Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 29

POSITION PAPER

 C ALDWELL JA, M ALLIS MM, C ALDWELL JL, P AUL MA, M ILLER JC, 

N ERI DF, A EROSPACE M EDICAL A SSOCIATION A EROSPACE F ATIGUE C OUNTERMEASURES S UBCOMMITTEE OF THE H UMAN F ACTORS C OMMITTEE . Fatigue countermeasures in aviation. Aviat Space Environ Med 2009; 

80:29 – 59. 

Pilot fatigue is a signifi cant problem in modern aviation operations, 

largely because of the unpredictable work hours, long duty periods, circadian disruptions, and insuffi cient sleep that are commonplace in both 

civilian and military fl ight operations. The full impact of fatigue is often 

underappreciated, but many of its deleterious effects have long been 

known. Compared to people who are well-rested, people who are sleep 

deprived think and move more slowly, make more mistakes, and have 

memory diffi culties. These negative effects may and do lead to aviation 

errors and accidents. In the 1930s, fl ight time limitations, suggested layover durations, and aircrew sleep recommendations were developed in 

an attempt to mitigate aircrew fatigue. Unfortunately, there have been 

few changes to aircrew scheduling provisions and fl ight time limitations 

since the time they were fi rst introduced, despite evidence that updates 

are needed. Although the scientifi c understanding of fatigue, sleep, shift 

work, and circadian physiology has advanced signifi cantly over the past 

several decades, current regulations and industry practices have in large 

part failed to adequately incorporate the new knowledge. Thus, the 

problem of pilot fatigue has steadily increased along with fatigue-related 

concerns over air safety. Accident statistics, reports from pilots themselves, and operational fl ight studies all show that fatigue is a growing 

concern within aviation operations. This position paper reviews the relevant scientifi c literature, summarizes applicable U.S. civilian and military fl ight regulations, evaluates various in-fl ight and pre-/postfl ight 

fatigue countermeasures, and describes emerging technologies for detecting and countering fatigue. Following the discussion of each major 

issue, position statements address ways to deal with fatigue in specifi c 

contexts with the goal of using current scientifi c knowledge to update 

policy and provide tools and techniques for improving air safety. 

Keywords: alertness , sleep , hypnotics , stimulants , fl ight time regulations , 

duty time regulations , sustained operations . 

FATIGUE COUNTERMEASURES IN AVIATION: 

OUTLINE OF CONTENTS 

I. Description of the Problem 

II. Current Regulations, Practices, and an Alternative Approach 

Crew Rest Guidelines 

Flight and DutyTime Guidelines 

Fatigue Risk Management System (FRMS): An Alternative 

Regulatory Approach 

Ultra-Long-Range Flights: A Nontraditional Approach 

Position Statement on Crew Rest, Flight, and Duty Time Regulations 

III. In-Flight Countermeasures and Strategies 

Cockpit Napping 

Activity Breaks 

Bunk Sleep 

a.

b.

c.

d.

a.

b.

c.

In-Flight Rostering 

Cockpit Lighting 

Position Statement on the Use of In-Flight Countermeasures 

IV. Pre-/Postfl ight Countermeasures and Strategies 

Hypnotics 

Position Statement on the Use of Hypnotics 

Improving Sleep and Alertness 

 i. Healthy Sleep Practices 

 ii. Napping 

iii. Circadian Adjustment 

 iv. Exercise 

v. Nutrition 

Position Statement on Improving Sleep and Alertness 

c. Non-FDA-Regulated Substances 

Position Statement on Non-FDA-Regulated Substances 

V. New Technologies 

On-Line, Real-Time Assessment 

Off-Line Fatigue Prediction Algorithms 

Position Statement on New Technologies 

VI.Military Aviation 

Relevant Regulations and Policies 

Crew Rest and Duty Limitations 

Stimulants/Wake Promoters 

Position Statement on the Use of Stimulants to Sustain Flight 

Performance 

d. Sleep-Inducing Agents 

Position Statement on the Military Use of Sleep-Inducing Agents 

e. Nonpharmacological Countermeasures and Strategies 

VII. Conclusions and Recommendations 

 I. DESCRIPTION OF THE PROBLEM 

 Pilot fatigue is a signifi cant problem in modern aviation operations, largely because of the unpredictable 

work hours, long duty periods, circadian disruptions, 

d.

e.

a.

b.

a.

b.

a.

b.

c.

 This Position Paper was adopted by the Aerospace Medical Association. It was prepared by a special subcommittee of the Aerospace Human Factors Committee chaired by Dr. David Neri and consisting of 

the authors. The paper is intended to review the relevant literature, 

describe fatigue-related issues and challenges, summarize applicable 

regulations, and present the Association’s position with respect to fatigue countermeasures. 

 This manuscript was received and accepted for publication in September 2008 . 

 Address reprint requests to: J. Lynn Caldwell, Ph.D., Air Force Research Laboratory, Human Effectiveness Directorate, Wright- Patterson 

AFB, OH 45433; lynn.caldwell@wpafb.af.mil 

 Reprint & Copyright © by the Aerospace Medical Association, Alexandria, VA. 

 DOI: 10.3357/ASEM.2435.2009 

Fatigue Countermeasures in Aviation 

 John A. Caldwell , Melissa M. Mallis , J. Lynn Caldwell , 

 Michel A. Paul , James C. Miller , and David F. Neri 

 for the Aerospace Medical Association Fatigue 

Countermeasures Subcommittee of the Aerospace 

Human Factors Committee 
30 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

and insuffi cient sleep that are commonplace in both civilian and military fl ight operations ( 147 , 186 ). The full 

impact of fatigue is often underappreciated, but many 

of its deleterious effects have long been known. Lindberg 

recognized the detrimental consequences of long duty 

hours (and long periods of wakefulness) on fl ight performance back in the 1920s and scientists began to appreciate the negative impact of rapid time zone transitions in the early 1930s ( 134 ). Compared to people who 

are well-rested, people who are sleep-deprived think 

and move more slowly, make more mistakes, and have 

memory diffi culties. These negative effects may and do 

lead to aviation errors and accidents. In the long term, 

the irregular schedules worked by many aircrews during a career may lead, as they do for shift workers, to 

higher incidences of stomach problems (especially heartburn and indigestion), menstrual irregularities, colds, 

fl u, weight gain, and cardiovascular problems. 

 In the 1930s, fl ight time limitations, suggested layover 

durations, and aircrew sleep recommendations were developed in an attempt to mitigate aircrew fatigue. Unfortunately, there have been few changes to aircrew 

scheduling provisions and fl ight time limitations since 

the time they were fi rst introduced. To add further complexity, scheduling and fl ight time regulations vary 

among different countries. 

 Although scientifi c understanding of fatigue, sleep, 

shift work, and circadian physiology has advanced signifi cantly over the past several decades, current regulations and industry practices have in large part failed to 

adequately incorporate the new knowledge ( 67 ). Thus, 

the problem of pilot fatigue has steadily increased along 

with fatigue-related concerns over air safety. Accident 

statistics, reports from pilots themselves, and operational fl ight studies all show that fatigue is a growing 

concern within aviation operations. 

 Long-haul pilots frequently attribute their fatigue to 

sleep deprivation and circadian disturbances associated 

with time zone transitions. Short-haul (domestic) pilots 

most frequently blame their fatigue on sleep deprivation and high workload ( 28 ). Both long- and short-haul 

pilots commonly associate their fatigue with night 

fl ights, jet lag, early wakeups, time pressure, multiple 

fl ight legs, and consecutive duty periods without suffi -

cient recovery breaks. Corporate/executive pilots experience fatigue-related problems similar to those reported 

by their commercial counterparts. However, again, they 

most frequently cite scheduling issues (multi-segment 

fl ights, night fl ights, late arrivals, and early awakenings) 

as the most noteworthy contributors ( 179 ). Weather, turbulence, and sleep deprivation, in combination with 

consecutive and lengthy duty days, time zone transitions, and insuffi cient rest periods, are blamed as well. 

Despite the many differences between civilian and military aviation operations, surveys of military pilots generally support the fi ndings obtained from the commercial sector. U.S. Army helicopter pilots and crews 

frequently blame inadequate sleep and/or insuffi cient 

sleep quality for impaired on-the-job alertness, and like 

their commercial counterparts, they indicate that fatigue 

in general is a signifi cant problem ( 51 ). U.S. Air Force pilots report the same problems ( 130 ). Noteworthy fatigue 

factors include scheduling issues (frequently changing 

work/rest periods, operating at night, etc.) and uncomfortable sleep conditions (leading to sleep deprivation). 

U.S. Navy fi ghter pilots deployed in Operation Southern Watch in 1992 commonly complained that sleep restriction aboard aircraft carriers led to somatic complaints, alertness diffi culties, and general performance 

degradations ( 18 ). U.S. Air Force F-15 pilots in Operation Desert Storm indicated that around-the-clock task 

demands, minimal rest periods, consecutive duty days, 

circadian disruptions, and sleep deprivation were commonplace ( 58 ), as did F-16 pilots ( 189 , 190 ). U.S. Air Force 

C-141 pilots in Operation Desert Storm likewise complained that insuffi cient sleep and lengthy fl ight times 

were primarily responsible for increased fatigue ( 147 ). 

 Duty times and aircrew fatigue will continue to be a 

challenge in both scheduled passenger airlines (major, 

national, commuter) and cargo operations, especially 

with the advent of ultra-long-range (ULR) aircraft (i.e., 

. 16-h block-to-block). Both Boeing and Airbus are currently manufacturing ULR aircraft. These aircraft have 

resulted in operations with longer duty periods than those 

encountered in current domestic and international 

fl ights. They will also increase the demands for crews to 

work nonstandard and nighttime duty schedules. Thus, 

an important question for ULR operations is whether 

the strains imposed by the extension of fl ight duty hours 

beyond the limits commonly fl own will effectively be 

mitigated by the standard fatigue countermeasures, 

which in part have been responsible for the acceptable 

safety record of existing fl ight operations. Without 

proper management, ULR operations may exacerbate 

the fatigue levels that have already been shown to impair safety, alertness, and performance in existing fl ight 

operations ( 143 ). 

 Clearly, fatigue is not a one-dimensional phenomenon, but rather the product of several factors related 

to physiological sleep needs and internal biological 

rhythms. In spite of its complex nature, the operational 

causes of fatigue are strikingly consistent across diverse 

types of aviation operations. The consequences of aircrew fatigue are consistent as well. 

 From a physiological perspective, both simulator and 

in-fl ight studies have documented that fatigue impairs 

central nervous system functioning. Cabon and colleagues ( 37 ) demonstrated that long-haul pilots were 

particularly susceptible to vigilance lapses during low 

workload periods, and that such lapses could simultaneously appear in both crewmembers fl ying the aircraft 

at the same time (an obvious safety concern). In one of 

the crews evaluated, both the pilot and the copilot evidenced periods of increased slow-wave electroencephalography (EEG) activity (indicative of sleepiness) by the 

4th and 5th hour of a lengthy fl ight. Wright and McGown 

( 232 ) found that pilot microsleeps occurred most frequently during the cruise portion of long-haul operations (in the middle-to-late segments of the fl ight) and 

that microsleeps were more than nine times as likely 
Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 31

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

during nighttime fl ights compared to daytime fl ights. 

Most of these lapses go unnoticed by the affected crewmembers. Samel and colleagues ( 187 ) essentially confi rmed the EEG results from Cabon et al. ( 37 ) and Wright and 

McGown ( 232 ) by showing that, in general, spontaneous microsleeps increased with increasing fl ight duration. Also, nighttime fl ights were again found to be more 

problematic than daytime fl ights. Rosekind et al. ( 177 ) 

documented the presence of physiological micro-events 

(slow brain activity and eye movements) even during 

the period from top-of-descent to landing. In one group, 

87% of the pilots experienced at least one microsleep 

greater than 5 s in duration, and on average, the pilots 

experienced six microsleeps during the last 90 min of 

the fl ight. In addition to microsleeps and lapses, many 

pilots admit to having fallen asleep in the cockpit. Of the 

1424 fl ightcrew members responding to a NASA survey 

of fatigue factors in regional airline operations, 80% acknowledged having “ nodded off ” during a fl ight at 

some time ( 55 ). For corporate/executive airline operations, 71% of 1488 fl ightcrew survey respondents reported having nodded off during fl ight ( 175 ). 

 From a safety perspective, improperly managed fatigue poses a signifi cant risk to crew, passengers, and 

aircraft. A National Transportation Safety Board (NTSB) 

study of major accidents in domestic air carriers from 

1978 through 1990 in part concluded that “ ... Crews 

comprising captains and fi rst offi cers whose time since 

awakening was above the median for their crew position 

made more errors overall, and signifi cantly more procedural and tactical decision errors ” ( 139 , p. 75). Kirsch 

( 103 ) estimated that fatigue may be involved in 4 – 7% of 

civil aviation mishaps, data from the U.S. Army Safety 

Center suggest fatigue is involved in 4% of Army accidents ( 48 ), and statistics from the Air Force Safety Center 

blame fatigue, at least in part, for 7.8% of U.S. Air Force 

Class A mishaps ( 124 ). Furthermore between 1974 and 

1992, 25% of the Air Force’s night tactical fi ghter Class A 

accidents were attributed to fatigue and from 1977 to 

1990, 12.2% of the U.S. Navy’s total Class A mishaps 

were thought to be the result of aircrew fatigue ( 166 ). * 

 Fatigue in aviation is a risk factor for occupational 

safety, performance effectiveness, and personal wellbeing. The multiple fl ight legs, long duty hours, limited 

time off, early report times, less-than-optimal sleeping 

conditions, rotating and nonstandard work shifts, and 

jet lag pose signifi cant challenges for the basic biological 

capabilities of pilots and crews. Humans simply were 

not equipped (or did not evolve) to operate effectively 

on the pressured 24/7 schedules that often defi ne today’s fl ight operations, whether these consist of shorthaul commercial fl ights, long-range transoceanic operations, or around-the-clock military missions. Because of 

this, well-planned, science-based, fatigue management 

strategies are crucial for managing sleep loss/sleep debt, 

sustained periods of wakefulness, and circadian factors 

that are primary contributors to fatigue-related fl ight 

mishaps ( 178 ). These strategies should begin with regulatory considerations, but should include in-fl ight countermeasures as well as both pre- and postfl ight interventions. The risks and benefi ts of each technique should be 

carefully considered and balanced. 

 In the following sections, this position paper will summarize relevant U.S. civilian and military fl ight regulations, evaluate various in-fl ight and pre-/postfl ight fatigue 

countermeasures, and describe emerging technologies for 

detecting and countering fatigue. † Following each major 

section, position statements and recommendations will be 

provided for addressing fatigue in that specifi c context. 

 II. CURRENT REGULATIONS, PRACTICES, AND 

AN ALTERNATIVE APPROACH 

 a. Crew Rest Guidelines 

 The Federal Aviation Administration (FAA) regulates 

crew rest for commercial aviation ( 1 ) in documents previously referred to as Federal Aviation Regulations 

(FARs) and renamed the Code of Federal Regulations 

(CFRs). Crew rest, as defi ned by the CFRs, is any time 

that a crewmember is free from all duties and responsibilities, including fl ying and administrative work. The 

FAA places strict limitations on minimum crew rest periods. The minimum mandatory rest period for both 

nonaugmented and augmented fl ightcrews is 10 h prior 

to a duty period. (An augmented fl ightcrew is composed 

of more than the minimum number required to operate 

the aircraft.) Nonaugmented crews are also required to 

have a minimum 10-h rest period after the duty period 

ends. It is important to note that this 10-h rest period includes local travel time to and from a place of rest (but 

not the time required to preposition a crew). Including 

travel time as part of the mandatory rest time between 

fl ights reduces the time that fl ightcrew have available 

for uninterrupted sleep periods. Therefore, fl ightcrews 

often fail to obtain 8 h of uninterrupted sleep. For example, if the crew were to land at the destination airport 

and the hotel where they planned to obtain their crew 

rest was a 1-h drive away, the travel between the airport 

and hotel (in both directions) would total 2 h and be 

 * Although differences exist between civil and military operations, it 

is clear similar factors and conditions lead to fatigue in both civilian 

and military aviation environments and fatigue mitigation strategies 

for both contexts should be scientifi cally based. Understandably, however, different regulations and operational considerations have resulted 

in fatigue countermeasure approaches that differ in important ways. 

For example, a variety of pharmacological countermeasures have been 

approved for use in certain circumstances by U.S. military aviators but 

not by civilian aviators. The current prohibition regarding use of pharmacological countermeasures by civilian pilots can be attributed to 

safety concerns and issues of adequate policies for oversight. The military services have addressed these issues through targeted research, 

explicit policies on medical oversight, and recognition of the sometimes overriding importance of operational considerations (e.g., 

NAVMED P-6410). The use of pharmacological countermeasures to 

fatigue in civilian (but not military) pilots is addressed in this paper. 

† U. S. civilian and military fl ight regulations were utilized due to 

space limitations and because of ready access compared to the corresponding sets of international regulations. While a full discussion in 

the context of the many international regulations is outside the scope 

of this paper, the proposed countermeasure approaches have broad 

applicability given their basis in human physiology. 
32 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

considered part of their rest time. Therefore, they would 

have 8 h maximum in the hotel to obtain recovery sleep, 

eat, and attend to personal needs. It is highly unlikely 

the crew would have the opportunity to obtain a minimum 8- to 8.25-h sleep period, the average sleep need 

for an adult ( 222 ). However, for augmented crews, the 

rest period after duty is 12 h and is extended to 18 h for 

multiple time zone fl ights. While the extended time period is an improvement, it should be noted that none of 

the rest period guidelines account for the timing of sleep 

with respect to circadian phase, despite the fact sleep 

propensity varies signifi cantly with time of day, making 

sleep obtained during the subjective daytime shorter, of 

poorer quality, and less restorative than nighttime sleep 

( 6 ). Instead, rest period durations are constant and independent of time of day. 

 b. Flight and Duty Time Guidelines 

 In addition to specifying crew rest times, the FAA regulates crew fl ight and duty time for commercial aviation 

( 1 ). Flight time duty limitations for the major airlines are 

covered in CFRs Part 121 and in Part 135 for commuter 

airlines ( 2 , 3 ). 

 Flight time is the time between “ block-out ” and 

 “ block-in ” . Flight time begins when the aircraft moves 

from its parked position and ends when the plane is 

parked at its destination. Although fl ight time and the 

workload endured throughout the fl ight are important, 

total duty time should be considered also when determining an individual’s level of alertness. Flight time is a 

subset of duty time. Duty time is longer and includes the 

time period between when pilots report for a fl ight and 

when they are released after a fl ight. Therefore, it includes any administrative work required by the airline. 

Maximum allowable fl ight time and duty time differ for 

nonaugmented and augmented crews (fl ight time: 10 h 

vs. 12 h and duty time: 14 h vs. 16 h). However, the augmented crews are limited to 8 h on the fl ight deck and 

are provided rest facilities for in-fl ight rest opportunities. Although maximum duty time is 2 h longer for augmented crews than nonaugmented crews, maximum 

fl ight time additive over 1 wk, 1 mo, and 1 yr are the 

same. These limits are summarized in Table I . 

 An examination of crew duty and rest guidance for 

commercial versus military aviation operations reveals 

fewer similarities than differences. The primary similarity is the requirement for the attainment of 8 h of 

sleep, but this is far from a hard-and-fast rule. There 

are usually detailed guidelines for the manner in which 

shorter sleep durations will be handled in civil fl ight 

operations (e.g., by requiring a shorter subsequent duty 

period or a longer recovery period). In most cases, 

single-pilot operations are more restrictive than dualpilot or augmented crew operations. Especially with 

regard to long-haul fl ights, careful consideration must 

be given to crew duty time, onboard rest scheduling, 

layover sleep opportunities (e.g., duration and recommended timing), and recovery sleep after returning to 

domicile. 

 c. Fatigue Risk Management System (FRMS): An 

Alternative Regulatory Approach 

 Each individual type of aviation operation offers its 

own complexity, whether it be working extended duty 

days, crossing multiple time zones, sleeping at adverse 

circadian times, or performing during a circadian nadir. These are just a few examples of the physiologically relevant factors that are unique to every schedule. 

They are also affected by specifi c organizational needs 

and airport operating requirements. The combination 

of these factors requires a new approach that addresses 

operations on an individual case basis and also allows 

for operational fl exibility. One option for approaching 

this is by addressing both physiological and operational factors as part of a Fatigue Risk Management 

System (FRMS). A multicomponent FRMS program, 

with a scientifi c foundation, helps ensure that performance and safety levels are not compromised by offering an interactive way to safely schedule and conduct 

fl ight operations on a case-by-case basis. Fatigue risk 

management systems offer an alternative approach to 

traditional prescriptive duty and fl ight time limitations 

and rest time regulations currently enforced by the 

FAA. 

 An FRMS is an evidence-based system for the measurement, mitigation, and management of fatigue 

risk. It includes a combination of processes and procedures that are employed within an existing Safety 

Management System ( 195 ). It is a nonprescriptive 

way to monitor fatigue risk associated with aviation 

operations. 

 Multiple groups worldwide are recommending some 

minimum requirements for an effective FRMS. Two examples of recommendations are provided below. 

The U.S.-based Flight Safety Foundation has suggested the following minimum activities as part of an effective FRMS ( 140 ): 

Develop a fatigue risk management policy; 

Formalize education/awareness training programs; 

Create a crew fatigue-reporting mechanism with associated 

feedback, procedures, and measures for monitoring fatigue 

levels; 

•

•

•

TABLE I. CFRS FOR MINIMUM REST PERIODS AND MAXIMUM 

FLIGHT AND DUTY PERIODS FOR BOTH NONAUGMENTED AND 

AUGMENTED CREWS. 

Non-Augmented 

Crew (Single- or 

Two-Pilot Crew) Augmented Crew 

Minimum preduty 

 rest period

10 h 10 h 

Minimum postduty 

 rest period

10 h 12 h 

 18 h for multiple time 

 zones 

Maximum fl ight time 10 h 12 h 

Maximum duty time 14 h 16 h 

Maximum duty time; 

 1 wk

30 h 30 h 

Maximum duty time; 

 1 mo

100 h 100 h 

Maximum duty time; 

 1 yr

1400 h 1400 h 
Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 33

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

Develop procedures for reporting, investigating, and recording 

incidents in which fatigue was a factor; 

Implement processes and procedures for evaluating information on fatigue levels and fatigue-related incidents, implementing interventions, and evaluating their effects. 

The Civil Aviation Safety Authority in Australia has defi ned impact areas that an FRMS must consider ( 13 ): 

Sleep opportunity provided by schedules; 

Sleep obtained by personnel to indicate fi tness for duty; 

Hours of wakefulness; 

Circadian factors; 

Sleep disorders; 

Operational demographics. 

 Other organizations are already testing the effectiveness of these approaches. One of the more commonly 

known efforts is easyJet’s implementation of an FRMS 

as part of their Systems Integrated Risk Assessment 

(SIRA). Preliminary results have demonstrated its effectiveness at reducing fatigue ( 200 ). Within the U.S., 

the Flight Safety Foundation (FSF) has suggested that 

an FRMS approach be used for ultra-long-range operations ( 83 ). Their specifi c recommendations are described in more detail in Section d , below. FRMS programs are not only being explor ed in fl ightcrew 

operations but are being used by Transport Canada 

with Canadian aircraft maintenance engineers ( 26 ). The 

International Civil Aviation Organization (ICAO) is in 

the process of compiling a report with the recommended components of a FRMS. The FAA is also exploring ways to implement effective FRMS based programs in operations where fatigue has been identifi ed 

as an inherent risk. 

 d. Ultra-Long-Range Flights: A Nontraditional Approach 

 Ultra-long-range (ULR) aircraft will extend the longest fl ight duty days from 14 – 16 h to 20 1 h. Current 

CFRs do not address this 4- to 6-h increase in fl ight 

duration. Consequently, there are no crew rest, fl ight 

time, or duty time regulations specifi c to ULR 

operations. 

 In anticipation of the physiological challenges associated with proposed ULR fl ights, the Flight Safety 

Foundation, Airbus, and Boeing conducted four ULR 

Crew Alertness workshops that involved both scientifi c experts and aviation operational groups from 

throughout the world. These workshops were interactive, allowing for focused discussions of the operational and technological issues associated with maintaining maximal alertness levels during ULR operations 

( 83 ). However, the workshops not only identifi ed the 

issues, but, with the guidance of the Steering Committee, developed common methods and approaches to 

reduce errors, incidents, and accidents involving fatigue. The recommendations were largely based on an 

FRMS program and included three main components: 

1) development of a fatigue risk management policy; 

2) formation of a Fatigue Management Steering Committee; and 3) implementation of education and training programs. Other important recommendations from 

the workshop subgroup meetings included the 

following: 

•

•

•

•

•

•

•

•

Mandatory in-fl ight rest periods (not optional for fl ightcrew); 

Identifi cation of departure windows that consider delays (not 

exceeding a specifi ed duration) and approaches to handle such 

disruptions; 

Informing fl ightcrew 36 to 48 h prior to departure of scheduled 

on-board bunk sleep periods; 

Recurring validation of schedules using both objective and 

subjective measures to inform management of necessary schedule changes. 

 The FAA is currently using a case-by-case approach 

to approve ULR city pairs. They are approving these 

operations by issuing a nonstandard operations specifi cation paragraph, (OpSpec A332) “ Ultra Long Range 

(ULR) Flag Operations in Excess of 16 Hours Blockto-Block Time ” to air carriers intending to conduct 

ultra-long-range operations. This paragraph contains 

requirements designed to “ optimize opportunities for 

fl ightcrew members to obtain adequate rest to safely 

perform their operational duties during all phases of 

this ULR trip sequence. ” OpSpec A332 has already 

been issued to one air carrier. 

 As detailed in OpSpec A332, carriers proposing a ULR 

city pair are requested to present a route-specifi c plan to 

the FAA. The FAA reviews the routes, from both a scientifi c and operational perspective, and carefully considers duty times, fl ight times, and rest periods to assess the 

opportunities available for rest and recovery periods in 

preparation for, during, and after scheduled ULR fl ights. 

The carrier is also requested to provide details of the onboard rest scheme, plans to assure preduty minimum 

rest periods and a method for addressing delays and 

cancellations. After a careful review process, the FAA determines the safety of the proposed city-pair plan and 

subsequently authorizes the carrier to fl y the route. Since 

issuing the original OpSpec A332, the FAA also considers predicted crew performance levels using the SAFTE 

model (101), a scientifi cally based modeling approach, 

in its evaluation of the proposed ULR operation. It can 

be an iterative process and require multiple changes in 

the proposed plan before approval is given. Other requirements of OpSpec A332 include both subjective and 

objective data collection during the ULR route within 

180 d of authorization for carriers to validate the effectiveness of the fatigue mitigation strategies included in 

OpSpec A332. The FAA requires that all ULR assigned 

crewmembers receive education and city-pair specifi c 

route guides that include suggested practices for maximizing total sleep times during ULR operations. 

 Position Statement on Crew Rest, Flight, and Duty 

Time Regulations 

 The prescriptive rule-making approach commonly 

used by regulatory agencies to regulate crew rest and 

fl ight and duty times is not derived from the foundational scientifi c research addressing the interaction of 

sleep and circadian processes and their effects on performance. The risks associated with nonscience-based regulatory approaches may have been unknown in the 

1930s when fl ight and duty time limits were fi rst addressed. At the time, research documenting the performance and alertness decrements associated with sleep 

•

•

•

•
34 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

loss and circadian disruption was limited and it seemed 

suffi cient to ensure safety via agreements between 

fl ightcrew and management. However, with the demands of 24/7 aviation operations, it has become increasingly apparent that such prescriptive approaches 

do not address inherent sleep and circadian challenges 

nor do they provide operational fl exibility. 

 The current FAA prescriptive regulations address 

duty time equally across all hours of the day (e.g., 8 h of 

nighttime fl ight duty is implicitly considered to be no 

more fatiguing than 8 h of daytime fl ight duty). However, a scientifi cally informed regulation would consider 

circadian placement or time of day when establishing 

work duty limits. It would also consider circadian variables when identifying the placement of opportunities 

for rest and sleep. 

 One example that clearly shows that regulatory limitations are arbitrarily chosen and are not informed by 

the scientifi c research is the regulation specifying maximum yearly fl ight times. The maximum fl ight time/year 

is 1400 h in the United States but is 900 h in Australia 

( 12 ). If the establishment of yearly fl ight time limits considered human physiology and had a foundation in relevant sleep and circadian science, it would be expected 

that these limits would be similar among countries. 

However, this is not the case. Based on this 500 h difference, U.S.-based pilots are authorized to fl y up to 64% 

more hours than Australia-based pilots. 

 Addressing fatigue as part of a scientifi cally based, 

comprehensive safety management system can help to 

minimize the risk associated with current and future 

aviation operations. An FRMS offers a way to more 

safely conduct fl ights beyond existing regulatory limits 

and should be considered an acceptable alternative to 

prescriptive fl ight and duty time and rest period 

regulations. 

 III. IN-FLIGHT COUNTERMEASURES AND 

STRATEGIES 

 In-fl ight countermeasures discussed in this section include the following: a) napping on the fl ight deck (cockpit napping); b) taking a break involving change in posture, mild physical activity, and increased social 

interaction (activity breaks); c) bunk sleep on long-haul 

and ULR fl ights; d) in-fl ight rostering approaches on 

long-haul and ULR fl ights; and e) increased exposure to 

available fl ight-deck lighting. While not all are either 

currently sanctioned or even frequently utilized, the list 

is intended to be inclusive and address the gamut of 

possible fatigue countermeasures for pilots operating in 

a restrictive environment acknowledging the need for 

safety and operational effectiveness at all times. 

 a. Cockpit Napping 

 In situations where some sleep is possible but the 

amount of sleep is limited, napping is the most effective 

nonpharmacological technique for restoring alertness. 

There is an abundance of evidence that a nap taken during long periods of otherwise continuous wakefulness 

is extremely benefi cial ( 22 , 23 , 74 , 128 , 171 , 174 , 217 , 221 ). 

How ever, while naps can be used as a preventive countermeasure in preparation of an upcoming duty schedule or during layover periods ( 176 ; see section IV.b.ii), 

cockpit napping is not currently sanctioned by the 

FAA. 

 A direct examination of the effectiveness of a 40-min 

cockpit nap opportunity, resulting in an average 26-min 

nap, revealed signifi cant improvements in subsequent 

pilot physiological alertness and psychomotor performance ( 177 ). Pilots in this study were assigned to either 

a rest group or a no-rest group. The rest group was allowed a planned, 40-min nap during a low workload 

portion of the fl ight. The no-rest group maintained their 

usual fl ight duties and were not allowed a nap period. 

Physiological data showed more alertness in the rest 

group during the last 90 min of fl ight than in the no-rest 

group. Reaction time and lapse data (failures to respond) 

from the Psychomotor Vigilance Test (PVT) indicated 

faster responses and fewer lapses in the rest group than 

in the no-rest group. 

 These naps virtually eliminated the inadvertent lapses 

in alertness immediately prior to landing present in the 

control group. Furthermore, in-seat cockpit naps have 

been authorized for use in a number of foreign air carriers (e.g., Air Canada, Air New Zealand, British Airways, 

Emirates, Finnair, Lufthansa, Swissair, Qantas; 92 ) without producing adverse effects. Survey results indicate 

U.S. commercial pilots are, in fact, already utilizing inseat cockpit napping strategies. In the NASA regional 

airline operations survey, 56% of fl ightcrew respondents 

reported they had been on a fl ight during which arrangements had been made for one pilot to sleep in the 

seat during the segment ( 55 ). For fl ightcrew responding 

to the corporate/executive fl ight operations fatigue survey, the number was 39% ( 175 ). In an earlier long-haul 

study ( 87 ), fl ightcrew were observed napping 11% of the 

available time with an average duration of 46 min (range: 

10 – 130 min). Finally, according to a National Sleep Foundation poll ( 141 ) in which respondents from the general 

public were asked to rate their level of agreement with 

the statement “ An airline pilot who becomes drowsy 

while fl ying should be allowed to take a nap if another 

qualifi ed pilot is awake and can take over during the 

nap, ” the vast majority of respondents (86%) said that 

they completely or mostly agree with this statement, 

with more than one-half (57%) saying that they completely agree. 

 b. Activity Breaks 

 Short breaks can serve to increase alertness by reducing the monotony of a highly automated cockpit environment through conscious disengagement with the fl ying task and, possibly, by allowing mild physical activity, 

depending on the type of break and the behaviors allowed during the break. Although not as effective as 

some other countermeasures reviewed in this paper, 

there are anecdotal reports from pilots indicating that 
Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 35

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

many take brief, out-of-the-seat breaks as a fatigue 

countermeasure. 

 Currently, the CFRs mandate a pilot remain seated 

through the fl ight, with few exceptions. ‡ Nevertheless, 

activity breaks that allow a pilot to change posture by 

getting up out of the cockpit seat and walking or otherwise physically moving while engaging in increased social interaction can increase alertness levels for brief periods. In a study directly addressing the effects of 

in-fl ight activity breaks, pilots fl ew a 6-h uneventful 

nighttime fl ight (~0200 to 0800) in a high-fi delity Boeing 

747-400 fl ight simulator after having been awake 18 to 

20 h ( 144 ). Pilots in the treatment group were provided 

a 7-min break every hour, at which time they exited the 

simulator and walked to a pilot briefi ng room where 

they could also engage in conversation with an experimenter. The control group received a single break midfl ight. The group that received hourly breaks showed 

signifi cantly less physiological sleepiness up to 15 min 

after the 7-min break and signifi cantly greater subjective alertness up to 25 min postbreak. However, performance on the psychomotor vigilance task (PVT), taken 

15 min after the break, showed no signifi cant differences. Nor were there signifi cant differences in subjective alertness and sleepiness 40 min after the break. The 

benefi cial subjective and physiological effects of the 

breaks were most pronounced around the low point in 

body temperature (i.e., circadian trough). Matsumoto 

and colleagues showed similar results but volunteers 

were provided a 15-min walking break at a leisurely 

speed ( 129 ). Subjects underwent the same sleep deprivation protocol two times: one with light exercise (i.e., 

walking breaks) and the other without exercise. Reductions in subjective sleepiness were seen up to 15 min after the walking breaks; however, there were no signifi -

cant differences in performance measures. Sleepiness 

ratings were signifi cantly greater when breaks were not 

taken. 

 The benefi cial effects of breaks are in part due to postural changes that occur when a pilot temporarily hands 

off fl ight-related tasks. There are consistent results from 

laboratory-based sleep deprivation research examining 

the effects of posture. In one study, subjects who underwent 20 h of continuous wakefulness showed increased 

EEG arousal, decreased reaction times and increased attention when completing the PVT while standing, compared to when seated ( 49 ). In another total sleep deprivation laboratory protocol of 40 h, changes in body 

posture improved alertness levels during the circadian 

trough ( 64 ). 

 What about a break in which the pilot briefl y disengages from the fl ying task (which may involve only 

monitoring instruments) during the cruise portion of 

the fl ight but does not leave the seat? Even if there is no 

associated increase in physical activity, several studies 

indicate an improvement in alertness and performance 

simply associated with a cognitive break from continuous tasks. A recently published study evaluated the effects of increasing the total break time received by individuals performing data entry, a task that can be 

monotonous and boring ( 86 ). Four 5-min supplemental 

breaks were added to the already scheduled two 15-min 

breaks in a workday. The data entry workers were studied for 4 wk in each of the break conditions (i.e., 30-min 

total and 50-min total). Results showed the additional 20 

min of break time, incorporated into the workday, was 

associated with signifi cantly faster data entry speeds 

(without a loss of productivity) and reductions in reports of physical discomfort. 

 Data have shown that breaks also can have positive 

effects when individuals are experiencing partial or total sleep loss. In two different total sleep deprivation 

protocols, ranging from 54 h to 64 h of continuous wakefulness, individuals who received fi ve 20-min rest breaks 

showed improvements in performance, alertness, fatigue, and overall mood when compared to those who 

received no breaks ( 96 ). These benefi cial effects also 

translate to actual aviation environments where rest 

breaks have been shown to help military pilots working 

sustained operations overcome increasing sleepiness 

and fatigue levels ( 7 ). 

 Whether engaging in a break involving activity or 

simply taking advantage of the opportunity to disengage from the current task, the available data suggest 

that the resulting increase in social interaction often accompanying a work break can play a role in maintaining 

alertness, especially during the early morning hours 

around the circadian nadir ( 64 ). However, despite substantial evidence that breaks are benefi cial, it should be 

noted that the fi ndings are not universally positive. For 

instance, in a study of industrial engineers, Tucker, 

Folkard, and Macdonald ( 208 ) found that, following a 

15-min break after 2 h of continuous work, the risk of 

on-the-job mishaps increased approximately linearly 

across the next 2 h such that it doubled during the last 

30-min period of the 2 h. Clearly, the decision whether 

or not to utilize rest breaks must take into account the 

context in which they are being considered, including 

the nature of the task itself. 

 c. Bunk Sleep 

 It was concluded during the ULR Crew Alertness 

workshops that ensuring adequate bunk sleep is one of 

the most important in-fl ight countermeasures that can 

be implemented to address sleep loss and circadian disruption during extended aviation operations ( 83 ). 

Obtaining sleep addresses the underlying physiology of 

sleep loss and is the only way to reverse cumulative 

sleep debt. Importantly, it is an operationally feasible 

‡ Note that the Code of Federal Regulation 121.543 specifi es that “ ... 

Except as provided in paragraph (b) of this section, each required 

fl ightcrew member on fl ight deck duty must remain at the assigned 

duty station with seat belt fastened while the aircraft is taking off or 

landing, and while it is enroute. (b) A required fl ightcrew member 

may leave the assigned duty station - (1) If the crewmember’s absence 

is necessary for the performance of duties in connection with the operation of the aircraft; (2) If the crewmember’s absence is in connection 

with physiological needs; or (3) If the crewmember is taking a rest period, and relief is provided ... ” 
36 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

approach to address sleep loss associated with extended 

hours of wakefulness, crossing multiple time zones, and 

fl ying during nighttime hours. 

 In-fl ight bunk sleep periods can be challenging because they need to be scheduled in consideration of operational demands and be of a duration that allows all 

crewmembers to receive ample rest periods to ensure 

the safety of the fl ight. The body is programmed for two 

periods of sleepiness throughout the day with the maximum sleep propensity occurring during the early morning hours (in the latter half of the habitual sleep episode) 

and a second period of increased sleep propensity occurring in midafternoon ( 65 , 213 ). Therefore, crews can 

estimate the times during a fl ight at which there is an increased risk of inadvertent sleepiness, and these are the 

best times (from a circadian standpoint) to schedule infl ight bunk sleep opportunities. If fl ight demands permit, utilizing these periods of increased physiological 

sleep propensity will help to increase both the quantity 

and quality of bunk sleep, subsequently reducing physiological sleepiness across the fl ight ( 53 , 63 , 65 ). Unfortunately, bunk rest periods often unavoidably end up at 

less than optimal times because of a crewmember’s job 

responsibilities. The signal or drive for wakefulness 

from the circadian clock increases throughout the waking day with a peak occurring several hours before habitual bedtime ( 111 ). Thus, trying to advance sleep initiation to a few hours before habitual bedtime will likely 

result in diffi culty with sleep initiation and reduced 

sleep duration. 

 Research has shown that environmental factors in the 

bunk facilities can help to promote good sleep. A survey 

study conducted by NASA showed that the most common factors to interfere with bunk sleep are ambient 

temperature, noise in the galley, and background lighting ( 179 ). These are all environmental issues that can be 

addressed in the design of bunk facilities. Pilots also indicated that making the sleeping quarters more private 

and the use of comfortable bedding and blankets help to 

promote the quantity and quality of their sleep. 

 d. In-Flight Rostering 

 In-fl ight rostering, although not commonly discussed 

as a fatigue countermeasure, can be used to minimize fatigue. It refers to the scheduling of fl ightcrew to assigned 

positions on the fl ight deck, freeing other fl ightcrew to 

obtain in-fl ight rest or bunk sleep. In-fl ight rostering is 

directly related to the crew complement, or number of 

pilots assigned to the fl ight and is determined — in advance — during the scheduling process. Research has 

shown that performance begins to deteriorate after 18 to 

20 h of continuous wakefulness with all aspects of cognitive functioning and mood being affected ( 24 ). Also, 

shift worker studies generally indicate that long duty 

hours increase the incidence of physical complaints, the 

use of unhealthy coping behaviors such as smoking and 

poor diet, domestic problems, and possibly musculoskeletal disorders. Furthermore, working shifts longer 

than 8 to 9 h is thought to increase the probability of 

having accidents or making errors ( 84 , 198 ). It has been 

shown specifi cally in aviation that when the “ time since 

awakening ” extends beyond the median for crew position, there is an increase in overall errors ( 139 ). Therefore, 

a suffi cient number of crewmembers is necessary to provide multiple opportunities for rest. 

 Proper in-fl ight rostering can help to minimize extended wakefulness and minimize fatigue by ensuring 

that at least one crewmember is always rested. Importantly, it allows for scheduling of bunk sleep in a way 

that minimizes the hours of continuous wakefulness for 

the landing pilots and utilizes crewmembers who are 

well rested during other critical phases of fl ight. However, this approach only works if crew rostering is considered in the planning stages of the fl ight, the crew is 

educated about the rostering approach, and the crew adheres to the plan during the fl ight. 

 No studies have evaluated, in the context of extended 

aviation operations, the specifi c number of crewmembers needed to ensure adequate sleep opportunities to 

maintain performance and safety. Simply adding crewmembers without a sound evidence-based plan of how 

this will improve the situation is not a valid approach. 

Simply providing pilots more opportunity to sleep does 

not ensure they will sleep longer. One study showed 

that when fl ightcrews were given a 5-h bunk sleep opportunity they averaged approximately 3 h ( 97 ). Another study found that fl ightcrews who were provided 

with a 7-h sleep opportunity obtained only 3 h 25 min of 

bunk sleep ( 194 ). 

 e. Cockpit Lighting 

 Much is now known about the use of properly timed 

bright light to shift human circadian rhythms. The use 

of bright light as an aid to circadian adjustment pre- and 

postfl ight is discussed in Section IV.b.iii. However, while 

investigated to a lesser extent, light also appears to have 

an acute, immediate, alerting effect on mood and performance independent of its circadian phase-shifting properties. A recent review of the literature on the acute alerting effects of light ( 38 ) shows it to be a potentially useful 

countermeasure at night where conditions allow its use. 

Light’s alerting effects are often believed to be tied to its 

suppression of melatonin, which is ordinarily released in 

the mid to late evening. Hence light has the potential to 

mitigate the usual alertness and performance decline 

seen in the nighttime hours, including on the fl ight deck. 

How much light is needed? Cajochen et al. ( 40 ) showed 

measurable increases in subjective alertness and reductions in slow eye movements with room light levels 

(100 – 200 lux). Short wavelength light appears to have 

the greatest alerting effect ( 122 ), with the spectrum of 

typical room light containing enough energy in the 

shorter wavelengths to be effective. There is also some 

evidence that the alerting effects of light are independent of the time of day, leading to the possibility of employing light during the daytime to improve alertness 

and performance in individuals impaired due to prior 

sleep deprivation ( 38 ). 
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FATIGUE COUNTERMEASURES — CALDWELL ET AL.

 Capitalizing on the immediate, direct alerting effects of 

light for fatigued fl ightcrew is particularly appealing because the fl ight-deck environment with its high automation level, limited opportunities for physical activity or 

social interaction, steady background noise, and low 

nighttime light levels creates a setting ripe for boredom, 

complacency, attentional lapses, sleepiness, and performance decrement. Adjusting the light level is one of a limited number of possible environmental manipulations. 

Provided increasing the fl ight-deck light level at night to 

at least 100 lux (room light level) does not interfere with 

fl ightcrew performance or visual requirements (e.g., dark 

adaptation level, or ability to see outside the cockpit), 

such light manipulation represents a potentially benefi -

cial in-fl ight countermeasure. While additional research 

is needed to more fully characterize the acute effects of 

light on both daytime and nighttime alertness and performance, it should be noted that increasing the light level is 

almost certain to have an effect on circadian phase ( 38 ), 

though it may be slight depending on the timing. 

 Position Statement on the Use of In-Flight 

Countermeasures 

 All of the in-fl ight countermeasures described above 

clearly have a place in sustaining the alertness and performance of aviation personnel. However, the manner in 

which these strategies are employed should be based on 

the currently available scientifi c knowledge and should 

be implemented only after thoughtful consideration. 

 We recommend the authorized use of in-seat cockpit 

napping in commercial fl ight operations, under appropriate circumstances, with appropriate safeguards, and 

in accordance with clear guidelines to ensure operational safety. Cockpit napping should be viewed as a 

risk management tool. Naps have been shown to signifi -

cantly improve alertness and performance in groundbased and in-fl ight studies, and naps can help sustain 

aircrew performance during situations in which unexpected delays require the postponement of the next consolidated sleep opportunity. In addition, naps can improve alertness during circadian low points, especially 

when schedule rotations or rapid time zone transitions 

require that work hours extend into the pilot’s subjective nighttime. In-seat cockpit naps have been proven 

safe and effective. However, despite the benefi cial effects of these naps, they should not be used as a replacement for in-fl ight bunk sleep during long-haul operations. Furthermore, in-seat cockpit napping should be 

utilized only when everyone on the fl ight deck concludes that this strategy is necessary to enhance the 

safety of fl ight operations. The duration of these naps 

should not exceed 40 min in order to avoid excessive 

postnap grogginess (sleep inertia). In a NASA study 

( 177 ), a 40-min nap opportunity resulted in 26 min of actual sleep. The short duration of the nap probably minimized sleep inertia due to the fact that only 8% of the 

participants reached slow-wave sleep (which has been 

associated with sleep inertia). According to Dinges ( 65 ), 

after 18 h of continuous wakefulness, the latency to slow 

wave sleep is approximately 30 min. Therefore, during a 

nap opportunity of 40 min, it is unlikely most people 

will fall asleep fast enough to obtain more than 30 min 

of sleep, and during that 30 min of sleep, enter into slow 

wave. Other studies have also shown minimal sleep inertia effects with naps less than 30 min ( 30 , 204 ). 

 We recommend the use of in-fl ight activity breaks in 

commercial fl ight operations, under appropriate circumstances, with appropriate safeguards, and in accordance with clear guidelines to ensure operational safety. 

As with cockpit naps, such breaks should be viewed as 

a risk management tool. In a cockpit environment, which 

can be conducive to sleep, breaks associated with mild 

physical activity and increased social interaction or even 

just temporary disengagement from monotonous tasks, 

have been shown to temporarily boost alertness. When 

using breaks as a fatigue countermeasure, it is recommended that shorter breaks (i.e., 10 min) be used hourly 

or more frequently as opposed to longer breaks, which 

can be relatively infrequent. 

 The use of bunk sleep and in-fl ight rostering go handin-hand when used as a fatigue mitigation strategy. 

Scheduling practices should always take into account 

the research on both sleep and circadian process when 

scheduling critical phases of fl ight as well as in-fl ight 

sleep opportunities. Since the development of the rostering pattern should help minimize fatigue during operations, policies are necessary to allow for fl exibility in 

these rostering approaches if a change, once the fl ight 

has begun, will contribute to the overall safety of operations. Additionally, future applied research is needed to 

determine the optimal timing for crewmembers to obtain rest in order to maintain maximum performance 

levels. Operational research evaluating the effects of 

varying crew augmentation options on the effi cacy of 

onboard sleep can help address some of these issues. In 

light of the fact that in-fl ight work/rest planning can be 

a complex matter, it is our position that: 1) aircrews be 

educated with regard to the circadian and environmental factors that infl uence in-fl ight bunk rest quality; and 

2) when possible, aircrews take advantage of validated 

work/rest scheduling tools to develop the most effective 

in-fl ight rest pattern given the available crewmembers. 

 Lastly, simply increasing the fl ight-deck light level, 

particularly at night, has the potential to temporarily 

boost alertness and performance. While several light parameters and the mechanism of action are still being investigated, the benefi cial effects have been established 

in several laboratory studies. Any use of light must include an awareness of its potential effect on circadian 

phase. 

 IV. PRE-/POSTFLIGHT COUNTERMEASURES 

AND STRATEGIES 

 a. Hypnotics 

 Sleep is often diffi cult to obtain in operational contexts, even in situations where efforts have been made to 

ensure the existence of adequate sleep opportunities. 

There are a number of reasons for this, but generally 
38 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

speaking, the diffi culties are due to one or more of the 

following: 1) the sleep environment is less than optimal 

(too noisy, hot, and/or uncomfortable); 2) the state of 

the individual is incompatible with the ability to sleep 

(too much excitement, apprehension, or anxiety); or 3) 

the sleep opportunity occurs at a time that is not biologically conducive to rapid sleep onset and/or suffi cient 

sleep maintenance. This misalignment of the sleep/

wake cycle and endogenous circadian rhythms could be 

the result of shift lag, jet lag, or attempting sleep at other 

than the habitual bedtime or at the second circadian dip 

in the afternoon. For such circumstances, the U.S. Air 

Force and Army have approved the limited use of temazepam, zolpidem, and zaleplon. § These hypnotics 

can optimize the quality of crew rest in circumstances 

where sleep is possible, but diffi cult to obtain. The choice 

of which compound is best for each circumstance must 

take several factors into account, including time of day, 

half-life of the compound, length of the sleep period, 

and the probability of an earlier-than-expected awakening, which may increase the risk of sleep inertia effects. 

Temazepam: Temazepam (Restoril w , Euhypnos w , 

Normison w , Remestox w , Norkotral w ) (15 – 30 mg) has 

been recommended in military aviation populations in 

Great Britain since the 1980s ( 150 – 152 ). Given the 

pharmacodynamics of this substance, it may be the 

best choice for optimizing 8-h sleep periods that 

are out-of-phase with the body’s circadian cycle because, under these circumstances, sleep is often easy to 

initiate, but diffi cult to maintain due to the circadian 

rise in alertness. Personnel who work at night generally fi nd that they can easily fall asleep after the work 

shift since sleep pressure is high from their previous 

night (and often day) of continuous wakefulness. Also, 

in the early morning, the circadian drive for wakefulness is typically low, so the body’s natural rhythms do 

not interfere with sleep onset. However, once daytime 

sleep has begun, night workers are frequently plagued 

by late morning or noontime awakenings that result 

from the increased prominence of circadian-based 

alerting cues. The net result is that the day sleep of 

night workers often is 2 or more hours shorter per day 

than their typical night sleep ( 5 , 205 ). 

 For these individuals, the longer half-life of temazepam is desirable because the problem usually is one of 

sleep maintenance and not sleep initiation . In addition to 

temazepam’s known facilitation of nighttime sleep 

( 133 , 138 ), this compound, particularly in the 30-mg dose, 

has been shown to objectively and subjectively improve 

daytime sleep as well ( 52 , 153 , 162 ). Temazepam’s intermediate half-life of approximately 9 h provides a suffi -

ciently lengthy hypnotic effect to mitigate the disruptive 

arousals that often lead to sleep deprivation in personnel suffering from shift lag or jet lag. The pharmacokinetic disposition of temazepam is affected by the time of 

administration; the absorption of the drug is faster and 

the half-life and distribution are shorter for daytime administration compared to nighttime administration 

( 138 ). Furthermore, in studies involving simulated night 

operations, temazepam has been shown to improve 

nighttime performance by optimizing daytime sleep 

( 162 ). A study using U.S. Army pilots who worked and 

fl ew at night in a simulated shift-work environment 

demonstrated that temazepam-induced improvements 

in daytime sleep led to better nighttime pilot performance (relative to placebo) as well as improvements in 

psychomotor vigilance and self-reported alertness ( 52 ). 

 Thus, temazepam appears to be a good choice for 

maximizing the restorative value of daytime sleep opportunities. However, caution should be exercised prior 

to using temazepam in certain operational settings since 

the compound does have a relatively long half-life. Although residual effects were not reported in a military 

study in which personnel were able to gain suitable 

sleep before reporting for duty ( 29 ), nor in some other 

situations in which 30 – 40 mg of temazepam were given 

prior to a full sleep opportunity ( 180 , 227 ), residual postdose drowsiness has been reported elsewhere. Paul, 

Gray, MacLellan, and Pigeau ( 158 ) observed that drowsiness was noticeable within 1.25 and 4.25 h of a midmorning 15-mg dose. They also noted that psychomotor 

performance was impaired between 2.25 and 4.25 h 

postdose (plasma levels were still elevated at 7 h postdose). These data suggest the possibility that temazepam’s long half-life could exacerbate sleep inertia upon 

awakening; however, the potential for this drawback 

must be weighed against the potential for impairment 

from sleep truncation in the event that temazepam therapy is withheld. Along these lines, it should be noted 

that Roehrs, Burduvali, Bonahoom, Drake, and Roth 

( 170 ) found that just 2 h of sleep loss produces the same 

level of sedative effect as the consumption of 0.54 g/kg 

of ethanol (the equivalent of 2 to 3 12-oz bottles of beer), 

whereas the effects of 4 h of sleep loss are similar to those 

of 1.0 g/kg of ethanol (5 to 6 12-oz beers). Other investigations have similarly shown that sleep restriction and 

sleep deprivation degrade performance as much as, or 

more than, alcohol intoxication. 

 The same qualities that make temazepam desirable 

for maintaining the daytime sleep of shift workers make 

it a good choice for temporarily augmenting the nighttime sleep of personnel who are deployed westward 

across as many as nine time zones ( 149 , 201 ). Upon arrival at their destination, these travelers are essentially 

facing the same sleep/wake problems as the night 

worker. Namely, they are able to fall asleep quickly since 

their local bedtime in the new time zone is much later 

than the one established by their circadian clock (from 

the origination time zone); however, they generally are 

unable to sleep throughout the night. The reason for this 

 § Note that at one time, the U.S. Air Force and Army both approved 

the use of triazolam (Halcion w ), but that at present, only the U.S. 

Army continues to authorize the limited use of this medication for 

pre-deployment rest or sustained operations (although in actuality, it 

is rarely prescribed). Triazolam’s purported association with adverse 

effects and its impact on memory have curtailed its use in many clinical settings. Therefore, a detailed discussion of triazolam will be omitted from the present paper in favor of concentrating on the more frequently used hypnotics (temazepam, zolpidem, and zaleplon). 
Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 39

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

is demonstrated by the following example: a 6-h westward time zone change places bed time at 2300 local 

time which is 0500 origination time; this is followed by a 

wakeup time of 0600 local which corresponds to a 

 “ body-clock time, ” still adjusted to the origination time, 

of 1200. Based on a readjustment rate of 1.5 d per time 

zone crossed ( 105 ), it could take up to a week for adjustment to the new time zone to occur. Until this adjustment is accomplished, temazepam can support adequate 

sleep maintenance despite confl icting circadian signals 

and the obvious benefi t will be less performance-

 degrading sleep restriction. While the problem with 

daytime alertness due to circadian disruptions will not 

be alleviated, the daytime drowsiness associated with 

increased homeostatic sleep pressure (from sleep restriction) will be attenuated. 

 Thus, temazepam is a good choice when a prolonged 

hypnotic effect is desired as long as there is relative certainty that the hypnotic-induced sleep period will not be 

unexpectedly truncated. This compound is especially 

useful for promoting optimal sleep in personnel suffering from premature awakenings due to shift lag or jet 

lag since the hypnotic effect helps to overcome circadian 

factors that can disrupt sleep immediately following a 

time zone or schedule change. However, temazepam 

should not be used longer than is necessary to facilitate 

adjustment to the new schedule. Depending on the circumstances, temazepam therapy probably should be 

discontinued after 3 to 7 d either to prevent problems 

associated with tolerance or dependence (in the case of 

night workers) or because adjustment to the new time 

zone should be nearly complete (in the case of travelers 

or deployed personnel) ( 149 ). When discontinuing temazepam after several continuous days of therapy, it is 

recommended that the dosage be gradually reduced for 

2 to 3 d prior to complete discontinuation in order to 

minimize the possibility of rebound insomnia ( 181 , 209 ). 

Zolpidem: Zolpidem (Ambien w , Stilnox w , Myslee w ) 

(5 – 10 mg) may be the optimal choice for sleep periods 

less than 8 h, and zolpidem would be a better choice 

than temazepam if there were a possibility that the 

hypnotic-induced sleep period is likely to be unexpectedly shortened. This compound is especially useful for 

promoting short- to moderate-length sleep durations (of 

4 to 7 h) when these shorter sleep opportunities occur at 

times that are not naturally conducive to sleep. As noted 

above, daytime naps would fall into this category because, just like daytime sleep in general, daytime naps 

are typically diffi cult to maintain ( 61 , 111 , 205 ), especially 

in non-sleep-deprived individuals. Furthermore, unless 

the naps are placed early in the morning or shortly after 

noon, they can be extremely diffi cult to initiate without 

some type of pharmacological assistance ( 89 ). Zolpidem 

is a good choice for facilitating such naps because its relatively short half-life of 2.5 h provides short-term sleep 

promotion while minimizing the possibility of postnap 

hangovers. Thus, it is feasible to take advantage of a nap 

without signifi cantly lengthening the postnap time 

needed to ensure that any drug effects have dissipated. 

However, as with temazepam, there should be a reasonable degree of certainty that there will not be an early interruption of the sleep period followed by an immediate 

demand for performance. 

 The effi cacy of zolpidem as a nighttime sleep promoter has been clearly demonstrated in clinical trials 

(with up to 1 yr of administration) in normal, elderly, 

and psychiatric patient populations with insomnia ( 21 ). 

Rebound insomnia, tolerance (treatment over 6 to 12 

mo), withdrawal symptoms, and drug interactions are 

absent, and the dependence/abuse potential is low ( 16 ). 

Overall, zolpidem is a clinically safe and useful hypnotic 

drug ( 156 , 188 ). 

 Zolpidem has been proven to possess utility in militarily relevant circumstances. An Army study ( 43 ) demonstrated that zolpidem-induced prophylactic naps enhanced the alertness and performance of sleep-deprived 

pilots (relative to placebo) during the fi nal 20 h of a 38-h 

period of continuous wakefulness without producing 

signifi cant hangover effects. Since these naps were 

placed at a time during which sleep is often diffi cult to 

obtain ( 111 ), the benefi ts in terms of sleep promotion 

and sleep quality were clear. Thus, zolpidem is an effective way to promote short naps, and, relative to placebo, 

is associated with improved subsequent alertness. 

 Zolpidem may also be helpful for promoting the sleep 

of personnel who have traveled eastward across 3 to 9 

time zones ( 202 ). Unlike westward travelers who experience sleep maintenance diffi culties, eastward-bound personnel suffer from sleep initiation problems. For example, a 6-h time zone change in the eastward direction 

creates diffi culty with initiating sleep because a local 

bedtime of 2300 translates to a body clock time of only 

1700, and it has been well established that such early 

sleep initiation is problematic ( 150 , 201 , 219 ). Thus, eastward travelers need something that will facilitate early 

sleep onset and suitable sleep maintenance until the 

normal circadian-driven sleep phase takes over; however, they do not need a compound with a long half life. 

This is because, in this example, any residual drug effect 

would only exacerbate the diffi culty associated with 

awakening at a local time of 0700 that corresponds to an 

origination time (or body-clock time) of only 0100 in the 

morning. As stated above, sleep diffi culties are only part 

of the jet-lag syndrome, but alleviating sleep restriction 

or sleep disruption will help to attenuate the alertness 

and performance problems associated with jet lag. 

 Thus, zolpidem is a good compound for facilitating 

naps of moderate durations (4 to 7 h), even when these 

naps occur under less-than-optimal circumstance and/

or at the “ wrong ” circadian time. Zolpidem is also appropriate for treating sleep-onset diffi culties in eastward 

travelers. However, as is the case with any hypnotic, this 

medication normally should be used only when necessary, i.e., prior to circadian adjustment to a new work or 

sleep schedule. More chronic zolpidem administration 

may be essential for promoting naps that occur under 

uncomfortable conditions or naps that are “ out of phase ” 

since, by defi nition, these generally are diffi cult to initiate and maintain, but zolpidem probably should not be 

used for more than 7 d to counter insomnia from jet lag. 
40 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

After this time, most of the adjustment to the new time 

zone should be accomplished ( 201 , 219 ). 

Zaleplon: Zaleplon (Sonata w , Starnoc w ) (5 – 10 mg) 

may be the best choice for initiating very short naps (1 to 

2 h) during a period of otherwise sustained wakefulness 

or for initiating early sleep onsets in personnel who are 

trying to ensure suffi cient sleep prior to a very early 

start time the next morning. With regard to facilitating 

early report times, zaleplon is an option to zolpidem, 

but both compounds are important for the same reason. 

As noted earlier, it is extremely diffi cult for most people 

to initiate sleep 1 to 4 h prior to their typical bedtimes 

unless they are severely fatigued ( 6 , 90 , 111 ). Since these 

individuals are unable to fall asleep early, the total length 

of their sleep period is truncated by the early rise time 

even if, once they fi nally go to sleep, they sleep relatively 

well. Personnel who are required to report to duty in the 

predawn hours can easily suffer 2 to 3 h of sleep deprivation because of physiologically based sleep initiation 

diffi culties. This is why short-haul pilots attribute a substantial percentage of their fatigue-related problems to 

early report for duty times ( 28 ). Sleep truncation of this 

amount has been shown to signifi cantly impair both 

alertness and performance ( 17 , 162 , 214 ). Similar to zolpidem (which has a 2.5-h half-life), zaleplon can overcome 

this sleep initiation problem, and its ultra-short 1-h half 

life is less likely to pose hazards in terms of residual 

drug effects that can exacerbate the drowsiness associated with the predawn awakening dictated by the early 

start time. 

 Clinical trials of the hypnotic effi cacy of zaleplon have 

shown improvement in sleep initiation, particularly 

with the 20-mg dose ( 54 , 80 , 85 ). In people diagnosed with 

primary insomnia, the latency to sleep onset decreased 

signifi cantly compared to placebo ( 54 ). After zaleplon 

exerts its initial effects, the drug is subsequently (and 

quickly) eliminated in time for more natural physiological mechanisms to take over and maintain the remainder of the sleep period. There is evidence that there are 

no hangover problems as early as 6 to 7 h later ( 54 ). The 

rapid initiation of sleep at an earlier-than-normal time 

permits a full sleep period despite the requirement for 

an early awakening, and thus bolsters subsequent performance. Paul et al. ( 157 ) found that 10 mg zaleplon 

impaired psychomotor performance for up to 2.25 h after ingestion. The same dose increased drowsiness from 

2 to 5 h after dosing ( 158 ), with plasma drug levels equal 

to placebo by 5 h postdose. These authors recommend 

zaleplon for times when an individual may have to 

awaken no earlier than 3 h after drug ingestion. 

 Thus, zaleplon (10 mg) is a good hypnotic for promoting short naps (2 to 4 h) which would otherwise be diffi -

cult to initiate and maintain, as well as for hastening the 

early-to-bed sleep onset of personnel who are faced with 

an acute demand to report for duty in the early morning 

(i.e., at 0400 to 0500). In addition, as was the case with zolpidem, zaleplon can be considered useful for the treatment of sleep-onset insomnia in eastward travelers who 

are experiencing mild cases of jet lag. For instance, those 

who have transitioned eastward only 3 to 4 time zones can 

use this short-acting drug to initiate and maintain what 

the body believes to be an early sleep period. As with any 

hypnotic, the course of treatment should be kept as short 

as reasonably possible to minimize drug tolerance and 

drug dependence ( 149 ). Table II summarizes some of the 

characteristics of each of the hypnotics discussed. 

Newer hypnotics: Some of the newer hypnotics available help with sleep maintenance without the extended 

long half-life of temazepam. For example, the extendedrelease zolpidem (Ambien CRw ) improves sleep maintenance beyond that of zolpidem ( 93 ). In addition, eszopiclone ( Lunestaw ) has a half-life of 5 to 6 h with minimal 

residual drug effects after as little as 10 h post dose ( 114 ). 

Ramelteon (Rozeremw ) is a novel hypnotic in that it targets the melatonin receptors in the brain in order to regulate the body’s sleep-wake cycle ( 119 ). Research indicates that this drug is effi cacious for sleep onset, but not 

for sleep maintenance ( 119 ). 

 New sleep-promoting compounds are being produced 

by the pharmaceutical industry each year. One hypnotic 

slated to come on the market in the near future is indiplon. This drug is similar in structure to zaleplon and 

has a half-life of approximately 1.5 h; it is also being formulated with a modifi ed release as well which will extend its half-life to aid in sleep maintenance ( 79 ). There 

are new compounds which are rapidly absorbed and 

TABLE II. LIST OF HYPNOTICS AND THEIR USES. 

Generic name Brand Name Dosage

Average 

Half-life Recommended Use Cautions 

Temazepam Restoril w

Euhypnos w

Normison w

Remestox w

Norkotral w

15 – 30 mg 9 h Sleep maintenance; daytime sleep; 

 prolonging sleep to avoid early 

 morning awakenings from jet lag/shift lag

Need an 8-h sleep 

 period; not recommended 

 if on-call 

Zolpidem Ambien w

Stilnox w

Myslee w

5 – 10 mg 2.5 h Sleep initiation; intermediate-length naps; 

 assisting early sleep onset due to early 

 bedtimes from shift or time zone change

Need to have at least 4-6 h of 

 sleep; not recommended 

 if on-call 

Zaleplon Sonata w

Starnoc w

5 – 10 mg 1 h Sleep initiation; short naps; assisting early 

 sleep onset due to early bedtimes from 

 shift or time zone change

Not recommended if 

 on-call 
Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 41

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

have a short half-life, and some have the ability to increase both slow-wave sleep and slow-wave activity, 

which improves sleep effi ciency. These compounds may 

improve sleep effi ciency to the point that effective wakefulness can be sustained on fewer than the 8 h of daily 

sleep that is now required. Perhaps short power naps of 

3 to 4 h could become equally effective, but research remains to substantiate this possibility. 

 Current civilian aviation policy allows limited use of 

zolpidem only. The FAA allows its use no more than 

twice a week, and states that it cannot be used for circadian adjustment. In addition, there is a 24-h grounding 

policy for any pilot who uses zolpidem. While melatonin 

is not a prescription hypnotic medication in the United 

States, it is a controlled substance in many other countries. The use of melatonin to promote sleep is discussed 

in a later section on nonpharmacological substances. 

 Sleep promoting compounds can be useful in operational contexts where there are problems with sleep initiation or sleep maintenance. However, it should be 

noted that, like all medications, there are both benefi ts 

and risks associated with the use of these compounds. 

These should be considered by the prescribing physician and the individual pilot before the decision to utilize hypnotic therapy is fi nalized. A hypnotic of any 

type probably should not be used if the crewmember is 

likely to be called back to duty earlier than anticipated 

because this would put them at risk of performing fl ight 

duties before the medication has been fully metabolized. Although temazepam, zolpidem, and zaleplon 

are widely recognized as being both safe and effective, 

personnel should be cautioned about potential side effects and instructed to bring these to the attention of 

their physician should they occur. Potential problems 

may include morning hangover, which may cause detrimental effects on performance, dizziness, and amnesia 

that may be associated with awakenings that are forced 

before the drug has been eliminated, and various idiosyncratic effects ( 14 , 131 , 149 , 181 ). If any diffi culties occur, it may be necessary to discontinue the specifi c compound or to abandon hypnotic therapy altogether. 

However, it is likely that signifi cant side effects can be 

reduced or eliminated by using the correct compound 

or by modifying dosages or dose intervals ( 150 ). For 

these reasons, military personnel are required to receive 

a test dose of the hypnotic of interest under medical supervision before using the medication during operational situations. Even after the test dose yields favorable results and it is clear that operationally important 

side effects are absent, hypnotics should be used with 

particular caution when the aim is to aid in advancing 

or delaying circadian rhythms in response to time zone 

shifts ( 149 , 201 , 219 ). Reviews by Waterhouse and associates ( 219 ), Nicholson ( 149 ), and Stone and Turner ( 201 ) 

offer detailed information on this rather complex 

issue. 

 While the use of sleep aids is authorized in both civilian and military aviation, the restrictions in the civilian 

community are such that pilots do not receive the intended benefi ts of their use. The policy that hypnotics 

not be used for circadian disruption is overly restrictive 

since it is precisely for this reason that hypnotics would 

be useful for pilots crossing multiple time zones or fl ying early morning fl ights. The policy adopted by the 

military community allows the use of hypnotics with 

specifi ed grounding times, allowing pilots to obtain restful sleep prior to a diffi cult schedule, but such that hypnotic use does not interfere with fl ight times. It would be 

useful for the civilian community to evaluate the hypnotic policy implemented by the military to allow safe 

use of hypnotics by civilian pilots. Education concerning 

the appropriate use of hypnotics, along with relevant 

grounding periods, would allow pilots to obtain sleep 

which may not otherwise occur. Also, by allowing a 

choice of hypnotics rather than allowing only one, a variety of hypnotics with varying length of action will allow the appropriate drug for the specifi c time of use. 

 Position Statement on the Use of Hypnotics 

 For the present time, it is our position that zolpidem 

be authorized for civilian commercial pilots a maximum 

of 4 times per week in situations where natural sleep is 

diffi cult or impossible due to circadian or other reasons 

provided that: 1) the pilot has checked for any unusual 

reactions to the medication during an off-duty period; 2) 

the dose does not exceed 10 mg in any given 24-h period; and 3) there is a minimal interval of 12 h between 

the ingestion of the medication and the return to duty. 

This recommendation is based on research which shows 

that: 1) zolpidem’s half-life of 2.5 h (extended release 

half-life is 2.8 h) allows it to be fully metabolized in 10 h 

(11.2 h for extended release); and 2) research has shown 

that repeated use of zolpidem in clinical settings continuously improves sleep quality without causing rebound 

insomnia or exerting a negative impact on next day 

alertness ( 107 ). Zolpidem should not be taken to promote any type of in-fl ight sleep. It should be noted that 

facilitating quality sleep with the use of a well-tested, 

safe pharmacological compound is far better than having pilots return to duty when sleep deprived or having 

them return to duty following a sleep episode that has 

been induced with alcohol. Studies have shown that despite the “ 8-h bottle-to-throttle ” rule, impairments due 

to even moderate alcohol consumption may persist 

throughout the night to the morning after ( 234 ). 

 b. Improving Sleep and Alertness 

 This section describes improving pre- and postfl ight 

sleep and alertness without the use of medications or 

pharmacological countermeasures. Such countermeasures are discussed in the context of military aviation 

(see Section VI.) where they are currently permitted under specifi ed circumstances and with specifi ed controls. 

i. Healthy Sleep Practices: Whenever possible, getting a 

suffi cient quantity of high quality sleep on a daily basis 

must be the number one focus in fi ghting fatigue. How 

much is suffi cient? Generally speaking, people require 

about 8 h of sleep per day in order to sustain optimum 

alertness ( 222 ). Although some people can function well 
42 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

on less, they are small in number. Two strategies can 

help determine individual sleep need. 

 The fi rst strategy is to extend the nightly sleep period 

an extra hour over the course of the next 7 d, and after 

the 7th d, self-refl ect on whether the additional sleep has 

been benefi cial in terms of cognitive performance, mood, 

and alertness. The second, and more reliable, strategy is 

to keep a sleep diary during the next vacation when it is 

possible to sleep ad lib for several days. After recording 

the time of natural sleep onset and natural awakening 

(without the aid of an alarm clock) for 5 to 7 d (excluding the fi rst 2 vacation days), obtain the average sleep 

time and make this amount of sleep each night the goal 

upon returning to work. 

 Obtaining the required quantity of sleep on a day-today basis obviously is important, but obtaining high 

quality sleep is benefi cial as well. Sleep fragmentation 

is known to degrade memory, reaction time, vigilance, 

and mood ( 25 ). Specifi c strategies can help optimize 

each sleep opportunity, and these are presented 

below. 

Strategies for Optimizing Sleep Opportunities: 

When possible, wake up and go to bed at the same time every 

day to avoid circadian disruptions. 

Use the sleeping quarters only for sleep and not for work. 

If possible, establish a consistent and comforting bedtime routine (e.g., reading, taking a hot shower, and then going to 

bed). 

Perform aerobic exercise every day, but not within 2 h of going 

to bed. 

Make sure the sleeping quarters are quiet, totally dark, and 

comfortable. For this to work, day workers should be housed 

separately from night workers. 

Keep the sleep environment cool (~26 ° C if you are covered). 

Move the alarm clock out of sight so you can’t be a clock 

watcher. 

Avoid caffeine in drinks and other forms during the 

afternoons/evenings. 

Don’t use alcohol as a sleep aid (it may make you sleepy, but 

you won’t sleep well). 

Avoid cigarettes or other sources of nicotine right before 

bedtime. 

Don’t lie in bed awake if you don’t fall asleep within 30 min –

instead, leave the bedroom and do something relaxing and 

quiet until you are sleepy. 

ii. Napping: In employing a napping strategy pre/

postfl ight, an important factor is nap timing or placement. A nap taken during the day before an all-night 

work shift (a prophylactic nap), with no sleep loss 

prior to the shift, will result in improved performance 

over the night compared to performance without the 

nap ( 23 , 191 ). Although naps taken later in the sleepdeprivation period also are benefi cial, these naps probably should be longer than prophylactic naps in order 

to derive the same performance benefi t. Schweitzer et 

al. ( 191 ) demonstrated that when subjects received a 2- 

to 3-h nap before a night work shift (with concurrent 

sleep loss) they performed better than when receiving 

no nap. Bonnet ( 23 ) showed that a nap before a 52-h 

continuous performance period was benefi cial in keeping performance and alertness from decreasing for up 

to 24 h compared to the no-nap condition, but by the 

second night of sleep loss, the benefi t of the naps could 

not be reliably measured. 

•

•

•

•

•

•

•

•

•

•

•

 Another important factor is nap length . A relationship 

between nap length and performance was reported by 

Bonnet ( 23 ) based on a study in which subjects were allowed either a 2-, 4-, or 8-h nap before 52 h of continuous 

operations. The results indicated a dose-response relationship between the length of the nap and performance 

during the fi rst 24 h of sleep deprivation. Bonnet concluded that the nap before an all-night shift should be as 

long as possible to produce maximum performance benefi ts and that prophylactic naps were better than naps 

designed to replace sleep that was already lost due to 

the requirement for continuous wakefulness. This conclusion was supported in a study by Brooks and Lack 

( 30 ), who tested afternoon naps of 5, 10, 20, and 30 min 

following nighttime sleep of 5 h. The longer 20- and 30-

min naps showed improvement in overall cognitive performance for as long as 155 min compared to the 10-min 

nap which showed cognitive performance effects for 

only 95 min. This fi nding is consistent with a recent 

meta-analysis on the effi cacy of naps as a fatigue countermeasure ( 75 ). This meta-analysis of 12 studies consisting of a total of 178 tests not only concluded that 

naps led to performance benefi ts equal to, and sometimes greater than, baseline performance levels, but also 

that the length of performance benefi t was directly proportional to the length of the nap (e.g., a 15-min nap led 

to 2 h of benefi t while a 4-h nap led to 10 h of benefi t). 

However, it was also noted that, regardless of nap length, 

the performance benefi t decreased as postnap interval 

increased (i.e., the benefi ts of a 4-h nap were greater 

shortly after awakening than after 10 h, though performance at the later time still met or exceeded baseline 

performance). 

 A fi nal consideration is the placement of the nap with 

regard to the phase of the body clock (circadian phase). Nap 

timing should take into account the impact of circadian 

phase on sleep propensity, structure, and quality across 

the day as well as the effects on performance both immediately after awakening and later in the work period. 

Sleep tendency is highest during the daily trough in 

core body temperature (in the predawn and early morning hours) and lowest when core body temperature 

peaks (in the early evening hours) ( 65 ). Thus, there may 

be signifi cant problems initiating and/or maintaining a 

nap during an adverse circadian phase when core temperature is near its peak, as during the “ forbidden zone 

for sleep ” a couple of hours prior to habitual bedtime 

( 111 ). Naps placed during the circadian troughs are the 

easiest to maintain and they show benefi cial effects on 

later performance. Gillberg ( 89 ) showed that a 1-h nap 

placed at 0430 (in the circadian trough) was more benefi cial to next-day performance than one placed at 2100. 

However, while naps during the circadian trough may 

be more effective for performance sustainment, they 

also are the more diffi cult naps from which to awaken. 

Generally, studies have shown that postnap sleepiness, 

termed “ sleep inertia, ” is higher and performance is 

lower immediately upon awakening from a nap taken 

during the circadian trough as compared to naps taken 

during the circadian peak ( 71 ). For this reason, some 
Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 43

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

authors suggest that naps in the circadian trough should 

be avoided, and naps should be taken before a person’s 

sleep loss extends beyond 36 h. However, it should be 

possible to take advantage of the improved quality of 

naps in the circadian trough while avoiding the negative sleep-inertia effects if napping personnel can be 

awakened about 1 h prior to their work shifts. This will 

allow time to overcome most of the effects of sleep 

inertia. 

iii. Circadian Adjustment: The circadian clock cannot 

adapt immediately to a change in the duty/rest cycle or 

changes in environmental cues, such as those experienced 

with transmeridien travel ( 106 ). When crossing time 

zones, the circadian clock is out of sync with the local environment. Adjustment is usually faster after traveling in 

the westward than the eastward direction ( 27 , 185 ). 

Adjustment depends on direction of travel, the number of 

time zones crossed, the rhythm being measured and an 

individual’s exposure to time cues (e.g., light/dark cycle). 

Adjustment does not appear to be linear and those who 

are evening types ( “ owls ” ) tend to adjust to the new time 

zone more quickly relative to morning types ( “ larks ” ). 

 Aircrew fatigue resulting from circadian disruption is 

subject to partial alleviation with hypnotics; however, in 

cases where the crewmember will remain in the new 

time zone on a consistent duty schedule for several consecutive days, it may be better to restore the body’s natural sleep/wake rhythm through other circadian re-

 entrainment techniques. Adjusting to new time zones or 

work schedules is largely a matter of controlling exposure to sunlight, placing meals and activities at appropriate times, and making every effort to optimize sleep 

during available sleep periods ( 11 , 33 , 196 , 220 ). Although 

operational requirements often make it diffi cult, aircrew 

should pay close attention to their behaviors following 

schedule changes. Several of the recommendations that 

are typically made to help industrial shiftworkers are 

also useful in aviation settings. 

Recommendations for Rotating to Different Shift Schedules: 

When remaining within the same time zone but rotating to 

night duty, avoid morning sunlight by wearing dark glasses and 

by staying indoors as much as possible prior to sleeping. 

For daytime sleep, make sure the sleep environment is dark and 

cool. 

For daytime sleep, use eye masks and earplugs (or a masking 

noise like a box fan) to minimize light and noise interference. 

For daytime sleep, make sure to implement the good sleep habits discussed previously. 

When on duty at night, try to take a short nap before reporting 

for duty. 

After waking from daytime sleep, get at least 2 h of sunlight (or 

artifi cial bright light) in the late afternoon or early evening if 

possible. 

 When traveling to a new time, crews will face circadian disruptions similar to those encountered by people 

rotating from day shift to night shift within the same 

time zone. Upon arrival in the new time zone (assuming 

that this will be the new duty location for several days, 

weeks, or months and that crewmembers will be fl ying/

working in the daytime rather than at night), the following recommendations are available to aid in adjusting to 

new time zones. 

•

•

•

•

•

•

Recommendations for Time Zone Adjustments: 

Quickly adjust meal, activity, and sleep times to the new time 

zone schedule ¶ . 

Maximize sunlight exposure during the fi rst part of the day. 

Minimize sunlight exposure during the afternoons. 

Avoid heavy meals at night because stomach discomfort will 

disrupt sleep. 

Follow good sleep habit recommendations to optimize nighttime sleep. 

Try self-administered relaxation techniques to promote nighttime sleep. 

If possible, prior to bed time, take a hot bath. Cooling off afterwards may mimic the circadian-related temperature reduction 

that normally occurs during sleep. 

During the fi rst few days of circadian adjustment, use sleep 

medications (if authorized) to promote sleep at night, and use 

caffeine to augment alertness during the day. 

 Properly timed bright light is an alternative strategy 

for resynchronizing circadian rhythms after schedule 

changes ( 62 , 88 , 185 ). Several researchers have published 

recommendations about the use of light to promote circadian adjustment, but they have pointed out diffi culties associated with the correct timing of administration 

of light therapy as well ( 77 , 117 , 168 ). Consensus reports 

summarizing issues related to the use of bright light as a 

treatment for jet lag and shift lag also have been published ( 27 , 78 ). 

 Unfortunately, the diffi culties associated with appropriate timing of artifi cial bright light therapy often leave 

experts to recommend a reliance on other approaches. In 

addition, it is often diffi cult to establish any type of 

bright light facility on the ground much less on board 

aircraft. Finally, an approximate understanding of one’s 

circadian status is a prerequisite for phase changes with 

supplementary melatonin. Self-administration techniques such as natural sunlight exposure, appropriately 

timed naps, and proper exposure to zeitgebers (time 

cues) may facilitate circadian adjustment to new duty or 

time zone schedules ( 154 , 167 , 201 , 219 ). 

iv. Exercise: Exercise has been shown to be an effective 

fatigue countermeasure in both the laboratory and aviation environments. Those who exercise regularly actually show improved sleep quantity and quality ( 199 ). 

However, if engaged in too close to bedtime, exercise can 

have negative effects on sleep, making it more disrupted 

( 137 ). Exercise increases physiological arousal and can 

help promote alertness in the short-term. However, it is 

important to consider the level of exercise and the timing 

when determining its effectiveness as a countermeasure. 

Research has suggested that only heavy exercise 

(70%VO 2max ) results in changes in objective vigilance 

performance, and the effects last no longer than 30 min 

( 98 ). These heavy exercise periods were brief (10 min) 

because if too long (~1 h), they would actually increase 

fatigue and sleepiness levels. When exercise levels were 

in the light to moderate range, subjects seemed to be 

more alert and less sleepy for up to a 15-min postexercise 

period. However, more recent research has shown that 

•

•

•

•

•

•

•

•

 ¶ If persons who have been working nights in the U.S. will be working days in Europe, it might not be necessary to readjust the body 

clock since it already will be on the proper schedule. 
44 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

the subjective effects of moderate exercise bouts can last 

up to 30 min ( 113 ). Subjects who engaged in 10 min of 

moderate exercise every 2 h throughout a 40-h sleep deprivation protocol showed less subjective sleepiness up 

to 30 min after exercising. Similar to other research, no 

differences were seen in objective performance. 

 While exercise can be used as a fatigue countermeasure to improve alertness levels in the short term, it can 

also induce phase shifts in the melatonin circadian 

rhythm and the circadian clock ( 35 , 78 ). Data collected 

by Shiota and colleagues on airline crewmembers fl ying a 4-d fl ight pattern between Tokyo and Los Angeles 

(8-h time difference) showed that moderate to heavy 

exercise (both in origin and destination cities) helped 

the pilots adapt to the local time zone ( 193 ). This conclusion was based on subjective sleep/wake diaries, 

subjective sleepiness levels, and urine excretion of 

17-hydroxycorticosteroids; however, due to data being 

collected during operations, there was no way to conclude that it was the exercise alone that helped resynchronize the individuals to the new environment. Since 

then, controlled studies have evaluated the ability of 

exercise to shift circadian rhythms ( 99 ). Barger and colleagues have evaluated exercise and its effect on circadian rhythms in a controlled environment in which light 

was held at a constant dim level ( 15 ). The data showed 

that over a 15-d trial, exercise of appropriately timed duration and amount (three 45-min nightly periods), altered the volunteers ’ melatonin profi les. Thus, the outcomes suggest that exercise can be helpful in facilitating 

a delay of the sleep/wake cycle which is experienced 

during westbound travel. 

v. Nutrition: While eating a meal immediately before 

the sleep period is not recommended, it is important to 

maintain good nutrition. If personnel eat immediately 

before sleep, they should favor grains, breads, pastas, 

vegetables, and/or fruits. At the same time, personnel 

should avoid large meals, high-fat meals, high-acid 

meals, sweets, and signifi cant hunger. 

 Normal variations in nutrition have few, if any, major 

effects on sleep structure ( 123 , 146 ). However, dietary 

supplementation and unusual variations in diet may 

have mild effects. For example, high carbohydrate 

(CHO) supplementation prior to bedtime has been associated with reduced amounts of wakefulness and stage 

1 sleep, decreased stage 4 sleep, and increased rapid eye 

movement (REM) sleep ( 164 ). The somnolent effects of 

high CHO meals may depend in part on gender, age, 

and time of day of consumption ( 197 ). A CHO lunch has 

been shown to increase the length of a siesta ( 236 ). Recently, it was observed that a 90% CHO meal with a high 

glycemic index (GI) shortened sleep latency by about 

50% compared to a low glycemic index meal, and about 

40% when fed 4 h prior to sleep onset compared to 1 h 

before ( 4 ). Conversely, drowsiness may be offset immediately after high- and low-GI CHO intake, but low-GI 

CHO intake may delay the onset of drowsiness ( 110 ). A 

comparison of low-fat, high-CHO meals to high-fat, 

low-CHO meals indicated that higher cholecystokinin 

(CCK) concentrations after high-fat, low-CHO meals 

were associated with greater feelings of sleepiness and 

fatigue ( 224 ). 

 The essential amino acid, tryptophan, is a precursor of 

the monoamine neurotransmitter serotonin. Serotonin is 

involved in the regulation of sleeping and waking ( 163 ). 

The presleep ingestion of an amino-acid mixture lacking 

tryptophan, compared to the ingestion of a mixture containing all essential amino acids, caused a decrease in 

stage 4 sleep latency and an increase in stage 4 sleep 

during the fi rst 3 h of sleep ( 135 ). Depletion has also 

been observed to decrease stage 2 sleep, to increase wake 

time after sleep onset and rapid eye movement density, 

and to shorten the fi rst and second REM period intervals ( 218 ). Midmorning tryptophan depletion delays 

REM sleep latency during the following night’s sleep 

( 10 ). 

 Thus, it appears that the purposeful manipulation of 

dietary CHO by aircrew to help induce and sustain their 

sleep periods may be ill-advised due to the unpredictability of effects. However, tryptophan depletion should 

probably be avoided. Obviously, those prone to gastric 

refl ux disorders should avoid large or high-fat meals before bedtime. 

 The failure to eat may trigger sleep disruption and fatigue. Low blood glucose may elevate plasma glucagon, 

with concomitant elevations of heart rate, and blood pressure. This is not conducive to restful sleep. Of course, hypoglycemia can lead to poor cognitive performance. Studies of the effects of intermittent fasting during Ramadan 

have revealed increased nocturnal sleep latency, decreased 

daytime sleep latencies, and decreased total sleep time. 

These effects may be dependent upon the late dinners ingested during Ramadan ( 172 , 173 ). 

 Position Statement on Improving Sleep and Alertness 

 A number of alertness-enhancing strategies are available that do not rely on medications of any type. 

Whenever possible, these should be applied during offduty periods to maximize the safety of fl ight operations. 

Promoting quality preduty sleep is essential for ensuring optimal fl ight performance. Since healthy sleep 

practices ensure that crews will be able to make the most 

of available sleep opportunities, all aircrew members 

should be provided with educational materials that outline natural sleep-promoting behaviors. In addition, 

they should be educated regarding the importance of 

naps for bridging the gap between consolidated sleep 

episodes. Naps should be as long as possible and whenever feasible they should occur at the circadian times 

most conducive to natural sleep (i.e., early afternoon or 

early predawn hours according to the body clock). The 

principles outlined for good sleep hygiene should be 

followed to promote optimal nap quality and duration. 

Upon awakening from a nap lasting more than 40 min 

(i.e., where sleep inertia upon awakening is likely), there 

should be a wake-up period of at least 30 min prior to 

the performance of any safety-sensitive tasks. 

 With regard to circadian adjustment techniques, it is our 

position that crewmembers who have moved to a new 
Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 45

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

time zone or work schedule and who expect to remain in 

the new location or on the new schedule for several days 

should employ natural adjustment techniques such as controlling the timing of light exposure, meals, and other activities. The detailed recommendations presented earlier 

in this paper should be followed to the extent possible. 

 Since aerobic exercise has been shown to improve the 

quality of a subsequent sleep period, it is our position 

that crewmembers engage in at least 30 min of aerobic 

exercise every 24 h. However, since exercise increases 

body temperature, most sleep experts say the best time 

to exercise is usually late afternoon. The exercise period 

should not be placed within 2 h immediately preceding 

bed time in order to allow the body to cool ( 76 , 199 , 235 ). 

 Although evidence is weak that nutrition exerts a 

practically signifi cant effect on sleep and alertness, we 

recommend that aircrews emphasize balanced meals at 

regular intervals to promote and maintain general 

health, and that they avoid consuming meals (particularly large meals) immediately prior to bedtime. It is 

possible that the ingestion of high-carbohydrate foods 

approximately 4 h prior to bedtime may promote sleep, 

but in general attempting to control sleep and alertness 

by manipulating dietary constituents is not advised. 

 c. Non-FDA-Regulated Substances 

 Alternative, non-FDA-regulated medicines and substances are sometimes used to counter fatigue through assisting with sleep or promoting alertness. Melatonin is 

probably the most used substance of the nonregulated 

ones available. Its effi cacy as a hypnotic continues to be 

debated ( 211 , 237 ). Generally, as a sleep aid, it has not consistently been shown to be clinically effi cacious for insomnia when taken during the biological night ( 32 ). However, 

there is evidence that melatonin has a soporifi c effect 

when taken outside the normal sleep period, particularly 

when taken to phase-advance the sleep period ( 8 ). 

 Melatonin administration may help to overcome shift 

lag in operations involving rapid schedule changes and 

jet lag in circumstances requiring rapid time zone transitions. There is a substantial amount of research which 

indicates that appropriate administration of this hormone can improve circadian adjustment to new time 

schedules ( 9 , 32 , 206 ). There also is evidence that melatonin possesses weak hypnotic or “ soporifi c ” properties 

that may facilitate out-of-phase sleep ( 118 , 231 ). Typically, exogenous melatonin should be administered at 

approximately the desired bed time since melatonin naturally peaks after sleep onset. Melatonin is especially useful for facilitation of daytime sleep (early circadian sleep) 

but less effi cacious for facilitation of normally timed 

nocturnal sleep unless one produces little or no melatonin. In normal individuals who are not stressed with circadian desynchrony [i.e., individuals who can safely be 

assumed to have a dim light melatonin onset (DLMO) in 

the range of ~2000 to 2200], melatonin should be ingested in the late afternoon (approximately 1700) to 

achieve a circadian phase advance, or in the morning 

(approximately 0800) to achieve a circadian phase delay 

( 34 ). For individuals who are suffering from circadian 

desynchrony, ingestion of melatonin or phototherapy 

should be used with proper guidance in order to avoid a 

circadian shift in the undesired direction. Since melatonin is not considered a drug, it is widely available for 

use with few restrictions, at least in the U.S. Unfortunately, most potential users of melatonin possess little 

knowledge about circadian rhythms and/or endogenous melatonin secretion, and this could lead to compromised alertness and decreased performance associated with improper use. 

 Other substances to promote sleep are also available, 

but most of them have not been studied thoroughly and 

their effectiveness has not been established. However, of 

these substances, valerian and kava have the most research on effi cacy. A systematic review of valerian concluded that, while some studies have found some evidence that valerian has signifi cant effects on sleep, it is 

does not have the clinical effi cacy needed to treat insomnia ( 203 ). However, evidence suggests that valerian is a 

safe herb which can be helpful with mild insomnia when 

taken continuously. Good clinical studies are needed to 

establish both its effi cacy for severe insomnia and its 

safety profi le ( 95 , 136 , 230 ). Kava has been shown to help 

with sleep latency and sleep quality in people with insomnia, but more studies are needed to establish its effi -

cacy and safety as well ( 136 ). 

 For promoting alertness, caffeine can be considered a 

valuable non-FDA-regulated pharmacological fatigue 

countermeasure. Numerous studies have shown that 

caffeine increases vigilance and improves performance 

in sleep-deprived individuals, especially those who normally do not consume high doses ( 142 ). Caffeine (generally in the form of coffee, tea, or soft drinks) is already 

used as an alertness-enhancing substance in a variety of 

civilian and military fl ight operations, and it has proven 

safe and effective. For a very complete review of the applicability of caffeine in operations, see the Institute of 

Medicine report, especially pp. 79 – 82 ( 56 ). Caffeine is 

used best for the short-term elevation of cortical arousal; 

regular use may lead to tolerance and various undesirable side effects, including elevated blood pressure, 

stomach problems, and insomnia. Caffeine is widely 

available and affects the nervous system within 15 to 20 

min. The effects of caffeine last for about 4 to 5 h and 

may include a more rapid heartbeat and sharply increased alertness/decreased sleepiness; the effects may 

last up to 10 h in especially sensitive individuals. There 

are individual differences in the effects of caffeine on 

sleep. For some personnel, even small amounts can 

cause problems sleeping. For others, caffeine has no apparent detrimental effect on sleep. Chronic overuse may 

also cause dehydration, nervousness, and irritability. 

Tolerance to cortical arousal occurs with the repeated 

consumption of caffeine at more than about 200 to 300 

mg per day. Personnel should consume caffeine sparingly, and save the arousal effect until they really need 

it. This is called “ tactical caffeine use. ” The U.S. Armydeveloped caffeine gum, Stay Alert , is now in Army supply channels (NSN #8925-01-530-1219). It provides an 
46 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

excellent delivery mechanism for caffeine when the latter is needed during prolonged operations. The caffeine 

content of commonly used substances is listed in Table 

III . More specifi c guidance regarding caffeine use is provided in Section VI.c.i. 

 The amino acid tyrosine, a precursor of the neurotransmitter norepinephrine, might be effective in 

countering the stress-related performance decrement 

and mood deterioration associated with sleep deprivation ( 155 ). In a direct test of its effectiveness on cognitive performance during one night of total sleep loss, 

150 mg z kg 21

 of tyrosine, administered in a split dose, 

resulted in an amelioration of the performance decline 

seen on a psychomotor task and a reduction in lapse 

probability on a vigilance task compared to placebo 

( 145 ). The results lasted approximately 3 h. While there 

are relatively few data, it appears that tyrosine is a relatively benign substance that may prove useful under 

high stress conditions, including those associated with 

sleep loss. 

 Position Statement on Non-FDA-Regulated 

Substances 

 While nonregulated substances are easy to purchase 

in many places in the U.S., they should still be consumed 

with the same caution as any prescription substance. In 

some individuals, many of the herbal remedies can lead 

to sleepiness levels which will impair performance. In 

addition, since these substances are not under federal 

control, the manufacturing quality is left to the individual companies. For example, one study found the stated 

amount of melatonin and the actual amount of melatonin varied considerably between lots as well as within 

bottles for several brands of melatonin sold over the 

counter ( 165 ). Research continues in determining the 

safety, dosage, formulation, and time of administration 

of melatonin since this substance shows the most promise in helping sleep and circadian disorders. However, 

there is still debate about its use and long-term safety, 

and for this reason we do not recommend the use of 

melatonin to readjust circadian rhythms or to promote 

sleep. Other substances such as valerian and kava also 

should not be relied upon to manipulate either sleep or 

performance. Caffeine, on the other hand, is an effective 

alertness-enhancing compound, and it is our position 

that it should continue to be used as an aviation fatigue 

countermeasure. Crewmembers should adhere to the 

following : 1) avoid ingesting more than 1000 mg of caffeine in any 24-h period; 2) make an effort to use caffeine 

judiciously (i.e., only when it is truly needed to reduce 

the impact of fatigue); and 3) avoid ingesting caffeine 

within 4 h of bedtime. However, the effects of caffeine 

on sleep are dependent on factors such as usual caffeine 

consumption and age ( 199 ). Here are some situations 

where using caffeine makes sense: 1) leading in to the 

predawn hours; 2) midafternoon when the alertness dip 

is greater because of inadequate nocturnal sleep; and 3) 

prior to driving after night duty, but not within 4 h of 

going to sleep. 

 V. NEW TECHNOLOGIES 

 The need for real-time fatigue detection technologies 

and predictive modeling algorithms that focus on minimizing fatigue-related errors, incidents, and accidents 

during fl ight has been realized for several years. This is 

largely due to fatigue’s continued persistence as an occupational hazard and the related cognitive defi cits that 

inhibit the ability of an operator to identify decreases in 

alertness ( 31 ). Therefore, many efforts have focused on 

developing unobtrusive technologies that aim to detect 

fatigue in pilots prior to its onset so that an operationally valid and effective countermeasure can be implemented. Advances in fatigue technologies and algorithm 

development have made this goal achievable. However, 

before being transitioned to operational environments, 

these technologies and algorithms must be shown to 

meet a number of engineering, scientifi c, practical, and 

legal/ethical standards and criteria ( 69 ). Efforts to demonstrate validity have been conducted through a variety 

of venues including controlled laboratory settings, simulation research protocols, operational evaluations, and 

workshops involving subject matter experts from the 

fi eld ( 68 , 70 , 72 , 100 , 125 , 212 ). 

 a. On-Line, Real-Time Assessment 

 On-line operator status technologies are the most 

common of the fatigue monitoring devices because of 

their ability to provide meaningful measures of alertness levels and performance ability in real time ( 69 ). 

They aim to monitor some aspect of the individual’s 

physiology or behavior that is sensitive to increasing 

fatigue and sleepiness levels. Available and developing 

on-line, operator status detection technologies monitor 

either the physiological behavior of the individual 

(EEG, eye gaze, facial feature recognition) or their 

physical characteristics (muscle tone, head position, 

percent eye closure, wrist inactivity). They offer great 

potential for pilots who are challenged with maintaining alertness and performance during long, uneventful 

fl ights ( 36 ). 

 Research over the past 40 yr has established the EEG 

as a highly predictive and reliable neural index of cognition along with event-related brain potentials (ERPs) 

( 82 ). It has been accepted as the ‘ ” gold standard ” for the 

TABLE III. CAFFEINE CONTENT OF COMMON DRINKS AND 

OVER-THE-COUNTER MEDICINES. 

Substance Average Caffeine Content 

1 cup Maxwell House w 100 mg 

1 Starbucks w Short 250 mg 

1 Starbucks w Tall 375 mg 

1 Starbucks w Grande 550 mg 

1 Coke w 50 mg 

1 Mountain Dew w 55 mg 

1 cup tea 50 mg 

2 Anacin w 65 mg 

2 Excedrin Xtra. Strength 130 mg 

1 Max. Strength NoDoz w 200 mg 
Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 47

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

detection of impaired alertness. These EEG signals and 

analyses are now being incorporated into a real-time 

technological countermeasure device for fatigue detection ( 109 ). For example, the B-alert w ( 20 ) has been validated as an alertness indicator for driver fatigue ( 115 ) 

and has also demonstrated sensitivity to individual 

fatigue vulnerability ( 116 ). The B-alert w system can also 

be implemented in combination with ERPs to capture a 

more detailed image of information processing in the 

brain ( 20 ). Other researchers (e.g., 120 ) are also developing EEG-based drowsiness estimation systems based on 

computed correlations between changes in EEG power 

spectrum and fl uctuations in driving performance. From 

this information, individualized linear regression models for each subject applied to principal components of 

EEG spectra can be constructed for further real-time 

monitoring. 

 Although the detection of fatigue based on the EEG 

changes that occur simultaneously in the delta, theta, 

alpha, and beta bands has been accepted as a valid 

measure of fatigue, obtaining brain wave activity in 

the operational environment is often times not feasible. 

Research has shown that the eye and visual system, 

under central nervous system control, can also provide 

information about an individual’s alertness level and 

cognitive state ( 39 , 121 , 112 , 207 ). Deteriorations in many 

ocular measures occur with fatigue and extended waking periods, with the most sensitive being those that 

change just prior to the sleep onset period, such as eye 

blinks, long duration eye closures, eye movements, 

and pupillary response. Various devices have been designed to monitor these ocular changes, but each device differs somewhat in terms of exactly what is measured, how it is measured, and how the data are 

processed. In addition, there are differences in the precise nature of the fatigue-monitoring algorithms and in 

the hardware technology used to obtain the ocular 

measures. Some are unobtrusive and require simple 

video while others can require the user to place a sensor near the eye or require the person to wear specially 

equipped eyeglasses. A number of promising ocular 

devices are in the validation phase for real-time, noninvasive detection of operator fatigue. These include 

devices that assess the percentage of eye closure, such 

as the Co-Pilot (Attention Technologies, PA), Optalert 

(Sleep Diagnostics, Australia), and Eye-Com (Eye-Com 

Corp., Reno, NV). Selection of the PERCLOS metric (a 

measure of the proportion of time subjects had slow 

eye closures; 228 , 229 ) for these devices is based on research demonstrating its high correlation with psychomotor vigilance behavior ( 70 ). 

 Facial feature recognition technology is also currently 

being validated as a fatigue detection device ( 73 , 94 ; 

Dinges DF. Personal communication; 2008). The simultaneous extraction of changes in multiple locations on 

the face such as around the eyes, nose, and mouth provide a great deal of information regarding individual 

alertness levels. Moreover, Ji, Zhu, and Lan ( 102 ) have 

incorporated other critical factors such as PERCLOS and 

circadian variations into facial feature recognition technology for the development of a real-time, nonintrusive 

monitor device for fatigue. 

 Additional fatigue detection devices that compared 

successfully to the EEG technique and/or the PERCLOS 

technique include a wrist-worn alertness device that 

triggers an alarm sound when wrist inactivity occurs for 

a preset amount of time (e.g., 5 min; 233 ) and a device 

that assesses head position “ XYZ ” data analyzed over 

various time periods to signify micronods or microsleeps ( 104 ). 

 All fatigue detection devices, independent of the variable being measured, have both positive and negative 

aspects. Their usefulness as real-time technologies is dependent on the requirements and conditions of the operational environment and some may not even be practical for use in highly restrictive environments such as the 

fl ight deck. For example, based on a study that showed 

an automated PERCLOS device was effective in improving alertness and performance in truck drivers ( 125 ), a 

similar study was conducted in a B747-400 fl ight simulator ( 127 ). The goal of the study was to establish the feasibility, potential usefulness, and applicability of the automated PERCLOS monitor for drowsiness detection and 

mitigation of fatigue on the fl ight deck. The automated 

PERCLOS system with feedback did not signifi cantly 

counteract decrements in performance, physiological 

sleepiness, or mood on the fl ight deck, which was very 

different from the results found in the truck-driving environment. This was largely due to the PERCLOS system having a limited fi eld of view that could not capture 

pilots ’ eyes at all times during the fl ight due to operational requirements of constant visual scanning and 

head movements. These results clearly demonstrate 

that, although an automated, real-time technology may 

be valid in one operational environment, it does not always transition to another operational environment 

without the emergence of implementation obstacles. 

 b. Off-Line Fatigue Prediction Algorithms 

 Off-line fatigue prediction algorithms are being developed to provide an estimate of an individuals ’ alertness level or performance effectiveness during a work 

period to be performed in the future. These measures 

(e.g., alertness levels, performance estimates) of physiological state are measured relative to a standard such as 

the individual’s baseline and/or a group norm ( 91 ). For 

example, ocular-based, readiness-to-perform, or fi tnessfor-duty devices often measure various aspects of the 

visual system of the individual prior to a duty period to 

determine if they can maintain optimal performance 

throughout the work period ( 60 ). Such a device as the 

FIT device ( 161 ) has already been shown to detect 

changes attributable to sleep loss ( 182 – 184 ). 

 Over the years, there have also been recent developments of biomathematical models of alertness for the 

prediction of alertness and performance levels ( 125 ). 

They can be very useful in the prediction of performance 

or effectiveness levels when comparing different operational schedules. Although models can differ in their 
48 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

specifi c algorithm, they all aim to model the interaction 

of sleep and circadian processes and effects on the sleep/

wake cycle and waking neurobehavioral performance. 

The operational usefulness of these models lies directly 

in them being incorporated into scheduling tools. Such 

tools can be used to develop work schedules that maximize safety by: 1) predicting times when performance is 

optimal; 2) identifying timeframes in which recovery 

sleep will be most restorative; and 3) determining what 

impact proposed work/rest schedules will have on 

overall neurobehavioral functioning ( 126 ). 

 Models of alertness and performance vary in their specifi c algorithms and differ in the number and type of input variables, output variables, and goals and capabilities. It is also important to consider the operational 

environment for their intended use. Of the seven models 

evaluated at a modeling workshop sponsored by the U.S. 

Department of Defense, U.S. Department of Transportation, and NASA, only two of them specifi cally relied on 

aviation data for development or stated their relevance 

to aviation operations ( 126 ). At the time of the workshop 

in 2002, the System for Aircrew Fatigue Evaluation 

(SAFE) model was specifi cally developed for aviation 

operations. It had been adjusted using data collected on 

long-haul fl ights and required aviation-specifi c variables 

for its input ( 19 ). Another model, the Sleep, Activity and 

Fatigue Task Effectiveness (SAFTE) model was developed for military and industrial settings and included a 

translation function for pilots. The SAFTE model is the 

foundation of the Fatigue Avoidance Scheduling Tool 

(FAST), which was designed to help optimize the operational management of aviation ground- and fl ightcrews 

( 101 ). While all of the biomathematical modeling software showed promise in the prediction of performance, 

there is room to improve their validity and reliability 

based on refi nements with real world data, and they 

should not be transitioned to operational environments 

until their scientifi c validity can be demonstrated ( 66 ). 

 Position Statement on New Technologies 

 Fatigue detection technologies (fi tness for duty and 

real-time assessment devices) and scheduling tools that 

incorporate biomathematical models of alertness should 

not be solely relied upon for the determination of safe or 

 ‘ fatigue-free ’ fl ights. They are tools that can be effectively incorporated as part of an overall safety management approach and should not be used in place of regulatory limitations. Selection of the ‘ best tool ’ should be 

dependent on its demonstrated validity for mitigating fatigue risk during aviation operations . 

 At present, none of the real-time fatigue detection 

technologies have been suffi ciently proven in an aviation environment (with the possible exception of the 

wrist-worn alertness device that triggers an alarm sound 

when wrist inactivity occurs for a preset amount of time) 

to warrant widespread implementation. However, some 

crew scheduling approaches based on validated fatigueprediction models have already been proven, to a limited extent, feasible and worthwhile. The SAFTE model 

for instance, is currently being used in a number of aviation settings to evaluate the fatiguing impact of different 

schedules and to help design better alternatives. 

 Refi nement of both the new fatigue monitoring technologies and scientifi cally based scheduling software 

must continue, and once they are validated for specifi c 

types of operations, they should be incorporated as part 

of an overall safety management approach supplementing regulatory duty limitations. Fatigue detection technologies and biomathematical models can also be used 

in combination. The online, realtime measurements (e.

g., actigraphy, performance measures) could be used as 

input data to the scheduling tools, thus increasing their 

predictive value, being refl ective of what is occurring 

during actual operations. Research is also needed to 

identify embedded (fl ying) performance metrics that 

are sensitive to fatigue over time, allowing for model refi nement and continuous assessment of the safety of 

operations. 

 A fi nal consideration in the development of new technologies is to combine biomathematical models of alertness with scheduling tools that do not have a foundation in sleep and circadian research (e.g., tools that 

incorporate labor contract rules, government regulations, available staff, vacation time, currency training, 

etc.). Combining the two would result in scheduling regimes that consider both the physiological limitations of 

humans and operational constraints, resulting in both 

compliant and safe operations. 

 VI. MILITARY AVIATION 

 a. Relevant Regulations and Policies 

 A review of the fatigue management (crew rest) policies implemented by the U.S. Army, the U.S. Air Force, 

and the U.S. Navy shows far less complexity than is 

found in the civil aviation regulations. Complete guidance may be found in Army Regulation 385-95 (10 Jan 

2000), Air Force Instruction 11-202 v3 (05 Apr 2006), and 

OPNAV Instruction 3710.7T (01 Mar 04). 

 b. Crew Rest and Duty Limitations 

 The primary requirement for crew rest and duty limitations is somewhat similar to that specifi ed in the civil 

aviation regulations; specifi cally, that 8 h of continuous 

rest be obtained prior to the duty period. The U.S. Air 

Force instruction requires a 12-h nonduty crew rest period in which 8 h of uninterrupted sleep must be obtained in the 12 h prior to duty. If this 8-h sleep period is 

interrupted, another 8 h must be added. The U.S. Navy 

instruction requires that 8 h of continuous rest be 

obtained within the 24-h period, and that any continuous wakefulness period should not exceed 18 h. If the 

18-h requirement is not met, a minimum of 15 h of continuous off-duty time must follow. The U.S. Army at one 

time had one of the most detailed crew rest and duty 

limitation guides of the three U.S. services. However, 

the Army guidance now more generally states that commanders are responsible for endurance management by 

ensuring that fatigue is controlled or eliminated as a risk 
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FATIGUE COUNTERMEASURES — CALDWELL ET AL.

factor in all operations by providing for suffi cient sleep 

time in each 24-h period as well as for circadian adjustment of the individual body clocks of personnel changing time zones or work cycles. Army commanders are 

directed to consult the Leaders Guide to Crew Endurance 

Management ( 57 ) for complete details. 

 Air Force Instruction 11-202, Vol. 3, offers some of the 

most detailed current guidance. It advises commanders 

and mission planners to consider fatigue-related factors 

for upcoming fl ight missions including the fatiguing impact of adverse weather, temperature extremes, night 

operations, and mission delays, as well as the fatigue 

from sleep loss and continuous work. Additional guidance, paraphrased from Air Force Instruction 11-202 

(waivers may be requested for specifi c circumstances) 

and the U.S. Navy guidance paraphrased from Chief of 

Naval Operations Instruction 3710.7T, are listed below: 

U.S. Air Force Guidance for Scheduling Flight Missions to Avoid 

Fatigue in Aircrew: 

Provisions should be made for augmenting fl ightcrews when 

possible to permit in-fl ight rest periods. 

Cockpit naps (taken by one crewmember at a time) of up to 45 

min in duration are authorized during noncritical fl ight phases, 

and multiple naps are permitted when feasible. 

Crew bunks or other suitable rest facilities should be provided 

on board aircraft when possible. 

Adequate crew rest is required prior to fl ight duty periods. 

Normally, this means 12 h off duty every 24 h. There should be 

a minimum of 10 h of restful time that includes an opportunity 

for at least 8 h of uninterrupted sleep during the 12 h preceding 

the fl ight duty period. 

Shorter off-duty periods of 10 h may be used as an exception in 

continuous operations, but this exception should be minimized, 

and after several days of shorter off-duty periods, commanders 

should provide suffi cient rest to counter cumulative fatigue. 

Maximum fl ying time should be limited to 56 h per 7 d, 125 h 

per 30 d, and 330 h per 90 consecutive days. 

If nonfl ight duties signifi cantly extend the overall duty period 

(by 2 h or more), consideration should be given to reducing the 

number of allowed fl ight hours. 

Generally speaking, the maximum fl ight duty period for any 

given day should fall within the range of 12 to16 h in situations 

where crew augmentation is not possible. 

When augmented crews are an option, duty days normally can 

extend to 16 to 24 h (in the case of the B-2 Bomber, some missions extend to 44 h). 

Factors affecting maximum fl ight duty period include: single vs. 

multiseat aircraft, level of automation, availability of onboard 

rest facilities, and type of fl ight mission. 

Alertness management strategies such as techniques to promote preduty sleep, extended crew rest periods, controlled 

cockpit rest, bright light exposure, activity breaks, pharmacological sleep and alertness aids, and fatigue management education should be implemented as appropriate. 

U.S. Navy Guidance for Scheduling Flight Missions to Avoid 

Fatigue in Aircrew: 

Schedule ground time between fl ight operations to allow fl ightcrew to eat and obtain at least 8 h of uninterrupted sleep. 

Flightcrew should not be scheduled for continuous alert or 

fl ight duty in excess of 18 h. If mission requirements exceed 18 

h, then 15 h of continuous off-duty time should be provided. 

Following a time zone change of at least 3 h, fl ightcrew requires close observation by the fl ight surgeon since performance will be compromised during the adjustment period. 

For single-piloted aircraft: Daily fl ight time should not exceed 3 

fl ights or 6.5 h total fl ight time for fl ight personnel. The weekly 

maximum fl ight time should not normally exceed 30 h, 65 h 

per 30 d, 165 h per 90 d, and 595 h per 365 d. 

For multipiloted aircraft: Individual daily fl ight time should not 

exceed 12 h for fl ight personnel. The weekly maximum fl ight 

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

time for ejection seat aircraft should not normally exceed 50 h, 

80 h per 30 d (100 and 120 for nonpressurized and pressurized 

aircraft, respectively), 200 h per 90 d (265 and 320 for nonpressurized and pressurized aircraft, respectively), and 720 h per 

365 d (960 and 1120 for nonpressurized and pressurized aircraft, respectively). These limitations assume an average requirement of 4 h of ground time for briefi ng and debriefi ng. 

If operational tempo requires the fl ight time limitations to be 

exceeded, the commanding offi cer, with the fl ight surgeon’s 

advice, will closely monitor and specifi cally clear fl ight personnel, commenting particularly in regard to stress level and adequacy of rest and nutrition. 

Particular notice should be made of fl ights involving contour, 

nap of the Earth, chemical defense gear, night and night vision 

devices, and adverse environmental factors (i.e., dust, cloud 

cover, precipitation) since these fl ights are more stressful and 

demanding than daytime VFR conditions. 

 c. Stimulants/Wake Promoters 

 As noted above, alertness-enhancing medications are 

one option for sustaining the wakefulness of fl ightcrews 

during extended missions in which adequate crew rest 

is not possible. Needless to say, these compounds should 

not be considered a replacement for adequate crew rest 

planning and they should never be considered a substitute for restorative sleep. However, in sustained aviation operations, the occasional use of the alertness-

 enhancing medications such as dextroamphetamine 

(authorized by all three U.S. services) and modafi nil 

(authorized for use in the U.S. Air Force) can often signifi cantly enhance the safety and effectiveness of sleepdeprived personnel. 

Modafi nil (Provigil w , Vigil w , Alertec w and others): The 

prescription drug modafi nil (100 to 200 mg) exerts a wide 

array of positive effects on alertness and performance. 

Lagarde and Batejat ( 108 ) found that 200-mg 

doses every 8 h reduced episodes of microsleeps and 

maintained more normal (i.e., rested) mental states and 

performance levels than placebo for 44 h of continuous 

wakefulness (but not the full 60 h of sleep deprivation). 

Wesensten et al. ( 226 ) found 200 to 400 mg doses of 

modafi nil effectively countered performance and alertness decrements in volunteers kept awake for over 48 h. 

Caldwell and colleagues ( 47 ) found that 200 mg of 

modafi nil every 4 h maintained the simulator fl ight performance of pilots at near-well-rested levels despite 40 h 

of continuous wakefulness, but that there were complaints of nausea and vertigo (likely due to the high dosage used). A more recent study with U.S. Air Force F-117 

pilots indicated that three 100-mg doses of modafi nil (administered every 5 h) sustained fl ight performance within 

27% of baseline levels during the latter part of a 37-h period of continuous wakefulness. Performance under the 

no-treatment condition was degraded by over 82% ( 46 ). 

Similar benefi cial effects were seen on measures of alertness and cognitive performance. Furthermore, the lower 

dose produced these positive effects without causing the 

side effects noted in the earlier study ( 47 ). Due to these 

and other positive results, modafi nil is gaining popularity as a way to enhance the alertness of sleepy personnel, 

largely because it is considered safer and less addictive 

than compounds such as the amphetamines. Modafi nil 

also produces less cardiovascular stimulation than 

•

•
50 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

amphetamine, and despite its half-life of approximately 

12 to 15 h ( 159 , 169 ), the drug’s impact on sleep architecture is minimal. However, it should be kept in mind that 

modafi nil has not been as thoroughly tested as dextroamphetamine in real-world operational environments 

and some data suggests that modafi nil is less effective 

than amphetamine ( 132 ). Nevertheless, approval has 

been received for the use of modafi nil in certain longrange U.S. Air Force combat aviation missions, and it is 

likely that modafi nil soon will be approved for use in the 

U.S. Army and the U.S. Navy. 

Amphetamine (Dexedrine w , Dextrostat w ): Dextroamphetamine (5 to 10 mg) has been authorized for use by all 

three U.S. services for certain types of lengthy (i.e., 12 or 

more hours) fl ight missions. In comparison to caffeine, 

dextroamphetamine appears to offer a more consistent 

and prolonged alerting effect ( 223 ). In comparison to 

modafi nil, studies suggest that amphetamine is either 

more effi cacious ( 132 ) or, at least in the case of 40-h sleepdeprivation periods, equivalent ( 41 , 160 , 225 ). In terms of 

the effi cacy of amphetamine as a fatigue countermeasure, Newhouse et al. ( 148 ) studied d-amphetamine 

(5, 10, or 20 mg) in people deprived of sleep for over 48 

h and found that 20 mg d-amphetamine (administered 

after 41 h of continuous wakefulness) produced marked 

improvements in addition/subtraction (lasting for over 

10 h), a gradual improvement in logical reasoning 

(signifi cant between 5.5 and 7.5 h postdose), a long-

 lasting improvement in the speed of responding during 

the choice reaction-time task (10 h), and an increase in 

alertness for 7 h. It was noted that the drug did not impair judgment. The 10-mg dose exerted fewer and 

shorter-lasting effects, whereas the 5-mg dose was ineffective. Two fl ight simulation studies involving U.S. 

Army pilots indicated that repeated 10-mg doses of dextroamphetamine (given at midnight, 0400, and 0800) 

maintained fl ight performance and alertness nearly at 

well-rested levels throughout 40 h of continuous wakefulness ( 44 , 45 ). Benefi ts were especially noticeable between 0300 and 1100, when fatigue-related problems 

were most severe. In a later study, 10 pilots completed a 

series of 1-h sorties in a specially instrumented UH-60 

helicopter during 40 h of sleep deprivation. The results 

revealed that 10-mg doses of dextroamphetamine sustained performance nearly as well under actual in-fl ight 

conditions as in the laboratory ( 42 ). A follow-on simulator investigation extended these fi ndings by showing 

that with additional amphetamine dosing, pilot performance and alertness could be sustained for over 58 continuous hours of wakefulness (2 nights of sleep loss) 

( 50 ). Reports from the fi eld indicate dextroamphetamine 

has been used successfully in a number of combat situations such as Vietnam ( 58 ), the 1986 Air Force strike on 

Libya ( 192 ), and Operation Desert Shield/Storm ( 59 ). 

Emonson and Vanderbeek ( 81 ) found that U.S. Air Force 

pilots who were administered dextroamphetamine during Operation Desert Shield/Storm were better able to 

maintain acceptable performance during continuous 

and sustained missions, and that the medication contributed to both safety and effectiveness. To date, no major side effects or other problems have been reported 

from the medical use of dextroamphetamine in military 

settings. In light of these and other fi ndings, dextroamphetamine doses of 10 to 20 mg (not to exceed 60 mg per 

day) are recommended for situations in which heavily 

fatigued military pilots simply must complete the mission despite dangerous levels of sleep deprivation. 

Guidance from the U.S. Air Force is shown below. 

U.S. Air Force Combat Aviation Operations Guidance for Use of 

Stimulants: 

Prior to the operational use of dextroamphetamine or 

modafi nil, an informed consent agreement must be obtained 

to ensure that crews are fully aware of both the positive and 

the potential negative effects of these compounds. 

The decision to authorize the use of alertness-enhancing 

compounds should be made by the Wing Commander in conjunction with the Senior Flight Surgeon. 

All distribution of alertness-enhancing medications must be 

closely monitored and documented. 

Ground testing (during nonfl ight periods) is required prior to 

operational use. 

The currently authorized dose of dextroamphetamine is 5 to 

10 mg, and although the dosing interval is not explicitly 

stated, a 4-h interval is often recommended. No more than 60 

mg should be administered in any 24-h period, and often, no 

more than 30 mg are administered. 

The currently authorized dose of modafi nil is 200 mg every 8 

h, not to exceed 400 mg in any 24-h period; however, recent 

F-117 research has indicated that 100-mg doses also are effi -

cacious (and this lower dose is authorized as well). 

The use of alertness-enhancing compounds normally can be 

authorized in fi ghter missions longer than 8 h or bomber missions longer than 12 h (although exceptions can be made). 

Caffeine generally is not considered to be a suitable alternative for modafi nil or dextroamphetamine; however, caffeine 

in the form of foods or beverages may be consumed without 

restriction. Caffeine in the form of tablets or capsules can only 

be used after fl ight surgeon approval. 

 The U.S. Army and U.S. Navy guidance is mostly consistent with U.S. Air Force guidance with the most notable exception being that modafi nil is not currently authorized in the Army or Navy. The U.S. Army guidance for 

use of dextroamphetamine endorses the administration 

of 5- to 10-mg doses and specifi es that no more than 30 

mg may be used in any 24-h period. It is also stated that 

the medication not be used to sustain wakefulness longer 

than 64 continuous hours. The U.S. Navy guidance suggests that dextroamphetamine be administered in 5-mg 

doses which may be repeated every 2 to 3 h; however, total dosage should not exceed 30 mg in any 24-h period. 

An upper level for the duration of any period of continuous wakefulness is not specifi ed, but it is clear that extended periods without sleep should be avoided. 

 Position Statement on the Use of Stimulants to 

Sustain Flight Performance 

 Alertness-enhancing compounds of some description are already authorized for use in all U.S. military 

services during periods of unavoidable sleep deprivation. Thus far, the U.S. Air Force is the only service that 

has authorized the use of both modafi nil and dextroamphetamine, whereas only dextroamphetamine is 

currently authorized by the U.S. Army and U.S. Navy. 

Based on Air Force experience, it is recommended that 

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FATIGUE COUNTERMEASURES — CALDWELL ET AL.

modafi nil use be sanctioned by all three U.S. services 

under guidance consistent with that currently followed by the Air Force. Relatively uncontrolled caffeine use is also an option in all three U.S. services, 

and the use of caffeine, while not recommended as a 

primary pharmacological fatigue countermeasure, 

should continue to be sanctioned by the U.S. services. 

Aircrew should avoid habituation to caffeine and take 

advantage of the cortical stimulant properties of caffeine when it is needed to help ensure safe operations. 

More specifi cally, when aircrews are not suffering from 

the effects of fatigue, they should limit their total daily 

caffeine consumption from all sources to 200 to 250 mg 

 per day . Additional doses of caffeine should be used 

during situations in which fatigue elevates the risk of 

a mishap. These situations may include low-workload, 

long-duration transits over land or water during the 

predawn hours; approach and landing during the predawn hours; and approach and landing at the end of 

an extraordinarily long crew duty day. In any given 

24-h period, the total amount of caffeine consumed 

should not exceed 1000 mg. Aircrew should be aware 

of the 4-6-h half-life of circulating caffeine and preplan 

its use such that postduty day sleep is disturbed minimally by caffeine use. 

 With the exception of caffeine and various nutritional 

supplements, no alertness-enhancing medications are 

currently authorized for use in any type of civil aviation 

operation. Due to the fact that civil operations generally 

are more predictable than military operations, and due 

to the fact that prolonged periods of sleep deprivation 

are not the norm in civil operations (whereas such periods are often unavoidable in the military sector), it 

would seem prudent to withhold widespread authorization of prescription alertness enhancers in the civilian 

aviation sector. Also, there is the matter that intense military operations are generally time limited, exposing 

military pilots to only relatively brief periods in which 

intense sleep deprivation necessitates the administration of appropriate counter-fatigue medications, whereas 

civil operations continue day in and day out for the duration of a pilot’s career, potentially exposing moderately fatigued pilots to years of chronic medication use if 

such medications were authorized. This difference between military and civil aviation scenarios likewise 

seems to argue against the widespread authorization of 

alertness-enhancing drugs in civil operations. However, 

it would be worthwhile to consider the temporary authorization of counter-fatigue medications in civil emergency fl ight operations such as when airlifting disaster 

relief supplies, rapidly evacuating medical casualties 

following some catastrophic event, etc. 

 d. Sleep-Inducing Agents 

 When individuals are given the opportunity to sleep, 

but are unable to do so due to various circumstances 

(i.e., wrong circadian time, poor sleep conditions), sleep 

aids represent a viable countermeasure. The characteristics of various hypnotics were discussed earlier. However, 

each branch of the military has its own policy concerning the use of hypnotics. Table IV indicates the U.S. military’s policies on hypnotic use. As with the stimulant 

policy, a ground test is necessary prior to use during operations. The U.S. Navy guidance explicitly forbids the 

administration of more than one dose of a hypnotic per 

24-h period, with no more than 2 d of consecutive use of 

temazepam. There is also guidance for planning and 

briefi ng in the grounding restriction ( 210 ). As with other 

medications, the use of hypnotics is voluntary. 

 Position Statement on the Military Use of 

Sleep-Inducing Agents 

 Sleep-promoting compounds are useful for mitigating the sleep loss associated with circadian disruptions, 

poor sleeping conditions, and poor sleep timing often 

associated with combat or other high-tempo military 

operations. They should continue to be authorized in circumstances where: 1) their use is justifi ed by the presence 

of one or more of the previously noted factors; 2) there is 

appropriate medical supervision; 3) there is evidence 

that the crewmember has completed a pre- mission 

TABLE IV. U.S. MILITARY POLICIES FOR HYPNOTIC USE. 

Medication Dose Half-life Grounding 

U.S. Army Rest Agent Policy

Temazepam (Restoril w) 15 or 30 mg 8.0 – 12.0 h 24 h 

Triazolam (Halcion w) 0.125 or 0.25 mg 2.0 – 4.0 h 9 h 

Zolpidem (Ambien w) 5 or 10 mg 2.0 – 2.5 h 8 h 

Zaleplon (Sonata w) 5 or 10 mg 1.0 h 8 h 

U.S. Air Force No-Go Pill Policy

Temazepam (Restoril w) 15 or 30 mg 8.0 – 12.0 h 12 h 

Triazolam (Halcion w) Not authorized na na 

Zolpidem (Ambien w) 10 mg 2.0 – 2.5 h 6 h 

Zaleplon (Sonata w) 10 mg 1.0 h 4 h 

U.S. Navy Sleep Initiator Policy

Temazepam (Restoril w) 15 mg 8.0 – 12.0 h 7 h 

Triazolam (Halcion w) Not authorized na na 

Zolpidem (Ambien w) 5 or 10 mg 2.0 – 2.5 h 6 h 

Zaleplon (Sonata w) Not authorized Na na 
52 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

ground-test to check for idiosyncratic reactions; and 4) 

the mission is such that there is little or no chance that 

the aircrew member will be subject to an unexpected 

truncation of the sleep period. Obviously, personnel 

who are “ on-call ” and may need to fl y a mission at a 

moment’s notice should not utilize sleep medications of 

any type due to the possibility that the medication 

would not have time to be adequately metabolized prior 

to returning to duty. Education concerning use and effects, ground testing, and grounding times are important for successful and safe use of sleep substances. 

 e. Nonpharmacological Countermeasures and Strategies 

 Of the U.S. military services, the Air Force guidance 

on nonpharmacological counter-fatigue strategies is the 

most specifi c. For instance, controlled cockpit rest is explained in detail below: 

Cockpit Rest Guidelines: 

Controlled cockpit rest may be implemented when the basic 

aircrew includes a second qualifi ed pilot. 

Cockpit rest must be restricted to noncritical phases of fl ight 

between cruise and 1 h prior to planned descent. 

Resting crewmember must be immediately awakened if a situation develops that may affect fl ight safety. 

Cockpit rest shall only be taken by one crewmember at a time. 

All cockpit crewmembers including the resting member must 

remain at their stations. 

A rest period shall be limited to a maximum of 45 min. 

More than one rest period per crewmember is permitted if the 

opportunity exists. 

Controlled cockpit rest is not authorized with any aircraft system malfunctions that increase cockpit workload. 

Cockpit rest should not be used as a substitute for any required 

crew rest. 

 Of course, the U.S. Air Force as well as the U.S. Army 

and the U.S. Navy brief personnel on the correct use of a 

variety of alertness-management strategies such as the 

promotion of preduty sleep, implementation of extended crew rest periods when possible, bright light exposure when feasible, in-fl ight activity/rest breaks, and 

general fatigue management. All can be used in combination when appropriate. 

 VII. CONCLUSIONS AND RECOMMENDATIONS 

 Given the state of the art in fatigue countermeasures, 

our summary recommendations, most of which apply 

to both civil and military aviation except where noted, 

are as follows: 

 Education — about the dangers of fatigue, the causes 

of sleepiness, and the importance of sleep and proper 

sleep habits — is one of the keys to addressing fatigue 

in operational contexts. All aviation personnel including supervisors, schedulers, and crewmembers should 

be educated regarding the effects of fatigue, the factors responsible for fatigue, and the available scientifi -

cally proven fatigue countermeasures. Ultimately, the 

individual pilot, schedulers, and management must 

be convinced that sleep and circadian rhythms are important and that quality day-to-day sleep is the best 

possible protection against on-the-job fatigue. Recent 

studies have made it clear that as little as 1 to 2 h of 

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sleep restriction almost immediately degrades vigilance and performance in subsequent duty periods 

( 17 , 214 ). Thus, educational programs should communicate the central points conveyed in this position 

paper: 

1) fatigue is a physiological problem that cannot be overcome by 

motivation, training, or willpower; 

2) people cannot reliably self-judge their own level of fatigue-related 

impairment; 

3) there are wide individual differences in fatigue susceptibility that 

must be taken into account but which presently cannot be reliably 

predicted; 

4) there is no one-size-fi ts-all “ magic bullet ”(other than adequate 

sleep) that can counter fatigue for every person in every situation; 

but 

5) there are valid counter-fatigue strategies that will enhance safety 

and productivity, but only when they are correctly applied. 

 Concurrent with the educational effort, a large-scale 

program should be undertaken to implement a nonprescriptive fatigue risk management system (FRMS) that 

determines optimum fl ight schedules from both a physiological and operational standpoint on a case-by-case 

basis since prescriptive hours-of-service limitations cannot account for human circadian rhythms or sleep propensity. With regard to in-fl ight counter-fatigue strategies, we concur with the present primary reliance on 

in-fl ight bunk rest in long-haul operations, but suggest 

that computerized scheduling tools be used to optimize 

crew rostering and bunk rest timing. We likewise believe 

that short in-fl ight breaks are benefi cial, and we recommend that any regulations governing the use of these 

breaks be liberalized (i.e., that alertness-promoting 

breaks be permitted as a clearly acceptable reason for 

pilots to deviate from the requirement to remain in their 

seats with seatbelts fastened at all times). Given the scientifi c evidence that cockpit napping is safe and highly 

effective, as well as clear indications that the general 

public appreciates the value of cockpit napping, we take 

exception to the current prohibition on in-seat cockpit 

napping in civil aviation, and instead recommend that 

in-seat cockpit naps up to 45 min in duration be permitted in U.S. commercial fl ight operations as long as the 

naps are not used as a replacement for other sleep opportunities (i.e., bunk sleep or pre/post duty sleep). This 

procedure is in agreement with current U.S. Air Force 

policy. 

 To promote on-duty alertness in the absence of suffi -

cient contiguous hours of preduty sleep, the importance 

of napping should be emphasized as a primary strategy. 

Off-duty naps should be as long as possible and whenever feasible they should occur at the circadian times 

most conducive to natural sleep (i.e., early afternoon or 

early predawn hours according to the body clock). The 

principles outlined for good sleep hygiene should be 

followed to promote optimal nap quality and duration. 

Upon awakening from a nap, there should be a wakeup period of at least 30 min prior to the performance of 

any safety sensitive tasks. When naps are insuffi cient, 

personnel should consider the ingestion of caffeine (up 

to 1000 mg per day) as an alertness-enhancing strategy, 

and they should make an effort to use caffeine judi-
Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009 53

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

ciously (i.e., only when it is truly needed to reduce the 

impact of fatigue). 

 With regard to the use of pharmacological compounds 

in civil fl ight operations, it is our position that on the one 

hand, prescription alertness-enhancing compounds not 

be authorized on a routine basis since they are not justifi ed by a cost/benefi t analysis for fl ight operations that 

are relatively predictable, and there is insuffi cient medical oversight to ensure appropriate use. Also, it should 

be noted that when civil as opposed to military fl ights 

are cancelled or modifi ed due to crew fatigue, there is 

virtually no “ downside ” from a safety perspective. A 

possible exception to the prohibition against alertnessenhancing compounds in civil operations could be to 

temporarily authorize these medications for pilots fl ying disaster relief or intense, but time-limited emergency 

medical fl ights when untreated fatigue would necessitate the cancellation or delay of these fl ights and thus 

jeopardize the safety of others. On the other hand, the 

prescription sleep-promoting compound zolpidem 

should be authorized for use by civilian commercial pilots in situations where quality natural sleep is diffi cult 

or impossible to obtain due to circadian or other reasons 

provided that: 1) the pilot has previously checked for 

any unusual reactions to the medication; 2) the dose 

does not exceed 10 mg in any given 24-h period; 3) the 

medication is used no more than 4 times in any 7-d period; and 4) there is an interval of 12 h between the ingestion of the medication and the return to duty. The 

benefi ts of restful sleep induced by a medication with 

short duration of action and excellent safety profi le (as 

established by military aviation experience) are far preferable to the adverse effects of sleep deprivation when 

medication is withheld or the adverse effects of alcoholinduced sleep. Zolpidem should not be taken to promote 

in-fl ight bunk sleep or cockpit naps. To minimize complete reliance on medication for the improvement of 

quality preduty or postduty sleep, it is our contention 

that crewmembers should be educated about proper 

sleep hygiene, the benefi ts of aerobic exercise for promoting quality sleep, and natural strategies designed to 

promote circadian readjustment (assuming crewmembers 

will remain in a new time zone for 5 or more days). 

In the United States, the use of non-FDA regulated substances such as valerian, kava, and melatonin is not recommended because the quality of the compounds cannot be assured and there is insuffi cient scientifi c evidence 

of safety and/or effectiveness. In other jurisdictions, 

melatonin is available in pharmaceutical grade. In laboratory environments, pharmaceutical-grade melatonin 

has been effective in circadian entrainment or facilitation of daytime sleep (8,9,118,119,196,231). 

 Fatigue detection technologies (fi tness for duty and 

real-time assessment devices) and scheduling tools that 

incorporate biomathematical models of alertness can be 

incorporated as part of an overall safety management 

approach but should not be used in place of regulatory 

limitations. Prior to using any of these technologies, the 

scientifi c literature should be consulted to establish the 

validity of the specifi c technique. 

 With regard to the use of prescription pharmacological alertness-enhancing compounds in military aviation 

operations, it is our contention that the compound dextroamphetamine remains an authorized option and that 

modafi nil, which is already authorized by the U.S. Air 

Force, be authorized by the other services as well. Military fl ight operations are intense and unpredictable, and 

fatigued pilots often have little choice (in consideration 

of all the relevant mission factors) except to complete a 

scheduled mission. Failure to do so could jeopardize the 

safety or survivability of other military personnel or civilians. The benefi ts of appropriate stimulant use have 

been shown by scientifi c study to far outweigh the negative effects of sleep deprivation. Furthermore, proper 

medical oversight is typically available in the military 

aviation context. 

 Concerning the use of prescription pharmacological 

sleep-inducing compounds in military fl ight operations, 

we believe the existing authorized use of temazepam, 

zolpidem, and zaleplon should be continued. Since adequate routine medical oversight is available in the military aviation context, a physician can choose the correct 

medication based on the specifi c situation and monitor 

for proper usage and the occurrence of unexpected side 

effects. Furthermore, it is certainly the case that the effects of restful sleep induced by one of the above medications are far superior to the effects of alcohol-induced 

sleep or to the adverse effects of sleep deprivation. 

 In developing fatigue countermeasures of every sort, 

individual differences must be better addressed. There 

are differences in how people respond to sleep loss, 

sleep disruption, and time zone transitions. Research is 

focusing on identifying individual differences in sleep 

regulatory mechanisms, circadian rhythmicity, recovery 

sleep, and responses to fatigue countermeasures ( 215 , 

216 ). Examining the impact of various individual factors 

(circadian phase, sleep need, etc.) on susceptibility to 

decrements and the effi cacy of countermeasures will 

facilitate optimal fatigue management in the aviation 

environment. Such data are being used for the development of biomathematical models of fatigue to predict 

performance and alertness levels at an individual level 

( 215 ). Due to a range of differences in how individuals 

respond to the operational challenges associated with 

long-haul and ULR fl ight operations, modeling work 

is also aiming to predict relative group performance for 

an overall trip pattern. Many issues associated with 

fl ight operations remain unanswered and can only be 

answered by collecting data during carefully scientifi -

cally designed research. 

 In sum, while fatigue represents a signifi cant risk in 

aviation when left unaddressed, there are currently numerous countermeasures and strategies that can be employed to increase safety. Furthermore, new technologies and countermeasures are being developed that hold 

great promise for the future. It is our hope that the countermeasures and strategies described in this paper, when 

employed appropriately, will serve to reduce the risk of 

aviation accidents and incidents attributable to the insidious effects of fatigue. 
54 Aviation, Space, and Environmental Medicine x Vol. 80, No. 1 x January 2009

FATIGUE COUNTERMEASURES — CALDWELL ET AL.

 ACKNOWLEDGMENTS 

 The authors wish to thank Dr. Thomas Nesthus, Chair of the 

Aerospace Human Factors Committee (AHFC) for his guidance and 

support throughout a lengthy process. We are also grateful to CAPT 

Nicholas Davenport for comments and information regarding U.S. 

Navy fl ight duty/rest regulations and Capt. Barry Reeder for information about corresponding U.S. Air Force regulations though any 

errors remain ours. We thank the members of the AHFC for their comments on an earlier version of the manuscript, especially Dr. Ronald 

Hoffman and Dr. David Schroeder as well as the Aerospace Medical 

Association Executive Council for its comments and review, particularly Dr. Russell Rayman, Dr. Guillermo Salazar, Dr. Estrella Forster, 

and CAPT Christopher Armstrong. 

Authors and affi liations: John A. Caldwell, Ph.D., Archinoetics, LLC, 

Honolulu, HI; Melissa M. Mallis, Ph.D., Institutes for Behavior Resources, Inc.; Baltimore, MD; J. Lynn Caldwell, Ph.D., Air Force Research Laboratory, Wright-Patterson AFB, OH; Michel A. Paul, M.Sc., 

Defence R&D Canada (Toronto), Toronto, ON, Canada; James C. 

Miller, Ph.D., Miller Ergonomics, San Antonio, TX; and David F. Neri, 

Ph.D., Offi ce of Naval Research, Arlington, VA. 

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