal to do its job. All of the key elements in the aviation 

industry must contribute to this wherewithal, including the manufacturer 

Who provides initial guidance concerning maintenance procedures and 

policies, the air carrier maintenance department which establishes 

specific procedures and tasks, the air carrier management which is 

responsible for procurement of the best maintenance facilities and test 

equipment, and carrier production personnel who must work closely with 

maintenance to strike a balance between the sometimes conflicting time 

demands for proper maintenance and the pressures to meet flight 

schedules. All parties must work together to support the maintenance and 

inspection team. 

Another factor affecting the quality of maintenance and inspection is 

the extent to Which information about operating experience is 

disseminated through the industry. The physical separation of an engine 

from the airframe of a DC-10 during takeoff from Chicago several years 

ago serves as an example here. In this case, the manufacturer had 

recommended earlier that, When removing and replacing the wing-mounted 

engine for maintenance purposes, the engine should be removed first in 

one operation and the pylon removed next in a separate operation. This 

was a labor intensive activity. The operator, when considering personnel time and costs involved, obviously reviewed the procedure to 

determine the best and, hopefully, easiest way to accomplish this engine 

change. The NTSB accident report notes that raising and lowering the 

engine and the pylon as a single unit reportedly saved 200 man-hours of 

maintenance time per aircraft. Also, and quite important from a safety 

standpoint, it reduced the number of disconnects - that is, the hydraulic 

lines, fuel lines, electrical cables, and wiring- from 79 to 27. In 

all, there were strong incentives to work with the engine and pylon as a 

single unit. On the other side, however, moving these two components as 

a unit was quite a task. The engine alone weighed about 13,000 pounds, 

the pylon weighed another 1,800. The movement of that weight up and down 

with a forklift, and the precision with Which it had to be done, was 

difficult at best. In retrospect, one can say that the engineering staff 

should have taken a more detailed look at the advisability of such a 

procedure and provided an assessment as to the potential for damage in 

implementing it. However, this was not done. 

During the same period of time, another airline was considering this 

same procedure for changing the engine on its DC-10 aircraft. This 

airline also decided that movement of the engine and pylon as a single 

unit would be advantageous because it would save considerable labor 

costs. Shortly after implementing this procedure, however, they found, 

somewhat fortuitously, that they had cracked part of the structure at the 

attach point between the pylon and the wing. Understandably, they 

immediately stopped using the procedure but they did not advise other 

DC-10 operators or the aircraft manufacturer of their experience. 

Whether they should have done so is debatable. They did not, in any 

event, have an obligation to apprise other airlines of their experience. 

The changing dynamics of the airline industry, in this period of 

deregulation, seem to have caused a decrease in industry "networking." 

Old timers in the airline industry contend that in earlier days there was 

much more frequent dialogue among operators; in other words, a more 

A-10 
1 

~e~ 

st 

h 

e 

and 

!d 

ln 

lis 

m-

~ine 

a 

of 

ety 

aulic 

n 

as a 

s as 

ds, 

down 

staff 

in 

this 

~le 

md, 

Lt the 

' 

:mce. 

f 

~-" 

~e was 

coope~ative grapevine. It would be interesting to speculate about 

informal means that might have been implemented to spread the word among 

DC-10 operators and l>ead off the catastrophic accident at Chicago. 

Closely allied to the topic of industry networking is that of FAA 

surveillance. Should the FAA have known of the DC-10 engine 

experiences? If aware of it, should they have been responsible for 

seeing that this information was made known immediately to all airlines? 

For good reason, the Federal Aviation Administration is one step removed 

from direct maintenance tasks. The FAA, understandably, is reluctant to 

tell maintenance professionals how to do their jobs. Their surveillance 

of maintenance and inspection practices is intended to determine whether 

the organization has a structure which is conducive to accomplishing the 

required maintenance; whether the people in key positions are qualified; 

and whether the policies, practices and systems in place are adequate to 

provide a reasonable assurance that the intent of FAA regulations will be 

maintained. Whether FAA surveillance should be expanded is a topic for 

consideration. There are pros and cons. 

Finally, there is the matter of communication between airline 

management and the labor force. During the nearly two-year period before 

the L-1011 flight from Nassau to Miami started gliding down to the 

Atlantic, the airline had twelve occurrences of engine oil leaks as a 

result of improperly installed chip detectors or 0-ring seals. Of these 

twelve, eight involved inflight engine shutdowns and seven necessitated 

unscheduled landings. Airline senior management, maintenance management, 

and supervisors were aware of these occurrences, but apparently 

interpreted them as unrelated mechanic discrepancies rather than a 

systemic problem. Although minor changes were made in some work cards 

and procedures, and these incidents were reported upward in the 

management structure, there appeared to be no flow of information back to 

the general foreman level. The working maintenance team remained 

uninformed regarding the magnitude of the chip detector installation 

problem. 

In summary, I submit that across the spectrum from the manufacturer 

~ to the working mechanic and inspector, including immediate supervisors J and foremen, the engineering staff, top management, and FAA surveillance 

1 

personnel, everyone needs to take a hard look at the human factor in the 

~ \maintenance function. Maintenance and inspection involves many very ~ labor intensive tasks which are necessarily susceptible to human error. 

v If we look at the frequency of human performance errors - pilot errors -

in commerical and in general aviation, we find that some 60 to 80 percent 

~:of these accidents have some human involvement. It is only reasonable to 

~ 'suspect that comparable proportions of human error exist in maintenance 

~ /and inspection activities. We cannot reduce these errors simply by 

~ /focusing singly on the person who is doing the work. We must consider in 

the broadest sense the total environment in which maintenance is done. 

A-ll 
rr-- . I 

I 

Day-to-Day Problems in Air Carrier 

Maintenance and Inspection Operations 

Robert T. Lutzinger 

Manager of Aircraft Inspection 

United Airlines 

In the typical inspection department of an airline the game plan, if 

you will, is accomplishing the Maintenance Plan. The preparation of that 

Maintenance Plan begins at the time of aircraft construction and the 

Maintenance Review Board. When the aircraft becomes operational, the 

airline has the responsibility to implement a Maintenance Plan of greater 

detail which spells out how they will systematically maintain that 

airplane in an airworthy fashion through regularly scheduled maintenance 

activities. This plan provides the timeframes within which we must 

perform certain functions of that aircraft maintenance program. The more 

comprehensive that program is, the more effective our Maintenance Plan 

will be and the better our opportunities to avoid incidents and 

irregularities. 

At United Airlines, our typical Maintenance Plan includes the 

following maintenance opportunities: 

Number 1 Checks - Activities requiring compliance for through flights 

with turn times of less than four and one-half hours. 

~umber 2 Checks - Activities we have identified as necesssary to meet 

the overall maintenance program for aircraft that lay over four and 

one-half hours or more. 

A Check - This occurs for the 737 aircraft, for example, every 200 

hours. This is somewhat more extensive than a walk-around, but the 

aircraft is not opened up. 

B Check - This occurs at about 550 hours and includes opening 

specific accessible areas of the aircraft. This generally is an 

overnight activity. 

c Check - This occurs essentially on an annual basis or at about 

3,000 hours. Access panels are opened and we go into the airplane 

extensively. 

D Check - This occurs about every four years or at 16,000 to 18,000 

hours. This check can last from 20 to 30 days. All access areas are 

opened and detailed work accomplished on the aircraft structure and 

systems. 

At United, the above activities are controlled and initiated with what we 

tet~ Routine Paper Packages, each task related to a specified level of 

maintenance. In all, these constitute our game plan. I personally think 

the United game plan is a good one; however, the charge we have today is 

to discuss problem areas involved in carrying out the Main- tenance Plan 

and the risks that might be associated with this plan. I will discuss 

these in terms characteristic to our airline operations. 

A-12 
if 

that 

ater 

nee 

more 

n 

r,hts 

meet 

100 

1t we 

>f 

'hink 

r is 

'lan 

IS 

Fleet Size. The different types of airplanes used by an airline can 

affect the maintenance pror,ram and the related behavior of maintenance 

inspectors. The ar,es of the airplanes and the types and various models 

of enr,ines also can complicate the Maintenance Plan. The more complex 

the fleet, the more problems one may have with maintaining a qualified 

and experienced staff of inspectors. 

In dealing with a complex fleet, it is particularly important that 

the routine maintenance package be as effective as possible so that the 

inspection function does not become a work r,enerator but is a quality 

verifier. With the age of our aircraft r,rowing daily, it is imperative 

that our Maintenance Plan be continually adjusted so that the plan is the 

maintenance driver rather than a compilation of non-routine unscheduled 

maintenance events. As fleet size and complexity grow, the more likely 

it becomes that the non-routine activities affect the maintenance 

program. When such an imbalance occurs, it follows that greater risks 

become part of the inspection process. 

Utilization. As the airline industry has r,rown, seekinr, ways to 

maximize the utility of its fleet bas become a basic part of corporate 

strategy. Since maintenance causes aircraft to be on the r,round, 

at.tention always must be given to minimizinr, maintenance down time. When 

United Airlines introduced its 747 fleet, for example, we started a phase 

check type program. Here, rather than havinr, an aircraft be out of 

service for two, three, or even six days a year, the required maintenance 

elements were identified and phased in a planned visit so that we could 

accomplish these tasks on overnight stops when the airplane was not 

flying. This reduced the out-of-service time for the 747 fleet and 

literally saved us, at that time, one equivalent airplane. 

Today, we have aircraft that have reached or gone beyond their 

"economic expected life." With these aircraft, we expect that structural 

inspections will find more discrepancies and that these aircraft must be 

dealt with using a somewhat different approach. This means that 

maintenance personnel must continually identify and make inputs into the 

Maintenance Plan strater,y so that the plan may be adjusted to address 

these new requirements. If a phase check program allowing only for an 

eir,ht hour turn is continually found to require 16 hours of work, we will 

soon have a major problem unless the Maintenance Plan is adjusted and we 

respond with chanr,es. An ongoinr, plan review is most important for a 

maintenance program to be successful and effective. 

-------·· ·---·-------------------~ ·- F'cilities and Work Environment. Flor the most part, the major 

facilit ~now used by the larger airl1nes for'maintenance and inspection 

are quite go'lJd.... While there may be some outdated facilities with 

significant environmental problems, I suspect they would be in a 

minority. 

Every effort is made at our maintenance facility to insure a proper 

and safe work environment. Company representatives meet once a month 

with the Union Safety Committee and our Safety Department personnel to 

consider issues concerning quality of the job and quality of the environment. An action list is reviewed which covers topics such as safety of 

equipment, heating and lighting problems, procedures for use in 

emergencies, job clothing, disposal of radioactive material, training for 

A-13 
r , 

I' 

.<j'<l ' ~ 'b 

,L 

\) ;:'- c ' ~ i f! 

''\ i 

{ 

•' 

X 

"'-'" 

~~ 

-" 

~ 

),_ 

' '-' 

~ " "' '-

~ 

particular jobs, and any other matter considered important. As a result, 

our work environment is kept in as good condition as feasible, 

considering the work which must be done . 

Personally, I have never found lighting conditions or heat/cold 

problems to be so severe at our location that quality of performance is 

adversely affected. We have always been able to get around these 

problems satisfactorily, whether through the use of local lighting, the 

use of warm clothing, or implementing some other solution. In addition, 

it is the expectation of an aircraft mechanic that he must, as part of 

his job, deal with some of these negative environmental elements. OUr 

employees seem to adjust well, and under severe conditions they work to 

overcome these negative factors. 

One problem with facilities for dealing with large jet aircraft 

concerns those structures necessary to effectively perform inspections on 

inaccessible parts of the airplane. At United, we have permanent 

structures around an airplane when it is in for a heavy maintenance check 

so that our inspectors have opportunities to inspect the aircraft. 

However, these structures are quite expensive. The cost of this 

equipment may represent a problem for some operators. 

An environmental issue which is becoming an industry problem is 

dealing with paint stripping. There are many state and local regulations 

today concerning the use of these chemicals and the required training of 

people who use them. Because of this, some operators attempt to find 

better or different ways to accomplish this process. 

yraining and Experie~;·> The rapid expansion of the airline industry 

over the past ten years bas resulted in a need for considerably larger 

numbers of qualified maintenance and inspection personnel. We have seen 

a real growth in our staffing requirements and found that the resources 

are simply not always there. In my opinion, it takes an inspector at an 

airline such as ours two years to become effective; six years to become 

efficient. 

When an air carrier has a complex fleet, one having a variety of 

aircraft and engines requiring maintenance, the time required for an 

inspector to become fully competent will be long even with the best of 

training. To further complicate the issue, many of the skills of an 

inspector will be of the "use it or lose it" type. When dealing with 

eddy current inspections, magnetic particle inspections, ultrasonic 

inspections, or radiography, the risk of performing an inspection 

improperly grows if the inspector is not performing that task with 

regularity - Use it or lose it! 

Skilled maintenance becomes even more important with areas of 

maintenance such as the Special Inspection Document (SID) Program which 

we will face more and more as our aircraft grow older. When an airplane 

reaches the special inspection threshold designated by cycles and hours, 

it becomes a candidate to have literally hundreds of additional 

inspec-tions performed. The inspector assigned this task must apply his 

knowledge and expertise in making very precise technical judgments 

concerning the discrepancies he is looking for. This is a difficult 

assignment if the inspector has not done these particular inspections 

with some regularity. Prior to that special inspection, he might have 

A-14 
t, 

'' 

on 

!Ck 

ms 

>f 

l:ry 

en 

s 

an 

• 

h 

ne 

s, 

been on a 747; the week before that on a 727; and the week before that on 

a 737. Maintenance of the necessary skills, some unique to the special 

inspection, presents a problem for maintaining skill levels and 

assignments. 

United Airlines recognizes the ongoing training requirement and this 

year will commit at least five percent of its inspection department for 

training on a regular basis. This means that some 15 to 17 inspectors 

will be in classroom training daily increasing their skill levels by 

engaging in special training experiences. 

An aircraft inspector needs not only the formal classroom training, 

involving the operation of detailed parts and aircraft components, but 

also must acquire unique skills related to aircraft structures and 

systems. He must understa~d exactly that signal on the scope which 

indicates that a crack has been found, the meaning of those unusual 

noises that may occur on gear retraction, and the apparent stiffness of 

that aileron movement when the aircraft control wheel is turned. He must 

also recognize the significance of those blue water stains on the 

fuselage when he sees them. He must know that this may represent the 

possible corrosion and delamination of certain skin laps, even though the 

Maintenance Plan may not say, "Inspect fuselage for blue water stains." 

Only experience produces these sensitivities. In an expanding industry, 

the time required to obtain these experience levels is not available and 

represents a problem we must learn to deal with. 

In order to assist in having desired performance levels maintained 

for our inspectors, United uses an error feedback process which we call 

the "C-3 Program." When a supervisory inspector discovers an aircraft 

discrepancy that was missed during an earlier inspection, he codes the 

item "C-3." We do not use these C-3 items for disciplinary purposes but 

instead attempt to employ them in a positive educational program for 

inspectors in which we point out the kinds of discrepancies being missed 

during aircraft checks. While this system is not always totally viewed 

as effective, it does assist in reviewing our process with our employees. 

Unions. In a unionized operation, seniority plays a paramount role. 

By contract, most organized unions require assignments by seniority. 

This means that the older and more experienced employees often bid for 

the preferred shift, usually "Days." If the aircraft is down at night 

for inspection and maintenance, your experience at night is affected. In 

some instances, the night maintenance opportunity represents the most 

valuable maintenance time. 

As they relate to company operations, unions see themselves as 

responsible more for "quality of life" issues for their members than for 

issues relating to quality or effectiveness of operation. Their concern 

centers on trying to insure a normal life for workers, i.e., proper 

vacations, appropriate economic reward, better shift work for senior 

workers, and similar matters. They do not give as great attention to 

workplace issues although, as I noted earlier, the Union Safety Committee 

does meet once a month with company representatives at United to discuss 

a variety of safety matters, some of which deal directly with the workpl~ce environment. 

A-15 
r r 

·I 

I 

The above topics represent some of the principal features of the 

maintenance and inspection process at United Airlines that I feel impact 

personnel performance. We recognize that we are in a growth industry; 

that we operate a mixed and complex fleet; and that our fleet is becoming 

older. Accordingly, we have increased our in-house training program and 

are beginning to employ new techniques such as video to inform and train 

our personnel. We are continually reviewing our Maintenance Plans to be 

certain that new problems are quickly incorporated into our routine tasks 

and inspections. We are in the process of developing specialized job 

fields as we begin to use more sophisticated equipment to meet new 

maintenance challenges. Finally, we are expanding our networking 

capabilities with the rest of our industry, in part through our 

participation in industry-wide activities such as those of the Air 

Transport Association to enhance our skills and problem solving. The 

skills we are developing and the skills other airlines are developing 

should be shared. We all have a stake in maintaining the highest quality 

of maintenance possible. 

A-16 
:t 

lng 

td 

ln 

)e 

;ks 

ity 

Maintenance and Inspection From the 

Manufacturer's Point of View 

Robert L. Oldani 

Manager, Maintenance and Ground Operations 

Boeing Commercial Airplanes 

The process of establishing and conducting a proper maintenance 

program to support airline operations has a number of points which hold 

the possibility for human error. To illustrate this, I would like to 

review briefly the steps involved in developing an airline maintenance 

program. Then I will describe some innovations made by Boeing which we 

feel reduce both the cost of maintenance and the potential for error. 

The maintenance process starts with the Maintenance Review Board 

(HRB). Figure 1 shows that the Maintenance Review Board is composed of 

representatives of the manufacturer, the Federal Aviation Administration, 

and.the airline that has just purchased the airplane. These representatives work together to develop a minimum maintenance program for that 

particular airplane. The MRB work lasts for a considerable period of 

time, in the order of eight to fourteen months, and draws on the 

expertise of a number of small working groups. These working groups 

consist of individuals with specific expertise in aircraft maintenance. 

They review the systems, the structures, the various other aspects of the 

airplane and, based on their experience, determine what should be 

inspected, when it should be inspected, and how it should be inspected. 

The end result of this procedure is the issuance· of a Maintenance Review 

Board Report. 

Three end products are produced by the manufacturer during the MRB, 

as shown in Figure 1; These are the maintenance manual for the airplane, 

which describes the accomplishment of maintenance tasks; the Maintenance 

Planning Document (MPD), which tells when and··wher_e to accomplish the 

task; and the task cards, which combine the information of the MPD and 

the maintenance manual .. 

The airline operator works from the Maintenance Planning Data 

document .. and the maintenance manual to develop their own Maintenance 

Operations Specifications. This becomes their official maintenance 

program when approved by the FAA. In addition, the airline also develops 

its own task cards. 

The common area of task card development by the manufacturer and by 

the airline was considered at Boeing to be part of the MRB in 'iilhich human 

error could be involved. Therefore, we developed what we call an 

Automated Customized Task Card. 

Under the old task card system, used until the introduction of the 

757/767 aircraft, the task cards told a maintenance man what to do and 

when to do it. Then he had to go to the maintenance manual to find how 

to do it. Figure 2 illustrates the operation of the old task card 

system. Information from the task cards and the maintenance manual is 

fed to an airline task card writer who prepares task cards for the 

particular airplane. These customized task cards then go to the mechanic 

to direct his labors. However, mechanics require more information 

concerning the exact way in which to perform a task. Therefore, information from the maintenance manual is put into cassettes which then can be 

A-17 
=:-

.... 

QO 

AIRLINES 

MANUFACTURERS 

DOCUMENTATION 

BOEING FAA 

MAINTENANCE MANUAL MAINTENANCE REVIEW 

(MM) BOARD REPORT 

MAINTENANCE PLANNING 

DATA DOCUMENT (MPD) 

TASK CARDS 

Figure 1. Airline scheduled maintenance program. 

, 

FAA 

AIRLINE 

MAINTENANCE 

OPSPEC 

TASK CARDS 
::-

.... 

"' 

Figure 1. Airline scheduled maintenance program. 

~--~ #w=-·":7 =¥f 

~t~~- ! .,t ·----·- ;,! 

., BOEING I 

!/j TASK , 

,[! c=~-. ...J 

J50N-C.UffTOMIZED 

AIRLINE 

TASK CARD 

WRITER 

AIRLINE 

CUSTOMIZED 

TASK CARDS 

. J~~ CASSETTE 

18mm ~ 

MECHANIC 

MICROFILM 

READER/ 

PRINTER 

Figure 2. Old method using non-customized task cards. 
I 

I 

( 

used with a microfilm or microfiche reader/printer. Mechanics then stand 

at the printer and wait to get their instructions as to how to do the 

job. Hopefully, they get the right printout to match the task card. 

This is a part of the process in which errors can be made. 

To expedite the maintenance process and to reduce the possibility of 

error, Boeing improved on the old system with the development of the 

"Automated CUstomized Task Card" method, illustrated in Figure 3. This 

method. eliminates the task card writer and the microfilm reader/printer 

from the process entirely. Material from the maintenance manual is 

computerized and then accessed through use of what we call "hooks" to 

obtain specific items. 

Under the new system, the maintenance manual is revised on a 60- to 

90-day basis. The Customized Task Cards thus are revised on the same 

basis, which means that the mechanic always is dealing with up-to-date 

data. In addition, the new task cards can provide all of the needed 

illustrations. 

Figure 4 presents a sample of an Automated Customized Task Card. 

This task card covers cleaning of a cooling pack/heat exchanger on a 767 

aircraft. Figure 5 shows the illustrations accompanying this particular 

·task card. With these new task cards, the mechanic now has everything he 

needs to properly conduct that particular task. He has the equipment, 

the material, the procedure, and all of the illustrations, all reflecting 

the latest changes. From a human factors point of view, we feel this is 

a considerably better maintenance support program. 

There are a number of benefits with use of the new customized task 

card system. It reduces the number of airline man-hours expended in 

writing and revising job cards; it eliminates a mechanic's need to refer 

to microfilm; it eliminates lines of mechanics waiting at the microfilm 

reader; and it eliminates errors due to manually transferring and 

retyping the manufacturer's data. A final benefit is that each airline 

receives the latest information from the maintenance manual. This 

eliminates guesswork in identifying applicable maintenance manual 

procedures, which can be a significant problem. Maintenance manuals can 

be complicated, with their particular accession and numbering systems. 

With the automated system, airlines can easily identify revisions in the 

maintenance manual affecting their scheduled maintenance. 

One airline operator who accepted our system and evaluated it over a 

one-year period estimated that they saved over $1 million. This was 

based on eliminating the task writing, eliminating the problem of 

mechanics waiting to look at microfilm, and generally expediting the 

labors. Several other airlines do not actually use our task cards to 

direct maintenance but, rather, use them to determine when we have 

revised the maintenance manual. Rather than going through the total 

revision, they just go to the task cards to look for a revised card. 

They then know the maintenance manual has been changed for that process. 

Finally, we provide this information on magnetic tapes to some airlines 

who prefer to develop their own computerized task card systems. 

A-20 
::-

N 

.... 

·--·--·-

BOEING 

TASK 

CARDS 

·AIRLINE 

TASK CARD 

WRITER 

AIRLINE 

CUSTOMIZED 

TASK CARDS 

"" "' 

e >L®~ CASSETTE » 

18mm 

MECHANIC 

Figure 3. New method using Automated Customized Task Cards. 

111 
0 

0 

0 

0 

8 

8 

ShUOOO IOUIIG. (llD 100. 

BDEIND767 21-017-01 ' TAIL till. UAL TASK CARD 'l"UIIIf t-100. 

tU( 

~1 ;;~ I ECS :A ~·u I ULATU to.sr. 

I l•flnAL I -· IE\IUIOII 

2C 12020 B FEB 10/88 , ... . TUU Sl'lll(t'\IIW. 1UUSTtt4UOII ltlJf:ltlftC.E lf't'LICAih.ltY 

CLEAN COOLING PACK HEAT EXCHANGERS ......- ...... ' 

ALL ALL 

·- --.-s I'MII.$ • 135 136 193NL 194LR 

I 

' I 

.... "" ""' ITIII -...tl I 

CLEAN PRIMARY & SECONDARY COOLING PACK HEAT EXCHANGERS 21-51-Q2-7Ai 

CIF HEAT EXCHANGERS ARE NOT CHECKED FOR EFFICIENCY). I 

I 1. R~fer~n~!~ Prg,12ur11 

A. 06-41-Q0/201, Fuselage Access Doo~s and Panels i I 

2. Egui Q!!!!;nl; 

I 

A. Spray Nozzle, 9702A-10-TM-TC-9502, Spray SystetOs Co. 

Wheaton, IL 

B. Air c~ressor (80 to 100 psi) coo-erciatly avai table I 

c. Spray gun (c~atible with air cQDPressor or stea• 

cleaner) co .. ercially available 

D. Steam Cleaner (80 to 100 psi) coamercially available I 

3. Materials I 

I 

A. Solvent, P-D-680, D~ Cleaning <Ref 20-30-Q2) I 

4. t~ll" Htll ~x'h1ngtr1 (fig. 701) 

A. Place peck control selector on Pilot's OVerhead PS Panel in OFF. Place 

DO-NOJ"-GPERATE identifier on selector. 

B. Open appropnate ECS access door 193NL or 194LR and locate heat 

exchangers <Ref 06-41-QO) • 

c. Remove access doors in plenu•, ra• air inlet duct, and between the heat 

exchangers. 

D. Clean the priury and seconda~ heat exchangers. 

' 

. 

EFFECTIVITY CLEAN COOLING PACK HEAT EXCHANGERS 

ALL 

' 21-51-Q2-7A 21-D17-o1 PAGE 1 OF 3 FEB 10/88 

Figure 4. Sample Automated Customized Task Card. 

A-22 
-01 

"" 

B 10/88 

ALL 

iii ...,.l. I 

51-Q2-7A i 

.ace 

\eat 

i 

'I 

I ' 

FEB 10/88 

0 

0 

0 

0 

9 

0 

OOZZLE 

EFFECTIVITT 

All 

ACass 1001 ,..,._ 

UAL 

BDE.ING 767 

TASK CARD 

. ~-

21-017-01 

SUGGESTED CLEANING PATH 

A•A 

...... , ... , EICIWtUI 

1M .Ul liiUT 

HW£•1UCT 

AZCUS111M All 

lOUT IUCT 

(_ 

Heat Exchangers • Clean;ng 

Figure 701 

CLEAN COOLING PACK HEAT EXCHANGERS 

21-51-o2·7A 21-Q17-Q1 PAGE 3 OF 3 

-

AUG 01/82 

Figure 5. Illustrations accompanying Automated Customized Task Card. 

A-23 
Another area of concern to the airlines is Service Bulletins. These 

are documents prepared by engineers working at desks in the manufacturer's facility. They can be rather complex, and may use language 

meaningful only at the engineering level. In order to make Service 

Bulletins more readable, Boeing is attempting to improve their content by 

using what we call "simplified English." This is English which we feel 

can be readily understood by the average mechanic. Again, the purpose is 

to reduce errors of interpretation. 

A final recommendation of mine is that we continue to use whatever 

means we have - such as this meeting - to review our maintenance problems 

and to spread word throughout the industry concerning new or improved 

ways of doing things. If we have a safety situation and have options to 

resolve the problem, everyone should know about it. We are talking about 

the total airline fleet. 

A-24 
hese 

~t by 

eel 

se is 

er 

blems 

~ 

s to 

about 

Human Performance in Aircraft Maintenance: 

The Role of Aircraft Design 

Anthony E. Majoros, Ph.D. 

Engineer Scientist 

Douglas Aircraft Company 

This presentation describes work being done by the Douglas Aircraft 

Company concerning human factors in maintainability and design for ease 

of maintenance. Specific topics are (1) human factors aspects of 

supplemental inspections, (2) maintainer workload, and (3) maintainer 

reliability. 

Supplemental Inspections 

A fundamental truth in design is that provision for supplemental 

inspections is seldom built in as part of the initial aircraft design. 

With an aging aircraft fleet, however, supplemental insp~ctions have 

become and will continue to be a way of life. For the insp<?.ctor dealing 

with an aircraft with no design provision for supplemental inspection, 

definition of the inspection concept may be unnecessarily complex and 

access to inspection areas may be difficult. 

We believe that it is possible to aid the inspector by defining 

inspection concepts. One way to do this is through use of a 

computer-generated anthropomorphic model. Figure 1 shows the manner in 

Which we used such a model to demonstrate two possibilities for 

inspecting the inner frames of a DC-3 vertical stabilizer. The model is 

based on anthropometric dimensions taken from Military Standard 1472 and 

the Navy Crew Assessment of Reach (CAR-4) algorithms. 

Not Recommended Recommended 

Figure 1. Computer simulated DC·3 vertical stablizer inspection. 

We would not recommend that the inspector lie with his back on the 

horizontal stabilizer as sho~ on the left in Figure 1. We would 

A-25 
recommend instead that the inspector lie with his stomach on the 

hori~ontal stabilizer and see the overhead view with a mirror. We 

compared our simulat.i.on of this task with actual attempts to perform the 

inspection on a DC-3. By personal experience, I can tell you there is 

good reason not to recommend the procedure shown on the left. It is 

difficult to get into and out of the position, it is painful, and very 

little can be seen. Inferences about the difficulties of this inspection 

made possible with computer simulation compared very well with the actual 

experience. 

In one design evaluation, we considered a maintainer attempting 

removal of a flight control module from the upper aspect of a vertical 

stabilizer. The analysis showed that the pull of gravity on that 

component, weighing about 44 pounds, presented sufficient risk that the 

maintainer would incorrectly remove the package and so damage the 

delicate ribs within the vertical stabilizer, that a recommendation was 

made to mount the flight control module on the outside of the rear spar 

of the vertical stabilizer and not on the inside. This illustrates 

consideration of. several variables during static simulation of 

maintainers. One is weight-lifting and carrying limitations, another is 

maintainer comfort (or pain), another concerns postural difficulties, and 

a final one is time required to hold posture and to generate force in 

certain postures. All of this information bears on the ability of the 

maintainer to perform the operation efficiently and accurately. 

There is an emerging belief within the Douglas Aircraft Company that 

computer-assisted design (CAD) environments represent the way all design 

will be done in the future. There will be less paper and more electronic 

models-. Within this environment, sophisticated anthropometric models can 

be used to predict the performance of people in any position within 

aircraft structures. Ultimately, these anthropomorphic models will show 

real-time motion characteristics and will have vision and strength 

capabilities as well. 

Kaintainer Workload 

In aircraft flight operations, excessive levels of workload are 

considered to be associated with increased error likelihood. We make the 

same assumption with maintainer workload. We believe that as workload 

increases beyond certain acceptable levels, the chances of error being 

made by the maintainer are increased. 

We have performed some preliminary work in an attempt to locate 

aircraft systems during design that we believe are likely sources of 

unacceptable levels of maintenance error. In Figure 2, ten selected 

aircraft systems are plotted for maintainability, reliability, and ratio 

of difficult to easy tasks within the system. Maintainability, 

specifically mean man-hours to repair (MTTR) is plotted on the left-right 

axis; reliability, specifically mean time between corrective maintenance 

actions (MTBM(C)) is plotted on the front-back axis; and the ratio of 

difficult to easy tasks, specifically the skew of the distribution of 

task times within a system, is plotted on the up-down axis. 

Task times for aircraft systems are generally positively skewed, and 

the greater the ratio of time-consuming (difficult, with many steps) to 

fast (easy, with few steps) tasks in the system, the greater the degree 

of skew. We made the assumption that systems whose task times are more 

skewed offer relatively more opportunities for maintenance error. In the 

figure, systems with longer stems are more positively skewed. With a 

A-26 
m the 

is 

s 

ery 

ection 

actual 

cal 

the 

was 

spar 

er is 

:S, and 

in 

the 

·that 

:esign 

:tronic 

:ls can 

show 

Lke the 

.oad 

Ling 

tf 

I 

ratio 

c-right 

1nance 

of 

of 

I, and 

o) to 

•gree 

more 

In the 

• a 

graph of three variables, we can detet-mine an aircraft system's availability by plotting the location of the bottom of its stem on the "floor" 

of the graph in tet-ms of reliability and maintainability, and we can 

check the system's potential for error by noting the length of the stem. 

In Figure 2, flight control (System 14) and independent position 

determining (System 72) contribute nearly identical burdens to aircraft 

availability, yet the position determining system offers relatively more 

opportunities for error. We would conclude that position determining -

in the design configuration under study - is a better candidate for t• 

faclors attention to maintenance error reduction than flighl control. 

-

,, 

Figure 2. Three-axis graph used to identify systems loaded with tasks requiring many 

time-consuming steps. 

Note that error rates are not used in the analysis in Figure 2. The 

three axis graph is used to locate aircraft systems that have a high 

proportion of time consuming tasks on' the assumption that those systems 

contain more chances for error. 

In our review of workload parameters relative to aircraft maintenance, we identified three aspects worthy of in-depth consideration. 

These are (1) infrequency or novelty of a task or defect, (2) the 

cognitive complexity of the task or the mental demands the task imposes, 

and (3) the physical and physiological demands of the task. Each of 

these is reviewed next: 

1. Infrequency or Novelty of Task/Defect. One of the rules of 

inspection and quality assurance is that rare defects are difficult to 

A-27 
detect. As you increase the percentage of defects present in a sample, 

the likelihood of catching a given defect increases. 

One way to aid an inspector in dealing with rare events is with 

procedural checklists that guide the user. To study the potential of 

checklists go guide the search for uncommon errors, we created three 

types of checklists for use in an experiment. The experiment required 

subjects to search for characteristics of a design that could be 

considered "errors" from the standpoint of maintainability, but the same 

logic could apply to an inspector checking a system for integrity. One 

checklist contained irrelevant items, a second contained conventional 

USAF maintainability checklist items that were not specific to any 

particular aircraft system, and a third contained items written at 

Douglas Aircraft that were specialized for the system under examination 

by the subjects. As shown in Figure 3, we found that more errors were 

dele '·' ,; wi.lh the specialized check list. 

0 

t 

w 

ti:i 

0 

Cl) 

a: 

0 

a: 

a: 

w 

LL 

0 

a: 

w 

m 

:::;: 

::::> 

z 

z 

L5 

:::;: 

7 

6 

5 

4 

-

-

NO 

~ ERRORS 

DETECTED 

IRRELEVANT 

CHECKLIST 

CONVENTIONAL 

CHECKLIST 

HIGHLY 

SPECIALIZED 

CHECKLIST 

Figure 3. Comparison of conventional vs. improved checklists. 

2. Cognitive Collll>lexity of Task. Aircraft obviously are complicated 

,;yste.ms. Nicholas Bond, in a recent chapter in the Handbook of Human 

~·act.9_r~. makes the observation that, in his opinion, no single person 

under·stands everything about certain aircraft systems. He uses the F-18 

flight contt"ol system as an example, and states that no one is alive who 

understands it all. Many systems within civil transport aircraft are 

similar. They are highly complicated and few individuals understand them 

completely. 

One problem with increasingly complicated systems is that the 

representation, or the mental model of what a person should look for, 

becomes difficult for a maintainer to hold for a long time. Methods that 

A-28 
le, 

f 

ed 

same 

)ne 

L 

lon 

re 

:a ted 

! 

l 

'-18 

who 

them 

that 

enhance the representation for that person can do nothing but help. A 

few years ago, in an attempt to improve this situation an "'Advanced 

llaintenance Information Packet" was developed. In this, maintenance 

.tasks are numbered in a step-by-step sequence, with accompanying graphic 

presentations. Even the position of the hand relative to where the 

maintainer would be standing or sitting is shown. Cautions and warnings 

are put before the action; tools and special equipment are identified 

before the action begins. 

The advanced maintenance infot~tion concept was tested with novice 

mechanics and for what were termed major errors. This would be an 

incorrect removal, an incorrect installation, isolating to the wrong 

part:, and actually removing and replacing the wrong part. In this test, 

use of the advanced maintenance information system produced a 55 percent 

reduction in errors. For minor errors, such as incorrect torque on 

bolts, there was a 79 percent reduction in error. 

One concern about the advanced maintenance information concept was 

that the many different and necessary illustrations made it prohibitively 

expensive. This is not the case today. Computer generated graphics, 

much less expensive to produce, can be used to illustrate maintenance 

actions. 

Another aid in overcoming the cognitive complexity faced by 

maintainers is through use of expert systems during the design stage. 

Designs can be more or less maintainable for a number of reasons. If 

these reasons are incorporated into an expert system, the designer will 

be able to rapidly evaluate a new design for its maintenance 

characteristics. The designer should be able to ask the expert system 

questions such as: "Given this task, a change of a filter requiring two 

seals in this location of the aircraft, how long will it take to make the 

change if the filter is in this location?" This is basic maintainability 

information 

__., 

and it can be very valuable during the design stage. 

\ A. Physical and Physiological Demands. Another aspect of workload 

c~~rns physical and physiological demands placed on the maintainer. 

Table 1 presents results of a .small survey done with operators of Douglas 

products. As can be seen, weight and access complaints are most frequent 

among civil aircraft maintainers. Visual lighting problems were next, 

followed by difficulties with connectors, seals and component 

installation. 

TABLE 1 

MAINTENANCE PROBLEM AREAS NOTED IN 

SMALL SURVEY OF OPERATORS OF DOUGLAS AIRCRAFT 

Access and weight 

Visual, lighting 

Connectors 

Seals 

Installation 

Others 

28'1. 

18'1. 

16'1. 

7'1. 

7'1. 

24'1. 

The Douglas sut·vey was small and informal. More data than we 

obtained are required. Many· questions concerning difficulty of 

maintenance were not asked in this survey. Such information is needed 

A-29 
for designers to understand how to develop a product that maintainers can 

work on most efficiently. 

Designers should be able to reduce physical and physiological demands 

by attention to placement of components when the sturcture permits some 

variation of placement. Figure 4 presents one approach to solve 

installation questions during design. The figure is a working envelope 

for removal of a slat lock valve. Spatial coordinates for this envelope 

were obtained by videotaping the removal of the valve from a wing 

mockup. Camecas wer-e sel above and to the side of the valve location in 

the mockup. 

Working envelope for slat lock val"" removal -

fir& ex tubing does not obstruct removal. 

MD PO TO. P. F 

Tubing In Place 

F 

Figure.4. Workload for slat lock valve removal compared with and without fire ex tubing 

in place. 

The working envelope shows the-maximum excursions of hands, tools, 

fasteners, and the valve itself during removaL Two trials were 

videotaped: removal without any o.bstructions - which required 12 1/2 

minutes - and removal when fire extinguisher tubing obstructed access -

which required 16 minutes. We can conclude that if the tubing were 

routed to avoid obstruction, valve removal would require about 25 percent 

less time. This study is a first step toward defining required working 

envelopes for components during design. If equipment is arranged in the 

aircraft with adequate working envelopes, maintenance workload can be 

reduced. 

A-30 
s can 

mands 

orne 

ope 

lope 

n in 

x tubing 

ls, 

12 

;s -

a:rcent 

i:ing 

1 the 

>e 

We developed workload measures on the above task using the NASA Task 

Load Index to measure operational workload. This system rates mental 

demands (MD), physical demands (PD), temporal demand (TD), performance 

(P), effort (E), and frustration (F). Here we see that effort and 

f.rustration are increased by having a design that includes the fire ex 

tube below the slot valve. This offers us a chance to understand some 

sources of error that could lead to damage during the performance of the 

task. 

Maintainer Reliability 

There is growing interest in maintenance reliability. Reliability 

concerns errors, departures from procedures, time to complete tasks, and 

damage or induced maintenance. The goal at the design stage is to aid 

the mechanic by designing to reduce error likelihood. 

Many aspects of maintenance affect error potential. Figure 5 is an 

example of labeling that led to error. Labels and placards are part of 

the world that guides inspectors and maintainers to do their job. In 

"this case, one can connect P26 to either JS or J6 of the adapter. This 

test is for an aerial refueling boom and in one case (JS) you test the 

elevator actuator. In the other (J6), you test the aileron actuator on 

the flying boom. However, mechanics interpreted the labeling to mean 

••take your choice," but that is not what it meant. This led to many test 

errors. The role of human factors here is to \dentify those design 

variables that lead to error and develop procedures to control them. 

DC58F12"12SN 

PLUG 11'281 

P28 TO ACTUATOR 

LVDT CONNECTOR 

~10 CABLE ASSY 

Figure 5. Test set lead and labels leading to maintenance error. 

G. From a manufacturer's standpoint, a number of approaches 

orthwhile in a program to reduce maintenance and inspection 

Briefly, these include: 

appear 

error. 

1. Manufacturers need to team with aircraft operators in the 

collection of necessary data. What errors are being made; what are the 

most frequent types; and, perhaps with workload measures, what are the 

components of error? 

2. Inspection concepts must be defined to facilitate inspection as 

much as possible and ensure best performance. 

A-31 
' 

3. Checklists must be improved. 

4. Maintenance aids should be developed with knowledge 

representation both in paper form and in expert system form. 

5. Aircraft systems should be designed for ease of access. 

6. Modelling should be employed to aid in the development of 

maintenance procedures. Anthropomorphic models are becoming so 

sophisticated that maintenance procedures could be modeled before an 

aircraft is built. 

7. A research center, or at least a coordinated research effort, is 

needed where problems can be studied indepth and where concepts can be 

tested to assess design configurations and their contribution to error. 

There is no place where regulatory agencies, operators, and manufacturers can team together to examine concepts and to examine the role of 

environmental variables that are often assumed to play a part in 

maintenance effectiveness. 

Finally, I would offer one comment on use of models. Models hold the 

illusion of solution, but they are not the solution. They aid in 

interpretation and/or application of human engineering judgment. They do 

not replace human engineering judgment. 

A-32 
an 

rt, is 

n be 

rror. 

.ctut"-

of 

1old the 

They do 

Maintenance and Inspection Issues 

in Ail" Carrier Operations 

Robert Doll 

Vice President of Technical Services 

United Airlines 

An important avenue for the coordination of maintenance improvement 

lnd the exchange of related information within the ait"line industt"y is 

tht"ough the Engineering and Maintenance Council (EMC) of the Air 

Tt"ansport Association. I am the representative of United Airlines to the 

IHC. My t"emarks today represent the activities of the EMC and the 

industt"y in general rather than a specific United Ait"linos position. 

The ATA Engineering and Maintenance Council recently formed with the 

FAA and other industry representatives, a steering committee to consider 

a numbet" of issues raised dut"ing the FAA conference on Aging Aircraft 

held on June 1-3, 1988 in Crystal City, Virginia. The fit"st item on the 

agenda of the steering committee is to examine the technical problems 

that underly the industry's and the public's concern about the 

manufacture of aging aircraft. The technical issues are stt"Uctural 

integt"ity and corrosion. At this time, there is no industrial standard 

for cot"rosion control. Fleet specific task groups have been formed to 

consider the integration of cot"t"osion contt"ol programs with the existing 

stt"Uctural inspection pt"ogram for individual fleet types. 

The second major item on the steet"ing committ~e's agenda is human 

factors, which, of course, is the topic of this meeting. We anticipate 

wot"king closely with the FAA human factot"s program to ensut"e that our 

activities are mutually suppot"tive. 

Within the scope of human factors, the issues we have selected as 

important closely parallel those mentioned earlier today. The first 

X issue is the work environment, and here we are concerned both with the 

work environment as designed at the time of manufacture and the work 

environment provided by the operatot". The second issue is of design and 

system maintainability. This is a problem with long range solutions but 

one which, as we have heard, manufacturers such as Douglas Aircraft are 

now addressing vigorously. The third issue concerns the preparation and 

tt"aining of an individual to work in a maintenance facility, whether he 

works as an inspector or as a mechanic. Here we must t"ecognize that we 

at"e not talking about clear-cut job entities. A lot of the inspection \ 

chot"es are actually cart"ied out by A&P mechanics. 

Mext we come to the matter of qualifications, and here we are talking! 

about the basic A&P license. There are questions as to whethet" we should 

go to mot"e certification and licensing at higher levels. While there 

might be advantages, one very pt"actical problem with increased licensing 

is that it generally leads to a mot"e complex pay stt"Ucture which, in 

turn, places a heavier administt"ative burden on the airlines. 

A final issue within out" human factot"s agenda concerns job 

instt"Uction. How do we instruct an inspector or mechanic to do a 

specific job? What kind of language do we use? This issue, of cout"se, 

A-33 
r 

! 

], 

goes well beyond our internal communications within an airline. It 

includes the manner in which a Service Bulletin prepared by the 

manufacturer, or an A.D. prepared by the FAA is written. The A.D., for 

example, is prepared by an engineer, reviewed by an attorney, sprinkled 

with "Washingtonese," and then delivered to the airline operator. We 

have a reasonable chance to interpret it properly in San Francisco, but 

consider the plight of the maintenance supervisor in Hamburg or Paris, 

translating to his language. 

The third area of inquiry for the steering committee is new 

technology. One part of this with human factors implications is the use 

of expert systems. One means of circumventing to some extent the 

requirement for experience and training is to have an expert system, a 

computerized means of providing the needed expertise rather than 

depending on an experienced mechanic. Expert systems, if incorporated 

properly, can play a very useful role. 

New technology also encompasses aircraft systems. Use of composite 

materials presents a new set of demands for inspection. Such materials 

are not compatible with some of the existing inspection procedures, one 

example being the use of eddy currents to explore possible cracks within 

composited structures. We have to understand these new materials from 

the point of view of maintainability, repairability, and associated human 

factors problems. 

Then there are the ground-related new technologies with potential to 

support maintenance and inspection. Here we refer to computer-based 

diagnostic equipment, expert systems, new NOT techniques, and other 

technologies. Perhaps one day we may develop a CAT-scan procedure for 

use with aircraft. Certainly, we must be alert to advances in medical 

diagnostic systems which might have possible applicability to aircraft 

inspection. Such new systems, of course, will present new challenges to 

our training establishment. 

The last agenda item for the steering committee, and perhaps the most 

important item, is that of communications. How do we share information? 

How do we communicate problems? In the maintenance base at United 

Airlines, we have about 12,000 employees, each one of whom is involved in 

many information transactions in a single day. How do we manage this 

information exchange so it best supports our maintenance objectives? 

At United, we have made attempts to better manage this information 

f.low and to better understand its dynamics. For example, many years ago 

~ we began a fault isolation program to code maintenance problems in order 

~ to classify them in a way that we could then run computer analyses. 

~ . K In a recent "classic" incident, we had an airplane problem which the 

~ s. crew coded as "Left brakes binding. Airplane pulls to left on landing." 

~ t So we went in and replaced the brakes on the left side. The airplane 

<:1 flew again and we got the same report from the crew: "Left brakes 

;£10 binding. Airplane pulls to left." This time we went in more deeply, 

~ changing parts in the anti-skid system and some other components. Well, 

guess what the problem turned out to be? The right brakes didn't work. 

Here we have a simple maintenance problem which, through neglect of 

human factors considerations, became a more complex problem. If someone 

had simply said "The airplane pulls to the left," we probably would have 

A-34 
·or 

.ed 

IUt 

'· 

use 

a 

•d 

.te 

llS 

•ne 

'hin 

•m 

ruman 

. to 

•r 

ll 

't 

1 to 

most 

.on? 

Ill 

ar;o 

~der 

the 

ll• n 

Ill, 

·k. 

of 

1one 

tave 

checked both brakes. But someone got one more level into troubleshooting than was required and the system led us down the wrong path. 

'l'l'ie issue here, of course, is one of information exchange. How can we / 

insure that the data we receive is translated to information appropriate, 1 

to our needs in maintenance? 

i I happen to believe that there is a fairly simple dictionary that 

could be put together for use in fault isolation that would be easier to 

learn than a system based on significant number codes. This approach 

would be more appropriate for human understanding. Problems would be 

reported in standard terms commonly used. For example, the report 

"Airplane pulls left" uses words well known to all. Certainly, humans 

relate to this better than to a problem described as "001--3002." Then, 

by use of a standard dictionary of tet,.,s, word-processing techniques 

could be employed with the key words, yielding a higher likelihood of an 

~ accurate diagnosis. · 

Another issue that falls under the scope of communications is the 

exchange of information among the different players in the industry. 

There is a need for an improved data base of maintenance information to 

be shared throughout our industry. As good as some of us think our 

networking is, I think that we have a major problem in this area. For 

example, at this meeting I have learned of work being done at Douglas 

Aircraft that I did not know about. The same is probably true for work 

at Boeing. Ours is a very complex industry. We need an efficient data 

base that will keep all of us abreast of advances. 

Maintenance and inspection programs are built on the premise of 

commonality- that we have common fleets. In fact, this is not true. 

United Airlines has nominally 400 airplanes. No two of them are alike. 

Some are more alike than others, but every one of our maintenance systems 

is based on the assumption that they are common and that we are going to 

find the differences. This can lead to serious consequences when an 

error is made. 

If I assume all aircraft are different and then look for the 

commonality, I don't have the same problem if I miss a commonality as I 

do if I assume they are common and then miss a difference. In terms of 

human factors, we are creating an error prone process by starting with a 

bad assumption. 

Another problem in our industry is that in the past our audits, 

includ.ing those conducted by the FAA and those conducted internally by an 

airline, accept a 95 percent performance level or above as okay. By 

comparison, segments of the manufacturing industry decided some time ago 

that anything less than 100 percent quality as a target only leads to 

problems. Why should one ignore five mistakes in 100 and consider tha~ 

good performance? 

In maintenance operations, we must come to realize that we are the 

ultimate example of a zero-defects industry. Statistics describing the 

low incidence of mechanically related accidents should not provide any 

measure of comfort. When you look at an accident classified as "pilot 

error," you frequently find a mechanical problem somewhere along the line 

of causal events leading to the accident. The L-1011 accident which 

occurred in the Florida everglades many years ago is an excellent 

A-35 
example. In this case, crew members were distracted from the flight 

regime by the failure of a landing gear light to illuminate when the nose 

gear was lowered. Trying to evaluate the problem took the full attention 

of the flight deck crew, during which time the low altitude alarm system 

was accidentally disengaged and the aircraft gradually descended into the 

swamp. 

We obviously cannot accept any level of defect in maintenance. It is 

just not good business. Every airline operator and every manufacturer 

has a stake in 100 percent safety. Every commercial carrier must have 

total dedication to safety. I want every airline to spend the same money 

on maintenance that I spend and to be as safe as I'm safe. 

Somehow this part of the industry (the least common denominator) must 

be brought up to the same level of commitment as the rest of the 

operators. This is one issue being examined now by the industry steering 

committee. The question is "What do we do as an industry to ensure that 

we have 100 percent quality performance on an industry-wide basis?" 

To meet a standard of 100 percent quality performance, we must design 

our systems so that we do not build errors into the system. In 

particular, we must build systems that allow aircraft inspectors and 

aircraft mechanics to do their jobs efficiently and to make their full 

contribution to aviation safety. The air carrier industry, both as 

individual operators and through industry-wide activities such as the 

aging aircraft program, is searching for means to manage human error 

during aircraft maintenance and inspection and to make ours truly a 

zero-defects industry . 

• 

A-36 
nose 

1tion 

1tem 

l the 

[t is 

u: 

re 

~oney 

rust 

~sign 

.1 

Inspection and Maintenance Issues 

in Commute~ Ai~ Ca~~ier Ope~ations 

No=an S. Grubb 

Vice President, Maintenance and Engineering 

Henson Ai~lines 

.I!J.t~oduction 

The commuter air car~ier indust~y of this count~y and the world has 

experienced a very volatile and rapid g~owth over ~ecent years f~om the 

"Hom and Pop" ent~ep~eneur ope~ations of ten years ago with a few 

ai~c~aft to the large corpo~ate regional air car~ie~s of today. La~ge 

fleets of sophisticated and new gene~ation aircraft cove~ ~oute 

st~ctures ove~ large segments of the United States. This explosive 

g~owth has b~ought with it a unique challenge in the human aspects needed 

to support the sophistication of the indust~y. (NOTE: The following 

remarks ~epresent input f~om four commuter ai~ ca~~ie~s). 

Thesis 

It is ou~ contention that the human elements of the equation have 

lagged behind and not kept pace with the technologies of today's new 

generation ai~c~aft, coupled with the market demands of the commute~ 

industry. I say this because of the many human factors issues that we 

see in today's workplace. These facto~s span the indust~y f~om the 

manufacturer of the equipment, to the regulatory agencies, to the 

mechanic on the job. 

~sues 

Let us examine these issues and discuss thei~ impact on the 

production of a safe and reliable product. 

1. Sophistication of t,he new generation commuter airc~aft vs. the 

"o1d ·school." 

2. Training. 

3. Manufacturer support. 

4. F~ictions between AP Mechanics and Quality Cont~o·l Inspecto~s. 

5. Clock-clilrd employee turnove~ and exp'e~ienc.e level..· 

6. Management tt,Jrnover arid competency .as· it affects the man on the 

job. 

,... 7. Airc~aft utilization· vs. ai~c~aft maintenance ground time. 

8. Fatigue. 

9. Morale/job satisfaction. 

10. Drug/alcohol dependency. 

A-37 
Sophistication of New Generation Commuter Aircraft vs. the Old School 

The technology of the new generation aircraft with the more extensive 

use of micro-processors, integrated circuits, and advanced avionics has 

surpassed the know-how of the majority of AP Mechanics and Inspectors. 

The AP School curriculum has not kept pace with advances in the 

industry. The "dope and fabric" days are over and yet this subject, as 

well as "woodworking," is still taught in AP Schools. Needless to say, 

the A&P curriculum is totally inadequate and a drastic overhaul of what 

we are teaching in the AP Schools is badly needed to prepare mechanics 

for the "high tech" commuter aircraft of today and tomorrow. 

Some of the more technically-trained and capable employees are the 

avionics technicians Who have gone through an FAA-approved avionics 

school. These people are virtually ignored in the traditional FAA 

organizational structure. For example, an Avionics Manager cannot be 

Director of Maintenance without an Airframe and Power Mechanic license, 

yet an old-timer can be Directo~of Maintenance strictly with an AP 

license, and understand very little about today's high tech aircraft. An 

avionics technician can graduate from an FAA avionics school, but there 

is no license that allows the technician to work on the aircraft or 

sign-off his own work. An avionics technician must obtain a repairman's 

certificate in radio and instrument repair before he can sign-off his 

work. An AP mechanic can be taken from the ranks and trained in-house in 

a few months and be doing work and signing off work that the trained 

avionics technician cannot do until he gets an airman's certificate 

requiring as much time as the FAA Administrator deems necessary. This 

can be up to 18 months of practical experience in the specific job 

category, and then this certificate is not transferable to another 

employer (FAR 65.101). Again, this is a deficiency in today•s school 

syst- for qualifying our technicians. 

Train ill& 

In view of the inadequate training of today•s AP in school, new hires 

are not ready for systems training on the commuter aircraft. After an 

initial indoctrination program, the new hire is put to work on the floor 

with an experienced mechanic for aircraft familiarization a month or two 

before systems training can be meaningful and absorbed by the mechanic • 

.; llaaufaeturer SUpport 

The manufacturers of today•s new generation aircraft have rushed the 

product to market before full technical support is developed. 

Maintenance manuals leave much to be desired in terms of wear limits, 

d-s,e limits, repair schemes and adequate or accurate wiring diagrams. 

As situations occur, the operators find themselves going back to the 

manufacturer frequently for repair limits, repair schemes and other 

relief, and this information is fortbc0111ing after the information is 

developed by the engineers and approved by the DER/DAR (Designated 

Engineering Representative/Designated Airworthiness Representative). In 

the meantime, an aircraft is A.OG ("Aircraft on Ground"). The operator is 

caught between not having adequate manual information for the aircraft 

and not being able to make subjective judgments in violation of the FAR's 

as interpreted by the Federal Aviation Administration. The industry 

needs some latitude in making judgment calls by mature and experienced 

maintenance personnel. 

A-38 
Lsive 

tas 

te 

;e, 

An 

m•s 

I 

1e in 

Ls 

I ires 

m 

loor 

two 

lc. 

the 

liS. 

In 

)r is 

ft 

rAR's 

ad 

~· Friction Between AP Mechanics and Quality Control Inspectors 

In my opinion, this issue has the most effect on people in the 

maintenance and inspection category in terms of mental and physical 

strains of the job. Maintenance people have the pressure of getting the 

aircraft to the gate on time, and inspectors have the pressure of making 

certain the aircraft is airworthy before it leaves maintenance for 

revenue service. This raises many questions b.etween the two groups as to 

what is airworthy and what isn't, and on what basis is the determination 

made? This situation causes an adversarial relationship between the 

inspectors and the mechanics and supervisors. Maintenance people think 

the inspectors do not feel responsible for getting the aircraft out on 

time and that they continue to write-up items and are "nitpicking." 

Maintenance is dedicated to putting out a safe aircraft, but on many 

occasions, the inspectors do not consider the aircraft airworthy by the 

strict definition or interpretation of the FAR's. The more experienced 

maintenance people feel they should be able to make subjective judgments 

and that the less experienced inspectors are looking for objective 

judgments or decisions only - in other words, they want to go strictly 

"by the book." I'm sure this is an old story to all of you; 

nevertheless, this causes mental and physical strain on both the 

maintenance group and the inspectors. 

In the Shop atmosphere however, where there is not a gate time to 

meet, an adversarial relationship does not exist between the mechanics, 

.supervisors and inspectors. In fact, maintenance welcomes the inspection 

group in the Shop atmosphere and sees them as a help rather than a 

hindrance. It appears the pressure of the gate time makes the difference. 

Clock-Card Employee Turnover and Experience Level 

The commuter industry has experienced an extremely high turnover due 

to the major air carriers' expansion and need for mechanics and 

inspectors. Since the commuters then have to fill the ranks from AP 

School, the military, or from Fixed-Base Operators (FBO's), there is a 

large percentage of inexperienced mechanics, particularly on a type 

aircraft. This makes both the inspectors' job and the supervisors' job 

more difficult, and it does result in less efficient operations, since 

not as much work is accomplished and more mistakes are made that must be 

corrected. 

Management Turnover and Competence As It Affects the Man on the Job ~ 

With the rapid expansion of the industry, there has been an 

increasing demand for experienced and competent management to fill the 

many positions that have become available. As a result, there has been 

considerable movement of managers from operator to operator and many 

managers in their present positions have not had longevity in that 

position with the particular company. Thw workforce sees instability in 

management and in the policies and procedures that ensue. Also, a lot of 

the administrative work falls on the lower-level supervisors as the 

learning process of the new manager takes place. This allows less time 

for the supervisor to spend with the mechanics or inspectors on the job. 

The second part of the increased need for management is that a number 

of young people have been promoted from within to authoritative positions 

A-39 

nt 

lt 

y 

ll 

[t 

L 

a.m. 

~re 

up 

ten 

.t 

!S to 

aft 

e not 

n& 

s 

about 

, what 

l this 

the 

rill 

:ce 

&ood 

:tin& 

!an, 

11 the 

I) 

Drug/Alcohol Dependency 

What can I say that hasn't already been said about dru&s and alcohol 

problems in our society today? However, in our industry, this problem 

must have particular emphasis as the lives of so many people are at 

stake. I am proud to say that Henson Airlines has mandatory dru&-testin& 

in the hirin& process and dru&-testin& of individuals involved in any 

incident or accident. However, the entire industry needs mandatory 

dru&-testin& in the hirin& process as well as periodic and random 

dru&-testin& of the workforce. This should be a top priority. 

I can honestly say that I have not personally seen any evidence of 

dru&s or alcohol use or abuse in our workforce. However, we must remain 

alert and always be on the lookout for the problem. OUr experience has 

been that less than one percent of mechanic applicants have been turned 

down for employment as a result of positive dru&-testin& results. 

Thank you. 

A-41 
Human Factors in Aircraft Maintenance and Inspection 

Rotorcraft Maintenance and Inspection 

Introduction 

James T. Moran 

Air Safety Investigator 

Aerospatiale Helicopter Corporation 

Several years ago, Harry Reasoner made a rather tongue-in-cheek 

comparison between pilots who fly fixed-wing aircraft and pilots who fly 

rotary-wing aircraft. The paraphrased statement indicated that 

fixed-wing pilots were extroverted, happy-go-lucky, bright-eyed people 

Who could not understand why people actually paid money to have them 

perfot~ their day-to-day duties; while on the other hand, helicopter 

pilots were beady-eyed, neurotic little people who know that if a 

catastrophic failure of some sort has not already happened, it is about 

to. This is due to the fact that rotor-wing aircraft are viewed by the 

pilots and maintenance personnel as 3,000 pieces of metal fatigue 

surrounding an oil leak, and these combined pieces don't really fly, but 

rather beat the air into submission. 

Due to the different environments that the helicopters operate in 

(i.e., high vibration levels, high torque levels, corrosive 

environments), a higher level of diligence is required by maintenance 

personnel. 

Standardization of Inspection, Maintenance and Repair Manuals 

Maintenance and inspection manuals come in a wide variety of shapes, 

sizes and formats. Although the majority of manufacturers have gone to 

the ATA Specification 100 Type System, there are still gaping differences 

in the way material is presented to the mechanic. Although the ATA 

System provides mechanics a standard format for finding material in 

maintenance manuals, once that material is found its presentation differs 

greatly among manufacturers. 

A standardization of language used in manuals is becoming 

increasingly necessary as the rotary-wing aircraft on the market attain 

greater degrees of sophistication. For example, turbine temperatures are 

expressed on different aircraft as: EGT, T4, T5, TIT and TOT. Although 

the areas of pick-up for these temperatures differ slightly among 

engines, all of the figures produce the same information. The same 

confusion applies to the nomenclature of turbine rotor speeds. While the 

compressor/gas producer sections of all turbine engines are referred to 

as either VG, N or Vl, the power turbine sections of the same engines are 

referred to as either N2, NTL, NF, N or HP. Admittedly, there are some 

differences in the operations between a free-turbine engine and a 

fixed-shaft engine. However, the number of different names outweigh the 

differences by far. 

Licensing of Mechanics 

In discussions with some of the larger helicopter operators in the 

United States, it has been observed that as the sophistication of 

A-42 
'ly 

es, 

to 

nces 

fers 

in 

are 

·ugh 

, the 

to 

1 are 

>1!\e 

the 

le 

aircraft becomes greater, the possibility exists that the necessity of 

"type rating" mechanics in different aircraft will arise. Although 

presently operators, in conjunction with insurance companies, limit the 

duti~s of certain mechanics to their experience level, there is no 

regulation pertaining to this. At the very least, consideration should 

be given to making it mandatory that aircraft above certain weight limits 

and complexities require factory-trained mechanics to perform the needed 

maintenance. This also applies to the level of maintenance which should 

be allowed to be performed on different type aircraft. An A&P mechanicwith an Overhaul Manual and no training can be very dangerous. Attempts 

are presently being made by the manufacturers to contain such 

activities. However, lack of regulation in this area makes the job 

difficult. 

Consideration should be given to bringing the FAA Regulations more in 

line with the Canadian Aviation Regulations which require licensing by 

aircraft type for mechanics, even after they have been to an approved 

manufacturer's maintenance school. 

Inibial Airframe and Powerplant Mechanic Training 

Under present day standards, there are no requirements for an A&P 

school to provide a potential mechanic with any training in rotorcraft 

maintenance. This means that a mechanic in today's market can 

conceivably finish his license requirements never having been any closer 

to a helicopter than seeing Airwolf on television. 

It has long been known that schools teach the requirements for the 

FAA test, and the test borders on being antiquated. There presently are 

sections of the initial training which deal with woodwork, welding, 

fabric skin repair and radial engines, which the mechanics will never see 

once they finish the curriculum they are enrolled in. Perhaps 

maintenance schools should take a cue from flight schools, which divide 

training into different phases. First phase would be initial entry level 

maintenance on all aircraft to cover standards and practices and other 

topics described in AC 43.13-lA. Later phases of training could be · 

devoted to either rotorcraft or the more advanced maintenance techniques 

required by the air transport industry. Having additional certifications 

such as these stamped on a mechanic's license would make him more 

valuable to the operators of different aircraft and put the mechanics in 

a better position to obtain gainful employment. 

Dynamic Components and Service Life Limited Parts in Rotary Wins Aircraft 

Certain parts in aircraft, to include the dynamic components in the 

rotor head, tail rotor, drive trains, and gearboxes, are "service life 

limited." These limits are determined by the manufacturer during fatigue 

testing and the development of a history on these parts over years of 

service. The term "service life limit" should never be confused with 

"time before overhaul," a term used in the fixed-wing market mostly 

connected with fixed-wing powerplants and components. A properly 

maintained helicopter should have separate logs and "serviceable" cards 

for all life-limited parts. Over the years, many catastrophic accidents 

have been attributed to having aircraft parts reinstalled that have 

reached their useful fatigue life, been ''overhauled," and returned to 

service. Having your alternator go out on a Beech Bonanza while in 

flight is "disturbing." The loss of a main rotor blade in flight could 

add a new dimension to that term. 

A-43 
i 

r: 

i 

I 

Constant vigilance by mechanics and supervisors is becoming more and 

more necessary with today's generation of helicopters. Small things like 

following the Standards and Practices sections of maintenance manuals, 

and giving particular attention to the corrosion protection sections of 

the aircraft inspection and repair manual can go a long way in reducing 

the accident rate, which has already been substantially reduced over the 

past ten years. 

Perhaps some day we can improve rotary wing maintenance to the point 

where our "beady-eyed, neurotic little pilots" become the "extroverted, 

happy-go-lucky" ones·they once were. 

A-44 
nd 

ike 

f 

~ 

he 

nt 

Nondestructive Inspection Equipment and Procedures 

George Ansley 

NDT Specialist, Service Engineering Department 

Boeing Commercial Airplanes 

This presentation describes the inspection techniques known variously 

as nondestructive testing (NDT), nondestructive inspection (NDI), and 

nondestructive examination (NDE). The principal methods used today to 

support nondestructive testing include: 

0 

/.----

X-ray. 

years. 

during 

These procedures have been 

X-ray can detect anomalies 

medical examinations. 

in use for roughly 50 

in metal just as in bone 

Ultrasonics. Alterations in patterns of 

are used to pinpoint structural faults. 

the most difficult NDT method. 

reflected sound waves 

Technically, this is 

o Eddy current. This is an electronic inspection method in which 

disturbances in an eddy current indicate a metal fault. 

Probably 90 percent of the NDT inspections made today use this 

procedure. 

o Penetrant. In 'this procedure, a dye is applied to the metal 

and then examined with different lighting sources for 

indications of unusual stress patterns. This is a well-known 

inspection procedure. 

o Magnetic Particle; This procedure is limited to the inspection 

of steels that can be magnetized and is commonly used in 

overhaul situations where parts are taken from the airplane, 

completely disassembled, and inspected. 

The above are referred to generically as methods, i.e., the eddy 

current method. When these methods are presented in specific written 

instructions for aircraft inspection they'are referred to as procedures. 

The primary method of aircraft examination is by visual inspection. 

This remains the best inspection method, with possibly 95 percent of an 

aircraft being inspected visually.· NDT procedures are used to supplement 

the visual inspection and, in general, are used in lieu of a costly 

tear-down process in which much hardware is removed to get to the 

structure requiring inspection. "NDT procedures are effective and also 

control costs. Finally, NDT procedures can be used for reliable 

detec~ion of smaller defects than could be found visually. 

Figure 1 illustrates the use of a nondestructive inspection. Some 

years ago we did a tear-down inspection of an older airplane and found 

small cracks in the lower wing surface spanwise splice stringer. This 

stringer goes through the fuel tank,, so the first visual evidence of such 

a crack would be a noticeable fuel ;leak on-the underwing surface. other 

than the surface inspection, the only other visual option consists of 

draining the tank, climbing inside, scraping sealant, and performing a 

visual check there of each of the 7,000 fasteners. It is our position 

that such an inspection simply is impossible. A nondestructive procedure 

must be used. 

A-45 
Approximately 7,000 fastener locations per airplane; 

inspection time: 2 men - 8 hours • 16 man hours_ 

There is no viable inspection option. 

Figure 1. Example of low frequency eddy current inspection of lower wing surface 

span-wise splice stringer. 

•.he NOT inspection used for the splice stringer consists of centering 

an eddy current probe in place and sliding it slowly the full length of 

the wing to detect possible c.racks in the underlying member. Inspection 

time for the 7,000 fasten&rs is approximately 16 man-hours.. Obviously, 

the IIDT procedure is superior to a visual inspection. However,. it comes 

with its own problems. Since this is a lower wing surface, typically one 

man holds the eddy current equipment while the other applies the probe to 

the aircraft while standing on a short ladder. The inspector thus is 

leaning back while looking straight up. This is quite uncomfortable and 

can cmJ.y be tolerated for short periods of time. However, in our mind, 

this inspection procedure is mandatory. There is no. viable option. 

The basic eddy curr81\t inspection in use today is illustrated in 

Figure 2. This shows the high frequency eddy current probe inside a 

fastener. Generally, the inspection probe is calibrated against a test 

base with a thirty-thousandth indt notch. If a crack of this extent is 

founcl duriq the inspection of a fastener hole, the hole is drilled and 

repaired·. For the remainiD& holes, we assw. smaller cracks are present 

even Ulou&h the required eddy current inspection shows nothiq. We then. 

oversize each of these &ood holes about l/16th of an inch and refasten 

t.he atructure with oversize bolts. This procedure is called out in many 

of tbe Service Bulletins we have issued. 

High ftequency eddy curtent fastenar hole: inspection to detect cracks .030 inch or larger. 

Figure 2. Example of non-destructive inspection to support structural repair or 

modification. 

A-46 
NDI Procedure Development 

The Boeing Company maintains a well-equipped NDT laboratory, with an 

extensive investment in equipment, which is used to study NOT procedures 

and to validate the inspection requirements we describe in Set·vice 

Bulletins. In a sense, we work for the airlines as we try to develop the 

most practical and effective options to visual inspection in maintenance 

programs. For the most part, the procedures we develop are considered 

mandatory since the alternative, taking the airplane apart to examine 

internal systems visually, generally is not feasible. 

The NOT laboratory also considers field conditions when developing an 

inspection procedure. For example, some eddy current and ultrasonic 

instruments provide the readout on an oscilloscope rather than a meter. 

This works fine in the laboratory. However, we deal with airlines all 

over the world, a great many of which operate in the tropics. For an 

outside inspection or in a hangar without doors, the sunlight simply is 

too bright for an oscilloscope to be used. Therefore, we look to 

alternate procedures or equipment that will be effective in the various 

environments in which they will be used. 

We also take into account cost of equipment to the airlines and 

training requirements imposed on inspectors. For example, When the FAA 

made the first low frequency eddy current inspection mandatory, we 

conducted a school for inspectors to insure that these inspections would 

be conducted properly. While the equipment and training does present an 

additional cost burden to airlines, there appears to be no alternative. 

Much laboratory work is concerned with establishing procedures and 

standards for critical crack detection. We know that a crack grows 

slowly as metal fatigues, and that as the crack gets larger its rate of 

growth increases. OUr Stress Department develops information on crack 

size versus aircraft landing cycles. In how many cycles does the crack 

go critical? From these data we establish inspection intervals, as shown 

in Figure 3. OUr Service Bulletin philosophy is that we want two 

opportunities to detect that crack before it reaches critical size. 

------- Critical Crack Size ---------¥ 

Inspection 

Interval~ 

Figure 3. Establishment of NOI inspection intervals to ensure detection before cracks 

become critical. 

A-47 
\, 

We also consider inspection options from an airline's point of view. 

If I can allow for a larger defect in a Service Bulletin, the inspection 

will be easier technically, a less expensive piece of equipment can be 

used, and the inspector might not require as much training. The 

disadvantage, however, is that the inspection interval must be shorter. 

For instance, the inspection might have to be made every six months. 

This is inconvenient since the airplane is not available for scheduled 

maintenance that often. Therefore, we can stretch the inspection 

interval by dealing with a smaller defect size. In turn, this may 

require special instrumentation and training. The inspection itself 

might be slow and tedious. These are difficult tradeoffs to consider. 

Lap Splice Inspections 

Considerable attention has been given recently to the 737 aircraft 

because of cracks discovered in the fuselage lap splice. At the splice, 

fuselage skins are thin, each of them only thirty-six thousandths of an 

inch. Because of these thin skins, the base of the countersink for a 

rivet tends to be a knife-edge, which is a poor fatigue detail. To 

counteract this, the aircraft were constructed with a cold bond system 

using epoxy over a thin layer of dacron or glass cloth as a means of 

distributing the load. The bonding shares the load with the fastener and 

picks up enough of the load so that a fatigue crack should never develop. 

We found with older airplanes that over a period of time, in the 

order of five years, the bonding material begins to deteriorate with 

moisture and you begin to lose the load-carrying capability that the bond 

gave you. Fatigue cracks then can form in the upper row of fasteners, as 

shown in Figure 4. 

typical cracks along 

0 0 0 o-

~ upper row of faoteners 

-o- .:0 0 0 

0 0 0 0 0 0 0 0 

0 0 0 0 0 0 0 0 

Figure 4. 737 aircraft fuselage lap splice inspection. 

Because of the potential for crack formation, there now is a 

mandatory eddy current inspection of the top row of fasteners in the 737 

airplane. The required area covers 659 inches, or 55 feet, of lap. 

Being roughly one inch apart, there are 659 fasteners in each lap and 

four laps to be inspected. 

The inspection is mandatory. However, there are various techniques 

for conducting an eddy current inspection. These include: 

o Pencil probe/template 

A-48 
ii. 

on 

e, 

n 

and 

op. 

ond 

as 

737 

es 

0 Pencil probe/oversize template 

0 Rotating probe 

0 Sliding probe 

0 Freehand pencil probe 

All of the above are variations on a theme. To illustrate their use, I 

will describe those frequently employed at this time. 

Use of the pencil probe/template technique is shown in Figure 5. The 

inspector visually centers the template on the fastener, then takes the 

pencil probe and scans the fastener looking for a telltale flick of the 

needle on his eddy current display instrument. The inspector must center 

the template before he can move the pencil proble. While working, he 

holds the instrument in one hand, scans using the pencil probe with the 

other, and watches the meter. Since this must be done for every 

fastener, this can be a laborious inspection. 

0 0 

meter display instrument -

~ 0 0 

upper skin 

""' 

.lower skin 

Figure 5. 

Figure 

technique. 

the shank. 

32 hours is 

template 

0 0 

pencil probe 

~ 

..__ pencil probe 

~template 

fasteners 

737 aircraft lap splice eddy current crack inspection using pencil probe/template 

technique. 

6 shows the key characteristics of. the pencil probe/template 

Detectable crack size is forty thousandths of an inch from 

Since 6 to 8. hours are required per lap, approxl.mately 24 to 

required to do one airplane. 

With use of an oversize template, as seen in Figure 7, inspection 

time can be reduced to 3 to 4 hours per lap. However, detectable crack 

size increases to 90 thousandths of an inch. So we have shortened the 

hours but reduced the sensitivity of the technique. 

A-49 
Detectable Crack Size 

Estimated Inspection Time 

Required Equipment 

Inspection Advantages 

and Limitations 

0.040 Inch From Shank 

6-8 Hours Per Lap 

Meter Display Instrument, Pencil Probe, 

and Circle Template 

• Sensitive to Very Small Cracks 

- Permits Economic Rework 

• Very Tedious 

• Detects Cracks in All Directions 

Figure 6. Inspection parameters for 737 aircraft eddy current crack 

inspections using pencil probe/template technique. 

Detectable Crack Size 0.090 Inch From Shank 

Estimated Inspection Time 3-4 Hours Per lap 

Required Equipment Meter Display Instrument, Pencil Probe, 

and Circle Tfll"l"ll)late 

Inspection Advantages • Detects Cracks in All Directions 

and Limitations 

Figure 7. Inspection parameters for 737 aircraft eddy current crack 

inspections using pencil probe/oversize template technique. 

A-50 
Figures 8 through 13 show the techniques and characteristics for the 

sliding probe, the rotating probe, and the freehand pencil probe 

systems. Note that inspection time can be reduced to one to two hours 

per lap with the freehand pencil probe system. However, detectable crack 

size is only two-tenths of an inch. A sunwary of characteristics for all 

of these eddy current crack inspection techniques is presented in 

Figure 14. 

impedance plane instrument ~ 

upper skin 

"" 

, 

lower skin 

I 

I 

scope 

fasteners 

0 0 

0 0 

0 0 

sliding probe 

______ ...... _Eil 

c::=====:> scanning direction 

Figure 8. 737 aircraft lap splice eddy current inspection using sliding probe technique. 

Detectable Crack Size 

Estima.ted Inspection Time 

Required Equipment 

Inspection Advantages 

and Limitations 

0.090 Inch From Shank 

2-3 Hours Per Lap 

Impedance Plane Scope Instrument 

and Nortec SPO 3806 Sliding Probe 

• Requires Only One Scanning Direction 

• Maximum Probe Off-Center+/- 0.050 Inch 

• Detects Cracks -45 Degrees to +45 Degrees 

From Fastener Line 

• Oversize Fasteners May Give Crack 

Indications 

Figure 9. Inspection parameters for 737 aircraft eddy current crack 

inspections using Sliding Probe Technique. 

A-51 
rotating probe instrument ~ 

0 0 

0 0 

scope 

gun and rotating probe ............ .-------~ 

--~--- ~ 

upper skin 

......... 

, 

lower skin 

Figure 10. 

l 

faoteners 

737 aircraft lap splice eddy current crack inspection using rotating probe 

technique. 

Detectable Crack Size 

Estimated Inspection Tim& 

Required Equipment 

Inspection Advantages 

and Limitations 

0.065 Inch From Shank 

2-3 Hours Per Lap 

RotatinQ Probe Instrument and 

Rotating Probe 

• Detects Cracks in All Directions 

• Oversi.ze Fasteners May Give Crack 

IndicatiOns 

Figure 11. Inspection parameters for 737 aircraft eddy current crack 

inspections using rotating probe technique. 

A-52 
-otating probe 

pencil probe 

4-- pencil probe 

upper skin 

" 

~ lower skin 

Figure 12. 737 aircraft lap splice eddy current crack inspection using free-hand pencil 

probe technique. 

Detectable Crack Size 

Estimated Inspection Time 

Required Equipment 

Inspection Advantages 

and Limitations 

0.20 Inch From Shank 

1-2 Hours Per Lap 

Meter Display Instrument and 

Pencil Probe 

• Detects Cracks -45 Degrees to +45 Degrees 

From Fastener Line 

Figure 13. Inspection parameters for 737 aircraft eddy current crack 

inspections using full·hand pencil probe technique. 

A-53 
Detectable 

Crack Size Estimated Equipment 

Technique From Shank Inspection Time Required 

Pencil Probe/Template 0.040 Inch 6-8 Hours Per Lap Meter Display 

Instrument 

Pencil Probe/Oversize 0.090 Inch 3-4 Hours Per Lap Meter Display 

Template. Instrument 

Rotating Probe 0.0651nch 2-3 Hours Per Lap Rotating Probe 

Instrument 

Sliding Probe 0.090 Inch 2-3 Hours Per Lap Impedance Plane 

Instrument 

Free-Hand Pencil 0.200 Inch 1-2 Hours Per Lap Meter Display 

Probe Instrument 

Figure 14. Summary of techniques for 737 aircraft lap splice eddy 

current crack inspections. 

There is a wide variety of excellent NDT equipment available "off the 

shelf" today. The NDT instrument manufacturers react rapidly to industry 

needs and are actively developing new equipment to support airframe 

manufacturers and the airlines. 

In general, the advances in NDT technology and application of NDT 

procedures have exceeded the availability of qualified NDT personnel. 

Our biggest need is for skilled, trained, and experienced inspectors. 

The instrument manufacturers have outdistanced the supply of trained 

personnel to use these instrumeats. This is a problem we must address. 

A-54 
Improved Information for Maintenance Personnel 

Robert C. Johnson 

Chief, Combat Logistics Branch 

USAF Human Resources Laboratory 

The Air Force has been working on the problem of providing proper 

technical information to maintenance personnel for many years. Our 

problem in this respect is not all that different from that of the 

commercial airlines. We both are concerned with the development of 

procedures and systems to support and enhance the performance of aircraft 

mechanics and inspectors. 

A significant Air Force activity in this field began about 20 years 

ago with the Job Perfot~nce Aids (JPA) program. This program literally 

redefined the technical information that Air Force maintenance personnel 

used to repair airplanes. Before this, technical data were found in 

books and in large paragraphs, written at probably a 12 to 14 grade 

reading level, far above most of our mechanics' ability to read it. 

Related information was scattered throughout a volume and possibly 

throughout several volumes. A mechanic had to have many books in order 

to follow a procedure. Procedures themselves were not clearly identified. Illustrations supporting the procedure also were scattered 

throughout the books. studies run to examine the performance of 

maintenance personnel at that time estimated that about one-third of a 

mechanics' total time was spent in finding the proper information. In 

all, there was ample justification to begin the JPA program. 

Even as job performance aids come into increasing use, the amount of 

maintenance data necessary to support a given airplane continues to 

grow. The number of pages of technical order data required to support 

four Air Force aircraft over a forty-year period is shown in Figure 1. 

During this time span, the number of pages of maintenance documentation 

has <:'-•,hl<'d approximately seven t i.mes. 

F-86 

1947 

(10.000} 

FB-111 

1967 

(250,000) 

F -16 

1974 

(750,000) 

B-18 

1986 

(1,000,000) 

Figure 1. Pages of technical order data required for four Air Force aircraft. 

The voluminous maintenance documentation lends itself naturally to an 

automalion process. Indeed, it is quite possible to automate technical 

data and print it out in stacks of IBM paper as one desires. While this 

A-55 
i 

' 

I~ ,. 

i 

l 

l 

would serve the purposes of automation, it would not serve the user's 

purpose of maintaining performance. For automation to be successful, it 

must be accomplished in a manner that supports user requirements. 

once the Air Force was committed to automation, the first step was to 

determine the requirements for technical info~tion to support effective 

job perfo~nce. A number of guiding principles were followed in the 

approach to automation. First, as noted, the user's requirements had to 

be kept in mind at all times during the design process. It was clear 

that we could not take existing technical data, process it through the 

computer, print it out, and expect improved perfo~nce. Second, the 

system should employ an effective technical order content/fo~t approach 

to be consistent with existing systems. A radical departure from 

conventional documentation would not be effective.. Third, usable 

controls and displays should be pt•ovided to the operator attempting to 

access the technical data and then employ it for his purposes. Finally, 

user acceptance was deemed to be critical. Even though all human factors 

issues might be addressed, user acceptance would not be guaranteed. User 

acceptance is a variable in itself. 

In an automation program, there are three areas of primary concern. 

In the Air Force program, as seen in Figure 2, issues of computer-aided 

authoring of materials is primarily a contractor effort. Issues of 

automated publient.ton nml d1.~tribut ion nre handled through the Air Force 

Logisli.cs Conunand. The parl of the efforl I am concerned with, as 

Contractor 

Computer 

Aided 

Authoring 

Automatic 

Formatting 

CAD 

Graphic• 

CAD Interface 

to Engineering 

Data 

--!> 

AFL.C (ATOS) 

Automated 

Publication &: 

Dl•trlbutlon 

Digital 

T.O. Data 

Computer-Aided 

Editing &: 

Modification 

Paper or 

Digital 

Output 

--!> 

Technician 

Electronic 

Delivery 

Maintenance 

Shop• 

(1-L.evel) 

Flight 

Un• 

Maintenance 

Figure 2. Areas of responsibility in Air Force integrated technical data system. 
conducted through the Human Resources 

delivery of maintenance information. 

level, whether to support performance 

conducted at the flight line. 

Laboratory, concerns electronic 

This is delivery to the hands-on 

in maintenance shops or maintenance 

A major issue in the delivery of automated maintenance information is 

that such information precisely match the needs of the user. However, we 

in the Air Force, as do you in airline operations, have a range of 

experience in our mechanics and inspectors. On one hand, we have 

exceptionally experienced people who have performed certain tasks 

hundreds of times and do not actually need technical data at all, except 

that Air Force doctrine says that t~y will use it. On the other hand, 

we have new personnel who need step-by-step detail to support their 

performance. In our program, maintenance personnel are separated into 

three tracks according to their needs. Figure 3 illustrates the levels 

of detail provided through the automated maintenance program to support a 

technician operating in each of these three tt·acks. 

LOW 

• Verify Equip. Condition 

• Remove Filter Element 

• Disassemble Filter 

• Inspect and Clean Fi Iter 

• Install Filter Element 

• Checkout Fuel System 

TRACK 1 

Task Summary 

For 

Experienced Technicians 

MEDIUM 

• Remove Filter Assembly 

From Fuel Pump Cavity 

• Disassemble Filter 

From Fuel Pump Cover 

CAUTION 

COVER FUEL PUMP 

OPENING WITH COVER 

TRACK 2 

Proceduralized Steps 

For 

Average Technicians 

HIGH 

• Remove Filter Assembly 

From Fuel Pump Cavity 

1. Cut Safety Wire 

2. Remove Bolts (1 I 

From Filter (2). 

h,~=~) JJ-2 

TRACK3 

Detailed Instructions 

For 

Novice Technicians 

Figure 3. Different levels of detail in maintenance instruction to support technicians with 

different experience levels. 

In 1979 I pt•epared a concept paper describing an Integrated 

Maintenance Information System (IMIS) which has subsequently turned into 

a major Air Force and DoD project. It was clear at that time that 

maintenance personnel needed more than simply the data describing 

disassembly and assembly.of components. They needed technical 

information of many kinds: training data, managP~ent information data, 

built-in test data on the airplane, flight parameters, supply information, and possibly access to historical information. In the course of a 

day, a maintenance man might have to interact with virtually all of these 

data systems at least once and possibly more. In this case, the 

maintenance man would be dealing with five or six different systems with 

different protocols, different software, different displays, and possibly 

conflicting information. No one would provide him with precisely the 

information he needed. 

A-57 
; 

:r 

. ~· 

The purpose of the Integrated Maintenance Information System was to 

provide one device that would allow a technician to interact with all 

data systems as if they were one. Software integration would be the key 

feature of the new IMIS system. At this time, we are well on our way to 

proving the !MIS concept and demonstrating the system in operation. The 

technical data to support IMIS are available. System components have 

been evaluated in three field tests using intermediate or shop-level 

automated technical data. Figure 4 shows the major topics of concern 

>Ver lhe period fcom 1985 to 1991. 

1986 

lntennediate-Level 

User Requirements 

Off-the-Shelf 

.......... 

Formats 

Levels of Detail 

Schematics 

Resolution 

Interactive Requirements 

1988 

Flight Line 

Flexible R-rch Tool 

Durable 

• •••••••• 

Memory Modules 

Multiple Po- Soun:es 

Interactive DiatP'eostics 

ABDR .t\luanJent 

DDDDDD 

()() 

1991 

Maintenance Complex 

lncreeled Capabilities 

Rugged 

• •••••••• 

Size/Weight 

Expen Diagnostics 

Ground SVttem Interface 

Training 

Information Integration 

Figure 4. Three P'- of the Air Force I ntegreted Maintenance Information System. 

The principal end product of !MIS is a portable computer which will 

plug into the maintenance bus on one of our airplanes and download at the 

flight line the built-in test data necessary to troubleshoot the 

airplane. All automated systems on the airplane can be checked without 

climbing into the cockpit. Following this, the same portable computer 

plugs into a keyboard and turns into a maintenance workstation that 

allows the technician to interact with ground systems, with airborne 

systems, and with the range of data bases necessary to support his 

performance. 

In February 1989, we plan to plug the portable IMIS computer into an 

F-16 aircraft and try the system on the flight line. We will have 

integration of step-by-step diagnostic procedures with supporting 

technical data, the two major elements of !MIS. All IMIS software will 

be integrated in late 1991, with the full IMIS system available in early 

1992. Figure 5 illustrates the operation of the IMIS information network 

at that time. 

A-58 
I I I Ground Syeteme ] 

I I 

AII"'ra:ft !<== Portable Maintenance Maintenance Computer Worketotlon Panel 

t 

Teohnlolon 

Figure 5. Operation of Integrated Maintenance Information System Network. 

There remain a number of associated technologies t·equiring work uy us 

to develop the IMIS system to its full potential. Some of these are (1) 

interactive diagnostic technology, (2) computer hardware technology, (3) 

data base development issues, and (4) problems of flight line operation. One of particular interest, however, is maintenance aiding 

technology, as shown in Table 1. For example, the size of the computer 

screen is a matter of genuine concern. 

TABLE 1 

EXAMPLE OF OME TECHNOLOGY REQUIRING 

WORK TO SUPPORT DEVELOPMENT OF THE 

INTEGRATED MAINTEMANCE INFORMATION SYSTEM 

Maintenance Aiding Technology 

Presenting Data on Small Screen 

Content 

Formats 

Man/Machine Interaction Techniques 

Presenting Schematics 

Enhancing Performance 

Levels of detail 

Highlight signal flow, etc. 

Computations 

Field Test 

Much of our information is presented in the form of schematics which, to 

be readable, are physically larger than the screen. We are working 

intensively with the problem of small screen presentations but, although 

we have made progress, we do not have the necessary answers as yet. We 

also are continuing to work on problems of man-machine interaction, 

although we feel this is an advanced technology at this time. We still 

need to know, however, precise levels of detail to use for a technician 

A-59 
' 

I' I 

" f 

~ 

at a given level of training performing a specific task. We also need to 

understand proper procedures to highlight signal flow through a schematic 

and to illustrate required computations. Finally, there is more work to 

be done on defining optimum procedures for field testing a system such as 

!MIS so that the test provides all information to support ongoing 

improvements. 

While the Air Force has a specific military mission, its requirement 

for quality aircraft maintenance is shared with civilian airline 

operators. If the technology for management and presentation of 

maintenance infot~tion that we have developed over the years can prove 

useful for the nation's civilian aviation industry, so much the better. 

A-60 
St~engths and P~oblems in 

Maintenance T~aining P~og~ams 

Richa~d Hlavenka 

Division chai~n 

Ta~~ant County Junio~ College 

This p~esentation desc~ibes the manne~ in which t~aining fo~ aviation 

maintenance is being conducted in colleges at this time and the way we 

~elate to the diffe~ent segments of the aviation indust~y. I would also 

like to dispel ce~tain misconceptions about ou~ t~aining p~og~ams. 

Finally, I would like to discuss some human facto~s pe~tain-ing to the 

scope of maintenance t~aining today. 

Pe~haps the best way to int~oduce the topic of maintenance t~aining 

is to desc~ibe b~iefly the p~og~am at Ta~~ant county Junio~ College. ou~ 

aviation facility is located at the Meacham/Fo~t Wo~th Municipal Ai~po~t. 

some th~ee miles f~om the main campus. The school ope~ates on a semeste~ 

system, with two semeste~s each yea~ plus a single summe~ session. 

Students who ente~ ou~ p~og~am fall into th~ee basic g~oups. Fi~st, 

the~e a~e those who a~e studying to ente~ the field of aviation 

maintenance but who have no p~io~ expe~ience. These students typically 

have been out of high school f~om one to ten yea~s. Second, we have 

those who a~e al~eady involved in aviation and a~e looking to upg~ade 

thei~ skills. In some cases, these a~e individuals who feel the ai~f~ame 

and powe~ plant mec~anics license will allow them to move to a bette~ 

position at thei~ p~esent P~ployment. Finally, we have those individuals 

with unique ~easons fo~ being in the p~og~am. Fo~ example, some a~e 

p~ofessionals who own ai~c~aft and want to unde~stand thei~ ai~lane 

bette~ and possibly do some pa~t of thei~ own maintenance. Of these 

th~ee g~oups, the la~gest numbe~ a~e those se~iously inte~ested in 

ente~ing aviation maintenance as a p~ofession. 

Ta~~ant County Junio~ College is simila~ to the othe~ 140 o~ so FAA 

app~oved and ce~tified ai~f~ame and powe~ plant mechanic p~og~ams in that 

we have a co~e cu~~iculum which complies with the guidelines of Pa~t 147 

of thn Fede~al Aviation Regulations. While Pa~t 147 influences 

conside~able simila~ity among these 140 schools, the~e is still 

flexibility in what can be done within thei~ cu~~iculum. At ou~ school, 

the ai~frame and powe~ plant mechanics p~og~am ~equi~es app~oximately two 

yea~s to complete the co~e cu~~iculum. Du~ing this time, a student 

becomes fully qualified to take the FAA examination. We also offe~ the 

student an option to continue into a two year Associate Deg~ee program. 

Here we offer additional academic courses, usually in the areas of 

mathematics, science, and communications. Beginning this year, we wi.ll 

also include a course in human relations and .a course in speech. It is 

estimated that over 90 percent of those graduating from the core two-year 

program continue on and are awarded the Associate of Applied Science 

Degree. 

For the past several yea~s. the majority of ou~ students have been 

employed by the majo~ airlines immediately upon graduation. In the past 

two years, most have gone to work for American and Delta. We are proud 

of the fact that, for the first time in the Dallas/Fort Worth area, 

American Ai~lines has started hiring our graduates and putting them 

A-61 
di<"ectly on the floo<" with othe<" mechanics. Thus, while we <"ecognize an 

ongoing need for certain impeovements within the program, we do feel that 

this certainly illust<"ates our prog<"am's effectiveness. 

The main area of st<"ength in training today is provided by Part 147, 

which assures a large degree of commonality among the prog<"ams of all 

maintenance schools. This is an advantage t.o the emp~oyer since he can 

assume that a newly graduated aircraft mechanic will have basic t<"aining, 

knowledge, and skills in at least ;,3 areas of aviation maintenance, 

ranging from basic electricity to aircraft p<"opellers. 

Within Part 147, there is considerable flexibility as to the way in 

which a school can cover requi<"ed topics. For example, we are still 

required to teach dope and fabric techniques, even though the number of 

fabric covered aircraft in the national inventoey certainly is limited 

today. However, Part. 147 does not specify whether this t.opic requires 

one hour or 500 hours of training. In our particular program, we offer 

24 hours of dope and fabric procedures. In this time, we teach students 

of the need for the procedure, how it is performed, and problems incurred 

with its use. 

one problem we faced until recently concerned getting students into 

the program who were academically qualified. About four years ago, we 

were experiencing approximately a 30 percent drop-out rate among students 

who entered the first semester of our aviation maintenance program. This 

caused us some concern, particularly since our enrollment is limited and 

we were having to turn away students each semester as we started that 

year's program. In order to improve this situation, we established 

academic entrance standards. All students now are required to take 

placement tests in mathematics, reading, and English prior to acceptance. In mathematics a student must be competent in basic algebra. He 

must be able to read at least at the tenth grade level, and be competent 

in English at the college freshman entry level. Students scoring below 

these levels are directed through remedial courses prior to entering 

aviation maintenance training. We now have a drop-out rate of five 

percent or less in the first semester of our program. 

Academic instruction is continued after the student enters his 

maintenance training. Mathematics is continued through basic 

trigonometric functions. Other courses emphasize writing and 

communication. Upon completion of the program, our average student 

probably is reading at the 14 year level. We consider this skill quite 

important since he is required to make logbook entries, to complete Form 

337's, to communicate well with others in writing, and interpret 

accurately the wording in Airworthiness Directives. 

Turning to the problems in aviation maintenance training today, we 

come back to Part 147. While I have peeviously identified it as a 

strength, it also has its weaknesses. One problem that must be solved, 

and is currently being worked on, is that the document basically has not 

changed for about 20 years. This means we are graduating students who 

are being taught from a 20-year old curriculum. While we have upgraded 

sections within that curriculum, it remains the same basic document. 

Aviation has changed considerably during the last 20 years; Part 147 must 

reflect these changes. It is suggested that those of you with concerns 

about Part 147 make them known to the FAA as input 

to the study now in progress. 

A-62 
When changes are made to Part 147, consideration should be given to 

time requit·ements. At the moment, the FAA requires that students have at 

least 1900 hours of training. Our program offers 1965 hours during an 

intensive two-year program in which students have a total of only six 

weeks of free time. If Part 147 is extended to require more hours, this 

automatically means that schools must extend their programs. I believe 

this will have an economic ripple effect all through the aviation 

industry. At the present time, for one price an employer can buy a 

product - an individual - with basic entry level skills and knowledge. 

This individual knows how to perform aircraft maintenance, how to 

interpret technical manuals, and how to work on his own. If his training 

is extended and his skills enhanced, however desirable these may be, the 

price of the package may well increase. This in turn would impact 

aviation maintenance costs in areas where operators are looking at close 

profit margins. 

One means of dealing'with the above issue could be to develop certain 

post-graduate packages. These specialized programs could be added to the 

core program and be elective. This would be a way of dealing with topics 

such as helicopter maintenance and repair of advanced electronics systems. 

Finally, there is another topic I offer for consideration. Table 1 

shows a typical core curriculum for an aviation maintenance program. 

This is basically the FAA curriculum and I would like to point out one 

thing about it. There is nothing in it that relates to human factors or 

human relations. With this curriculum, we produce an individual who is 

strictly limited to the maintenance phase of aviation. 

It is my belief that the Part 147 core curriculum, and the profession 

in general, could be improved by adding some topics related to 

employee/employer relations. Areas of coverage could include 

professional ethics, professional communications, and personal commitment 

to one's job. I believe these to be areas that are vitally important to 

the aviation maintenance technician of the 1980's and 1990's. 

In an expansion of Part 147, we could without great effort include 

newer areas of coverage such as topics concerned with "glass cockpits," 

etc. If we are going to do that, however, I still recommend that we 

include coverage of human relations topics as suggested. By doing this, 

we will produce a better and safer mechanic who will not only be a person 

who can do the job well, but also be a person who will understand the 

responsibilities that go along with that job. 

A-63 
I 

Table l. Typical Core Curriculum for an 

Aviation Maintenance Program. 

GENERAL AVIATION MAINTENANCE COURSES (17 Hours) 

AER 1313 

AER 1323 

AER 1344 

AER 1364 

AER 1383 

Background for Aircraft Science 

Advanced Aircraft Science 

Ground Operation and Servicing 

Materials and Processes 

Basic Electricity 

AIRFRAME COURSES (29 Hours) 

AER 1333 

AER 1335 

AER 1356 

AER 1372 

AER 1374 

AER 1392 

AER 1402 

AER 1403 

AER 1412 

Assembly and Rigging 

Sheet Metal Structures 

Airframe Electrical Systems 

Aircraft Landing Gear Systems 

Hydraulic, Pneumatic and Fuel Systems 

Aircraft Covering and Finishing 

Welding 

Utility Systems 

Airframe Inspection and Review 

POWERPLANT COURSES (26 Hours) 

AER 2412 

AER 2425 

AER 2434 

AER 2442 

AER 2456 

AER 2465 

AER 2472 

Turbine Engines 

Powerplant Fuel Systems 

Propellers 

Powerplant Lubrication Systems 

Reciprocating Engines Overhaul 

Powerplant Electrical Systems 

Powerplant Inspection and Review 

A-64 

n 

i 

i 

t 

E 

f 

I 

( 

t 

I 

l 

l 

f 

~ 

l 

( 

' 

( 

I 

n 

n 

t 

( 

l 

l 

l 
The Human Operator as an Inspector: 

Aided and Unaided 

Colin G. Drury, Ph.D. 

Professor of Industrial Engineering 

SUNY, Buffalo 

The thrust of this presentation is toward human factors in 

inspection, a key element within the broader field of industrial 

maintenarce. The objective is to point out human factors concerns in the 

inspection process and, in particular, to illustrate how the human 

inspector can be viewed as a quantitatively defined technical system. 

The term "human factors" can be considered synonymous with 

"ergonomics," which has been defined as the science of ''fitting the job 

to the pet•son to enhance human efficiency and well-being." There are 

specific techniques to be used in fitting the job to the person. The 

first activity is a systPJRS analysis in which the objective, or end 

product, of the system is clearly defined. The role of the human as one 

component within the syst~n also is specified, to the extent feasible, at 

this point. Once the role of the human has been spelled out in general 

terms, a task analysis is conducted. This task analysis feeds back into 

system design in that hardware changes may be necessary at this point to 

begin to fit the job requirements to the human ergonomically. This .same 

task analysis also becomes the basis for development of selection 

criteria and the establishment of a training pt·ogram. 

The human as a system component has specific capabilities and 

weaknesses. Humans are incredibly flexible and constitute possibly the 

best general purpose device ever built. Humans can do. almost anything 

reasonably well. However, the error rate in human performance can be 

high. An individual asked to perform some critical task over and over 

and do it exactly right every time generally will be unable to do so. We 

have exceeded his capability in ter1ns of reliable performance. In human 

factors design terms, this means it i.s a mistake to design a system in 

Which 100 percent reliability is required of the human operator. 

To ensure proper system design, much specific infot·nlBtion concerning 

human capabilities must be obtained. Some of this comes from the field 

of psychology, where considerable work has been done in defining human 

information processing capabilities. How are data obtained, interpreted, manipulated, and acted on? The field of anatomy provides information 

concerning body size, t·each chac-acteristics, and other anthropometric 

qualities. The field of physiology, finally, provides data concerning 

physiological limitations for energetic and sustained activities. 

One characteristic of the human component which separates it from the 

machine is the manner in which it fails. When seriously overloaded, a 

machine component will tend to fail suddenly. It will simply break. On 

the other hand, humans exhibit What is called "graceful degradation" 

where they begin to disregard things considered less important and 

concentrate only on t.he central elements of. i.'he ta:>k. By so doing, a 

human can maintain a significant measure of system performance beyond the 

point. where a totally machine system wi.ll fail. How ... v~r, oveC'all 

perfot-mance reliability will be impaired dudng this pel'iod. 

A-65 

... 
j 

'I I 

i \ 

l 

I 

! 

~ 

' !. 

Reliability of human performance is a key element to be addressed 

during a human factors analysis. A machine, when working perfectly, 

generally will exhibit reliability many times better than that of a 

human. The object, however, is to match the human and the machine 

components together so that overall system reliability can be improved 

over that achievable independently with either component. 

Much of the study of human reliability in industrial settings has 

centered on the inspection process, whether simple unaided inspection or 

that in which various· devices are used to "aid" the process. Inspection 

can be part of product.ion, where it provides a quality control over the 

production p~rocess. It can also be part of maintenance, where it serves 

to guide attention to components in need of replacement or repair. In 

the aviation industry, inspection for maintenance is of greatest concern 

at this moment. 

In the inspection process, where we are trying to detect something, 

there are two things that can go wrong. A Type 1 error occurs when a 

good item is identified incorrectly as faulty. This is the false alarm 

problem, or the false replacement of a part. A Type 2 error occurs when 

a faulty item is missed. A Type 1 error is costly because it results in 

an unnecessary economic burden. A Type 2 error generally is of greater 

concern since it can lead to more serious trouble later as a result of 

the faulty pa~rt.. 

In aviation, the problem is one of trying to detect a fault. at. an 

early stage rather than simply trying t.o detect one. However, the 

earlier we try to detect a fault, the more the fault looks like a 

fault-free item. In other words, the signal/noise ratio is very low, 

making detection much more difficult. Under these circumstances, we can 

define the percentage of Type 1 errors (E1) and Type 2 errors (E2). 

Performance then can be specified in terms of E1 and E2 plus "T," which 

is the time to do the job. An assessment of job performance then becomes 

a matter of examining the relationship between these three quantities. 

Table 1 presents a model used in the study of industrial inspection. 

It is called a first-fault inspection model. While not entirely relevant 

to aviation inspections, it does illustrate the logic of the inspection 

process. 

• 

TABLE 1 

PRINCIPAL STEPS IN FIRST-FAULT INSEPCTIOH MODEL 

DEVELOPED FOR IVDUSTRIAL INSPECTIOH 

1. Present pre-selected items for inspection 

2. Search each item to locate possible faults ("flaws") 

3. Decide whether each flaw is sufficiently bad to be classified as 

a fault 

4. Take the appropriate action of acceptance or rejection 

A-66 
In the fault inspection process, an item is presented to an inspector 

who fixates some small area, either with direct vision or with some tool, 

and decides whether a flaw is present. Then, as shown in step 3, the 

inspector decides whether the flaw is sufficiently bad to be classified 

as a fault. Finally, he recommends the appropri.ate action of ac•ceptance 

or rejection. Figure 1 Hhows the logic of inspect i.on in flow d«u·l focm. 

l"'a 

I 

Item to lnopeotor" 

l"'ocate •mall area 

w ~ I 

•• flaw rejeotable'P 

Ve• 

I 

... ,... .. 

I •• trm• ...... ..,. .. 

No 

Vee 

Aooopt 

Item 

Figure 1. Flow chart depicting the process of inspection. 

l'tte fault inspection model of ~·igur·e 1 e'ln lead to inler:est 

conclusions concerning the inspection process. First, to commit a Type 1 

error, the rejection of a good item, one must make two errors. The 

inspector first must find a flaw that is not actually severe enough for 

rejection and then must make an incorrect fault classification decision. 

To make a Type 2 error, acceptance of a faulty item, the inspector 

can make either one of two errors in parallel. The inspector can either 

fail to find the flaw or he can find it and make the wrong classification 

decision. Thus, everyting else being equal, one would expect many more 

Type 2 errors (defects being accepted) than Type 1 errors (good items 

being rejected). So immediately we do not expect Eland E2 probabilities 

to be equal. 

Of the four tasks presented in Table 1, the first and last are 

relatively reliable operations. If the system is designed well, these 

two should not represent a problem. The other two, the search and the 

· decision-making phases of inspection, are points where there is a high 

chance for human error. Therefore, attention will be centered on these 

phases. 

The search phase of visual inspection can be influenced by several 

factors. For example, Figure 2 shows the reduction in visual performance 

during a test in which a known flaw was presented at different 

eccentricities, or angle from the line of central vision. Results show a 

steady decrease in search effectiveness as the flaw is moved away from 

direct vision. At 20 degrees off axis, subjects could identify a defect 

A-67 
with a 10-minute visual angle size. At 40 degrees off-axis, the 

detectable size increased to 20 minutes. While this is for one type of 

target, comparable results can be found for other sizes and for different 

conditions of illumination. The important point is to recognize that any 

detection task which requires peripheral vision will be less efficient 

than one t•elying completely on centL"al vision. 

100~------------------------------------------, 

eo 

eo 

40 

20 

0~~~-+~--~+-~~-.~--~+-~~-+~--~ 

o :ao 40 eo 

Eao•ntrlolt)' (In d•e,...•) 

Anet• off Vl•ual Axl• 

figure 2. Decrease in visual acuity as target is moved from line of 

direct vision. 

In studying visual detection, a human factors engineer'is concerned 

with visual lobe, that is, the area around the line of sight within Which 

a fault can be detected. Factors affecting lobe size include the size of 

the target, or fault; the amount of light placed on the target, and in 

turn the eye; and the contrast between the target and its background. 

All of these variables may be manipulated in an effort to increase the 

visual lobe size and hence either reduce the time required to do the job 

or reduce the errors made during job performance. 

Another factor with a dramatic effect on visual search performance is 

search time, as shown in Figure 3. These results show that, when a 

difficult-to-detect target is used, a search time of two seconds will 

result in only 20 percent of the faults being identified. If the search 

time is increased to six seconds, 80 percent of the faults can be found. 

This is a direct speed/accuracy tradeoff curve. When longer search time 

is allowed, more faults will be identified. Note also in Figure 3 that 

making the fault easier to detect (larger visual lobe size) gives 100 

percent detection at two seconds per item. 

A-68 
• 100 

I 

g eo 

:J 

fll 

.r: eo 

e 

I 40 

fll 

.. 

c 20 • e 

-•l•r tmperfeotlon 0 

more dlffloylt lmperfeotlon A 

l 0 

0 2 e e 

Searoh 'T1me (•eo) 

Figure 3. Cumulative probability of detecting two different in;rerfections. 

An examination of the decision-making task also reveals some 

interesting features. Here there are two aspects of performance, as 

noted earlier. Figure 4 plots these two aspects, i.e., the percentage of 

faulty items being rejected (100-E2); the percentage of good items being 

accepted (100-El). In Figure 4, perfect performance is represented in 

the top left hand corner. At this point, 100 percent of good items are 

accepted and 100 percent of faulty items are rejected, the ultimate goal 

of the inspection process. Figure 4 shows the results taken from seven 

inspectors in an industrial operation. The data point at the bottom 

shows an inspector who is accepting over 90 percent of the good items but 

is finding only 25 percent of the faults. On the other hand, the 

inspector at the top is finding 80 percent of the defects but, 

unfortunately, is rejecting almost 50 percent of the good i l•·ms. 

100 

1 

oi eo 

'i' 

•.: D eo 

.s• 

c E •• 40 e!! 

llJ 

"3 20 

:. 

0 

0 

Peroentoe• of Oood Item• Aooept•d 

Figure 4. Performance of seven inspectors in an industrial operation. 

The results in ~·iguc~ 4 t.cll q•_; ,::;J;nethin.g ahoul t.he £.1e,:i.·;i.on ,:l:i_l_,-q·i.a 

used by inspectors. The individual at the bottom is using a criterion 

which says "Unless something is really bad, I'm not going to report it." 

The person at the top, on the other hand, is using a criterion which says 
"I am going to report the slightest flaw I can see." Neither criterion 

is acceptable. Improved training for on-line inspectors is required. 

Improved training is only one requirement dictated by Figure 4. The 

real need is to move all points on the curve toward the upper left 

corner. Use of signal-detection theory is of value in deciding how to 

proceed. Basically, this tells us that the signal-to-noise ratio must be 

increased. What makes the curve so bad is that there is considerable 

noise mixed with the signals. Achieving an increase in signal to noise 

can be a difficult matter, but there are many ways one can make 

improvements in that direction. 

Signal detection theory tells us that detection criteria can be expressed mathematically, to show that two factors influence the inspector's choice of criterion. One is related to the prior probability of a 

signal being a real signal. The more a person expects to see a signal, 

the more likely he is to call any aberration a signal. so, as the probability of a signal increases, inspectors modify their criteria. Secondly, the inspector's perceived costs of error and rewards for good performance affect the criteria. As the costs and payoffs balance towards 

either acceptance or rejection, inspectors modify their criteria 

appropriately. 

A major concern in maintenance inspection is the time pressure. 

Figure 5 illustrates the effect on inspection performance of increasing 

inspection time. Here, inspection time was increased by a factor of one, 

two, and three times the normal. With this increase, the probability of 

rejecting a faulty item increases. More and more faults are found. Not 

all are found because the line does not level at 100 percent. Its final 

level depends on the decision performance. At this point all search is 

complete and the inspector is now into decision, so that the curve is 

decision limited. On the left side of the curve, the search has not been 

completed, so it is search limited. 

f 

100 

eo 

eo 

20 

·---· -- • 

Aaoept Oood Item• ··--- __. -· 

___....--=.----: .. 

• A•J•ot F"aulty Item• 

0~----~----~------.-----~-----.------~--~ 1X 2X 

Ttm•, Nor-mal Tlm•• 

Figure 5. Effect on inspection performance of increasing inspection time. 

A- 70 
The upper curve of Figure 5, the probability of accepting a good 

item, shows a marginal decrease in performance with increased time. This 

simply means that as individuals are given more time to search, they are 

more likely to be successful in finding something, whether a real fault 

or not a real fault. More false alarms are produced with excessive 

search time. 

The above data illustrate some features of inspection theot•y. Search 

theory and signal detection theory together offer guidance concerning 

ways to improve the inspection process. A number have been mentioned. 

Target/background contrast can be increased. Search time can be adjusted 

optimally. Operators can be trained to use appropriate search criteria. 

Defect size, unfortunately, is a variable not subject to manipulation, 

although the size of an acceptable defect can be varied. 

Another feature which CQn be varied is the feedback given an 

inspector concerning his success. Figure 6 shows performance on a task 

where, as marked, a change in feedback to inspectors was made. They were 

simply pt·ovided more rapid feedback as to how well they were doing. This 

made a significant change in their discrimination of flaws and effectively halved the number of errors. For a given false alarm rate, it halved 

the number of misses. For a given miss rate, it halved the false alarm 

rate. Their performance was essentially doubled by providing more rapid 

feedback. The feedback was not in fact better, it simply was provided 

more rapidly. This makes sense when one realizes that without rapid 

feedback, the inspection loop is open for longer periods of time and 

increased errors can occur without the inspector being aware of them . 

.. 

·'= c: 

~ 

> 

= :s 

.. 

. 5 

·f 

.~ 

0 

~ .. 

e 

i 

~ 

... 

0 

I 

E 

4 

3 

~~ i ~\ 

2 

1 

Change 

0 • 

0 10 20 30 40 

Time (Weeks) 

Figure 6. Effect of providing more rapid feedback on inspector 

performance. 

In summary, human factor·s has grown into a sci.entifi.c discipline in 

Which the role of the human operator in an industrial system can be 

examined in terms of well-developed models and mathematical relationships. Improvements in aircraft maintenance and inspection can be 

achieved with proper application of tested human factors procedures for 

performance enhancement. 

A-71 
Vigilance and Inspection Performance 

Earl L. Wiener, Ph.D. 

Professor, Department of Management Science 

and Industrial Engineering 

University of Miami 

Vigilant behavior initially was studied as a problem in its own 

right. In time, however, a bridge was made between the world of vigilant 

behavior and that of inspection performance. Certainly, what we have 

learned through the years about human vigilance will be of value as we 

consider problems in the inspection of systems and materials. 

Vigilance research shows the human to be a poor monitor. Yet this 

same research illustrates opportunities for management intervention to 

improve vigilance. Human factors engineers can contribute to this 

improvement through their understanding of vigilance and its relation to 

inspection. 

The routes of formal vigilance research can be traced to wartime 

experiences during World War II. At that time, the British Coastal 

Command was flying long anti-submarine patrols over the Bay of Biscay, 

searching by radar for surfaced German submarines. These missions were 

long, lasting for over 10 hours. During these missions, a navigator or a 

pilot on occasion would walk past the radar operator's position, look at 

the radarscope, and reach over the operator's shoulder to say, "Hey, 

there's one right there." The person least qualified to detect radar 

targets, who happened to be just passing by, spotted radar signals that 

had not been seen by the radar operator. 

Problems of radar detection became so severe that a laboratory 

investigation was begun at the Medical Research Council under Dr. Norman 

Mackworth. These studies demonstrated that the longer operators were on 

patrol, the less likely it was that they could detect a submarine. This 

was one of the first findings of vigilance research. 

Vigilance refers to the likelihood that a human will respond to a 

signal, so vigilance can be defined operationally in terms of 

probability. Vigilance differs from an inspection task in that it is 

event driven; the signal occurs in real time in the real world. You 

either see the submarine now or it is gone. With inspection, you 

frequently have an opportunity to go over the inspection a second time. 

Another characteristic of a vigilance task is that the signal is 

subtle; it is hard to detect. Another way of saying this is that the 

signal-to-noise ratio is low. Also, there generally is a low signal 

rate. Targets do not appear freqUently. Finally, there is temporal 

uncertainty. This, of course, makes the task unpredictable. We do not 

know if a signal will appear in so many seconds or in so many minutes. 

There is a short test Which can be used to demonstrate some of the 

issues in vigilance. Done properly, the following sentence is projected 

on a screen for 15 seconds: 

FINISHED FILES ARE THE RESULT OF 

YEARS OF SCIENTIFIC STUDY COMBINED 

WITH THE EXPERIENCE OF MANY YEARS 

A-72 
subjects are asked, during their 15 seconds of viewing, to count the 

number of times the letter "F" appears. In any group, most people will 

guess three. Others will guess four or five. Very few will answer with 

the correct number, which is six. 

The above test shows that the human is not a good inspector. The 

problem here is a basic one in cognitive psychology. Apparently, since 

humans pronounce "OF" as "OV," the "F" in "OF" is frequently missed. The 

human serves as an information processor and, in this case, tends to 

distort the information. In any event, the monitoring and inspection 

process certainly is subject to error. 

Vigilance performance inevitably shows a decrement through time. In 

one study involving a 48-minute vigil, probability of detection dropped 

from just below 80 percent in the initial stages to approximately 60 

percent at the conclusion. This illustrates the rather dramatic decrease 

in performance effectiveness that can occur for a pure vigilance task. 

The same study measured performance of subjects on two consecutive 

days. No significant difference was found. There was no evidence of a 

practice effect on the vigilance task. This is not to say that subjects 

cannot be trained for vigilance, but practice alone is not sufficient. 

In other studies, subjects have been run for many days and, as here, no 

practice effect has been found. 

Another feature of vigilant performance concerns the signal/rate 

effect. In another study, again conducted for 48 minutes, subjects saw 

either 16, 32, or 48 signals occur during that period. There was a 

dramatic increase in the rate of detection of these events as a function 

of whether 16, 32, or 48 signal events were produced during the test 

period. The more frequently a signal occurs, the higher the probability 

of detection for any given signal. If you have low probability of the 

appearance of a signal event, then you will have low probability of 

detecting that event When it does occur. This clearly has implications 

for aircraft inspection. Rare faults·will be most difficult to detect. 

All of the above factors can operate to produce vigilance decrement. 

The dynamics of vigilance, and vigilance decrement, can be illustrated by 

an experiment in which adaptive training was used. As a subject's 

performance improved, the task was made more difficult in proportion. As 

performance then decreased, the task was made easier. The objective was 

to produce a constant level of performance. In this study, by continuing 

to adjust task difficulty, an essentially constant target detection rate 

of 75 percent was achieved. In terms of aircraft maintenance, this means 

that if you want a constant detection rate in an inspection task, over a 

period of time the flaws would have to become larger and larger to be 

detected at a constant rate. 

Figure 1 shows some of the forces impinging on the human inspector 

which might be viewed as opportunities for management intervention in any 

program to increase detection probabilities. At the top we see a block 

containing specifications, photographs, standards, training, and past 

experience of the operator. These are the variables which directly 

affect the judgment of the inspector. When an inspector looks at a rivet 

on an airplane or a pattern appearing on an eddy current scope, he is 

comparing what he sees to a stored experience. Experience and training 

can be manipulated to improve performance. 

A-73 
POSSIBLE 

INCOMING 

INSPECTION 

OF RAW 

MATERIALS 

AND VENDOR 

SUPPLIED 

PRODUCTS 

SPECS, PHOTOS 

STANDARDS 

EXAMPLES 

TRAINING 

EXPERIENCE 

PAYOFF 

MATRIXCOSTS AND 

VALUES 

~ 

~ 

Figure 1. Production, inspection and disposition of items with K acceptance cate· 

gories (classifications) and one rejection category. Upon rejection, 

numerous courses of action are available. (From Weiner, 1984). 

ln studying inspection performance, the consequences, or payoffs, of 

inspection decisions should be considered. Figure 2 shows the case in 

which inspection decisions can be classified in a 2x2 matrix. While some 

industrial processes call for a 2xn matrix, the 2x2 appears most 

appropriate for aviation inspection. In Figure 2, there are only two 

classes in which each event can be categorized. There also are only two 

response opportunities on the part of an inspector. He can either accept 

or reject an item. If he accepts an effective item, he has made a cor-

•. -.,cL decision. I.ikewise, if he rejects a defective item, he is correct. 

§ 

.... 

Ill 

.... 

~ Accept 

~ Rojoot 

State of Prodyct 

Effect lye 

Correct 

Type 1 Error 

Commissive Error 

Pefectfye 

Type 2 Error 

Omfssive Error 

Correct 

Figure 2. Categorization of inspector decisions. 

·'ow let. us examine the incot'cect decisions, as shown in Figure 2. 

thee> .. > are the Type l and Type 2 errors mentioned in Dr. Drury's paper. 

If the product is effective and the decision is made to reject, the 

inspector has made a Type 1 error - a commissive error. This has a value 

or cost, here referred to as VRE - the value of rejecting an effec- tive 

product. In aviation, these are the unnecessary removals of aircraft 

parts or unnecessary redrilling of rivets. 

A-74 
If the item is defective, and the inspector fails to detect it, he 

has n~de a Type 2 error - an emissive error. This also has an attached 

cost or value. In aviation, these are the errors of considerable 

consequence. This is where a defective part goes undetected and remains 

in the aircraft. The ultimate consequences can be quite costly. 

In one instance, a company producing a medical product .considered the 

cost of Type 2 errors (missing a defective product) to be so high that 

the inspection process was adjusted to make such an error almost 

impossible. However, the adjustment greatly increased Type 1 errors. 

They now are rejecting 50 percent of all products. One-half of 

everything manufactured is thrown away prior to use. For them, this cost 

tradeoff appears appropriate. 

In another study of inspector performance, more rational results were 

obtained. In this study, 39 inspectors each examined 1,000 solder 

connections into which 20 defects had been inserted. There were thus a 

total of 39,000 inspections conducted. Table 1 shows that of the 780 

defective parts, 646 were correctly rejected. On this basis, the success 

rate was 83 percent. For the 38,220 effective components, 25 were 

falsely rejected. He we see the probability of false rejection to be 

less than one in one-thousand. This is excellent inspection performance. 

Inspector's 

Action 

Accept 

Reject 

Total 

TABLE 1 

RESULTS OF AN INSPECTION OF 39,000 PARTS SHOWING 

TYPE 1 AND TYPE 2 ERRORS 

Defective Effective Total 

134 38,195 38,329 

(Type 2) 

646 25 671 

(Type 1) 

780 38,220 39,000 

Data from Jacobson (1952) 

In summary, what is known about human vigilance? Han is a poor 

monitor. Where vigilance is required over time, a vigilance decrement is 

almost inevitable. Han starts off as an imperfect monitor and the 

situation only gets worse. 

There is a signal rate effect on vigilance. If the rate of 

appearance of a signal is low, the probability of detecting it is 

lowered. In aviation this means that the higher the quality of the 

product, the lower the signal event rate, and therefore the lower the 

probability of detection of a fault. 

A-75 
Selection of individuals to perform monitoring tasks does not work 

well. Selection by categories particularly is ineffective. Men versus 

women or old versus young are not good variables in determining who makes 

a good inspector. 

Training, if well structured, can make a difference in vigilance 

performance. Practice alone, however, is not effective. The practice 

must take place within a well defined training effort. 

Finally, let me review briefly the available intervention strategies 

and indicate for each What I consider the probability of producing 

improvement with that strategy. These are: 

Job Redesign - High. Here we can consider such matters as 

conspicuity of the signal; increasing the signal-to-noise ratio, if 

possible; length of inspection periods; social atmosphere and the 

general work environment; and feed-forwardand feed-back mechanisms 

which are providing information to the inspector both before and 

after performance. 

Training = High. Any improvements which can be introduced for the 

workforce or for the promise of performance benefits. 

Selection = Poor. There is little probability of significant payoff 

here. 

In all of the above, there is of course no magic solution. No single 

step will result in a dramatic improvement in vigilance or maintenance 

perfot~nce. However, appropriate application of known human factors 

principles, with continuing review of the problems encountered, should 

result in a steady and definable improvement. 

References 

Jacobson, H.J. A study of inspector accuracy. Industrial Quality 

Control, 1952, 9, 16-25. 

Weiner, E.L. Vigilance and inspection. In J.S. Warm (Ed.), Sustained 

attention in human performance. Vew York: 

John Wiley & Sons Ltd., 1984. 

A-76 

a 

c 

a 

~ 

~ 

~ 

Ol 

il 

il 

01 

tl 

I 

' ' I 

.. 

! 

! 
Human Performance Issues in 

Nondestructive Testing 

Douglas H. Harris, Ph.D. 

Chairman 

Anacapa Sciences, Inc. 

Human performance plays a vital role in all inspections and tests. 

In some tasks, such as visual inspections, the importance of human 

performance is obvious. But even when technically sophisticated 

equipment is employed, the outcome is highly dependent on human control 

actions, observations, analyses, and interpretations. The primary 

consequences of inadequate performance are missed defects and false 

reports; and the costs that accompany these errors. 

Human-Performance Framework ~ A variety of techniques are available for the inspection of aircraft 

engine and airframe structures. Visual, eddy-current, ultrasonic, , 

radiographic, magnetic particle, and penetrate testing methods are used [ 

(Hagemaier, 1988). However, the types of human actions and the sequence; 

in which these actions are performed are comparable among t.h<'se various 

techniques. The typical sequence of acl i.ons i.s ;;hown in ,. tgw·• 

COLLECT '· 

INmATE & ANALVZE 

THE TASK ~ 

DATA 

·'"'' . .; N-•W><«•NO'>. "·•·••••·•"'"·· 

SELECT ' COMPARE 

APPROPRIATE RESULTS TO 

STANDARDS CRITERIA 

,_,,, .•• _ . ..;:;.,-.,.;•.->;« ..:•..:.;.;<,,-;,.,~.-. '· 

.. .. PREPARE ASSESS 

EQUIPMENT & REPORT (AND VERIFY) FINDINGS PROCEDURES ' I' ' FINDINGS ' ,, ---~-.;.;··~->-·=<->-<•'-· »-»-~·:-; . .;.;.. xi <·>»»~·>:·o>·-,.,-,;,c_ ••..• • -h. 

Figure 1. Types of actions and typical action sequence for inspections and tests. 

the model illustrated in hgure 2 shows the relationships th<l.L exist 

among the various factors that can influence human performance in 

conducting any task or action required for the successful completion of 

an inspection or test. As shown, any action will always require the 

input of information through one or more sensory channel (visual, 

auditory, tactile, etc.) and the execution of some motor activity (hand 

movement, speech, etc.) to produce a required outcome. Poor performance 

often occurs with tasks that do not provide an adequate match between 

information input and action output. For example, information that is 

incomplete, not timely, ambiguous, or irrelevant will lead to incot-rect 

or delayed actions. Information presented in a form not compatible with 

the mode of the action can also lead to inadequate performance. 

A-77 
,-----------------------------, 

I 

.... ----FEEDBACK 

• ~~ :::::.·· .. ·.~; .. ~ .••. ,·.... • ACTION 

:::~::::~ .. ;.:.;:·.;:::·.; ... ;.;.:,:: .. ,:::=::~:{': ::::::·., .. :;,: :-:.=.:.~: c 

INFORMATION 

PERFORMANCE-SHAPING FACTORS 

Figure 2. Model of human performance. 

To attain and maintain satisfactory levels of performance, feedback 

is needed on the outcomes of actions taken. Feedback must be complete, 

relevant, and timely to be effective. However, feedback requirements are 

highly dependent on the nature of the task or action. For example, 

feedback of the result of pressing a button during the calibration of an 

ultrasonic tester must be nearly instantaneous and must be provided each 

time the button is pressed. On the other hand, feedback on the accuracy 

of flaw characterization might be effective even if delayed in time and 

not provided after each characterization. 

The information-action-feedback loop is dictated by the 4esign of the 

equipment and procedures employed in the inspection or test. 

Consequently, improvement of human performance by addressing inadequacies 

in this loop must necessarily lead to design changes in equipment and 

procedures. 

The final category illustrated in Figure 2, performance-shaping 

factors, are those influences that are outside the information-actionfeedback loop of the task. They include the following: 

o Environmental conditions 

o Communications 

o Time effects (vigilance, fatigue, stress) 

o Organizational structure and support 

o Knowledge and skills 

o Personal work habits and attitudes 

The actions shown in Figure 1 can be combined in a matrix with the 

human-performance factors shown in Figure 2 to provide a framework for 

addressing human performance issues in inspection and testing. The 

resulting framework, provided in Figure 3, suggests that each of four 

types of performance factors can be examined for each of the seven 

inspection or test actions. 

A-78 
l 

I 

,.,~ 

INSPECTION AND TEST ACTIONS :,:,:: 

:;:;:: 

=~:· 

~ ~~\\~ :,;-

ffi ~~~~ 

~\ 

~ :::::: 

@ 

{:: 

fa 

~ il 

.;:: M 

;::;:: 

fi 

PERFORMANCE FACTORS 

m 

,:,-.,: 

~~ ·l:':; 

INFORMATION INPUT 

ACTION OUTPUT I 

FEEDBACK 

PERFORMANCE-SHAPING 

Figure 3. Framework of human-performance issues in inspection and testing. 

Human Performance Issues in EddY-CUrrent and Ultrasonic Testing 

Human performance issues in eddy-current and ultrasonic testing were 

studies recently with the framework described above (Harris, 1988). The 

context of the study was eddy-current and ultrasonic examination of the 

structural integrity of nuclear power plant components. The inspection 

technologies examined were similar to those employed in inspections of 

aircraft structures. Information was obtained from the following types 

of sources: 

o Industry procedural reference documents 

o Training materials - coursebooks, guides, worksheets 

o Research reports and related documents 

o Interviews with subject-matter experts and job incumbents 

o First-hand observations of task performance. 

The studJ identified numerous human-performance issues in 

eddy-current and ultrasonic testing, and produced the following nine 

recommendations for improving human performance on these types of tests. 

Develop Guidelines for Operator-Control Interface Design 

In the design of new eddy-current and ultrasonic inspection systems, 

the application of human-factors principles and techniques has not kept 

pace with the introduction of new technology. New, computer-based 

inspection and testing systems are cumbersome to set up and operate, 

require excessive manipulation to get the job done, require control 

actions not logically organized, and rely excessively on human short-term 

memory. Because a large body of human-factors information now exists to 

guide the design of human-computer systems, a handbook of selected 

information should be developed to guide designers of inspection 

A-79 
systems. The handbook would contain human-factors principles, data, and 

techniques specifically applicable to the design of the operator-system 

control interface for computer-based inspection and testing systems. 

Application of the handbook could help produce more effective future 

systems, reducing the time and expense required for performance of 

inspection tasks. 

Analyze Eddy-CUrrent Performance Data 

Little information has been generated, to date, on eddy-current 

testing performance from systematic studies capable of producing 

scientifically valid, statistically significant results. Consequently, 

research is needed to answer some very fundamental questions such as the 

following: For each of the various damage mechanisms encountered, what 

are the expected rates of alternative inspection outcomes - correct 

calls, false calls, and missed detections? How is each inspection 

outcome for each damage mechanism influenced by structure type, geometry, 

location, and extraneous variables? What is the relative reliability of 

different cues used for detection and characterization of different types 

of flaws? Answers to the questions posed can point to the specific 

aspects of eddy-current testing where improvements in system design, 

inspection strategies and procedures, analyst training and qualification, 

and inspection organization are likely to have the greatest payoff. 

Assess Eddy-Current Information-Integration and SignalInterpretation Strategies 

Eddy-current testing requires the analyst to integrate a substantial 

amount of information to provide the context for signal pattern 

recognition and interpretation. What is the most effective way to 

organize and integrate relevant information in support of signal 

interpretation? What data integration and signal interpretation 

procedures are most amenable to computer aiding? Alternative 

data-integration and pattern-recognition strategies and methods should be 

developed and experimentally evaluated. Alternatives would incorporate 

applicable human-factors principles (from previous related research) as 

well as techniques found to be employed by successful inspectors. The 

research results would identify and define any significant differences 

among altet~ative strategies and methods of information integration and 

signal interpretation, generate the basis for guidelines for more 

effective eddy-current inspection strategies and methods, and provide 

criteria for the design of future eddy-current testing systems. 

Develop More Effective Eddy-current Display Designs 

The principal displays employed for eddy-current flaw detection and 

characterization are variations of meter, oscilloscope, and strip-chart 

type displays. These displays originated with, and have been little 

changed since, the initial use of analog systems. The geometric forms 

(signals) presented on these displays typically do not relate directly to 

the physical characteristics of what is being inspected, but rather to 

the characteristics of an induced electric current. Therefore, the 

information contained in the displayed signals must be mentally 

transformed by the analyst for purposes of flaw detection and 

characterization. Such mental transformations are likely sources of 

A-80 
inspection errors because they add complexity and ambiguity to the task. 

They also consume valuable inspection time and effort. The availability 

of digital signal processing and display technology now provides the 

opportunity to explore display formats other than those previously 

dictated by analog technology. Displays that are more representative and 

directly-interpretable could increase the accuracy of inspections and 

reduce inspection costs. Costs could be reduced by minimizing inspection 

time and, with increased accuracy, by reducing the need for redundant 

inspections and the time required for the resolution of conflicting 

results. 

Research Automatic Eddy-Current Signal Screening and Analysis 

Recently, systems have been developed and employed for the automatic 

screening of eddy-current data by means of computers equipped with 

detection-rule based programs. The systems are designed to screen the 

data for signals of potential flaws which are, then, analyzed by an 

experienced analyst. Research and development work is also being 

conducted on computer-based systems designed to both detect and 

characterize flaws. Automatic screening and analysis raise some 

sensitive human-factors issues: What guidelines and techniques are 

required to assure that the screening criteria selected wi.ll produce the 

desired results? What is the most effective form of interaction among 

analyst and system? What steps will be required to gain acceptance for 

the system, among those who have the ultimate decision-making authority 

for structural integrity? A human-factors study effort should address 

the above questions in parallel and in close coordination with system 

research and development efforts. The effort would be mainly analytical, 

reviewing and applying appropriate data and principles to answer the 

issues raised. The answers obtained would help assure the success of 

increased levels of automation in eddy-current inspection systems. 

Collect and Analyze Ultrasonic Performance Data 

Round-robin studies of ultrasonic inspections, in which each of a 

sample of inspectors inspects each of a sample of welds, have shown that 

inspection accuracy is typically much lower than expected. However, 

these studies have produced little insight into why inspection accuracy 

is no better than it is, or specifically what might be done to redesign 

the task or instrumentation to produce better results. Specifically, 

answers are required to the following questions: What task and 

procedural variables correlate, positively and negatively, with 

inspection accuracy? What signal-interpretation strategies are most 

successful? What logical steps are correlated ·with the different 

inspection outcomes - correct call, false report, missed flaw - for 

different flaw types? Perfot~nce data should be collected and analyzed 

to answer these types of questions. Results .could identify improvements 

required in inspection procedures, instrumentation, and training. 

Reduce the Complexity of Manual Ultrasonic Detection of IGSCC 

A substantial amount of evidence suggests that ultrasonic detection 

of intergranualr stress-corrosion cracking (IGSCC) by manual methods, as 

the task is presently designed and under the conditions in Which the task 

is typically performed, is too complex to produce reliable results. 

IGSCC is the type of cracking that results from the continuing effects of 

A-81 

.. / 
structural stress combined with the corrosive effects of environmental 

elements, and is often referred to simply as "metal fatigue." The 

research question is how to increase the accuracy and reliebility of 

ultrasonic inspection by reducing the burden and complexity of the task. 

Preliminary analyses and observations suggest that, although a major 

breakthrough is not likely, the cumulative effect of many small changes 

in task design could have a significant effect on performance. 

Specifications for task redesign - instrumentation and procedures -

should be developed through detailed task analysis and application of 

human-factors design principles. The recent availability of 

microprocessor technology for ultrasonic inspection, in particular, 

provides new opportunities for increasing the compatibility between 

inspector capabilities and task design. 

Define Optimal Strategies for Ultrasonic Testing 

There appears to be no single, agreed-upon, best strategy (or 

strategies) currently employed for the ultrasonic detection and 

discrimination of flaws. A relatively large number of possible overall 

strategies exist because many options are available to select from -

inspection parameters, inspection techniques, scanning patterns, 

discrimination logic, and others. For any type of application, a model 

strategy should be constructed from the collective experience and 

judgment of a sample of senior, experienced inspectors. The model would 

specify the analytical sequences used, the emphasis to be given to 

different variables, the techniques and cues to be employed, and the 

reasons for each. Inspector trainees could then be provided an optimal 

strategy, based on the collective insights and experience of senior 

inspectors, as part of their instruction in the ultrasonic inspection. 

As a consequence, they could more quickly attain the confidence and 

proficiency required for this difficult task. 

Assess Human-Factors Issues in Enhanced Automated Scanning and Data 

Recording for Ultrasonic Testing 

The development and employment of automated scanning and data 

recording techniques have overcome important performance problems in some 

applications of ultrasonic inspection. However, management residtance to 

automated scanning and recording exists because these methods are often 

perceived to require more time and money than manual methods. As a 

consequence, future research and development efforts will undoubtedly be 

directed toward increasing the efficiency of scanning and reducing the 

costs of inspections, raising new issues related to the human-system 

interface. Research on these issues should be conducted in parallel 

with, and in close liaison with, research conducted in support of the 

development of advanced ultrasonic inspection systems. Addressing 

human-factors issues during the development process will assure that 

advanced ultrasonic inspection systems produce accurate, reliable, and 

efficient inspector performance. As has been demonstrated in many 

successful system development efforts, these issues are best addressed as 

an integral part of the design effort. 

A-82 
Develop Methods of Sustaining the Effectiveness of Ult~asonic Testing 

Pe~fo_rmance 

One of the most powe~ful facto~s to influence pe~fomatH!P. on any task 

is feedback - infomation p~ovided to the pe~fome~ of a task about the 

effectiveness of task pe~fo~mance. Ult~asonic inspection p~esents a 

pa~ticula~ly difficult feedback p~oblem because infot~tion needed fo~ 

feedback is typically not available. For example, if a c~ack is missed, 

the en·o~ might not be discove~ed until a late~ inspection o~ a 

structu~al failu~e occu~s. At that time, even if the infoC"lllation finds 

its way back, the inspecto~ who missed the defect may be long gone. 

Mo~eove~, some inspection outcomes ~eceive mo~e attention than othe~s and 

thus add potential bias to the p~ocess. Fo~ example, any repo~ted defect 

(whethe~ co~~ect o~ not) will get mo~e attention than any un~epo~ted 

defect (whethe~ co~~ect o~ not). In spite of the inhe~ent difficulties 

in p~oviding feedback on this task, a~e the~e cost-effective innovations 

that can be introduced to take bette~ advantage of this powe~ful means of 

sustaining accu~ate inspection pe~fo~mance? If feedback cannot be 

enhanced in a p~actical manne~, a~e the~e othe~ app~oaches that can be 

substituted? One possibility is application of the concept of 

feed-forwa~d, analogous to p~ocedu~es employed in the calib~ation of 

equipment, fo~ fine-tuning an inspecto~'s detection and disc~imination 

skills p~io~ to a se~ies of inspections. Alte~native feedback and 

feedfo~wa~d techniques fo~ sustaining effective ult~asonic inspection 

pe~formance should be developed and evaluated. 

Conclusion 

Eddy-cu~~ent and ult~asonic inspections a~e two of the p~incipal 

techniques available fo~ the nondestructi.ve examination of ai~c~aft 

engine and ai~f~ame st~uctu~es. Although each of these techniques can be 

applied by means of technically sophisticated equipment, inspection 

~esults a~e highly dependent on human control actions, obse~vations, 

analyses, and inte~~etations. Consequeitly, substantial potential 

payoff in the cost-effectiveness of the application of these techniques 

to ai~c~aft inspections can be ~ealized th~ough imp~ovements in human 

pe~formance. Thi.s pape~ identified nine human pe~fomance issues in 

eddy-cu~~ent and ult~asonic inspection, and p~ovided a ~ecommended 

app~oach to add~essing each of them. 

Refe~ences 

Hagemaie~. Donald J. Cost benefits of nondestructive testing in ai~c~aft 

maintenance. Mate~ials Evaluation, Septembe~ 1988, 46, 1272-1284. 

Ha~~is, Douglas H. Human pe~formance in nondestructive inspections and 

functional tests (EPRI Repo~t NP-6052). Palo Alto, Califo~nia: 

Elect~ic Powe~ Resea~ch Institute, Octobe~ 1988. 

A-83 
APPENDIX B 

... 
l 

- Program -

Human Factors Issues 

in 

Aircraft Maintenance and Inspection 

12 - 13 October 1988 

Old Colony Inn 

Alexandria, Virginia 

FEDERAL AVIATION ADMINSTRATION 

Washington, D.C. 

B-3 

) 
WEDNESDAY. 12 OCTOBER 1918 

Ballroom A 

7:30 a.m. 

8:30 a.m. 

10:00 a.m. 

10:15 a.m. 

12:00 noon 

1:00 p.m. 

Registration 

- INTRODUCTION/ORIENTATION -

Meeting Welcome 

Anthony J. Broderick 

Federal Aviation Administration 

Meeting Background and Objectives 

William T. Shepherd, Ph.D. 

Federal Aviation Administration 

Aircraft Maintenance Parameters 

James F. Parker, JR., Ph.D. 

BioTechnology, Inc. 

FAA Regulatory Requirements for Aircraft 

Maintenance and Inspection 

Raymond E. Ramakis 

Federal Aviation Administration 

Break 

- THE PROBLEM -

Maintenance and Inspection Issues in 

Aircraft Accidents/Incidents 

Barry Trotter 

National Transportation Safety Board 

James w. Danaher 

National Transportation Safety Board 

Day-to-Day Problems in Air Carrier 

Maintenance and Inspection Operations 

Robert Lutzinger 

United Airlines 

Lunch 

Martin Room 

- MANUFACTURER PERSPECTIVE -

Maintenance and Inspection from the 

Manufacturer's Point of View 

Robert Oldani 

Boeing Commercial Airplanes 

Human Performance in Aircraft 

Maintenance: The Role of Aircraft Design 

Anthony Majoros, Ph.D. 

Douglas Aircraft Company 

B-4 
WEDNESDAY, 12 OCTOBER 1988 - Continued 

Ballroom A 

2:30 p.m. 

2:45 p.m. 

Break 

- INDUSTRY PERSPECTIVE -

Maintenance and Inspection Issues in Air 

Carrier Operations 

Robert Doll 

United Airlines 

Commuter Air Carrier Maintenance and 

Inspection 

Horman s. Grubb 

Henson Airlines 

Rotorcraft Maintenance and Inspection 

James Moran 

Aerospatiale Helicopter Corporation 

- MAIHTEHAHCE AHD INSPECTION TECHNOLOGY -

Nondestructive Inspection Equipment and 

Procedures 

George Ansley 

Boeing Commercial Airplanes 

5:00 p.m. Adjourn 

5:00 p.m. - 7:00 p.m. Reception - Martin Room 

THURSDAY, 13 OCTOBER 1988 

Ballroom A 

- MAIHTEHAHCE AHD INSPECTION TECHNOLOGY -

8:30 a.m. 

10:00 a.m. 

Improved Information for Maintenance 

Personnel 

Robert c. Johnson 

USAF Human Resources Laboratory 

- TRAINING ISSUES -

Strenghs and Problems in Maintenance 

Training Programs 

Richard Hlvenka 

Tarrant County Junior College 

Break 

B-5 

.... 
THURSDAY. 13 OCTOBER 1988 - Continued 

Ballroom A 

10:15 a.m. 

11:45 a.m. 

1: 15 p.m. 

2:00 p.m. 

2:15 p.m. 

4:30 p.m. 

- HUMAN FACTORS TECHNOLOGY -

The Human Operator as an Inspector: 

Aided and Unaided 

Colin G. Drury, Ph.D. 

SUNY, Buffalo 

Vigilance and Inspection Performance 

Earl L. Wiener, Ph.D. 

University of Miami 

Lunch (On OWn) 

Human Performance in Non-Destructive 

Inspection Processes 

Douglas H. Harris, Ph.D. 

Anacapa Sciences, Inc. 

Break 

- SUMMARY SESSION -

Development of Summary Statements and 

Recommendations 

Adjourn 

B-6 
APPENDIX C 

Human Factors Issues in 

Aircraft Maintenance and Inspection 

MEETING ATTENDEES 

Allen, Robert 

Manager, Continued Airworthiness Staff 

Federal Aviation Administration 

Washington, DC 20591 

Ansley, George 

NOT Specialist, Service Engineering Department 

Boeing Company 

Seattle, WA 98124 

Austin, Frank H., Jr., M.D. 

Human Factors Specialist 

Federal Aviation Administration 

Washington, DC 20591 

Baer, Judith 

Editor, Ops Update 

Helicopter Association International 

Alexandria, VA 22314 

Broderick, Anthony J. 

Associate Administrator for Regulation and Certification 

Federal Aviation Administration 

Washington, DC 20591 

Christensen, Diane G. 

General Manager 

BioTechnology, Inc. 

Falls Church, VA 22042 

Cook, Robert D. 

Assistant Manager, Accident Investigation 

Federal Aviation Administration 

Washington, DC 20591 

Danaher, James w. 

Chief, Human Performance Division 

National Transportation Safety Board 

Washington, DC 20594 

Doll, Robert 

Vice President of Technical Services 

United Airlines 

San Francisco, CA 94128 

Drury, Colin G., Ph.D. 

Professor of Industrial Engineering 

SUNY Buffalo 

Amherst, NY 14260 
Easton, Locke 

Aerospace Engineer 

Federal Aviation Administration 

Burlington, MA 01803 

Grubb, Norman S. 

Vice President, Maintenance and Engineering 

Henson Airlines 

Salisbury, MD 21801 

Harris, Douglas H., Ph.D. 

Chairman 

Anacapa Sciences, Inc. 

Santa Clara, UT 84765 

Hawkins, Joseph Technical Assistant to the Executive Director for Regulatory 

Standards and Compliance 

Fed.eral Aviation Administration 

Washington, DC 20591 

Hendricks, William R. 

Director, Accident Investigations 

Federal Aviation Administration 

Washington, DC 20591 

Hlavenka, Richard P. 

Chairman and Associate Professor 

Division of Aeronautical and Industrial Technology 

Tarrant County Junior College 

Fort worth, TX 76179 

Johnson, Robert c. 

Chief, Combat Logistics Branch 

Air Foree Human Resources Laboratory 

Wright-Patterson Air Force Base, OH 45433 

ICacerguis, Peter 

Special Assistant to the Associate Administrator for 

Regulation and Certification 

Federal Aviation Administration 

Washington, DC 20591 

Lotterer, Dave 

Director, Airworthiness 

Air Transport Association 

washington, DC 20006 

Lutzinger, Robert T. 

Manager, Aircraft Inspection Department 

united Airlines 

San Francisco, CA 94128 

Macintosh, Robert 

Air Safety Investigator 

IaU.onal Transportation Safety Board 

Washington, DC 20594 

C-2 
Kadayag, A. James. 

Ai~c~aft Ce~tification Specialist 

Fede~al Aviation Administ~ation 

Kansas City, KO 64106 

Kajo~os, Anthony E. 

Enginee~ Scientist 

Douglas Ai~c~aft Company 

Long Beach, CA 90846 

McConkey, Edwin D. 

Manage~. Helicopte~ P~og~ams 

Systems Cont~ol Technology, Inc. 

A~lington, VA 22209 

Kea~s, Allen 

Di~ecto~ of Special P~ojects 

Flight Safety Foundation 

A~lington, VA 22204 

Kelton, Ca~l 

Consultant to the Fede~al Aviation Administ~ation 

No~n, OK 73072 

Ko~an, James 

Ai~ Safety Investigato~ 

Ae~ospatiale Helicopte~ Co~po~ation 

G~and P~ai~ie, TX 75053 

Nightingale, Lau~a 

Reco~ding Sec~eta~y 

BioTechnology, Inc. 

Falls Chu~ch, VA 22042 

Oldani, Robe~t L. 

, ... ~ 

Manage~. Maintenance and G~ound Ope~ations 

Boeing Comme~cial Ai~lanes 

Seattle, WA 98124 

Palme~ton, William 

Aviation Safety Inspecto~ 

Fede~al Aviation Administ~ation 

Kansas City, MO 64106 

Pa~ke~, James F., Ph.D. 

P~esident 

BioTechnology, Inc. 

Falls Chu~ch, VA 22042 

Pick~el, Evan 

Consultant to the Fede~al Aviation Administ~ation 

Alexand~ia, VA 22309 

Ramakis, Raymond 

Manage~, Ai~c~aft Maintenance Division 

Fede~al Aviation Administ~ation 

Washington, DC 20591 

C-3 

-
Rohrbach, Peter 

Professional Aircraft Mechanics Association 

Potomac, MD 20850 

Shepherd, William T., Ph.D. 

Actin& Manager, Biomedical and Behavioral 

Federal Aviation Administration 

Washington, DC 20591 

Siegman, James 

Air Safety Inspector 

Federal Aviation Administratioq. 

Washington, DC 20591 '' · · 

Thackray, Richard, Ph.D. 

Research Psychologist 

Civil Aeromedical Institute 

Federal Aviation Administration 

Oklahoma City, OK 73125 

Trotter, Barry 

Air Safety Investigator 

Bational Transportation 

Washington, DC 20594 

Watson, Jean 

Safety Board 

•. 

Research Program Assistanl. \: 

• ' 

.•:" 

Federal Aviation Administration.· · · 

Washington, DC 20591 · ··.,, .;.·. ~· · •· ·' 11it 

·, -.~ .. ~ 

Sciences Division 

. "' .... : 

,. 

. :. • .'1)'o 

;;,·~··· ·.") 

.... '' :. • _,J' 

Wiener, EarlL., Ph.D. 

Professor, Department of 

Engineering 

university of Miami 

Coral Gables, FL 33124 

K8rtagement Science.and Industrial 

' .Jru.s. GOVERNMENT Mli.NllNG OFnC£:.,., • '761-01~ 

C-4