DOT/FAA/AM-86/2 

Office of Aviation Medicine 

Washington, D.C. 20591 

BIOLOGICAL RHYTHMS AND 

ROTATING SHIFT WORK 

Some Considerations for Air 

Traffic Controllers and Managers 

Carlton E. Melton, Ph. D. 

Office of Aviation Medicine 

and 

RobertS. Bartanowicz, Ed. D. 

Air Traffic Plans and Requirements Service 

January 1986 

Final Report 

This document is available to the public 

through the National Technical Information 

Service, Springfield, Virginia 22161 

US. Department of Transportation 

Federal Aviation Administration 
IDI'ICE 

This docurent is disseminated under tre sponsorship of tre 

U.S. Departirent of Transportation in tre interest of infonnation 

exchange. The United States Goverrurent assures no liability for tre 

contents or use thereof. 
1. Report No . 2. Government Accession No. 

oor /FM/PM.-86 /2 

4. Title and Subtitle 

BIOLOGICAL RHY'lliMS AND IVI'ATING SHIFT WJRK 

Same Considerations for Air Traffic Controllers 

and Managers 

Technical ~eport Oocu .. ntation Page 

3. Recipient's Catalog No. 

S. Report Date 

Januarv 1986 

6. Performing Organization Code 

1----------------------------------! 8. Performing Organization Report No. 

7. Authorl s) Carlton E. Melton, Ph.D. and 

Robert S. Bartanowicz , Ed. D. 

9 . Performing Organization Name ond Address 

IX>T/FM/PM.-86-2 

10 . Work Unit No . (TRAIS) 

11 . Contract or Grant No . 

13. Type of Report and Period Covered 

~----------------------------------------------~ 12. Sponsoring Agency Name and Address 

Office of Aviation Medicine 

Federal Aviation Administration 

800 Independence Avenue, S.W. 

Washington, D.C. 20591 

15. Supplementary Notes 

16 . Abstract 

14 . Sponsoring Agency Code 

This report is a general review of sare of the current themes and practices 

regarding shift work; to inform controllers, technicians, and managers 

of these issues; and to offer sare ideas that may be helpful in dealing 

with difficulties in this area. There is no pat or easy single solution 

to the problems of every employee. Managers are always faced with difficult 

decisions, and shift work is one of the most difficult because it can 

become an emotionally charged issue. 

17. Key Words 

Shift Work 

Biological Time Clocks 

Rotation 

Performance 

Fatigue 

19. Security Clauif. (of this report) 

Unclassified 

Form DOT F 1700.7 C8-72l 

18. Oi atribution Statement 

Document is available to the public 

through the National Technical 

Information Service, Springfield, 

Virginia 22161 

20. Security Clouif. (of this page) 21· No. of Pages 22. Price 

Unclassified 9 

Reproduction of completed page authorized 
TABLE OF CONTENTS 

IN TROD UCT ION •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1 

BACKGROUND •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1 

Biological Time Clocks ••••••••••••••••••••••••••••••••••••••••••••••2 

Shift Work Rotation ••••••••••••••••••••••••••••••••••••••••••••••·••3 

FAA SHIFT WORK SCHEDULE DESIGN/PRACTICES ••••••••••••••••••••••••••••••••3 

Shift Work Models .•..•.•••.••.•..•.••••.•••••....•••••.••••..•••••• . 3 

Mid shift Work •.•.....•••.••.••••••••••.....•.•..••••...•••••.••••••• 5 

Performance Impairment and Shift Work ••••••••••••••••••••••••••••••• 6 

Considerations for FAA Managers 1n Designing Schedules •••••••••••••• 7 

Possible Employee Strategies for Coping with Shift Work ••••••••••••• 7 

CONCLUSIONS ••••••••••••••••••••••••••••••••• •••••••••••••••••••••••••••• 8 

REFERENCES •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 8 
Biological Rhythms and Rotating Shift Work: 

Some Considerations for Air Traffic Controllers and Managers 

INTRODUCTION. 

Rotating shift work and rapid travel across time zones has given rise to a 

relatively new set of physiological and psychological problems that have 

received considerable public exposure. The term "jet lag" has become a 

household expression; the Public Broadcasting Company put on a series called 

"The Brain" in which time sensitive nervous functions were explained. 

Congress has heard much testimony on the effects of rotating shift work on 

human health and industrial production. There is now active scientific 

research underway attempting to find ways to help people adapt quickly to 

these temporal dislocations. This is not a new subject for the FAA in that 

air traffic control specialists (hereinafter referred to as "controller," 

working in all three career options/facilities, i.e., centers, towers, and 

flight service stations) and managers have been dealing with rotating shift 

work since the inception of air traffic control over 50 years ago. 

The purpose of this paper is to review in a general way some of the 

current themes and practices regarding shift work; to inform controllers, 

technicians, and managers of these issues; and to offer some ideas that may be 

helpful in dealing with difficulties in this area. There is no pat or easy 

single solution to the problems of every employee. Managers are always faced 

with difficult decisions, and shift work is one of the most difficult because 

it can become an emotionally charged issue. 

BACKGROUND. 

All FAA studies, and there have been many, regarding air traffic 

controllers' attitudes have shown them to like their jobs and to take pride in 

their work. However, because of the life-disrupting effects of inconsistent 

hours of work and rest, many controllers find rotating shift work 

disagreeable. Controllers are not alone in their opinion; thousands of pages 

of research data attest to the fact that other worker groups around the world 

share that view. Depending on one's source of information, the literature 

indicates that there are 14 - 25 million people in the United States alone 

whose work calls for them to rotate between day and night shifts. These 

people are involved in keeping the machinery of civilization running 24 hours 

a day; they are engaged in activities that range from public safety functions, 

such as police and firefighters, to medical personnel, members of the armed 

forces, and factory and service workers. One FAA bibliography of shift work 

lists over 1300 references to work done since 1950 and other bibliographies 

are almost as extensive. Granting that there are duplications in these lists, 

one is still struck with the mountainous quantity of information available on 

this broad subject. 

There is a thread of consistency that runs throughout the literature on 

attitudes toward shift work. Firstly, workers generally consider work and 

off-duty time as an integrated concept; in order to obtain desired time off 

for discretionary use, workers will commonly accept long hours and/or arduous 

1. 
work schedules. Secondly, most workers everywhere dislike the midshift 

(midnight to morning), prefer day or evening shifts, and desire a steady work 

schedule to any pattern of rotating shifts. Of these factors, there is the 

greatest commonality of opinion about the midshift. In fact, "shift" is 

almost a code word for midshift (day and evening assignments are accepted as 

normal ., non-shift work hours). Among shift workers, practically all reported 

problems are related to the "graveyard shift" because of the physiological, 

psychological and social disruptions associated with it. For these reasons, 

FAA shift workers have a high level of interest in this issue. 

Biological Time Clocks 

Eating, sleeping, waking, and other regular activities are such common 

human experiences as to need no description. Such functions are usually 

thought of as being regulated by external or environmental factors; however, 

it is a well-established fact that these and, indeed, all bodily functions are 

coordinated and regulated by discrete groups of cells in the brain that 

comprise the so-called biological clocks. Because these internal clocks 

continue to run on their accustomed schedules, problems arise when a person's 

activities are displaced by several hours, such as a shift change or by rapid 

crossing of several time zones. Such people are said to suffer from 

desynchronosis, dyschrony, dysrhythmia, jet lag, or jet syndrome. The most 

prominent symptom is fatigue, but many also include indigestitin, confusion, 

irritability, sluggish mentality, various aches and pains, insomnia or 

somnolence, constipation or diarrhea, and a general malaise. 

These problems are rooted in the relationship of almost all living things 

(viruses and some bacteria possibly excepted) to the light/dark cycle 

attendant on the earth's rotation. The first recorded observation of such 

daily, diurnal or circadian (pronounced either circaDian or cirCAdian) rhythms 

was made by a French astronomer, Jean de Mairan, in 1929, who noted that a 

heliotrope plant that opened its leaves at daylight and closed them at dusk 

continued that cycle of activity when kept in a dark closet. It was evident 

that the plant kept time by some internal mechanism. Thus, it has been known 

for over 250 years that living systems' regular .activities are controlled by 

biological clocks. 

In humans, the wake/sleep cycle and the internal body temperature cycle 

are synchronized, or phase related. Phase refers to the time reference on the 

circadian cycle. A phase shift means that the reference point is either 

advanced or delayed without changing the length of the cycle. When no time 

cues exist, as in artificial experimental environments, the wake/sleep and 

body temperature cycles lose their phase relationship or dissociate, a 

condition known as internal desynchronosis. Under these circumstances, the 

free running cycles also become extended to about 25 hours instead of the 

customary 24 hours. Because of this extension of the intrinsic biological 

day, the biological clocks must be reset each day of normal life to conform to 

the solar day. 

For people who do day work and sleep at night, the body temperature swings 

through its low point between three and seven o'clock in the morning, with 

considerable individual variation. Alertness, which is related to body 

2. 
temperature, is lowest at this time and ·people are then most prone to error 

and accidents. It has been shown, for example, that single vehicle truck 

accidents most commonly occur in the early morning hours. The body 

temperature high point occurs about 12 hours later, in the afternoon, and 

alertness is greatest at that time. This circadian swing in body temperature 

amounts to 1 to 2 degrees Fahrenheit. 

When one changes from day to night work, about a week is required for the 

biological clocks to become readjusted to the new schedule, depending on how 

many hours are involved in the change. The clock controlling the wake/sleep 

cycle is located - in the deep part of the brain called the hypothalamus. The 

brain cells controlling the temperature cycle have not yet been located but 

are known to exist and comprise a separate oscillator (clock). 

Shift Work Rotation. 

The observation that the intrinsic cycles are longer than the solar day 

has led to the recommendation that shifts should rotate in the same direction 

as the biological day; that is, workers should progress to later instead of 

earlier shifts. Rotations to later shifts are phase delayed and those that 

progress to earlier shifts are phase advanced. While the advantages/ 

disadvantages of such rotation patterns are fairly subtle and may perhaps be 

overridden by environmental factors, it is claimed that adaptation to phase 

delayed schedules is easier than with phase advanced schedules just as 

east-to-west flight across several time zones produces fewer jet lag symptoms 

than does west-to-east flight. It has been estimated that a person can 

readily adapt to a span of about 3 hours of displacement without experiencing 

desynchronosis. However, it is claimed that such acceptance occurs for only 

about 30 minutes of displacement for advanced schedules or eastward flight and 

2.5 hours for delayed schedules or westward flight. There is not a great deal 

of data comparing delayed and advanced shift work schedules, but such 

experiments as have been done indicate, for whatever reasons, that 

phase-delayed rotations were characterized by increased productivity, improved 

worker health, and job satisfaction. 

FAA SHIFT WORK SCHEDULE DESIGNS/PRACTICES 

A variety of shift work plans in effect at ATC facilities range from 

straight shifts, that allow employees to work the same hours, sometimes of 

their choice; to rotation patterns, that may change rapidly (compressed) or 

slowly (expanded), and may be either phase delayed or advanced. On paper, one 

could design a number of shift rotation patterns, but not all of them would be 

practical or usable in the ATC setting. 

Shift Work Models 

The familiar 2-2-1 rotation preferred by many controllers, especially the 

younger ones, is an example of a phase advanced, compressed schedule. The 

long interval between work weeks (about 80 hours, or 48 percent of the 7-day 

week) is realized by compressing 40 hours of work into an 88-hour period. 

Obviously, such compression takes place at the expense of shortened intervals 

between work sessions (quick turnarounds). 

3. 
TABLE 1 

Compressed 2-2-1 and Expanded 1-2-2 Schedules 

(Phase Advanced) (Phase Delayed) 

Day Work Off Total Work Off Total 

Hours Hours Week Hours Hours Week 

(24-hour clock) (24-hour clock) 

1 1600 - 2400 0000 - 0800 

14 22 

2 1400 - 2200 0600 - 1400 

10 18 

3 0800 - 1600 0800 - 1600 

14 22 

4. 0600 - 1400 1400 - 2200 

10 18 

s. 0000 - 0800 1600 - 2400 

40 48 88 40 80 120 

Off Duty 80 Off Duty 48 

168 168 

If the 2-2-1 is reversed, it becomes a 1-2-2 expanded, phase-delayed 

schedule. Thus, the work week starts with a midshift, progresses through two 

day shifts and two evening shifts, ending at midnight on the fifth day. The 

result is an expanded work week with 40 hours of work spread over 120 hours. 

The off duty period between work weeks would be 48 hours and intervals between 

8-hour work periods would range from 18 to 22 hours (slow turnarounds). As 

mentioned above, it is possible to devise compressed, phase-delayed schedules 

as well as expanded, phase-advanced schedules. However, all schedules call 

for 40 hours of work in five 8-hour days; the difference between them is in 

the distribution of time off. The importance of long weekends to workers 

everywhere is emphasized by the fact that the expanded 1-2-2 is not known to 

be in use in any industrial setting. Workers will accept almost any work 

schedule that will provide preferred time off. In the nuclear power industry, 

some plants operate on 12- and 16-hour shifts. Some law enforcement officers 

work 12-hour shifts for 4 days, then have 4 days off. One of the perquisites, 

"perks," of seniority or rank is the choice of work schedules, thus of time 

off. More and more often workers are bargaining for time off instead of 

monetary compensation. Swedish industrial workers now put in an average of 

28.8 hours per week, the least in the industrial world; they would rather have 

leisure time than cash because of the high tax rate - "The more we make, the 

more they take". West German metal workers struck in 1984 for a 35-hour week; 

they won a 38.5-hour week, thus breaking the 40-hour barrier. Apparently, 

once cash compensation is adequate, it is not as powerful an issue as is time 

off for life enrichment activities that can be indulged with the cash. 

Table 1 compares the compressed, phase advanced 2-2-1 schedule with the 

expanded, phase delayed 1-2-2 schedule. 

4. 
Another schedule in common use is the "straight five" pattern of shift 

rotation, meaning that employees work five days on the same watch, have 48 

hours off, then change to another, usually earlier, shift. Some straight five 

patterns keep the controller on the day and evening watches for 2 week~, 

followed by 1 week of midwatches. In most, if not all cases, phase advancing 

patterns of rotation are used. FAA research has shown, and other researchers 

agree, that 5 days is the wrong rotation frequency from the standpoint of 

circadian rhythmicity. Five straight midshifts lead to accumulated fatigue 

because of inadequate time to entrain circadian rhythms to night work and day 

sleep. Day sleep is almost always reported to be unsatisfactory with noise 

and light being blamed. However, circadian principles reveal that bedtime and 

wakeup time are related to particular places on the wake/sleep and temperature 

cycles. The problem with day sleep is that the unadapted worker tries to 

sleep when his/her biological rhythms are preparing him/her for waking 

activity. Thus, fatigue-induced sleep is brief and generally inadequate. 

The 2-2-1 as presently worked is better than the straight five because 

four of the ' five watches are contained within the normal range of 

wakefulness. Most people sleep 6 to 7 hours per night and go to bed between 

2200 and midnight. Except for the single midshift, the 2-2-1 provides 

essentially day work and night sleep and minimal circadian disruption. The 

single midshift is followed by an 80-hour weekend that provides abundant time 

for rest. Because traffic is characteristically light on the midshift, 

staffing is adjusted so that most crewmembers double back to day or evening 

shifts for the last workday of the week. 

Reduced to the simplest terms, problems with rotating shifts and the 

attendant circadian disruption are almost exclusively connected with midshift 

work. Sleepiness is inevitable on the midshift, particularly during the 

period of circadian low, and is exacerbated by the work underload that 1s 

usual during the night. A demanding workload is arousing and, in many 

respects, is easier to deal with than is underload. Obviously, during periods 

of heavy traffic, ATC facilities adjust staffing to meet the need. This means 

that a variety of work is available, providing relief through duty changes. 

Also, social interactions are plentiful and breaks are readily provided. 

Midshift Work 

Two strategies are available for dealing with midshift work in towers, 

centers and TRACONs: (1) working the midshift long enough to become entrained 

to the schedule or (2) keeping midshift work to the minimum. Most controllers 

prefer the latter option and are probably wise in their choice. Arguments 

against the first option (prolonged midshift scheduling) are as follows: 

(1) Circadian disruption occurs when the change back to day activity and 

night sleep is made on the weekend. 

(2) Loss of proficiency by dealing with low traffic volume for long 

periods. 

(3) Isolation from mainstream of facility activities. 

5. 
(4) Problems as crew briefings are given during the daytime. 

(5) Loss of training experience, both giving and receiving. 

(6) Reduced social contacts at work as well as away from work. 

(7) Disruption of normal family life. 

Another variant is the work pattern used at the Miami International Flight 

Service Station (MIA IFSS). Day, evening, and midshifts are covered by people 

who work those periods without rotation. This pattern of work is popular at 

that facility because it affords regular, and sometimes preferred time off. 

This regular time off is of great importance to people who use it for farming, 

business, recreation, or whatever their lifestyle calls for. Measurements 

made at the MIA IFSS during a recent FAA study showed that there was 

significantly less subjective fatigue on the steady shift compared to the 

2-2-1 rotation also worked at that facility. The amount of sleep obtained in 

connection with the two work patterns was not significantly different; the 

difference in subjective fatigue was probably related to better quality sleep 

associated with the steady shift than the 2-2-1. It must be remembered that 

the work distribution patterns at the MIA IFSS were customized to be 

consistent with operational needs at that facility. This same model might not 

work as well at a terminal or center facility. 

The Miami study focused our thinking on some important aspects of shift 

work. While the importance of circadian effects is not disputed and we must 

always be mindful of them, we have come to realize that they are not 

all-important; that is, social, economic, industrial and environmental factors 

as well as personal preference are also important and can override circadian 

effects. Of these factors, personal preference or freedom of choice is of 

great importance because it means that a worker has more control over his/her 

life than might otherwise be the case. For this reason the FAA has 

established the practice of local option with input from controllers regarding 

shift work. 

Performance Impairment, Health, Fatigue, and Shift Work 

Many studies point to performance impairment associated with 

desynchronosis. As mentioned previously, when body temperature is lowest, 

error proneness is greatest. This would then translate to the midshift period 

between 3:00 a.m. and 7:00 a.m. as being a critical period. However, in 

actual practice, controllers errors do not occur in any greater number here. 

This can probably in part be explained by low traffic during midshifts. Short 

term memory is one function known to be adversely affected at the time of 

circadian low temperature, which can lead to human error. In some 

professions, such as air traffic control and medicine, however, error-free 

performance is the expected norm. There is evidence that such error-free 

performance, when attained by greater than ordinary effort, occurs at a 

commensurately greater physiological and psychological cost, sometimes called 

stress. 

6. 
Fatigue is the commonest complaint associated with rotating shift work. 

When fatigue is not reversed by an off-duty rest period, it means that the 

worker returns to work in a tired condition. A week of consecutive midshifts, 

for example, might lead to accumulated fatigue that could affect the next 

week's performance on the day shift if the weekend does not provide complete 

recuperation. 

It is not possible to make an unequivocal all-encompassing statement about 

the effects of rotating shifts on workers' health. Some studies in which 

large populations of industrial workers were examined have claimed that deaths 

from cardiovascular diseases were more common among shift workers than among 

straight day workers. An FAA air traffic controller health change study, 

conducted in the late 1970's, showed that controllers had a higher occurrence 

of high blood pressure than did comparable people in general population. 

However, there are so many factors (variables) involved in such studies that 

is is not possible to attribute the findings to one factor alone, such as 

rotating shift work or even to the work itself. The general statement can be 

made, though, that people experiencing desynchronosis are temporarily in a 

state of internal disarray. Glandular secretion rates vary and become 

greatest or least at inappropriate times of day, thus rendering the person 

ill-equipped either to deal with crises or to go to sleep. 

Considerations for FAA Managers in Designing Schedules 

(1) Operational requirements and considerations must come first. The 

literature is clear that any shift work design must take into consideration 

the nature of the work, and the work itself may limit various scheduling 

options. 

(2) Administration of shift schedules must be manageable and 

understandable by both management and controllers. Trying to accommodate too 

many needs may create confusion and dissatisfaction. 

(3) To the extent practicable (consistent with operational requirements) 

employee desires and needs should be taken into consideration. 

(4) Midshift duty should be minimized. 

that causes the most circadian disruption. 

worked, the better. 

The midshift is clearly the shift 

As such, the fewer midshifts 

(5) Educate employees. Employees and supervisors should be aware of the 

circadian process. Desynchronosis is mainly associated with the midshift; 

awareness of the circadian low temperature that occurs in the predawn hours is 

of prime importance to everyone. 

Possible Employee Strategies for Coping with Shift Work 

Dietary regimens have been proposed for reducing the effects of jet lag by 

speeding up the circadian adjustment process. There is evidence, primarily 

from animal experimentation, that certain food components act directly on the 

biological clocks. Travelers are advised to alternate light and heavy meals 

several days prior to flight, to fast during the flight and to eat breakfast 

7. 
upon arrival at the destination. It is further recommended that travelers eat 

high protein breakfasts and high carbohydrate, low protein dinners to hasten 

entrainment to advancing schedules (eastward flight). Caffeine is a so-called 

chronobiotic substance; when used according to common sense can aid 

wakefulness, it can also speed the entrainment process. If these principles 

apply to air traffic controllers working a series of midshifts, and we are not 

saying this is the case, one would expect that (1) high protein meals before 

going to work; (2) high carbohydrate, low protein meals upon leaving work; and 

(3) together with caffeine in coffee or tea during the first half of the shift 

and abstinence the last half, would aid the entrainment process. For 

controllers working only one midshift, however, it is doubtful that dietary 

adjustments would accomplish very much. 

In no case should stimulant drugs, such as amphetamines, be used on duty 

to enhance wakefulness, nor should sedatives be used for sleep induction. 

Dependancy or addiction can develop, of course, but one should also be aware 

that drug effects can wear off at inappropriate times and leave one worse off 

than might be the case had drugs not been used. Further, proponents of 

dietary manipulation as a way of dealing with desynchronosis, advise strict 

abstinence from alcohol during the entrainment process. 

CONCLUSIONS 

Circadian rhythm displacements as a consequence of air traffic control 

work are recognized and accepted by controllers as part of the job and are 

usually dealt with effectively on an individual basis. 

The FAA's policies regarding shift work are fair, mature, flexible, and 

democratic. Controllers are well compensated for their work and are aware of 

the necessity for working unusual hours. Night work is distributed fairly by 

rotation practices. Workers have considerable input into present shift work 

practices, allowing maximum flexibility in conduct of their lives. No safety 

problems in ATC are known to be related exclusively to circadian effects; no 

medical problems are known to result from rotating shift work. 

Though the negative aspects of shift work are usually emphasized, there 

are also positive features, such as premium night differential pay and daytime 

hours for other pursuits. 

8. 
REFERE_NCES 

The following books and articles are suggested for further insights into the 

nature of biological rhythms and the problems of shift work. 

(1) "A Review of Human Physiological and Performance Changes Associated 

with Desynchronosis of Biological Rhythms". Charles M. Winget, Charles W. 

DeRoshia, Carol L. Markley, and Daniel C. Holley. Aviation, Space and 

Environmental Medicine 55:No. 12:1085 - 1995, December, 1984. 

(2) "Biological Clocks." Introduction by Beatrice M. Sweeney. 

BioScience. 33:424-457, 1983. 

(3) "Biological Clocks and Shift Work Scheduling." Hearings before the 

Subcommittee on Investigation and Oversight of the Committee on Science and 

Technology, Ninety-Eighth Congress, First Session, March 23, 1983. 

(4) "Human Circadian Rhythms." R. T. W. L. Conroy and J. N. Mills. J. 

A. Churchill, London, 1970. 

(5) "Human Sleep: Its Duration and Organization Depend on Its Circadian 

Phase." Charles A. Czeisler, Elliot D. Weitzman, Martin c. More-Ede, Janet C. 

Zimmer, and Richard S. Knauer. Science, 210:1264 - 1267, December 12, 1980. 

(6) "Rotating Shift Work Schedules that Disrupt Sleep Are Improved by 

Applying Circadian Principles." Charles A. Czeisler, Martin c. Moore-Ede, and 

Richard Colemen. Science 217:No. 4558:460-462, 1982. 

(7) "The Clocks That Time Us: Physiology of the Circadian Timing 

System." Martin C. More-Ede and Richard Colemen. Harvard University Press, 

Cambridge, Mass., 1982. 

(8) "The Future of Work." Fred Best. Prentice-Hall, 1973. 

9 • tc U.S. GOVERNMENT PRINilNG OFHCE: lOOl 660-08lflOOU