Review of the Scientific Basis for 

the Mandatory Separation of an Air 

Traffic Control Specialist at Age 56

Dana Broach 

David Schroeder

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

April 2005

Final Report

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iii

TABLE OF CONTENTS

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Evidence available in 1971 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Inherent stress of the ATCS job . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Loss of proficiency with age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

ATCS medical retirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Evidence available after 1971 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Inherent occupational stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Disability retirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Age and performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

FIGURES

1: ATCS responses to “In general, how stressed do you feel at work” compared with

responses from national samples in 1999 and 2001 ................................................................ 23

2: Responses of terminal and en route CPCs 1999 survey question, “In general, how

stressed do you feel at work?” by age....................................................................................... 23

3: Responses of FSS controllers to 1999 survey question, “In general, how stressed do 

you feel at work?” by age......................................................................................................... 24

4: Burnout Index items and responses from Jones, Bowers, & Fuller (1982) ............................... 24

5: Comparison of % of Air Traffic employees exceeding 3.75 criterion on “Burnout Index” 

in 1984 and 1986 FAA surveys............................................................................................... 25

6: Comparison of proportions of non-supervisory ATC employees and all FAA employees 

indicating the factors as “frequently” or “always” a source of stress in the 1986 survey ............ 25

7: Cubic regression of likelihood of OE (p(OE)) on controller age at beginning of 5-year 

observation period (1991-1995) from Broach (1999) ............................................................. 26

TABLES

1: Medical retirements data presented in 1971 testimony ........................................................... 27

2: Disability retirements for controllers less than age 45 compared to their

representation in the FAA workforce....................................................................................... 27

v

Scope of review

Why Age 56?

Scientific evidence 

offered in support of the 

“ATCS Age 56 Law”

Evaluation of evidence 

available in 1971

Scientific data developed 

since 1971

Physiological indicators 

of stress

Anxiety, personality, 

attitudes, and stress

The scope of this review is limited to studies relevant to the specific rationales proferred 

in support of mandatory separation of controllers at age 56. The review is not a comprehensive examination of the extensive literature on aging, health, stress, shiftwork, 

cognitive abilities, or job performance, including errors, as related to the air traffic 

control specialist (ATCS) occupation.

The testimony offered in 1971 before U.S. Congress did not explicitly describe why 

age 56 was chosen. No scientific data definitively demonstrating a remarkable decline 

or change at that specific age were presented. Rather, the argument appears to have 

been that (a) the mid-50s were the ages in which “burnout” was likely to occur among 

controllers, (b) age 56 would allow a controller to accumulate 25 years or more of 

creditable service if hired prior to the proposed maximum entry age of 31, and (c) age 

56 was a young enough age to allow a “burned out” controller to pursue an alternative career, if desired.

Studies of self-reported symptoms of stress, biochemical markers or indicators 

linked to stress, medical disorders, and disability retirements among controllers 

were cited in testimony as evidence in support of the need for an early retirement 

rule for controllers.

Overall, the evidence available in 1971, when carefully reviewed, was not as strong 

as characterized in testimony. The studies and statistics cited suffered from various 

defects that, in retrospect, make them less persuasive as the scientific foundation for 

the “ATCS Age 56 Law.”

Research since 1971 has investigated (a) physiological indicators of job-related stress, 

(b) anxiety, personality, attitudes, and stress, (c) shiftwork and fatigue, and (d) age 

and performance. Moreover, the research since 1971 must be considered within the 

context of advances in the understanding of stress, the etiology of disorders such as 

hypertension, the role of genetics, personality, and lifestyle choices, and changes in 

the environment and working conditions of the job.

Melton (1982) reviewed 10 years of research on ATCS stress and concluded that 

objective evidence did not support the popular perception of the occupation as being 

unusually stressful.

Smith (1980) reviewed previous research and concluded that controllers were 

less anxious than the general population. Subsequent research has confirmed 

Smith’s conclusion.

(Continued)

EXECUTIVE SUMMARY
vi

Shiftwork and fatigue

Age and performance

Medical disability 

retirements

Conclusions

Melton et al. (1973) found no differences in physiological and biochemical indicators 

of stress after introduction of the counter-clockwise rotating 2-2-1 shift pattern. Cruz 

and Della Rocco (1995) reported no significant differences in subjective ratings of 

sleep quality or sleepiness for persons age 30-35 and 50-55 in a laboratory study of 

two shift rotations (2-2-1 versus 2-1-2). A national survey of controllers conducted 

at the direction of Congress in 1999 provided little evidence that controllers experience any increase in self-reported occupational stress, chronic fatigue, or stress-related 

symptoms as they age.

While correlations with age are consistently observed on both objective and subjective 

criterion measures, relationships are very modest. However, all studies currently available are cross-sectional. No long-term longitudinal studies of changes in performance 

are available, so no conclusions can be drawn to support or refute the hypothesis that 

ATCS proficiency is lost with age.

Analysis of FY1997-2003 disability retirements shows that younger (age 44 and 

younger) controllers retire at a rate proportionate to their representation in the FAA 

workforce, in contrast to the 1971 testimony.

The scientific evidence available in 1971 provided only weak objective support for 

the rationale given for the “ATCS Age 56 Law.”

Research since 1971 does not support the inherent stress rationale articulated in 1971 

for the “ATCS Age 56 Law.” However, the available studies also do not offer a “firm 

foundation” for either supporting or rejecting the mandatory separation of controllers at age 56 in view of the age and performance results. Although cross-sectional in 

design, the age and performance studies suggest that performance may decline with 

age and that variability in performance between controllers is likely to increase. Additional research is suggested to assess changes in knowledge, skills, and abilities with 

age and to determine the impact of any changes on job performance.

EXECUTIVE SUMMARY (Continued)
1

REVIEW OF THE SCIENTIFIC BASIS FOR THE MANDATORY SEPARATION OF AN AIR

TRAFFIC CONTROL SPECIALIST AT AGE 56

INTRODUCTION

The U.S. Congress amended Section 8335 of Title 5 

of the United States Code (USC) in 1972 (Public Law 

92-297) to provide for the mandatory separation of an 

air traffic controller from employment at age 56 unless 

otherwise exempted by the Secretary of Transportation 

as “having exceptional skills and abilities as a controller.” 

Passed on the heels of the 1970 report of the Air Traffic 

Controller Career Committee and two public hearings 

in 1971, the law was based on the argument that declines 

in skill with age and cumulative stress in the controller 

workforce will result in diminished safety and efficiency 

in the air traffic control system (“Hearings”; U.S. House 

of Representatives, 1971, p. 3, testimony of John Volpe, 

Secretary of Transportation). The testimony by John Shaffer, FAA Administrator, made the case that:

From the thrust of these proposals, you can see that 

your principal concern is with the use of older personnel 

in the controller positions. This is the basis for a specific 

maximum retention age provision. We believe that an 

individual should embark on a career as a controller 

while in his twenties, and in the usual case, retire or 

change to another line of work before he reaches 56 

years of age. This makes him available during his most 

productive stage and while his interest, stamina, and 

general health are at their highest level.

As a general rule, we find that our controllers simply do not maintain their proficiency as they progress 

through the second half of the normal period of service 

of a career employee.

In some cases, the work becomes too stressful. In other 

cases, conditions of health force the controller to leave 

the work altogether. The maximum retention age level, 

with the early retirement and retraining provisions in 

our proposal, would give the controller the assurance 

of eventual relief from a long span of control work. 

He will have the opportunity to turn to a new career 

at a time when he otherwise might find it necessary 

to remain in controller work under conditions that 

he finds nearly intolerable. The bill will also allow the 

Secretary to maintain a safer, more proficient controller work force, and to operate a safer, more efficient 

national airspace system (Hearings, p. 9).

This testimony was presented against the backdrop 

of tremendous expansion of the aviation industry with 

the concomitant perception of ever greater burdens being placed upon controllers by the work (Kent, 1980). 

Three principal lines of evidence in support of mandatory separation of controllers at age 56 were articulated 

in 1971 hearings before the Post Office and Civil Service 

Committees of the U.S. House of Representatives and 

Senate:

(a) the inherent stress of the job;

(b) loss of proficiency with age; and 

(c) medical retirements.

This review will consider these major lines of evidence 

first, from the perspective of the scientific data available 

in 1971, and second, from the perspective of relevant 

scientific research since the passage of P.L. 92-297. The 

review closes with an assessment of the degree to which 

current scientific evidence supports the hypothesis that a 

controller may no longer perform the core and essential 

functions of the job without hazard to others or self at or 

beyond age 56, and recommendations are presented for 

continued research on the questions of stress, shift work, 

performance and age, and disability retirements.

Evidence Available in 1971

Inherent Stress of the ATCS Job

Testimony

The premise of an inherently stressful job was presented in the testimony of Don Leyden, the President 

of the Professional Air Traffic Controller Organization 

(PATCO) as follows:

We believe that the intense pressure which attaches to 

practically every working minute the controller is on the 

job merits special consideration. The controller does, literally, hold in his hands the lives of the people on those 

airplanes.

Thus he must not only be constantly – every minute – on 

the alert, he is also working under severe stress and strain 

– to an extent that is equaled in few, if any, other jobs or 

professions (Hearings, p. 59).
2 

The consequences of an error in control judgment 

were highlighted as an important component of that 

inherent stress and strain:

I have encountered experiences where I have handled 

up to 20 and 25 jet aircraft at one particular time on a 

scope. There is no room for error for that individual.

The person working the scope is fully cognizant of 

that, which adds to the stressful nature of the work 

(Hearings, p. 72). 

The testimony of Donald Francke, Executive Director 

of the Air Traffic Control Association (ATCA), reinforced 

the theme of inherent stress to the ATCS job. Describing 

the job as “arduous,” Mr. Francke began his testimony 

by noting that the need to provide controllers with an 

opportunity for “relief” was well documented (Hearings, 

p. 95). He went on to testify:

The undisputably [sic] valid basis for early retirement 

for controllers rests upon the provable fact that the 

business of assuring expeditious and orderly movement 

of air traffic, safeguarding against midair collision, is 

a highly stressful occupation which lays a heavy toll 

on the mental and physical capacity of the controller 

and which limits his productive life. There must be 

an orderly phasing out of the older controllers when 

they can no longer make the rapid and accurate decisions essential to the preservation of human life. This 

calls for recognition of the highly important fact that 

early retirement is not solely a matter of fairness to 

the controller, it is primarily a safety measure (Hearings, p. 97–8).

At this point, Mr. Francke identified several reports 

“proving” that the business of air traffic control was 

highly stressful. He first contrasted the description of 

the pilot occupation as “hours of boredom intermixed 

with moments of sheer terror” to a description of the 

ATCS occupation:

The controller has no such hours of boredom; he must 

frequently work for 8 hours at a stretch without rest 

periods and gulping his lunch at his position. Because 

of shortages of personnel, many of them have been on 

6-day weeks for several years. This situation is further 

worsened by the fact that air traffic control is a 3 shift 

per day, 7-day a week operation, and each controller 

must take his turn standing midwatches. This is usually 

not too onerous on the younger man, but older men 

usually have difficulty in changing the rhythm of their 

life, and in sleeping during the daytime in the periods 

that they are on midwatches (Hearings, p. 98). 

Next, Francke asserted that “Unrelieved pressure and 

tension will ultimately take its toll of even the hardiest 

constitution” based on a summary of studies finding that 

an “overwhelming majority” of coronary patients had 

been subjected to unusual occupationally-related stress 

(Hearings, p. 98). Francke highlighted the conclusions 

of the summary study author that “the results clearly 

demonstrated a striking correlation of coronary heart 

disease prevalence and emotion [sic] stress.” Francke also 

testified that “Of course, it is well proven that stress and 

mental illnesses result from stress...” and even suggested 

that the medical profession had come to believe that 

diabetes resulted from stress (p. 98).

To buttress his characterization of the ATCS occupation 

as inherently stressful, Francke then summarized several 

studies that were “conducted by responsible bodies over 

the years.” The first study he cited was published by the 

U.S. Air Force in 1963:

The second important point which merits special 

attention is the fatigue and feelings of tension that 

were reported time after time in interviews with both 

individuals and groups.... The job is not physically 

demanding and yet operators talked about spending 

an unusual amount of time sleeping, particularly after a 

day of heavy traffic.... However, it was pointed out in 

interview situations that even experienced men develop 

tenseness and irritability.

Francke also cited an even earlier study, conducted by 

the Royal Norwegian Air Force Aeromedical Institute 

in 1949, as evidence of the inherent stress and strain of 

the ATCS job:

If one thinks of the concentration and strain which 

the air traffic controller goes through during rush periods and the constant anxiety in view of the serious 

consequences which may result from a mistake, these 

are typical psychological factors which have proved 

to be contributory causes of digestive disorders (dyspepsia) and gastric ulcer. To this is added the fact that 

the work is carried out in watches at widely differing 

hours which has a very disturbing effect upon the 

bodily functions. 

(Quoted by Francke, Hearings, p. 99. )

These two studies cited by Francke explicitly pointed 

to three factors contributing to the inherent stress and 

strain of the job: (a) workload (especially during rush 

periods); (b) the inherent responsibility of the position; and (c) shiftwork. The primary evidence for stress 

among controllers consisted of observed and self-reports 

of tension, anxiety, trouble sleeping, and the incidence 

of “digestive disorders.”
3

Francke next cited a joint Flight Safety Foundation 

(FSF)-FAA (1959) study as providing evidence that 

the “major air traffic control problem lay in the area of 

subjective” rather than objective fatigue (Hearings, p. 

99). In his view, the FSF/FAA study showed “that the 

controller’s job carried inherent mental stresses and that 

the psychological and emotional factors were the major 

ones governing controller fatigue.” Moreover, Francke 

testified that

The foundation found that the almost continuous 

responsibility for the proper separation of aircraft, accompanied by the fear of the consequences of mistakes 

was the major underlying cause of controller fatigue. 

"Without laboring the point," the FSF concluded, 

"there is a growing body of evidence in the medical 

and scientific literature that such anxieties or fears are 

producing reactions similar to what has been defined 

here as subjective fatigue, and furthermore will lead 

to real psychological impairment of individuals over 

periods of time” (Hearings, p. 99-100).

To further support his argument, Francke next cited 

an FAA Office of Aviation Medicine (OAM) study of 

the self-reported symptoms often associated with stress 

(Hauty, Trites, & Berkley, 1965a,b). In his testimony, 

Francke characterized the FAA study as having found “a 

startling increase in the incidents of stress-related symptoms with an increase in ATC experience” (Hearings, p. 

100). He concluded that the study results showed that the 

pressures of the ATCS job began “to affect a controller’s 

health significantly after the age of 40, and to a steadily 

increasing degree as his years of service as a controller 

increase” (p. 100).

His testimony continued in this vein with a lengthy 

excerpt from an unidentified 1969 Office of Aviation 

Medicine report on controller stress. The quote asserted 

that as traffic density increased, the stress level rose correspondingly and that ultimately, the stress level that 

controllers could tolerate would become the “limiting 

factor on the workload that the system can handle with 

safety” (Hearings, p. 101). The report suggested that 

the point in time at which a controller’s traffic handling 

capabilities began to decline depended, at least in part, 

on two factors: (a) “the type of management” that had 

been exercised over the controller; and (b) “the amount of 

stress” experienced by the controller up to that point.

Evidence for Inherent Stress

While much of the testimony offered in 1971 was 

anecdotal or personal, objective studies were available. 

Francke cited four specific studies in his testimony as 

supporting the hypothesis that the air traffic controller 

job was inherently stressful: a 1963 U.S. Air Force study; 

the 1949 study for the Royal Norwegian Air Force; an 

unidentified 1969 OAM report; and the 1965 studies 

by Hauty et al. The 1963 U.S. Air Force and 1965 

Hauty et al. studies were located and reviewed; the cited 

1949 Norwegian and 1969 OAM reports could not be 

located due to a lack of identifying information in the 

testimony.

Other primary sources of information available to the 

agency in 1971, but not cited in testimony, included:

• a study of controller performance measures (Nagay, 

1949);

• a National Research Council report (Fitts, 1951);

• the Congressionally-mandated FSF studies of controllers (FSF, 1958, 1959);

• the Air Traffic Controller Career Committee (1970) 

report;

• a study of physiological indicators of stress (Hale, 

Williams, Smith, & Melton, 1971); and

• a study of self-reported symptoms (Dougherty, Trites, 

& Dille, 1965). 

The FSF studies led directly to the establishment of 

the Controller Health Program. Each of these primary 

sources, including the U.S. Air Force and the Hauty et 

al. (1965a,b) studies cited by Francke in his testimony, 

and the Controller Health Program, will be summarized 

below.

Nagay (1949). The American Institutes for Research 

(AIR) contracted with the Civil Aeronautics Administration for the development of measures to assess the 

proficiency of en route air traffic controllers. In the first 

phase of the work, the research team made observations 

every 15 seconds of the activity of controllers during 

three watches at two air route traffic control centers. 

Nagay noted that less time was spent in the 2nd half of 

the watch on interphone activities than in the 1st half; 

no other differences in activities were noted. However, 

apparently on the basis of this decline in interphone activities across the watch, Nagay’s study was cited by the 

1963 U.S. Air Force study as evidence of the fatiguing 

nature of the controller job.

National Research Council. The National Research 

Council (NRC) Committee on Aviation Psychology 

prepared a report “on the application of the principles and 

techniques of human engineering to the improvement of 

the air-navigation and traffic-control systems” (Fitts, 1951, 

p. iv). The report was not a direct study of age, stress, or 

performance but described what are now termed human 

factors concerns and issues in the design, development, 

and operation of the air traffic control system. The report 
4 

cited the perception that younger men were more suited 

to the demands of air traffic control without attribution 

or supporting data (p. 10). The committee conducted 

site visits and interviews with controllers at a number 

of facilities as part of the fact-finding process. Inquiries 

were made as to the personnel and personal problems 

controllers experienced as a consequence of the job. Only 

3 of 35 center controllers mentioned a concern relevant 

to the rationales given for age 56, and that was phrased 

as “early disability requiring semi-retirement” (Table II, 

p. 70). None of the 25 tower controllers interviewed 

mentioned any personnel or personal factor relevant to 

the rationales articulated in support of mandatory separation at age 56 in the 1971 testimony.

FSF study of controllers. In 1956, the U.S. Congress 

appropriated funds “to provide for an objective evaluation of current medical standards and their administration” (Flight Safety Foundation, 1958, p. xi). The Civil 

Aeronautics Administration contracted with the Flight 

Safety Foundation (FSF) to conduct the investigation, 

with particular attention to air traffic controllers. The FSF 

produced two reports in the course of the investigation: 

(a) Physical Qualifications for Air Traffic Control Personnel

(FSF, 1958); and FSF/FAA Air Traffic Control Personnel 

Study: Effects of Activity and Environment (FSF, 1959). 

Data relevant to shiftwork, fatigue, and performance were 

collected by both on-site observation and a survey. Over 

4,000 controllers completed the FSF survey.

The first FSF report (1958) focused on medical 

qualification standards for the controller occupation. 

Recommendations in that report included (a) establishing 

medical qualification standards at hire for all controllers, 

(b) periodic (annual) medical evaluation of controllers, 

and (c) establishment of a general health maintenance 

and protection program for controllers. The second 

report (FSF, 1959) considered in more detail the work 

performed by controllers, the environment in which the 

work was performed, and the impact of the work on the 

controllers. The FSF considered controller fatigue from 

three perspectives. First, the FSF did not find evidence 

for “objective fatigue” defined as observable decrements 

in job performance. However, that negative finding was 

attributed to the lack of sensitive, reliable, and interpretable measures of job performance. (p. 120). Second, FSF 

considered evidence of “physiological” fatigue. Evidence 

for visual fatigue, particularly for radar controllers, was 

found in the form of changes in visual test scores pre- and 

post-shift (p. 122). However, findings of “physiological” 

fatigue “from blood pressure and pulse rates were negative” 

(p. 122). Finally, the FSF considered evidence for “subjective” or “psychological” fatigue. In a rational analysis, 

the FSF researchers constructed the case for “psychological” fatigue among controllers (pp. 123-125). First, they 

noted the difficult environmental conditions, including 

noise, temperature, and illumination problems as a likely 

source of subjective fatigue among controllers. Personnel 

practices, as highlighted in the survey, were next cited as 

factors contributing to controller fatigue. These factors 

included dissatisfaction with working schedules, supervisory practices, pay and retirement provisions, and “a 

feeling of being ‘let down’ by superiors in cases of disputes 

between ATC and others” (p. 124). The FSF concluded 

that “the overall work situation is one that is conducive 

to ‘Subjective Fatigue’” (p. 124).

U.S. Air Force (1963). The U.S. Air Force air traffic 

control tower operator (CTO) was the focus of a field 

survey conducted in the midst of a significant expansion 

of the Air Force. An investigation of the adequacy of 

controller training methods in use at the time was requested in order to increase the effectiveness of the CTO 

program (U.S. Air Force, p. 1). A six-item open-ended 

questionnaire was administered to 99 Air Force controllers 

as part of the data collection effort to identify CTO job 

requirements. Other data sources included interviews, 

published reports, and observations of the CTO job. 

Drawing on these data, the study authors highlighted 

fatigue and tension among the controllers as an area of 

concern (p. 11). There appeared to be no obvious physical explanation for the fatigue and tension reported by 

controllers in both individual and group interviews. The 

authors recommended further study of these feelings of 

fatigue and tension in relation to job proficiency, time 

on the job, and age (p. 13).

Controller Health Program. The FSF studies were the 

impetus for the establishment of the Controller Health 

Program. The FSF concluded that medical qualification 

standards were needed for the occupation and should be 

tailored to the particular demands of the position (Holbrook, 1974). In addition, periodic (annual) examinations 

were recommended to ensure that controllers were fit 

for duty as part of a health maintenance program. The 

Controller Health Program was implemented in October 1965 to provide continuing medical observation of 

controllers “oriented toward the maintenance of both 

employee health and system safety” (FAA, 1965, 1966). 

The medical examination for controllers given under the 

auspices of the CHP ensured that controllers at any age 

met minimum physical and medical standards.

Air Traffic Controller Career Committee. One of the 

tasks of the Air Traffic Controller Career Committee was 

to determine the “true nature and extent” of occupational stress among controllers and assess its importance 

relative to other problems in the occupation (Air Traffic 

Controller Career Committee, 1970, Appendix XVII). 

The operational question was, “Is there evidence that 

job-related stress has a significant effect on the psycho-
5

physiological condition of the FAA air traffic controller?” 

Three classes of data were considered by the Committee 

as evidence of job-related stress among controllers: (a) 

anecdotal, personal experiences of incumbent controllers; 

(b) statistical data on the incidence of medical disorders 

and retirement; and (c) preliminary data from an assessment of biochemical markers of the stress response of 

controllers under actual working conditions.

The Committee described two kinds or sources of 

job-related stress among controllers, based on anecdotal 

reports and discussions with controllers. The first source 

was sudden emergency events that occurred while controlling traffic. The second source appeared to be a sense of 

personal inadequacy “to cope with the overall demands 

of the job” (Air Traffic Controller Career Committee, 

Appendix XVII, p. 2). Controllers described both acute 

and chronic anxiety reactions. While acknowledging that 

there may have been instances of exaggeration or embellishment, the Committee felt that the reports made by 

controllers were credible, valid, and candid. The Committee concluded that the controller self-reports were 

“impressive evidence that the air traffic controller job 

imposes, at least on occasion, conditions which are highly 

stressful to the employees” (ibid).

The second class of evidence considered by the Air 

Traffic Controller Career Committee was medical statistics. The Committee considered two sets of data: (a) 

the incidence rate of specific disorders among controllers 

compared to other occupational groups; and (b) medical 

disability retirements. The disorders of interest to the 

Committee were coronary artery disease, coronary thrombosis, hypertension, and peptic ulcer, which were then “all 

generally regarded as more or less stress-related illnesses” 

(p. 3). The Committee reported that the incidence rate 

for these disorders among controllers was 1.5 to 4 times 

higher than comparable rates for civil airmen and up to 8 

times higher than rates for Air Force pilots age 35 to 39. 

The Committee noted that comparisons may have not 

been statistically valid since identical medical diagnostic 

criteria and examination techniques were not used for the 

comparison groups. However, the Committee went on 

to reason that the higher incidence rate, compared with 

groups subject to similar annual examinations, was “in 

keeping with the expected findings, if one postulates the 

presence of a high degree of occupational stress among air 

traffic controllers” (ibid). In other words, if one accepted 

two premises – (1) the air traffic controller occupation 

was stressful, and (2) the disorders such as coronary artery 

disease, coronary thrombosis, hypertension, and peptic 

ulcer were “caused” by stress – then the finding of a higher 

incidence of “stress-related” disorders among controllers 

is evidence that the occupation is highly stressful.

Medical disability retirement data for calendar years 

1967 through 1969 were also examined by the Air Traffic Controller Career Committee in an appendix titled 

“Review of Medical Information Regarding Occupational 

Stress Among FAA Air Traffic Controllers.” On one hand, 

controllers accounted for 45% of the agency workforce 

in those three years and 45% of all the medical disability 

retirements. In other words, the rate of medical disability retirement for controllers was proportionate to their 

representation in the workforce. On the other hand, air 

traffic controllers accounted for 67% of all medical disability retirements among employees under age 45. In 

other words, the rate of medical disability retirement for 

younger controllers appeared to be disproportionate to 

their representation in the workforce. The Committee 

concluded, in view of the anecdotal reports, the higher 

incidence rate for “stress-related” disorders among controllers, and the disproportionate rate of medical disability 

retirement for younger controllers, that there was “a 

significant degree of stress associated with the air traffic 

control occupation” (p. 3-4).

The third class of supporting evidence examined by 

the Committee was a study of stress indices among controllers at the Chicago O’Hare terminal. That study was 

conducted in the summer of 1968 and involved 22 controllers. Several physiological and biochemical measures were 

collected, including epinephrine, norepinephrine, and 

17-hydroxycorticosteroid, a metabolite of cortisol. The 

Committee compared the relative magnitude of change 

in excretion of these hormones with that of Mercury 

astronauts. A direct comparison of concentrations of 

the hormones could not be made due to differences in 

assay methods between the two programs. Based on this 

comparison and the opinion of a medical doctor serving on the Air Traffic Controller Career Committee, the 

Committee concluded that these data provided “clearcut evidence of a strong biochemical response by the 

Air Traffic Controller personnel ... to conditions which 

were perceived within their bodies as acutely stressful” 

(ibid, p. 5). The results of the Chicago O’Hare study 

were published as an OAM technical report (Melton, 

McKenzie, Polis, Funkhouser, & Iampietro, 1971). A 

parallel study was published in Aerospace Medicine (Hale, 

Williams, Smith, & Melton, 1971) prior to the March 

1971 Congressional hearings.

Physiological indicators of stress. While the Air Traffic 

Controller Career Committee focused on the hormonal 

indicators related to the stress response, Melton and colleagues (Melton et al., 1971) investigated other measures, 

including heart-rate, galvanic skin response (GSR), blood 

pressure, fibrinogen (e.g., blood clotting factors), and 
6 

phospholipids (e.g., serum fats such as cholesterol, lowdensity and high-density lipids). The involuntary, physiological response of controllers to their work was “assumed 

to arise from their concern for the consequences of their 

instructions” as the actual physical component of the job 

was relatively light (p. 7). Heart rates were higher during 

periods of higher workload (upwards of 200 aircraft per 

hour) in the evening than under lighter workload (< 25 

aircraft per hour) in morning shifts. GSR is a nonspecific 

response to events or stimuli that are attention-getting, 

arousing, exciting, or emotional. GSR, measured as 

electrical resistance, decreases in response to stimulating 

events. GSR increased over the 5-day observation on the 

morning shift but not on the evening shift. Melton et 

al. interpreted this as indicating that the controllers were 

adapting to the workload on the morning shift but not the 

evening shift. In other words, the controllers were more 

reactive to stimuli on the evening shift. Average pre- and 

post-shift blood pressures were not different from each 

other, and overall, the controllers were not hypertensive. 

Controllers were normal with respect to the assessment 

of fibrinogen. However, the controller phospholipid 

profile was significantly higher than in non-controller 

occupations. Phospholipids were associated with the 

sustained action and excretion of catecholamines such 

as 17-hydroxycorticosteroid. Melton et al. concluded that 

the measures indicated that the O’Hare controllers were 

“generally in a state of sympathetic [nervous system] excitation, particularly on the evening shift” (p. 10). Melton 

et al. found that controllers, particularly under heavier 

workload, were physiologically aroused or excited, where 

such arousal is a requirement for performance under demanding conditions.

The work published by Hale, Williams, Smith, and 

Melton (1971) focused on three hormones. Urinary 

epinephrine provided evidence of work-associated adreno-medullary hyperactivity, where such hyperactivity 

is considered a sign of stress (p. 129). This adreno-medullary response was characterized as “early in onset and 

progressive in intensity” regardless of shift (p. 129). 

Urinary norepinephrine provided evidence of workassociated hyperactivity in the sympathetic nervous 

system, where such hyperactivity is considered another 

sign of stress (p. 130). Hale et al. found that the pattern 

of norepinephrine excretion corroborated their findings 

on epinephrine: arousal and hyperactivity of the sympathetic nervous system associated with working traffic. Hale 

et al. found that 17-hydroxycorticosteroid output “fell 

during the period of work load decrease (late evening) 

and rose during the period of work load increase (late 

morning)” (p. 133).

Hale et al. compared the excretion patterns of controllers in their sample to those of other occupational groups. 

By one measure (epinephrine), the morning shift “induced 

a higher degree of stress ... than resulted from unusually 

long or difficult flying operations” (p. 135). However, the 

authors went on to note that the “stress induced by the early 

evening work in the O’Hare tower (the heaviest load of 

the entire day) was of moderate degree, exceeding slightly 

the levels established for aircrewmembers during flights of 

unusual length or difficulty” (p. 135). By another measure 

(17-hydroxycorticosteroid), the authors characterized the 

morning shift as “fairly stressful,” approaching the levels 

induced by 10-hour transpacific flights in a military aircraft (p. 136). The evening shift produced a level in the 

same range as the 10-hour transpacific flight.

Self-reported symptoms of stress. Hauty, Trites and Berkley 

(1965b) obtained data from incumbent controllers from 6 

air route control centers and 6 high- and medium-activity 

terminals. Controllers completed a self-report inventory 

of symptoms thought of “as being related to or induced 

by stress” (p. 4). The symptoms were:

• Headache

• Dizziness

• Constipation

• Sweating

• Twitching muscles

• Poor appetite

• Chest pains

• Loose bowels

• Loss of temper

• Difficulty in breathing

• Aching or burning eyes

• Indigestion or heartburn

• Difficulty staying awake

• Stiffness or body tenseness

• Bothered by distracting noise

• Nausea or sick to your stomach

• Asthma

• Insomnia (Pre-shift only)

• Nightmares (Pre-shift only)

• None

There were 300 participants at the start of the study, 

with data collected over 90 days. By the end of the first 

30 days of the study, some subjects had dropped out, 

leaving 273 participants. At 60 days, there were 250 

participants, and by day 90, the number of participants 

had been reduced by almost a third, to 201 incumbent 

controllers.

While Francke characterized the participants in his 

1971 testimony as having been “tested ... to ascertain 

the number of days on which they experienced various 

incidents of stress” (emphasis added), the data were in 

fact daily self-reports of symptoms experienced pre- and 
7

post-shift. The primary measure reported by the study 

authors was the proportion of days for which at least 

one symptom was experienced by any controller. Note 

that data were pooled across both subjects and days for 

this analysis. Analyses consisted of inspection of graphs 

of the proportion by facility, pre- and post-shift, by age 

group, by experience group, and by the combination of 

age and experience; no formal statistical analyses were 

reported. 

Hauty et al. (1965b) found on visual inspection of the 

graphs of the proportion of days for which at least one 

symptom was reported (by any controller) was generally 

highest “for those symptoms most likely to be judged as 

being stress-induced or related; further, the incidence of 

these particular symptoms is generally greater following 

a work shift” (p. 4). They then grouped the participants 

into three age groups (20-29, 30-39, 40 and over) and 

three experience groups (3 years or less, 4-10 years, 11 or 

greater). They reported that “the percentage of reported 

physical symptoms increases as air traffic control experience increases, but a similar increase does not appear in 

the groupings of subjects by age” (p. 4). The researchers 

regrouped the data into nine age-experience subgroups 

and re-examined the proportion of days for which at 

least one symptom was reported (by any controller). The 

authors concluded that, although age and experience are 

both related to the incidence of reported symptoms as they 

are covariants, length of expericnce was the factor “most 

highly and systematically related to such symptoms.”

Another study conducted at about the same time as the 

Hauty et al. work specifically compared the incidence of 

new symptoms in controllers with non-controllers in the 

FAA. This study by Dougherty, Trites, and Dille (1965) 

was not cited in the 1971 testimony before either the 

U.S. House of Representatives or the U.S. Senate Post 

Office and Civil Service Committees in hearings on the 

controller career legislation. As noted by Dougherty et 

al., the impact of air traffic control work on the health 

of the controllers had been of concern to the FAA for 

some years and led to the establishment of the Controller 

Health Program. While the belief that the inherent stress 

of the job had an adverse effect was widely held, there 

was “little objective evidence on which an evaluation of 

this belief” could be based (p. 956). This study was an 

attempt to evaluate the impact of the work of controllers on their health. Dougherty et al. collected survey 

data from participants in a regional health awareness 

program, resulting in a sample of 569 controllers and 

330 non-controllers. Six symptoms were listed in the 

questionnaire:

• Frequent or severe headaches

• High blood pressure

• Frequent indigestion or stomach pain requiring antacids or milk over several days period

• Chest pain on exertion relieved by rest

• Taken tranquilizers for more than one week

• A physician’s diagnosis of ulcer

The symptoms were listed on the left side of the questionnaire form, with spaces for responses on the right 

side. Respondents were required to make two responses 

to each symptom, one indicating the presence or absence 

of a symptom prior to becoming an FAA employee, and 

the other indicating presence or absence of a symptom 

after becoming an FAA employee. The analysis focused 

on those symptoms for each respondent that were marked 

as being present after joining the FAA but not present or 

experienced prior to becoming an employee. The data 

were analyzed as multi-way contingency tables with the 

techniques available at the time, where cell entries were 

expressed as rates (number reporting a symptom per 

1,000 persons). The proportion of “new symptoms” 

was computed for each cell entry as well.

For example, the rate for headaches among controllers 

was 135 instances per 1,000 controllers, with 74% of 

those instances being “new symptoms.” In comparison, 

the incidence rate for headache among non-controllers 

was 61 instances per 1,000 persons, with just 35% of 

those being “new symptoms.” The headache incidence 

rate for controllers was significantly greater than the rate 

for non-controllers (p < .001; Table III, p. 957). Overall, 

the incidence rates for headache, indigestion, chest pain, 

and ulcer were significantly greater for controllers than 

incidence rates for non-controllers. Subsequent analyses 

focused on the incidence rate of new symptoms in relation 

to age and experience. For example, incidence rate were 

about the same for new symptoms for controllers and 

non-controllers with 3 years or less experience. However, 

incidence rates increased with experience for controllers 

but not for the non-controllers. The incidence rate for 

new symptoms was stable across age groups for controllers 

but declined with age for non-controllers. The authors 

reached essentially the same conclusion as Hauty et al. 

(1965a,b): the incidence of stress-related symptoms increases with experience for controllers but not necessarily 

with age. Moreover, by including data from non-controllers, Dougherty et al. were also able to conclude that the 

incidence rate for controllers of stress-related symptoms 

was greater than the rate for non-controllers. They concluded that the data supported “the contention of Air 

Traffic Controllers [sic] that their occupation subjects 

them to unusual stress” as evidenced by the incidence of 

symptoms (p. 960).
8 

Evaluation of Evidence for Inherent Stress

To what degree did the scientific data available at the 

time support or justify the conclusion that the controller 

job was inherently stressful? There were five classes of data 

available in 1971 from the studies cited in testimony and 

the other primary sources described above:

• Controller self-reports, anecdotes, and descriptions of 

job-related stress;

• Activity analysis data indicating the fatiguing nature 

of the job;

• Medical disability retirements;

• Self-reported “stress-related” symptoms; and

• Biochemical markers of a stress response.

Self-reports of occupational stress. Clearly, the experience 

of the incumbent controllers reported by the Air Traffic 

Controller Career Committee and in the Congressional 

testimony in 1971 cannot be denied. However, these anecdotes and descriptions were not collected in a systematic 

fashion, with appropriate controls for response bias, exaggeration, and systematic sampling across facilities, shifts, 

and positions. Therefore, while informative, they do not 

constitute scientific data with any great probative value 

on the question of the inherent stress of the occupation. 

Rather, they are suggestive, but not definitive.

Activity analysis data. The primary source for job or 

activity analysis data are the Nagay (1949) and FSF (1958, 

1959) reports. Despite the citation by the 1963 U.S. Air 

Force report as finding evidence for fatigue, Nagay (1949, 

p. 19) hedged the analysis of the observed differences in 

activities across shifts: “Whether the difference is also 

partly the result of fatigue, of errors due to sampling or 

some other factor not readily discernible is not known.” 

Moreover, his report did not speak to any differences in 

activities or fatigue as a function of age.

The 1958 and 1959 FSF studies of controllers and 

their working conditions are another primary source for 

evidence of the fatiguing nature of the controller job. 

More than 4,000 controllers responded to the survey of 

job-related factors conducted by FSF. However, the FSF 

report did not analyze the activity or survey data with 

respect to controller age. Nor were any conclusions about 

the relative vulnerability of older controllers to the effects 

of fatigue presented. The only reference to age was in the 

recommendations of the first report to conduct further 

research on “aging and its relationship to proficiency” 

(p. 87). Overall, the FSF reports presented some data 

to indicate that the controller job was, unsurprisingly, 

demanding and tiring. The second FSF report made the 

argument that the fatigue was psychological in nature, 

rather than physical, but did so on the basis of a logical 

chain of reasoning rather than on the basis of empirical 

data. Neither report presented data about fatigue and 

age or the cumulative effects of fatigue with reference to 

older controllers.

Medical disability retirements. The two sources of information about medical disability retirements are the Fitts 

(1951) report and the report of the Air Traffic Controller 

Career Committee (1970). The probative value of the 

reports depends, in part, on acceptance of the assumption 

that reported disability retirements can be attributed to 

stress-related disorders rather than to disabilities resulting 

from accidents or disease.

Considering that just 3 out of 60 respondents mentioned disability, overall, the Fitts (1951) report does not 

provide substantive empirical or scientific data indicating 

that controllers took disability retirement as a consequence 

of job stress at a greater rate than any other group. In fact, 

no comparisons were made. Moreover, the report does not 

consider the diagnoses underlying the “semi-retirement” 

cited by the three controllers. Overall, the Fitts report has 

little probative value in justifying the argument that job 

stress results in early disability retirement for controllers 

at a greater rate than would be expected for the general 

population.

The Air Traffic Controller Career Committee report 

(1970) also implicitly linked disability retirements and 

stress by placing the analysis of retirements in an appendix with the words “occupational stress” in the title. In 

addition to accepting the assumption that all disability 

retirements were a consequence of job-related stress rather 

than accident or disease, the Air Traffic Controller Career Committee analysis depended on a comparison of 

percentages without knowing the underlying numbers 

involved. Specifically, the Career Committee asserted that 

the rate of disability retirement for controllers less than 

age 45 was disproportionate to their representation in 

the workforce (Appendix XVII, p. 3). That is, 67% of 

medical disability retirements between 1967 and 1969 

were for controllers less than age 45, compared with 

their overall 45% representation in the FAA workforce 

in 1970. This comparison, however, is somewhat misleading for two reasons. First, the appropriate comparison 

was not to the percentage of the overall FAA workforce 

represented by controllers (45%) but to the percentage 

of the overall FAA workforce under age 45. Second, the 

apparent difference (45% of the overall FAA workforce, 

67% of medical disability retirements for employees age 

45 and under) may or may not be statistically significant. 

The actual numbers of persons in each category – controllers under age 45, medically retired controllers under 

age 45, FAA employees under age 45, medically retired 

non-controllers under age 45 – are needed to determine 
9

if the proportions were significantly different. So, again, 

while informative, the medical disability retirements data 

are suggestive but they are not definitive.

Self-reported “stress-related” symptoms. The assumption 

underlying the OAM studies of self-reported symptoms 

was that overt symptoms such as headache and tenseness 

were induced by the job. The credibility of those studies 

depends upon acceptance of that assumption. However, 

alternative explanations are possible, including eye-strain 

due to poor illumination and poor equipment design, as 

documented in the Fitts (1951) review and the 1959 FSF 

study of the controller working environment. Another 

explanation for overt symptoms might be undiagnosed 

or unreported underlying medical conditions.

Moreover, there are several problems with the analyses reported by Hauty et al. even within the limits of 

statistical techniques available in the mid-1960s. First, 

Hauty et al. did not compare the incidence rate for a 

given symptom with its base rate of occurrence in the 

general population. It may be the case that the prevalence 

rate for controllers for any given symptom is no greater 

(or less) than the “natural” prevalence rate; Hauty et al. 

simply did not make the comparisons. The second major 

problem is the lack of appropriate statistical analyses in 

the comparison of symptom prevalence rates by age and 

experience groupings, particularly in view of the relatively 

fewer older controllers. Third, Hauty et al. did not compare the symptom prevalence rate for controllers with the 

prevalence rate in other shift workers. Fourth, Hauty et al. 

assumed that the symptoms were stress-related, and made 

no assessment of the baseline health of the participants. As 

a consequence, it is not clear to what degree the incidence 

of a given symptom – say headache – was a function of 

underlying pathology such as essential hypertension or 

of exposure to the job. These methodological problems 

reduce the probative value of the Hauty et al. studies as 

evidence of the inherent stress associated with air traffic 

control. In short, the studies by Hauty et al. are descriptive in nature rather than inferential.

The Dougherty et al. study provided at least some 

measure of control for the base rate of symptoms by 

comparing the symptom incidence rate for controllers 

with the rate for non-controllers in the FAA. It also used 

inferential statistics for comparisons of controllers with 

non-controllers. However, the Dougherty et al. study is 

vulnerable to the same criticisms made of the Hauty et 

al. studies. The Dougherty et al. work appears to assume, 

as did Hauty, that overt symptoms were “stress-related.” 

While statistical comparisons were made between FAA 

employee groups (e.g., ATCS and non-ATCS), no comparisons of incidence rates to rates observed in the general 

population were presented. Moreover, the reference group 

(non-ATCS FAA and CAA employees) for comparisons 

did not include employees working rotating shifts similar 

to those of controllers. Persons working shifts generally 

have higher prevalence rates of digestive and cardiovascular complaints than persons working traditional day 

shifts only (Smith, Folkard, & Fuller, 2003). The apparent higher rate for symptoms, therefore, may have been 

confounded with shiftwork. Overall the Dougherty et 

al. study is not entirely persuasive as evidence that the 

controller job is inherently stressful.

Biochemical indicators of stress. The last class of scientific 

evidence available in 1971 consisted of analyses of biochemical and physiologic measures taken on controllers 

working at Chicago O’Hare tower. Overall, the biochemical evidence presented by Melton et al. (1971) and Hale et 

al. (1971) clearly indicated that the work of an air traffic 

controller had physical consequences in terms of arousal 

of the adreno-medullary and sympathetic nervous systems. 

For example, higher heart rates were recorded during 

evening shifts with as many as 200 operations per hour 

than on morning shifts with as few as 25 operations per 

hour. At the time, elevations in specific hormones, heart 

rate, and other physiological indicators were interpreted 

as evidence of a stress response. Carefully collected and 

analyzed, these data are the most persuasive in supporting 

the conclusion that the work of an air traffic controller 

was inherently stressful.

Loss of Proficiency With Age

Testimony 

Francke’s influential testimony takes up the theme that 

controllers lose proficiency with age by citing a 1967 Office of Aviation Medicine study (Cobb, 1967). Francke 

characterized the study as finding that “job performance 

generally tended to increase up to age 41, and up to 

11 years of experience, and then steadily deteriorated” 

(Hearings, p. 100). 

Continuing the theme of age and performance, Francke 

cites “another” FAA study reporting that 40% of controllers age 40 and over were rated as unsatisfactory or 

barely acceptable while only 11% of those between ages 

26 and 30 were rated in the same way. The cited study 

also reported that failure rates in training increased from 

a low of 19% for ages 20 to 25 to 86% of trainees age 

45 or over.

Evidence for Loss of Proficiency with Age

A primary thrust of testimony offered in 1971 and 1972 

was that air traffic control was “a young man’s game.” This 

theme had been sounded repeatedly through the years. 

For example, the National Research Council Committee 

on Aviation Psychology (Fitts, 1951) reported that:
10 

Most traffic controllers today believe that their jobs 

can be done only by fairly young men. Many controllers told us that fifteen years is considered to be a long 

time to work as a traffic controller (p. 10).

The scientific foundation for this perception was a series 

of studies conducted by Bart B. Cobb, David K. Trites, 

and colleagues at the Civil Aeromedical Research Institute 

(CARI). The principal focus of the research conducted 

by Cobb and Trites was on the selection of air traffic 

controllers. Cobb, Trites, and colleagues investigated the 

validity of aptitude tests as predictors of ATCS training 

outcomes and job performance. In addition, they also 

investigated other individual or biographical characteristics such as background, previous experience, and age. 

Prior to passage of P.L. 92-297, there was no maximum 

age at entry restriction for the ATCS occupation. As a 

consequence, applicants as old as about age 45 entered 

into ATCS training throughout the 1960s.

In the first study, Trites (1961) obtained job performance evaluations made by supervisors of 149 controllers 

initially trained in 1956. Trites reported a correlation 

of rxy = -.23 (N = 149, p < .01) between age and average supervisor rating. From this, he inferred that older 

trainees were not as likely as younger classmates to be 

considered by supervisors as being among the better 

controllers. Another study in 1962 (Trites & Cobb) 

specifically focused on the relationship of age with 

training and job performance. In five samples of ATCS 

trainees, the correlation between age and a composite 

of academic and laboratory grades in training was rxy = 

-.38 for 126 trainees from 1960, and rxy = -.31 for 183 

trainings from 1961. The researchers pooled the data 

from 319 trainees in 10 en route and 7 terminal classes 

conducted in 1960 and 1961, and examined job-related 

outcomes. Of the 41 persons in the 39-45 age bracket, 

48% (or 20) failed ATCS training at some point. Just 

15% of these older controllers were considered “satisfactory,” compared to 55% of 181 persons in the 21-26 

age bracket (Figure 7, p. 9). Trites and Cobb concluded 

that there was “no doubt” that training failures could be 

reduced by specifying a maximum age for entry into air 

traffic controller training. They also recommended, on 

the basis of their analysis, that an upper age limit (for 

retention) be established as well (p. 10).

Trites continued this line of work with a 1965 study investigating the interaction of age at entry with intellectual 

and personality characteristics. A large number of aptitude 

and personality tests were administered to more than 900 

en route and terminal trainees ranging in age from 21 to 

about 46. The age distribution was bi-modal, with the 

first peak in the mid-20s and a second, but much lower 

peak around 40. Based on a correlational analysis, Trites 

reported that (a) older trainees had lower test scores on 

measures of immediate memory and non-verbal abstract 

reasoning, (b) older trainees scored higher on arithmetic 

and verbal ability than younger trainees, and (c) older 

trainees did less well on speeded tests. Trites attributed 

the higher failure rate among older trainees, in part, to 

“inferior aptitudes for non-verbal abstract reasoning, 

memory for new material, and by the inability to work 

as rapidly and accurately as required in training and on 

the job” (Trites, 1965, p. 1193).

Francke cited Cobb’s 1967 study of age and job performance in particular as justifying a maximum retention 

age. In that study, supervisory performance ratings on a 

total of 568 en route controllers were collected at four 

air route traffic control centers (ARTCCs) at least five 

years after entry into the ATCS occupation. Correlations 

of chronological age at the time of rating with various 

alternative combinations of supervisory ratings ranged 

from rxy = -.14 (N = 525) to -.19 (N = 568). The ratings 

were uncorrelated with “experience,” defined as length of 

service as an ATCS (5 to 11 years); length of experience 

was correlated (rxy = .45, N = 568) with chronological age. 

As 75% of the subjects were between 28 and 35 years, 

Cobb conducted an analysis of variance (ANOVA) of 

performance ratings by age. Five age and five experience 

groups were used. Overall, Cobb found that the mean 

performance rating declined from youngest to oldest. 

He reported that the mean performance ratings for the 

two oldest groups (41-45, 46 and over) were significantly 

lower than the ratings for the two youngest groups (ages 

30 or less, 31-35). However, due to sparseness of data for 

some of the age-experience combinations, Cobb could 

not formally examine the statistical interaction of age and 

experience. However, he did present a graphical analysis 

contrasting the mean performance ratings for controllers age 41 and older, versus those for controllers age 40 

and under, by experience. He found younger controllers consistently had higher mean performance ratings 

than older controllers across all experience groupings. 

He concluded that job performance ratings tended to 

improve with length of ATC experience for journeyman controllers younger than age 41 but not for older 

controllers. In discussing these results, Cobb pointed out 

their consistency with previous research indicating that 

the older a person was at entry into the occupation, the 

more likely he or she was to separate, change occupations, 

or be rated less satisfactorily. Cobb noted that additional 

research into the reasons why older controllers received 

lower ratings was required. Moreover, he plainly said 

that, on one hand, it was “possible that the ratings have 

been biased by attitudes regarding age” but that on the 

other hand older controllers may have simply been less 

proficient than younger controllers (p. 9).
11

Evaluation of Evidence for Loss of Proficiency with Age

Overall, the objective evidence available in 1971 spoke 

more to the difficulty of acquiring proficiency with age 

than to the loss of proficiency with age. The studies by 

Trites and Cobb clearly demonstrated that older trainees 

were less likely to be successful than younger persons. The 

studies of job performance are less compelling for two 

reasons. First, the studies relied solely upon subjective, 

global assessments of job performance, rather than objective measures of core technical performance. As noted by 

Cobb (1967, 1968), such subjective ratings are vulnerable to biases. Second, the studies of job performance 

are cross-sectional in design, not longitudinal. In each 

case, a measure of job performance was obtained at a 

single point in time. The traditional correlational and 

regression analyses, by definition, modeled the effects 

of the predictors (age, aptitude, other biographical factors) on the mean criterion score. These analyses did not 

investigate within-individual change (in performance) 

over time. As a result, these studies do not provide any 

evidence about at what particular age, if any, controllers begin to lose proficiency. Overall, these studies are 

not persuasive in making the case that controllers lose 

proficiency with age.

ATCS Medical Retirements

Testimony

Testimony presented in 1971 also suggested that controllers took medical retirement at an earlier age than 

“average agency employees.” For example, the Federal 

Air Surgeon testified that between 1966 and 1970, there 

were 538 medical retirements of controllers in towers, 

centers, and stations (Hearings, p. 11). The medical retirements data, as presented in the written testimony of 

the President of the National Association of Air Traffic 

Specialists (NAATS), is reproduced in Table 1.

The medical specialist for PATCO testified in the same 

1971 hearing that there were 65 cases of journeyman 

controllers in their 30s and early 40s in Chicago that 

applied for (mostly temporary) disability, blaming tension, physical, and mental problems of the job. The 1970 

Air Traffic Controller Career Committee report was cited 

by the President of the National Association of Government Employees (NAGE) in his 1971 testimony before 

Congress in support of the perception that controllers 

were younger than average at medical retirement:

3. The average age at which disability retirements are made 

[are] lower for air traffic controllers than for all other FAA 

personnel. For example, of those under age fifty, retiring 

for disability, fifty-four percent are controllers; forty-five 

percent are other; between the ages of twenty and forty-four, 

sixty-seven percent are controllers, while only thirty-three 

percent are other (and here the report notes that controllers approximate forty-five percent of the total FAA work 

force).

4. Nervous and psychological reasons accounted for thirtyeight percent of the controller disability retirements during 

FY67-69, compared to only twenty percent for other FAA 

employees (Hearings, p. 77).

Evidence for Medical Retirements

Aside from the data offered at testimony and the data 

presented in the 1970 Air Traffic Controller Career Committee report, there do not appear to have been any published systematic studies of medical retirements available 

in 1971. Nor were data from annual controller medical 

examinations analyzed to determine the prevalence or 

incidence rates for disabling, chronic, or stress-related 

disorders and diseases.

Evaluation of Evidence for Medical Retirements

The essential argument made in 1971 on the basis 

of medical retirements data presented in testimony and 

in the Air Traffic Controller Career Committee report 

were that (a) disability retirements were a consequence 

of job-related stress, and (b) younger controllers made 

up a disproportionate number of medical retirements 

compared with their representation in the workforce. But 

as noted in the previous discussion of Fitts (1951) and 

the Air Traffic Controller Career Committee report, the 

comparisons offered in testimony and in these reports were 

misleading. First, disability retirements may have resulted 

from injury, accident, and chronic diseases unrelated to 

stress; it was misleading to assume that all disability retirements were stress-related. Second, the raw percentages 

themselves were uninformative without knowing the 

actual numbers of persons involved. Therefore, while 

informative, the medical disability retirements data were 

suggestive but were not definitive.

Evidence Available After 1971

Substantial research has been conducted on the ATCS 

and other occupations since passage of P.L. 92-297. 

Moreover, there have been significant advances in the 

understanding of the etiology of hypertensive and other 

cardiovascular disorders. Models of job-related stress, and 

their linkage to health outcomes, have also been transformed through research. For example, stress is no longer 

conceptualized as an entirely negative factor (Nelson & 

Simmons, 2003). Finally, the significant role of genetics, 

personality, and lifestyle choices such as cigarette smoking 

and individual differences such as weight in disease etiology have been highlighted. The purpose of this section 

is to summarize relevant research conducted since 1971 

with respect to the three principal themes underlying the 
12 

“ATCS Age 56 Law”: (a) inherent occupational stress; 

(b) medical conditions and retirements; and (c) loss of 

proficiency with age.

Inherent Occupational Stress

Research on physiological or biochemical markers of 

air traffic controllers continued throughout the 1970s, 

resulting in multiple OAM technical reports. C. E Melton 

summarized the ten-years of research on physiological 

stress in controllers in an OAM technical report published 

in 1982. In setting the stage, Melton noted that the 1956 

mid-air collision over the Grand Canyon aroused substantial concern about the “crowded sky.” These concerns 

increased in the late 1950s by the introduction of jet 

airliners and questions about the adequacy of the ATC 

system to provide safe separation for aircraft flying at 

higher altitudes and ever greater speeds. Controllers felt 

under intense pressure and complained of task overload 

and excessive responsibility. The word “stress” began to 

be more and more closely and frequently associated in 

the public’s mind with air traffic control. In response, 

the FAA developed a two-pronged research program. 

The first line of research focused on the assessment and 

quantification of stress among controllers. The second 

line of research focused on the assessment of changes 

in controller health over time as a consequence of the 

work. Essentially, the two lines of research addressed 

the questions, “How much stress do controllers experience?” and “What are the consequences of that stress on 

controller health?”

How Much Stress

Over the period 1968 through 1978, CAMI conducted 

a series of multidisciplinary studies to investigate the 

physiological, biochemical and psychological changes 

associated with the job of the air traffic controller. The 

overall pattern for the research was similar for each study. 

Controllers at selected air traffic control facilities were 

asked to volunteer to participate in a research study that 

would last for up to 10 days. Controllers were assessed 

in these studies with a varied battery of physiological, 

biochemical, and psychological measures including heart 

rate, galvanic skin response, urinalysis, blood chemistry, 

personality, anxiety, and job attitudes. Overall, the CAMI 

research team conducted 22 field studies at air traffic 

control facilities and 2 laboratory studies. A total of 402 

controllers were evaluated during the research across a 

spectrum of facility types, levels, and workload. Based on 

the evidence accumulated in numerous studies, Melton 

(1982) concluded with respect to the physiological and 

biochemical measures that controllers were not subject 

to excessive or unusual stress (p. 46-47):

It should not be inferred from these within-group 

studies that excessive or unusual levels of stress were 

present in the ATC work force. Studies of non-ATC 

populations in which exactly comparable measurements 

were made are almost nonexistent. However, Hale et 

al. compared O’Hare ATCS’s [sic] (the ATCS’s who 

showed the most stress) with various groups previously studied at the U.S. Air Force School of Aerospace Medicine. They found that ORD ATCS’s did 

not uniformly show greater stress levels than did Air 

Force aircrews, men undergoing altitude chamber 

tests, or laboratory scientists off duty at home (citation omitted). Smith et al., using an anxiety inventory, 

showed that psychological measures remained relatively 

uniform across facilities and suggested that air traffic 

work, no matter what the nature of the facility, had 

no dramatic impact on the psychological states of the 

controllers. Thus, it is clearly inappropriate from the 

psychological perspective to describe ATC work, as is 

commonly done in the popular press, as an unusually 

stressful occupation. Popularized accounts of controller 

stress deal with the exceptional rather than the typical 

controller or facility. Further, such accounts tend to 

assume that physiological and psychological changes 

associated with simple workload effects are undesirable 

and invariably have long-term negative consequences. 

That assumption is highly questionable, particularly in 

view of the expressed preference of ATCS’s for heavy as 

opposed to light workloads (reference omitted).

Moreover, results from the administration of the StateTrait Anxiety Inventory (STAI), a well-established measure 

of anxiety, to controllers at these facilities revealed that 

controllers in general reported lower levels of state and 

trait anxiety than individuals in other occupations. State 

anxiety scores increased significantly from the start to 

the close of a shift schedule, much like they did in other 

occupational groups. They also noted that the increase in 

state anxiety was greater for difficult than for easy shifts. 

Further support for the lower anxiety levels in controllers is found in the Rose, Jenkins, and Hurst (1978) 

study (discussed below) where 80% of the controllers 

involved in the longitudinal study evidenced scores on 

the Tension/Anxiety Scale of the Profile of Mood States 

that were over a standard deviation below the mean for 

college students. Likewise, in a study involving 22 different occupations, Caplan et al. (1975) found that the 

average anxiety and depression scores for two groups of 

controllers from a facility in the Midwest were near the 

middle of the 22 occupational groups. In conclusion, 

Smith and colleagues, using the STAI and other attitudinal 

measures, also found “... little evidence to support the 

notion that ATCSs are engaged in an unusually stressful 
13

occupation. This is not to say that ATCSs never encounter 

unusual stress on the job; however, it does appear that 

this is the exception rather than the rule. ATCSs appear 

both well qualified and well suited for air traffic control 

work” (Smith, 1985, pg. 106-7).

Smith (1980) summarized a decade of research on 

controllers, stress, and anxiety by noting that controllers, on average, have lower trait anxiety scores than the 

normal adult population. Moreover, state anxiety scores 

increased from the beginning to the end of work shifts 

for controllers just as they did in non-ATC jobs such as 

engineers. He concluded that controllers were “well within 

normal limits on every indicator of psychological states” 

and appeared to experience less anxiety than is average in 

other work settings. More recently, Collins, Schroeder, 

and Nye (1991) investigated psychological measures of 

anxiety and found that individuals who entered the FAA 

Academy screen program and moved on to become successful certified professional controllers reported lower 

levels of state and trait anxiety than those who were unsuccessful. The levels of state and trait anxiety were also 

lower than that of the average college student. Data from 

the 16PF also supports the view that individuals entering 

the profession are generally less anxious and tense than 

individuals in general (Schroeder & Dollar, 1997).

Other research focused on identifying and quantifying stress as a function of shiftwork and fatigue. From 

the beginning, shiftwork and fatigue have been cited as 

sources of controller stress. For example, Hauty, Trites, and 

Berkley (1965c) investigated self-reported, stress-related 

symptoms as a function of shifts. They found that controllers reported a higher incidence of symptoms when there 

were less than 8 hours between successive shifts. However, 

the study did not compare the symptom incidence rate for 

controllers with that of other shift workers. In the 1970s, 

CAMI researchers investigated changes in physiological 

and biochemical measures after the introduction of the 

counter-clockwise rapidly rotating 2-2-1 shift pattern in 

1973 (Melton et al., 1973). They found no significant 

differences on the physiological measures between the 

shift patterns (straight 5-day and 2-2-1). Moreover, they 

found that the stress measures did not vary greatly from 

those found in the general population. More recently, in 

a field study, Cruz and Della Rocco (1995) compared the 

sleep quantity and quality for controllers on the 2-2-1 

pattern with those of controllers on a 2-1-2 variation. 

They observed a characteristic decline in sleep quantity 

through both rotations from about 8 hours to less than 

3 hours before the midnight shift. They also reported no 

significant differences between shift patterns with respect 

to sleep quality or sleepiness. A laboratory study by Della 

Rocco and Cruz (1996) compared sleep quantity and 

quality for two age groups (30-35 and 50-55) on the 

2-2-1 rotation. They reported no significant differences 

by age group. A subsequent study comparing the 2-2-1 

rotation with straight days found significant performance 

decrements on a synthetic work task (the Multiple Task 

Performance Battery) for both age groups on the night 

shift. Schroeder, Rosa, Witt and Banks (1995) examined 

the effects of an alternative work schedule (four 10-hour 

shifts) with the more common 2-2-1 rotation. In their 

field study, they found that performance on the National 

Institute of Occupational Safety and Health fatigue test 

battery did not differ by shift pattern with the exception 

of the single midnight shift on the 2-2-1 schedule. Lower 

performance was observed on the fatigue test battery in 

the early morning hours at the end of the midnight shift. 

Controllers on the four 10-hour shifts did not work a 

midnight shift.

Most recently, CAMI conducted a large-scale surveybased study of controller shiftwork and fatigue in response 

to a 1999 Congressional directive (Ramos, McCloy & 

Burnfield, 2001). Occupational stress was assessed in the 

survey with a single, but straightforward, question: “In 

general, how stressed do you feel at work?” with responses 

on a 5-point Likert scale ranging from “Not at All” to 

“Extremely.” This item has been used for several years as 

part of a nationwide telephone survey of the American 

workforce conducted by the Harris Interactive (the Harris 

Poll), thus allowing responses from air traffic controllers 

to be compared to a statistically representative sample 

of U.S. employees. The responses of terminal and en 

route Certified Professional Controllers (CPCs) and 

Flight Service Station controllers (FSS) are illustrated 

in Figure 1.

On one hand, just 3% of CPCs and FSS controllers 

indicated that they felt “Extremely” stressed at work, compared with 6 to 8% of the national sample of employees. 

On the other hand, comparable percentages of controllers 

and employees indicated feeling some stress. About 52 to 

55% of the national sample and the controllers indicated 

feeling “Extremely,” “Somewhat” or “Quite a Bit” of stress 

at work. The proportion of FSS controllers indicating 

feeling “Somewhat” to “Extremely” stressed at work was 

slightly lower (46%). In other words, controllers appear 

to feel about as stressed at work as representative national 

samples of U.S. employees. The results also indicate that 

smaller percentage of controllers reported that they were 

“Not at all” stressed at work than the national sample 

of employees.

Responses to the stress question are broken out by 

age for terminal and en route controllers in Figure 2 and 

for FSS controllers in Figure 3. The percentage of CPCs 

who said they felt that their work was “Somewhat” to 

“Extremely” stressful increased from around 42% at age 

26-30 to nearly 60% at ages 41- 45, after which there 
14 

was a gradual decline to a little over 40% for those in 

the 56-60 age category. Age-related changes in the FSS 

respondents was not as clear cut as for CPCs and may peak 

at an earlier age. However, there was a general decline in 

the last two age categories. These differences may be, in 

part, because FSS respondents were slightly older than 

their CPC colleagues. These results suggest that there is 

little evidence that the oldest controllers (ages 51 and 

greater) are more stressed than middle-aged controllers.

Controllers were also asked in the survey about the 

degree to which they experienced chronic fatigue and 

symptoms often linked to fatigue and/or stress. There 

did not appear to be any increase in chronic fatigue or 

gastrointestinal and cardiopulmonary symptoms among 

older controllers (over age 50). Older controllers in this 

sample reported lower levels of chronic fatigue than 

middle-aged controllers. This may be attributable, in 

part, to the greater flexibility in shift rotation schedules 

for older controllers as a consequence of their seniority. 

It is also possible that individuals with poorer health and 

other medical problems may have been screened out by 

the annual medical examinations or may have retired.

The Consequences of Stress

Health changes. While Melton and colleagues were 

conducting field and laboratory studies in the mid-1970s, 

the Boston University School of Medicine was conducting, under contract to the FAA, a “prospective study to 

determine the kinds and degrees of health changes occurring in air traffic controllers and the extent to which 

these health changes might be predicted by other factors” 

(Rose, Jenkins, & Hurst, 1978). Beginning in 1973, the 

five year longitudinal “Controller Health Change” study 

was designed to gather psychological, physiological, and 

organizational data from controllers at two en route centers, a major terminal, and the common IFR room in 

the eastern U.S.

Earlier research by Dougherty, Trites, and Dille (1965) 

and Hauty, Trites, and Berkley (1965a,b) revealed a higher 

incidence of gastrointestinal disorders and hypertension. 

In an investigation involving 22 occupations (including 

controllers at a large and a small facility) Caplan et al. 

(1975) found that controllers expressed more somatic 

complaints than employees in most of the other occupations; however, the average blood pressures and heart 

rates for the two groups of controllers were comparable 

to averages noted in the other occupational groups.

A total of 416 controllers participated in the Controller 

Health Change study. Only 5% of the initial group were 

not available for the final testing session. The results were 

complex and contradictory. Overall, Rose, Jenkins, and 

Hurst (1978) reported that: 

(a) Stress, as evident in the physiological and behavioral 

measurements, was most likely to occur in individuals who 

were more vulnerable;

(b) Air traffic control work, per se, was not the sole factor 

associated with the appearance of a stress response in some 

controllers, with job dissatisfaction and other organizational 

factors contributing significantly to the emergence of individual health changes, burnout, and other physiological 

problems;

(c) There was a higher incidence of hypertension and ulcers 

in this group of controllers than in the general population; 

and

(d) Controllers, in general, were heavier drinkers than the 

general population.

These researchers initially concluded that:

...the relationships that were found between our 

selected indicators of stress and some few outcomes 

may implicate work difficulty as having some partial 

role, when combined with other biological and psychological factors, toward ultimate illness. Specifically, 

the physiological measures at work did significantly 

predict hypertension and mild and moderate illness 

(p. 626).

In other words, with some caveats, the Controller 

Health Change study can be interpreted as providing some 

support for the hypothesis that the “stressful” nature of 

the controller’s work resulted in adverse health outcomes. 

However, in a subsequent report, they demonstrated that 

hypertension was most closely linked with obesity and 

alcohol intake (DeFrank, Jenkins, & Rose, 1987).

Controller morbidity. Other studies conducted at about 

the same time also cast doubt on the hypothesis that the 

stress of the job and shiftwork resulted in adverse health 

consequences for controllers. For example, in an assessment of hypertensive diagnoses in some 25,000 air traffic 

controllers, Booze (1978) reported that the incidence rate 

for hypertension was below the expected rate based on 

national averages. In a follow-on analysis of aeromedical 

certification data, Booze and Simcox (1984) compared 

the distribution of blood pressure by age for all airmen, 

airline pilots, and a sample of air traffic controllers who 

were pilots. The prevalence of borderline and definite 

hypertension increased with age for all groups studied. 

Overall, the prevalence of hypertension was lowest in airline pilots and highest among controllers. However, when 

compared to other national databases, air traffic controllers 

had a lower prevalence rate for definite hypertension and 

a comparable level for borderline hypertension. Booze 

and Simox cautioned that differences between airmen 

and controllers could be attributed to the more liberal 

waiver and retention criteria for controllers.
15

In a 1978 report, Booze analyzed the morbidity 

experience of 28,086 ATCS personnel for the 1967 to 

1977 time period. Once again, the rate of hypertension 

experienced by this group of controllers during the course 

of the study was significantly lower than that of the wellknown Framingham and National Health Survey studies. 

The incidence of cardiovascular disorders was also lower 

than rates reported in other large scale studies. Over age 

50, the incidence of coronary heart disease in controllers 

was lower than that evident in either pilots or reported in 

the Framingham study. Booze also reported that there was 

no association or correlation of disease occurrence with 

length of service and age. Booze concluded that “While 

some isolated trends found in these data are supportive 

of an occupation/disease relationship, they are neither-

-as would be expected if the association were a strong 

one--impressive nor consistent” (p. 1).

Booze (1978, p. 13) also reported that “substantial 

increases were seen for most all diseases” after implementation of P.L. 92-297 with its provisions for retraining 

of controllers in alternative careers at the government’s 

expense. The largest increases were found for neuropsychiatric and cardiovascular disorders. Staten and Umbeck, 

(1982) analyzed the effects of changes in the federal Workers’ Compensation Program requiring identification of a 

specific job-related event precipitating the claimed injury 

and allowance of stress-related claims. They found that 

system error (e.g., operational error) reporting rates increased after the change. In their analysis, they attributed 

the increase to the need for objective evidence linking 

the disability to a stressful event on the job and that, 

perhaps, the financial benefits available under these programs served as incentives for some controllers to report 

stress-related disorders. As a consequence, the overall rates 

for psychological and cardiovascular disorders might have 

been inflated by this reporting bias.

Organizational consequences. The 1978 Controller 

Health Change study reflected the widespread concern in 

the agency and in public opinion about the consequences 

of job-related stress in terms of the individual controller’s 

health. Yet job-related stress may have wider consequences 

for the organization as a whole. For example, job-related 

stress appears to have played a role in the 1981 PATCO 

strike as one of many complaints raised by controllers 

about working conditions, equipment, the job, and 

management. Post-strike investigations conducted by a 

special task force (the “Jones Committee”; see Jones, Bowers, & Fuller, 1982) found that an individual’s decision 

to strike or stay on the job was influenced substantially 

by five major factors, including the frequency of acutely 

stressful episodes or incidents experienced on the job 

and the degree of job burnout felt by the person. Other 

factors included the organizational climate experienced 

in the workplace, the degree of alienation or goal integration felt by the person, and the frequency of equipment 

outages experienced on the job. The Jones Committee 

analyzed survey data from controllers who struck and 

those who remained on the job shortly after the August 

1981 strike. The questionnaire included items focused 

on the frequency of stressful incidents in the past three 

years, recovery time, helpfulness of other employees and 

supervisors/managers, whether the stress associated with 

air traffic control work was chronic/situational/acute 

episodic or a mixture, and the level of burnout in the 

respondents. 

Using a modified version of the burnout index developed by Rose, Jenkins, and Hurst (1978; see Figure 4 

for items), the Jones Committee found 85 (19 working 

and 66 striking) controllers that exceeded their cutoff 

score. The percentage of controllers age 41 and older who 

exceeded the burnout criteria was 21%. For those with 

19 or more years of service, the percentage was much 

higher (69%). Four factors were found to contribute to 

burnout: (a) frequency of occurrence of acutely stressful 

incidents; (b) length of service in the job; (c) perceived lack 

of concern for people by the FAA; and (d) dissatisfaction. 

One consequence of this report was an extensive effort 

to improve the quality of supervision and management 

within the FAA through programs such as the Supervisory 

Identification and Development Program.

To assess progress in addressing issues associated with 

the strike, the FAA initiated a biennial employee survey 

in 1984. In 1986, the content of the employee survey 

was expanded to include items assessing employee perceptions of stress associated with aspects of their work. 

In addition, the modified Burnout Index used by the 

Jones Committee was used to assess burnout among all 

FAA employees. An average score of 3.75 on the Burnout 

Index was established as the criterion for determining 

the percent of the workforce that would be considered 

to be “burned-out.” Responses were received from 63% 

of the FAA workforce.

Overall, just 6.8% of all responding FAA employees 

reached or exceeded the 3.75 criterion, that is, would be 

characterized as possibly experiencing “burnout.” The 

proportion of Air Traffic respondents reaching or exceeding the criterion for “burnout” was 6.5%, compared to 

8.5% of the Airway Facilities and Aeronautical Center 

respondents. A slightly greater proportion of Air Traffic 

manager and supervisors (7.5%) exceeded the criterion 

for “burnout,” compared with 6.6% of the Air Traffic 

specialists. Within the various air traffic control options, 

en route specialists had the highest percentage exceeding 

the criterion (8.1% versus 5.9% for terminal and 5.7% 

for FSS specialists). The 1986 percentages were lower 

than those noted in 1984 (Figure 5). In 1984, 22% of en 
16 

route managers and supervisors exceeded the criterion for 

“burnout,” compared with 9.8% in 1986. The proportion 

of en route specialists exceeding the “burnout” criterion 

in 1984 was 15% compared with 8.1% in 1986.

The 1986 survey also included 14 items that assessed 

potential sources of stress. Respondents indicated how 

often each item had been a source of stress during the past 

six months on a “Never” to “Always” scale. The proportions of respondents marking “Frequently” or “Always” 

for each item were reported, as shown in Figure 6 for all 

respondents (“FAA”) and for non-supervisory ATC employees (“ATC Non-supv”). There are similarities and some 

differences in response patterns of the ATC employees and 

the FAA as a whole that are worth noting. For example, 

less than 20% of both groups (non-supervisory ATC and 

all FAA employees) marked “Unwanted overtime,” “Increased automation,” “Personal concerns,” “Accountable 

for others,” and “Delays in automation” as “Frequently” 

or “Always” sources of stress in the last six months. It is 

somewhat surprising, in view of the complaints about 

equipment inadequacies and mandatory overtime in 

testimony supporting the mandatory retirement age 

and in the complaints preceding the 1981 strike, that 

“delays in automation” and “unwanted overtime” were 

not endorsed as sources of stress by a larger proportion 

of ATC employees. More of the non-supervisory ATC 

employees (27.1%) than all FAA employees (21.5%) 

indicated that “Decisions about safety” was frequently 

or always a source of stress. While one would hope that 

ATC employees are concerned about decisions about 

safety, compared to the FAA as a whole, the proportion 

indicating that the decisions were a source of stress was 

surprisingly low, at just over a quarter of the non-supervisory ATC employees. Even more surprisingly, in view 

of the wide-spread perception of the ATC job as being 

“stressful,” smaller proportions of the non-supervisory 

ATC employees than of all FAA employees indicated that 

factors such as “Extended periods with too much work to 

do,” “Too much work to do in an ordinary day,” “Amount 

of time to meet job demands,” “Amount of resources 

available” were “Frequently” or “Always” sources of stress 

in the last six months. Feelings of being overwhelmed 

with too much to do, not enough time, and of being 

“stretched too thin” are common hallmarks of job-related 

stress. Yet in this instance, less than 25% of non-supervisory ATC employees (presumably, primarily working 

controllers) indicated that these factors were sources of 

stress. However, “Opportunity for advancement” and 

“Supervisory/management practices” were “Frequently” 

or “Always” sources of stress for non-supervisory ATC 

employees (42.7% and 48.6% respectively). In contrast, 

the proportions of all FAA employees indicated “Opportunity for advancement” and “Supervisory/management 

practices” as sources of stress were slightly lower (38.6% 

and 44.2%). These two factors represent more about the 

organizational culture and climate in which the work of 

controlling is done than the inherent nature of the work 

itself. Finally, the proportion of controllers indicating that 

“Federal issues” such as pay and retirement were a source 

of stress (47.7%) was slightly less than the proportion 

of all FAA employees indicating the topic as a source of 

frequent stress (51.3%). 

It is surprising that those factors reflecting the nature 

of the work itself (such as decisions about safety, the 

complexity of the job, and the amount of work) appear 

not to have been major sources of job-related stress for 

the majority of controllers in 1986. Moreover, factors 

reflecting the conditions under which the work was performed (e.g., unwanted overtime, time to meet the job 

demands, and resources to do the work) also seem not to 

have been major sources of stress for the non-supervisory 

ATC employees. Taken together, these survey data tend 

to undercut the hypothesis underlying the mandatory 

retirement age that controllers are subject to extraordinary 

stress and strain.

SUMMARY

Overall, the results of scientific research since 1971 

designed to quantify the stress purportedly experienced 

by controllers and to assess the impact or consequences of 

that stress on controller health do not support the popular 

image of the ATCS occupation as being among the most 

stressful in the U.S. Nor do the results strongly support the 

perception that, as a consequence of the job, controllers 

experience adverse health consequences at a higher rate 

than might be expected in the general population.

Disability Retirements

The second major class of data cited in support of the 

“ATCS Age 56 Law” was disability retirements. In this 

section of the review, data on disability retirements among 

controllers for the period FY1997 through 2003 will be 

analyzed to determine to what extent the “ATCS Age 56 

Law” is still supported by this line of evidence.

Data

As part of continuing research in support of human 

capital management for Air Traffic Services, CAMI 

receives quarterly extracts of personnel actions and 

on-board data from the FAA Consolidated Personnel 

Management Information System (CPMIS). A Notice of 

Action (NOA) is generated for each personnel action for 

an employee, such as hiring, promotion, pay change, and 

retirement, and recorded in CPMIS. For this analysis, all 

NOAs for disability retirement (code = 301) generated 
17

between October 1, 1996 and September 30, 2003 for 

controllers and non-controllers were analyzed in relation 

to on-board staffing numbers at the end of each fiscal 

year. In keeping with the 1971 testimony, retirees and 

employees were grouped into two age groups: age 44 and 

younger; age 45 and older.

Analysis

The testimony in 1971 was that the proportion of 

disability retirements represented by controllers under 

age 45 was disproportionate to their representation in 

the FAA workforce. To test this hypothesis, we compared the proportion of disability retirements that were 

for controllers under age 45 with the proportion of FAA 

employees less than age 45 (e.g., “younger controllers”) in 

each fiscal year 1997 through 2003 using a conventional 

Z-test of proportions.

Results

The results of the analysis are presented in Table 2. 

In FY1997, there were 108 disability retirements, 40 of 

which were for controllers less than age 45. “Younger” 

controllers accounted for 37% of all disability retirements 

from the FAA in FY1997. There were 16,407 controllers on-board in FY1997 less than age 45, representing 

33% of all FAA employees. As shown in the table, these 

two proportions – 37% of disability retirements, 33% 

of all employees – were not significantly different. That 

is, the proportion of disability retirements represented 

by “younger” controllers was about the same as their 

representation in the FAA workforce in FY1997. The 

same pattern of results was obtained for each fiscal year 

through FY2003 – the proportion of disability retirements 

represented by “younger” controllers was about the same 

as their representation in the workforce. Note also that 

the proportion of FAA employees who were “younger” 

controllers declined from .33 in FY1997 to .25 in FY2003, 

and the proportion of disability retirements represented 

by “younger” controllers also declined.

Conclusion

In contrast to the testimony of 1971, younger controllers do not seem to be taking disability retirement in 

numbers disproportionate to their representation in the 

workforce. Therefore, current disability retirement data 

do not support the assertions made in 1971 to justify 

mandatory retirement at age 56.

Age and Performance

The third major class of evidence supporting the “ATCS 

Age 56 Law” was the argument that controller proficiency 

declined with age. The purpose of this section is to review 

more recent studies of controller performance and age 

and to summarize research that might be relevant.

Training Outcomes

Recent studies of the post-strike generation of controllers, in general, find the same association between chronological age at entry into the occupation and performance 

in initial and subsequent field training as found in the 

older scientific research literature. For example, Collins, 

Nye, and Manning (1990) found a negative correlation 

(-.31) between age and performance in the FAA Academy 

ATCS Nonradar Screen. Schroeder, Broach, and Farmer 

(1998) analyzed the relationships of age to outcomes such 

as training for the post-strike generation of controllers. 

They found that the older a new controller was at the 

time of entry into the occupation, the more likely he or 

she was to attrite from training either at the Academy 

or in the field. However, as noted before, these studies 

do not directly speak to the issue of age and on-the-job 

performance.

Operational Errors

Broach (1999) investigated the relationship of age to 

involvement in en route operational errors based on data 

for 3,724 controllers for the period 1991 through 1995. 

The prevalence rate for errors was computed as the ratio 

of the total number of errors for controllers of a given 

age group to the total number of controllers in that age 

group, as measures of exposure (e.g., hours worked on 

position) were not available. There was a curvilinear 

relationship between age and the error prevalence rate 

(Figure 7) and some evidence that experience moderated 

the relationship. However, the study was not definitive 

due to the lack of an appropriate measure of exposure or 

controls for workload and sector characteristics.

Job Performance

Heil (1999) investigated the relationship of age to a 

measure of core technical job performance in the en route 

environment. The data were collected in the course of 

validating a computerized controller selection test battery. 

Overall, data were available for 838 incumbent CPCs. 

Almost half (391, or 47.6%) were between the ages of 32 

and 37; there were 89 CPCs age 44 and greater (10.9%). 

The criterion measures were peer and supervisor rating 

scales and a computer-based assessment of core technical job skills in the en route environment known as the 

Computer-based Performance Measure (CBPM; Hanson 

et al., 1999). The peer and supervisor ratings consisted of 

behavior-based scales for 10 dimensions and an overall 

effectiveness scale. The CBPM was a 38-item, 2-hour 

assessment in which controllers were presented with a 
18 

series of realistic air traffic scenarios and several multiple 

choice questions about each scenario.

Heil (1999) found a curvilinear relationship between 

current age (at the time of data collection) and the 

scores on the CBPM. However, the relationship was 

very modest (R2 = .04, p < .01). Comparisons by age 

group also suggested differences in performance by age, 

with controllers age 50 and greater earning lower scores 

on the CBPM than controllers in the other age groups. 

Overall, mean CBPM scores increased with age, reaching their highest for controllers between ages 38 to 43. 

CBPM scores then declined, dropping significantly for 

controllers age 50 and older. The ratings data followed 

a similar pattern. Heil concluded that, when viewed as a 

group, older controllers were found to have lower levels 

of performance. However, as with the previous studies 

by Trites and Cobb, the Heil study is cross-sectional in 

design and does not address change within an individual. 

He recommended that longitudinal studies of age and 

performance be conducted to better understand the ageperformance relationship.

Changes in Cognitive Abilities

Interpretation of the studies comparing the performance of younger with middle age and older workers is 

complicated by some of the issues raised regarding the 

use of cross-sectional research. Younger cohorts are more 

likely than older cohorts to have a higher overall level of 

education and greater experience with computers and 

other new technologies. In addition, the composition of 

the workforce changes as employees age. Some productive 

and involved employees may have been selected to become 

managers. Less productive employees may have moved 

on to other jobs or they may have been dismissed. Thus, 

additional selective processes may complicate interpretation of any age-related changes in performance.

Substantial research has been conducted on changes 

in cognitive abilities with age. There are three substantive findings relevant to age 56: (1) speed of central 

processing declines with age; (2) sensory and perceptual 

abilities decline with age; and (3) variability in cognitive 

abilities measures increases with age (Corso, 1981; Park 

& Hedden, 2001; Salthouse, 1996; Welford, 1985). 

The research suggests that from year to year, age-related 

changes in cognitive functioning occur at a relatively 

predictable rate (except for changes involving the overall 

health of the individual). The rate of decline in cognitive functioning is not dramatic (again, absent a major 

change in health). Salthouse (2000) suggested that there 

is an age-related decline in cognitive abilities of between 

one and two standard deviations across a range in age 

from about 18 to 80, or something on the order of less 

than 1% per year. Changes in perceptual ability appear 

to follow a similar course up until middle age, although 

some evidence suggests that declines in vision and hearing, particularly, may accelerate slightly, on average, after 

about age 50 (Corso, 1981).

It is important to note that the observed declines in 

cognitive and sensory abilities are based on the mean or 

average performance for each age level and may or may 

not reflect the performance of any given individual. Moreover, within each age group, there are those individuals 

whose performance is superior to the group, as well as 

some who perform worse than the average for the group. 

Thus, some older persons may perform better on a given 

measure than their younger colleagues. Because of this 

variability, the scientific merit of basing retirement solely 

upon chronological age rather than demonstrated ability to continue performing the job is debatable (Landy, 

1992; Mavor, 2001; Schneider, 1996).

However, the implications of age-related changes 

in cognitive abilities for job performance are not well 

understood, and the available evidence is equivocal. 

Theoretical models linking changes in fundamental 

cognitive abilities to changes in knowledge, skill, and 

performance are lacking. Davies and Sparrow (1985) 

cited studies in non-controller jobs where performance 

declines with age in situations where the work demand is 

most closely aligned with changes in sensory/perceptual 

and cognitive processes. They determined that the inverted U-shaped relationship between age and work 

performance was most evident in production records 

for skilled and semi-skilled jobs. Supervisory ratings, 

on the other hand, suggested that older employees were 

rated similarly to their younger colleagues on overall 

efficiency but were viewed less positively with respect 

to speed of work and learning ability. However, later 

studies involving meta-analyses of the literature suggest 

that there is little evidence of any age-related changes in 

either actual job performance or in supervisor ratings. In 

their meta analysis of age differences in job performance, 

Waldman and Avolio (1986) found a pattern of increased 

performance as age increased. Supervisory ratings, on 

the other hand, tended to show a slight decline in the 

older age groups. McEvoy and Cascio (1989) found 

little evidence of age-related differences in performance 

measures (ratings or production records) across types 

of jobs. Interviews with working controllers in Europe 

(European Air Traffic Management Programme, 2003) 

suggested concerns about adaptation to changes in equipment and procedures as well as “keeping up with traffic” 

among older controllers. A number of the interviewees 

mentioned that night shifts were more demanding with 

age. Yet 20 of the 76 controllers interviewed felt that age 

itself had little or no effect on performance, while 17 felt 

age negatively impacted job performance.
19

Moreover, as noted by the European controllers, 

compensatory strategies may be developed and used to 

off-set subtle declines in fundamental cognitive abilities 

with age. For example, a large number of the European 

controllers (42 of 76) referred to having better situational 

awareness as a function of their experience. Research on 

pilots also suggests that experience may compensate for 

age-related changes (Morrow et al., 1994; Tsang, 2003). 

Research is needed to assess how, and under what circumstances, controllers develop and use compensatory 

strategies to offset age-related changes in factors such as 

speed of processing.

The differing findings with respect to age and performance highlight the fact that changes in cognitive abilities, 

as assessed by measures of specific abilities, do not necessarily result in observed changes in job performance. On one 

hand, perhaps changes in some cognitive abilities do not 

matter, fundamentally, to the performance of a controller. 

On the other hand, changes in a cognitive ability such as 

short-term memory might have a substantial impact on job 

performance. However, because there has been relatively 

little research to develop models linking specific abilities 

with specific performance dimensions, we are unable at 

present to make and test predictions about the effects of 

age. In addition, most controller performance measures 

currently available are relatively coarse (Broach & Manning, 1998), with the exception of the CBPM. CBPM 

items are linked to specific, important controller tasks 

(Hanson et al., 1999). However, the CBPM is restricted 

to the en route radar environment, and assesses how well 

a controller can identify a problem rather than how well 

he or she can resolve a problem. Research is needed to 

develop similar measures for the tower cab, TRACON, 

and FSS environments and to extend the assessment 

beyond problem identification.

CONCLUSIONS

The scientific basis for the “ATCS Age 56 Law” consisted of three lines of evidence: (a) the inherent stress of 

the job; (b) disability retirements; and (c) loss of proficiency 

with age. Overall, the evidence available in 1971, when 

carefully reviewed, was not as strong as characterized in 

testimony. Moreover, research conducted since 1972 also 

does not provide a firm foundation to either support or 

reject the mandatory separation of controllers at age 56. 

On one hand, the research on physiological measures 

of stress since passage of P.L. 92-297, as summarized by 

Melton (1982) and Smith (1980), does not support the 

public myth that the controller job is among the most 

stressful in the U.S. Analysis of seven years of CPMIS data 

indicates that younger controllers take medical disability 

retirements at a rate proportionate to their representation 

in the overall FAA workforce. On the other hand, available research on performance and age in the controller 

occupation, as well as in other occupations, suggests that 

differences in performance have been observed in crosssectional designs. While older individuals, on average, 

exhibit lower performance, there are older persons who 

out-perform some of their younger colleagues due to 

increasing variability in performance with age. Additional 

research is needed to provide more definitive answers to the 

questions raised in this review. As a part of those efforts, 

longitudinal research is suggested to assess age-related 

changes in cognitive abilities and their possible relationship to changes in performance of complex jobs. Such 

studies might provide a reasonable basis for determining 

if the statutory requirement to separate controllers at age 

56 should be changed.

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23

FIGURES

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Nat. 1999 Nat. 2001 FAA CPC FAA FSS

Not at All

A Little

Somewhat

Quite a Bit

Extremely

Figure 1: ATCS responses to In general, how stressed do you feel at work compared to 

responses from national samples in 1999 and 2001 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

26-30 31-35 36-40 41-45 46-50 51-55 56-60

Not at All

A Little

Somewhat

Quite a Bit

Extremely

Figure 2: Responses of terminal and en route CPCs by age group to 1999 survey 

question, In general, how stressed do you feel at work? 
24 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

26-30 31-35 36-40 41-45 46-50 51-55 56-60

Not at All

A Little

Somewhat

Quite a Bit

Extremely

Figure 3: Responses of FSS controllers by age group to 1999 survey question, In 

general, how stressed do you feel at work? 

In the last six months at work, how difficult has it been for you to bounce back to peak

performance when you have been away from the boards? 

In the last six months of work, how difficult have ��� found it to shift between peak and

���� periods?

1

Extremely 

difficult

2

Fairly difficult 

3

Somewhat

difficult

4

Fairly easy 

5

Extremely easy 

How often have you found yourself worrying about your own burnout? 

1

Practically 

never

2

Rarely 

3

Sometimes 

4

Often

5

Almost 

constantly 

At the present time (last time you worked), how close to burnout do you (did you) 

feel? 

1

Not close at all 

2

Not very close 

3

Somewhat close 

4

Fairly close 

5

Very close 

Figure 4: Burnout Index items and responses from Jones, Bowers, & Fuller (1982) 
25

0 5 10 15 20 25

Flight Service Specialists

Flight Service Mgr/Supv

Terminal Specialists

Terminal Mgr/Supv

En route Specialists

En route Mgr/Supv

1984

1986

Figure 5: Comparison of percent (%) of Air Traffic employees exceeding 3.75 criterion score 

on Burnout Index in 1984 and 1986 FAA surveys 

0 10 20 30 40 50 60

Unwanted overtime

Increased automation

Personal concerns

Accountable for others

Decisions about safety

Delays in automation

Complexity of job

Extended periods with too much work

Too much work in ordinary day

Time to meet job demands

Resources to do job

Opportunity for advancement

Supervisory/management practices

Federal issues

ATC (Non-supv)

FAA

Figure 6: Comparison of proportions of non-supervisory ATC employees and all FAA 

employees indicating the factors as frequently or always a source of stress in the 1986 

survey 
26 

.00

.10

.20

.30

.40

.50

.60

.70

.80

.90

1.00

18 23 28 33 38 43 48

Age @ 1991

R2 = .45, F(2,27) = 10.88, p < .001

p(OE) = 0.116 - 0.00013*age2

 + 0.0000075*age3

Figure 7: Cubic regression of likelihood of OE (p(OE)) on controller age at beginning 

of 5 year observation period (1991-1995) from Broach (1999) 
27

TABLES

Table 1: Medical retirements data presented in 1971 testimony 

Type of Facility 

N ATCS 

(as of Dec 31 1970) 

Total medical 

retirements 

(1966-1970) 

% of ATCS 

medically retired 

(1966-1970) 

Centers (ARTCCs) 10,848 160 1.5 

Towers (Terminals) 8,713 229 2.6 

Stations (Flight Service) 4,217 134 3.1 

Table 2: Disability retirements for controllers less than age 45 compared to their representation in the 

FAA workforce 

Disability Retirements N Employees 

Year 

Younger 

ATCS 

FAA 

Total p1

Younger 

ATCS FAA Total p2 Z Sig 

1997 40 108 .37 16,407 49,690 .33 0.86 .39 

1998 39 119 .33 16,011 50,381 .32 0.23 .82 

1999 30 104 .29 14,729 48,940 .30 -0.28 .78 

2000 22 79 .28 15,351 49,662 .31 -0.61 .54 

2001 23 75 .31 13,668 50,683 .27 0.69 .49 

2002 26 86 .30 13,157 55,218 .24 1.29 .20 

2003 19 93 .20 12,569 49,434 .25 -1.19 .23 

Notes: Younger ATCS = ATCS less than age 45