Fatigue and Stimulant Use in Military Fighter Aircrew During Combat Operations

Gore, Webb and Hermes conducted a study into the effects of stimulant use on military flight crews in an operational environment. It was published in August 2010 in the Aviation, Space, and Environmental Medicine monthly journal.

The study revealed that stimulant use by military air crews whilst on deployment in an operational environment can effectively decrease fatigue. However, the results show that a number of additional variables contribute to the fatigue levels of crew members in such an environment. Gore, Webb and Hermes suggest that too much emphasis has been placed on regulating the length of deployments, and variables such as preflight hypnotic medication use, circadian patterns and sleep quality may have been given less attention than required.

Study's Scope

This research was conducted on a selected group of U.S. military pilots in an undisclosed location. Therefore, any conclusions or findings that result from this study can be generalised to similar populations under similar operational conditions. Generalisations may not be drawn to wider reaches or other areas of aviation such as the commercial or general aviation sectors. The operations environment and tasks required of military flight crew are very unique and often unpredictable, thus the relatively narrow scope of subsequent findings generated from this study. However, this research may provide valuable insight into the effectiveness of stimulant use on minimising fatigue and provide a basis for further research in other areas of aviation.


Research approach

This study conducts exploratory research on the use of stimulants by military flight crews, as well as the effect of such use on fatigue during combat and deployment situations.


The study consisted of a purposive sample of 29 USAF F-15E crew members on deployment in a forward operating location. The sample consisted of 29 Crew members, 16 pilots and 13 Weapon System Officers (WSO) with an average age of 29.9 and an average of 1231 total flight hours, of which 218 hours were classified as combat flight hours.

Questionnaires and Results

29 flight crew members completed 3 questionnaires at 3 different stages of operation: pre, during and post flight. The initial questionnaire required participants to answer questions relating to demography, deployment and flight history, sleep quality whilst on deployment, historical sleep behaviour and frequency of stimulant use (caffeine, alcohol or nicotine) whist on deployment. Illustration I details the results of the initial questionnaire.

Illustration I: Participant Information - Questionnaire One
(N=29) Mean Standard Deviation
Age 29.9 3.9
Total Flight Hours 1231.0 745.0
Total Combat Hours 218.0 159.6
Nicotine units/day* 3.0 5.3
Alcohol units/day* 0.7 0.6
Caffeine units/day* 2.9 3.4
Sleep Per 24Hours, Flight day 7.0 1.3
Sleep Per 24 Hours, Non-Flight day 7.9 1.3

* One nicotine unit defined as one cigar, cigarette, or “ pinch ” of smokeless tobacco. One alcohol unit defined as 1 oz of liquor, one glass of wine, or one 12-oz beer. One caffeine unit defined as one cup of coffee or one can of soda.

The preflight questionnaire covered the crew members perceived level of fatigue at that time using the Stanford Sleepiness Scale (SSS). Frequency, doses, and timing of any hypnotic medication or stimulant use (caffeine, alcohol or nicotine) prior to the deployment, were also covered in the preflight survey. Hypnotic medication, in this study, refers to the use of either Zolpidem, Temazepam or Zaleplon. There were 111 deployments in which questionnaires were completed by flight crews. The results of the preflight questionnaire are shown in Illustration II.

Illustration II: Preflight fatigue, Stimulant or Medication use and Deployment Information Frequency of total (N=111) % of total Mean Standard Deviation
Deployment Duration > 8 Hours 51 45.9 - -
Deployment Duration - - 7.6 1.2
Caffeine Use Prior to Takeoff 70 63.1 - -
Caffeine Units Prior to Takeoff - - 1.0 1.1
Tobacco Use within 24 h of Takeoff 20 18.0 - -
Tobacco Units Prior to Takeoff - - 1.1 3.1
Alcohol Use within 24 h of Takeoff 14 12.6 - -
Alcohol Units Prior to Takeoff - - 0.5 1.3
Hypnotic Used within 24 h of Takeoff (Any of the 3 stated) 25 22.5 - -

The postflight questionnaire again used SSS to measure the fatigue level of crew members. Participants were also asked to report any physical side symptoms experienced after the flight. Illustration III shows comparisons between crews who took stimulants and those who did not whilst on deployment. Illustration IV details the results of the postflight survey and the the common physical symptoms associated with stimulant use experienced by crew members.

Illustration III: Comparisons Between Stimulant use and No Stimulant use on deployment Stimulant Used N=39 (35.1%) Stimulant Not used N=72 (64.9%)
Preflight Characteristics N (%) N (%)
Hypnotic Medication use prior to take off (any 3 within 24 h) 12 (30.8) 13 (18.1)
Mean (SD) Mean (SD)
Preflight SSS 2.2 (0.9) 1.9 (0.8)
Deployment Characteristics N (%) N (%)
Deployment Airborne between 0300 and 0600 hours local time 24 (61.5) 20 (27.8)
Deployment Airborne between 1800 and 0600 hours local time 34 (87.2) 60 (83.3)
Deployment Duration > 8 hours 24 (61.5) 27 (37.5)
Mean (SD) Mean (SD)
Deployment Duration in hours 7.9 (1.2) 7.4 (1.2)
Postflight Characteristics
Any Postflight physical symptoms reported 10 (25.6) 19 (26.4)
Postflight SSS 2.6 (1.1) 3.1 (1.2)
Illustration IV: Postflight Physical Symptoms Reported for all Surveyed Deployments Physical Symptoms Reported [N (%)]
Any Physical Symptom [N (% of N total)] Jittery Racing Heart Drugged Feeling Nausea Dizziness Headache
All Deployments (N=111) 29 (26.1) 16 (14.4) 2 (1.8) 6 (5.4) 4 (3.6) 3 (2.7) 14 (12.6)
Stimulant used (Any, N=39) 10 (25.6) 5 (12.8) 1 (2.6) 1 (2.6) 2 (5.1) 1 (2.6) 5 (12.8)
Dextroamphetamine use (N=30) 7 (23.2) 3 (10.0) 1 (3.3) 1 (3.3) 2 (6.6) 1 (3.3) 4 (13.3)
Modafinil use (N=9) 3 (33.3) 2 (22.2) 0 0 0 0 1 (11.1)
Stimulant Not used (N=72) 19 (26.6) 11 (15.3) 1 (1.4) 5 (6.9) 2 (2.8) 1 (1.4) 9 (12.5)

Hourly logs conducted by crew members detailed perceived fatigue levels throughout recorded flights. Any stimulants consumed whilst in flight were recorded along with the dosage and time of consumption. The results of these hourly logs showed, with 95% confidence intervals, that on average for the first 4 hours of deployment, crew members who used stimulants were significantly more fatigued than those who did not (P<0.05). After one hour into their deployment, those crew members that used stimulants during the flight scored 1.5 points higher on the in-flight fatigue rating. The average time of stimulant admission was 2.8 hours post takeoff. After the first 4 hours of deployment, the fatigue level of stimulant users was no longer significantly higher than that of non-stimulant users. Approximately 7.5 hours post takeoff, the average fatigue level of stimulant users dropped below that of stimulant users.


The results of the study indicate that stimulants effectively decrease fatigue in military air crews when consumed whilst on deployment. It is also evident that stimulant use in flight yields minimal physical symptoms and in fact stimulant users reported fewer physical symptoms than those who did not use stimulants. However, the results of the questionnaires suggest that several other factors contribute to increased levels of fatigue. 39 of the 111 deployments recorded involved crew members that used stimulants, and of those 39, 12 had used at least one type of hypnotic medication in order to induce sleep within 24 hours of the flight. It is probable that this medication was a contributing factor in the higher average SSS result indicated by stimulant users versus non users prior to deployment.

Stimulant use was also more frequent in deployments that took place during the circadian trough (between 0300 and 0600 hours), with 61.5% of stimulant users stating use during this time period. 87.2% of stimulant users claimed to have used stimulants on night deployments between 1800 and 0600 hours. Both of these statistics suggest that disrupted sleep patterns is a prevailing cause of fatigue which requires the use of stimulants in flight.

The results of the post flight surveys suggest that stimulant use in flight decreases fatigue. On average, stimulant users began their deployment more fatigued, but finished their flight less fatigued, than those crew members who did not use stimulants in flight. The post flight SSS indicated an average result of 2.6 for those crew that used stimulants in flight and 3.1 for those who didn't. This result indicates that those who did not use stimulants in flight were more fatigued than those who did. Given that preflight SSS results showed on average those who used stimulants in flight were more fatigued than those who didn't, it can be said with a high level of confidence, that the stimulant use in flight effectively decreased fatigue levels.

The results of the study also suggest that the use of stimulants such as dextroamphetamine or modafinil are safe to use in flight, and have minimal physical side-effects that are commonly associated with stimulant use. More non-stimulant users reported physical symptoms post deployment than those who did use stimulants. The relationship between stimulant use and physical symptoms was found to be not significant.


In this specific operating environment, stimulant use is an effective counter-measure for fatigue in air crews. The consumption of the two stimulants used in this study can be deemed safe and, in this study, did not produce physical side-effects, given the results of the surveys. However, this alone is not conclusive as other variables such as sleep inducing medication, sleep quality and disrupted sleeping patterns all contribute to levels of fatigue. Yet, for the specific purpose of decreasing fatigue levels of crew members during deployment, stimulant use is effective and safe.

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Authors / Editors

Henderson, J. (2013)

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