FAA-AM-82-1 

PERFORMANCE OF AIR TRAFFIC CONTROL SPECIALISTS (ATCS'S) 

ON A LABORATORY RADAR MONITORING TASK: AN EXPLORATORY STUDY 

OF COMPLACENCY AND A COMPARISON OF ATCS AND NON-ATCS PERFORMANCE 

Richard I. Thackray and R. Mark Touchstone 

Civil Aeromedical Institute 

Federal Aviation Administration 

Oklahoma City, OK 73125 

APRIL 1982 

Document is available to the public through the 

National Technical Information Service 

Sptingfield, Virginia 22161 

Prepared for 

U.S. DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

Office of Aviation Medicine 

Washington, D.C. 20591 
NOTICE 

This document is diss,eminated under the s,ponsorship of the 

Department of Transportation in the interest of information 

exchange. The United States Government assumes no liability 

for its content or use there.of •. 
Technical ~eport Documentation Page 

1. Report No . 2. Governmen t A cce ss ion No. 3. Recipient 's C~ta og No . 

FAA-AM-82-1 

4 . Title and Subti t le 5 . Report Date 

PEP~ORMANCE OF AIR TRAFFIC CONTROL SPECIALISTS (ATCS'S) APRIL 1982 

ON A LABORATORY RADAR MONITORING TASK: AN EXPLORATORY ~~~~~~~~------~ 6. Performing Organization Code 

STUDY OF COMPLACENCY AND A COMPARISON OF ATCS AND 

NON-ATCS PERFORMANCE 8 . Performing Organ i zation Report No. 

7 . Autho rl s) 

Richard I. Thackray and R. Mark Touchstone 

9 . Performing Organi zot ion Name and Address 

FAA Civil Aeromedical Institute 

PO Box 25082 

Oklahoma City, Oklahoma 73125 

10 . Work Unit No . (TRAIS) 

11 . Contract or Grant No . 

~------------------------------------------------------------~ 

13. Type of Report and Period Covered 

12. Sponsoring Agency Name and Address 

Office of Aviation Medicine 

Federal Aviation 

800 Independence 

Washington, D.C. 

15. Supplementary Notes 

Administration 

Avenue, S.H. 

20591 

14 . Sponsoring Agency Code 

Work was performed under task AM-C-81/82-PSY-88 

16. Abstract 

The role of the air traffic control specialist (ATCS) in proposed highly automated 

air traffic systems of the future is currently receiving considerable attention. At 

the present time, a prevalent conception of the controller's role in such systems is 

that of a "systems monitor" or "systems manager." Inherent in this view is the 

belief that the role of the future controller will be less that of an active planner 

and more that of a passive responder to alternative courses of action presented by 

the computerized system. Such a change in role has raised concerns that increased 

controller complacency, inattentiveness, boredom, and reduced readiness to react in 

emergencies may become serious problems in some of the systems being planned. A 

complex monitoring task was used to study the effect of complacency on attentional 

processes. The task was designed to approximate an automated air traffic control 

radar system. Sixteen experienced ATCS's were tested over a 2-hour session, with 

half assigned to a subject-controlled and half to a computer-controlled condition. 

Although the subject-controlled appeared to be generally superior to the computercontrolled condition, the differences in target detection time were not significant. 

Additional comparisons of ATCS's with non-ATCS's on the radar monitoring task revealed 

that ATCS's were significantly superior to non-ATCS's in target detection time, number 

of targets detected, and rated attentiveness. Both groups, however, showed a similar 

increase in target detection time after 90 minutes of task performance. The results 

suggest that 90 minutes may be the maximum time that attention can be uniformly 

sustained in a laboratory monitoring task of this type. 

17 . Key Words 

Air Traffic Control 

Attention 

Automation 

Monitoring 

19. Security Classif. (af this report) 

Unclassified 

Form DOT F 1700.7 (8-72) 

18. Distribution Statement 

Performance 

Vigilance 

Document is available to the public 

through the National Technical Information 

Service, Springfield, Virginia 22161. 

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

Unclassified 8 

Reproduction of completed poge authorized 
PERFORMANCE OF AIR TRAFFIC CONTROL SPECIALISTS (ATCS'S) 

ON A LABORATORY RADAR MONITORING TASK: AN EXPLORATORY STUDY 

OF COMPLACENCY AND A COMPARISON OF ATCS AND NON-ATCS PERFORMANCE 

Introduction. 

The role of the air traffic control specialist (ATCS) in proposed 

highly automated air traffic systems of the future is currently receiving 

considerable attention. At the present time, a prevalent conception of 

the controller's role in such systems is that of a "systems monitor" or 

"systems manager." Inherent in this view is the belief that the role 

of the future controller will be less that of an active planner and more 

that of a passive responder to alternative courses of action presented 

by the computer system. Such a change in role has raised concerns 

that increased controller complacency, inattentiveness, boredom, and 

reduced readiness to react in emergencies may become serious problems 

in the systems being planned (2). 

Over the past 5 years, our laboratory has been engaged in a program 

of research to examine some of these concerns, as well as several others, 

through the use of a simulated radar monitoring task (5,6,7,8,9,10,11). 

This task was designed to incorporate some of the basic skills (e.g., 

sustained attention, continuous scanning activity, minimal information 

processing) that might characterize future, highly automated air traffic 

control (ATC) systems. Two of the concerns noted previously (i.e., inattentiveness and boredom-monotony) have already been studied and found to show 

some relationship to performance decline on this task (5). Another, readiness to react and the time course of emotional recovery to an emergency 

situation, will be addressed in a study planned for next year. 

Of all of the concerns that have been expressed with respect to 

high levels of automation, the one heard most frequently is that of 

complacency. In the context of automated systems, complacency refers 

to a feeling of well-being or security engendered by a system that 

presumably operates smoothly, efficiently, and quite reliably with minimal 

controller input. It now seems likely that future En Route systems will 

be able to process and handle most of the routine situations currently 

handled by controllers, leaving the controller with the task of simply 

verifying that those options presented by the computer are appropriate 

(2,3). This reduced level of controller involvement (relative to existing 

systems) could easily lead to some major shifts in the task of the controller 

in advanced systems, and the possibility that these shifts could result in 

increased controller complacency seems to be a realistic concern. 

The present study was undertaken to explore the feasibility of one 

technique for varying complacency and to determine its effect on sustained 

attention. In essence, the study compared experienced ATCS's under one of 

two conditions: (i) a condition in which the subject took a designated 

action in order to correct departures of displayed target altitudes from 

assigned limits, and (ii) a condition in which the subject took corrective 

1 
action only if the computer failed to correct the altitude deviation. It 

was hypothesized that complacency would be greater 'under the latter condition and that this would be reflected in a greater decline in attentiveness 

(increase in detection times). 

In addition to studying complacency, the present study, by virtue of 

the fact that ATCS's were used as subjects, allowed t'S to compare the 

general performance level of experienced controllers on our radar monitoring 

task with the patterns oh.tained in our previous studies, all of which used 

subjects with no prior experience or training in air traffic control. 

Method. 

A. Subjects. Sixteen volunteer ATCS instructors (15 men and 1 woman) 

participated in the experiment. All were from the Federal Aviation Administration Academy at the Mike Monroney Aeronautical Center in Oklahoma City. 

Half of the 16 subjects were randomly assi~ned to the com~ut~r-contxolled 

condition and half to the subject-controlled condition. The respective 

mean ages and years of field experience of subjects assigned to these 

two conditions were 38.75 years (age), 10.6 years (experience), and 34.75 

years (age), 12.6 years (experience). The groups did not differ significantly in either age o~ year5 of experience (E > .05). All were tested 

and found to have normal near-point visual acuity (corrected to 20/20 if 

necessary). 

B. Design and Task Apparatus. Task programing and recording of 

responses were accomplished using a Digital Equipment Corporation (DEC) 

PDP-11/40 computer. The computer was interfaced with a VT-11 (DEC) 17-inch 

(43 em) cathode-ray tube (CRT), which served as the subject's display. The 

CRT was located in a console resembling an air traffic control radar unit. 

The stimuli (targets) consisted of alphanumeric data blocks, each representing an aircraft. Data blocks comprised two rows of symbols: the top row, 

consisting of two letters and three numerals, identified the aircraft, 

while the bottom row of six numerals indicated its altitude and speed. 

The first three of these numerals gave altitude in hundreds of feet and 

the last three gave groundspeed. 

A simulated radar sweeplirie was employed that made one complete clockwise revolution every 6 seconds. A target was updated as to (i) location 

and (ii) any change in its data block moments after the sweepline passed 

the target's prior location. Sixteen targets were present at all times; 

as one left, another appeared on the screen. The critical stimulus or 

signal to which the subject was instructed to respond consisted of a 

change in a target's displayed altitude to a value greater than 550 or 

less than 150. The values of the increases or decreases in altitude were 

randomly determined, except that the changed altitude value could not 

be greater than 599 or less than 100. Ten such critical stimuli appeared 

in each 30-minute period; five occurred in the first 15 minutes and five 

in the second. 

For both subject- and computer-controlled conditions, the subject's 

initial response was the same and consisted of pressing a button held in 

2 
the right hand as soon as. a critical altitude change was detected. The 

time between stimulus occurrence and this response constituted the measure 

of target detection time. In the subject-controlled condition, the button 

response was followed by the act of holding a light pen over the critical 

target which, in turn, caused the altitude to revert to its previous 

within-limirs value. If a critical stimulus was not detected within 60 

seconds, the data block automatically reverted to its previous value. In 

the computer-controlled condition, pressing the response button not only 

recorded detection time, but also served to activate a red indicator 

light located adjacent to the right side of the screen. This light 

remained on for 60 seconds. The subject was instructed to use the light 

pen to correct the altitude departure only if the altitude did not change 

to a within-limits value before the red light went off. Since a critical 

target always timed out (reverted to its previous value) 60 seconds after 

the altitude departure had occurred, the subject's variable detection 

time plus the 60-second time that the red light was activated ensured 

that a target always returned to a within-limits value prior to the red 

light's offset. Target detection times for both conditions were recorded 

by the computer for subsequent processing. 

C. Procedure. On arrival, the subject was taken to the experimental 

room and an orientation tape played. The orientation explained that this 

study was one of a . series designed to investigate various aspects of 

highly automated systems. The subject was told that the role of controllers in future ATC systems would likely be quite different from the role 

of present-day controllers, and that this experiment was being conducted 

to examine the possible effects of some of these changes. Following this, 

a 9-point subjective rating scale was administered dealing with present 

feelings of attentiveness, fatigue, tension, and boredom. 

The instructions for the task itself emphasized the necessity of 

pressing the button immediately upon detection of a critical stimulus. 

The subject was told that a critical stimulus (any altitude value greater 

than 550 or less than 150) could occur in any target at any time, regardless of the current altitude values of the targets. It was explained 

that occasional large changes in altitude would not normally occur in 

an actual radar system, but that this departure from normal conditions 

was necessary to insure that all targets would be given equal priority 

in scanning. 

In the subject-controlled condition, he/she was told to initiate an 

action with the light pen to correct the altitude departure after the 

button press had been made. In the computer-controlled condition, subjects 

were told to take corrective action with the light pen only if the computerized system did not act to correct the altitude deviation within the 

time that the red light was on, i.e., their role was to act as a backup 

in the event the system failed. As noted earlier, corrective action with 

the light pen was never necessary, since the altitude changes always 

reverted back to within-limits. values before the offset of the red light. 

A 7-minute practice period followed the instructions for both conditions. 

3 
After the 2-:-hour task session, the subject completed a second form of 

the subjective rating scale. Thls form was identical to the first except 

that the subject was asked to rate each. item, plus one additional item 

dealing wi.th task monotony, on the bas.is of how he/she felt near the 

end of the test period just completed. 

Results. 

k Comparison of Computer..:...corttrolled and Subjected-Controlled Conditions. 

Figure 1 shows mean target detection times across 30~minute scorinp periods 

for the two conditions. Analysis of variance applied to these data revealed 

a significant main effect for the" four 30-minute periods_ (!_(3/42) = 6.00, 

12_ < .01). Although Figure 1 suggests detection times to be slower under 

the computer-controlled condition, analysis of variance revealed no significant main effect for the two conditions (!_(1/14) =· 1.16, . .E.> .05) and 

no significant conditions by periods interaction (!:_(1/14) = T.41,, 12_ > .05). 

Likewise, there was no evidence of any difference between the conditions 

in the total number of critical stimuli missed. One subject in each 

condition missed one stimulus; the rest did not miss any. 

(/) 

0 

~ 8 

u 

w 

(/) 

6 

COMPUTER CONTROLLED 

SUBJECT CONTROLLED 

2 3 4 

30- MINUTE PERIODS 

Figure 1. Mean target detection times for the subject-controlled and 

computer-controlled conditions. 

4 
\. 

Separate .!_ tests applied to .. the rating scale data revealed no differences (.E_ > .05) between the computer-controlled and subject-controlled 

conditions. at either the beginning or end of the experiment, Statements 

on the scales corresponding to the mean ratings obtained at the completion 

of the task period suggested that the subjects felt attentive, more tired 

than usual, relaxed, indifferent (neither bored nor interested)~ hut 

felt the task itself to be very .Eonotonous. 

B. Comparison of ATCS with Non-ATCS Subjects. Since there were no 

differences between the two experimental conditions, the data shown in 

Figure 1 were combined across groups. These combined data were then· 

compared with data from a sample of non-ATCS'-s. This latter sample was 

obtained by randomly selecting 15 men and 1 woman from a larger group 

of 45 subjects used in a previous study (9). Subjects in this earlier 

study ranged in age from 18-29, were. all college students, and were 

tested under conditions identical to those of the subject-controlled 

condition employed with the ATCS' s in the present study._ 

A comparison of mean target detection times of the ATCS and non-ATCS 

subjects is shown in Figure 2. An analysis of variance of these data 

revealed a significant difference between groups (~ (1/30) = 4.43, E_ <.05), 

as well as a significant difference between the four 30-minute periods 

(~(3/90) = 12.70, E.< .01). There was no significant interacti.on effect 

(~ < 1. 00). 

14 

NON-ATCS's 

12 

C/) 

0 

z 

0 

(.) 

LIJ 

C/) 

6 

0 ~~----------~~----------~----------~ 2 3 4 

30- MINUTE PERIODS 

Figure 2. Mean target detection times for ATCS and non-ATCS subjects. 

5 
In addition to detecting targe-ts more rapidly, ATCS.ls also _missed 

fewer targets. Fourteen of the. ATCSls_missed none of the stimuli1 and 

the remaining two only missed one stimulus. In contrast, five _of the 

non-ATCS's missed two to four stimuli, three missed one st:f;.~ulus, and 

eight missed none. A Fisher Exact Probability Test performed on these 

data indicated the differences between groups to be significau.t · (.E. = .044). 

A comparison of the subjective rating scale measures obtained on both 

groups revealed no differences between groups on any of the presession 

measures, but significant differences on two postsession measures..: ATCS's 

rated themselves as being more attentive than non-ATCS 1 s (t (30} "" 3.19, 

.E. < .01). There were also differences in rated monoton¥ (b~t not boredom). 

The ATCS's found the task to he "very monotonous," while non-ATCS's rated 

the task as only "moderately monotonous" (!_(30) = 2.74, _£__< .a~n. These 

differences are not too surprising when one realizes that the re<tuirement 

to maintain high levels of attentiveness is a necessi.ty for ATCS' s in 

the performance of their jobs. Also, it would be expected that ATCS's 

would find our radar monitoring task quite monotonous relative to reallife air traffic control work in contemporary systems. 

Discussion. 

Although target detection times of ATCS's were generally longer under 

the computer-controlled than under the subject-controlled condition, the 

difference between conditions was not statistically significan~. There 

are several possible explanations that may account for the lack of significance. The first and most obvious one is _that the experimental manipulations designed to increase complacency did not produce the desired effect. 

The subject-controlled condition used in the present study was essentially 

identical to that used in most of our previous studies, and the speeific 

intent of this condition was to produce a task that simulated a level of 

passive, low involvement felt to approximate the task conditions of highly 

automated air traffic control systems. It may be difficult, if not 

impossible, to decrease the level of involvement beyond that already 

inherent in this condition. The second possibility is that complacency 

may indeed have been greater under the computer-controlled condition, but 

that controllers, because of their training and experience, may be able 

to sustain a high level of attention in spite of lower task involvement. 

If training and experience were relevant variables, the two conditions 

compared in this study might have differed significantly had non-ATCS's 

been used as subjects. 

That controllers are able to perform a radar monitoring task more 

effectively and efficiently than subjects without training in air traffic 

control was clearly shown by the fact that ATCS's detected targets more 

rapidly, made fewer omission errors, and rated themselves as more attentive 

than did non-ATCS's. The superiority of ATCS's in speed of detecting 

targets was particularly striking in that this superiority was maintained 

across the entire 2-hour session. 

Despite their superiori.ty in target detection, however, ATCS' s showed 

a decline in performance during the last 30-minute measurement period 

that essentially paralleled the decline shown for non-ATCS's. This 

6 
general decline, known in the vigilance literature as the "decrement 

function," has been found in all of our previous studies using this 

task. Since this type of performance decline has been found to occur 

in auditory vigilance tasks as well (1), it cannot be attributed 

simply to visual fatigue. Rather, it appears to involve a decline in 

some central attentional process which is known to promote or induce 

drowiness, microsleep episodes, and certain trance-like (highwayhypnotic) conditions (4). Previous research conducted with the present 

task has shown that this decline in performance is due primarily to an 

increase in long detection times which, in turn, appear to result from 

lapses of attention (6,7,10). Because this decline in performance 

(attention)occurs in ATCS's in spite of their extensive experience with 

similar displays, our results suggest the possibility that controllers in 

future systems, in which monitoring may be a major task requirement, may 

show a like decline in attentiveness after approximately 90 minutes of 

continuous system monitoring. The magnitude of the decline in detection 

efficiency shown in our study is not overly impressive in terms of the 

absolute increase in detection time, but if taken as an indication of 

decreased alertness, ability to react rapidly and efficiently to an 

emergency condition or sudden task overload during this period of 

declining attentiveness could be substantially impaired. The question 

of how effective is the response to emergency situations during a period 

of declining alertness will be addressed specifically in a laboratory 

study currently being planned using a simulation of advanced radar monitoring 

concepts still in the development phase. 

7 
REFERENCES 

1. Davies, D. R., and G. S. Tune. 1969. Human Vigilance Performance. 

New York: American Elsevie-r Publishing Company, Inc. 

2. Department of Transportation - Federal Aviation Administration Fourth 

Human Factors Workshop on Aviation: Air Traffic Control. May 13-15, 

1981. Atlantic City. 

3. Guillen, M. A., 1981. AERA: A flight into the future. Science News. 

120: 125-126. 

4. Shor, R. E., and R. I. Thackray. 1970. A program of research in 

"highway hypnosis": a preliminary report. Accident Analysis and 

Prevention. 2, 103-109. 

5. Thackray, R. I., J. P. Bailey, and R. M. Touchstone. 1977. 

6. 

Physiological, subjective, and performance correlates of reported 

boredom and monotony while performing a simulated radar control 

task. In R. R. Mackie (Ed.), Vigilance: Theory, Operational Performance, and Physiological Correlates. New York: Plenum Publishing 

Company. 

Thackray, R. I. , 

of the vigilance 

task. Aviation, 

R. M. Touchstone, and J. P. Bailey. 1978. Comparison 

performance of men and women using a simulated radar 

Space, and Environmental Medicine. 49: 1215-1218. 

7. Thackray, R. I., J.P. Bailey, and R. M. Touchstone. 1979. The effect 

of increased monitoring load on vigilance performance using a simulated 

radar display. Ergonomics. 22: 529-539. 

8. Thackray, R. I., and R. M. Touchstone. 1979. Effects of noise exposure 

on performance of a simulated radar task. FAA Office of Aviation 

Medicine Report No. AM-79-24. 

9. Thackray, R. I., and R. M. Touchstone. An exploratory investigation 

of various assessment instruments as correlates of complex visual 

monitoring performance. FAA Office of Aviation Medicine Report 

No. AM-80-17. 

10. Thackray, R. I., and R. M. Touchstone. 1980. Visual search performance 

during simulated radar observation with and without a sweepline. 

Aviation, Space, and Environmental Medicine. 51: 361~366. 

11. Thackray, R. I., and R. M. Touchstone. Age-related differences in 

complex monitoring performance. FAA Office of Aviation Medicine 

Report No. AM-81-12. 

8 

*U.S . Government Pr inting Office 1982 - 376-657/1120