(U.S. Air Force photo by Staff Sgt. Ryan Callaghan)

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Factoring Fatigue into an Aircraft Maintenance System

By:  MSgt Scott R. Thiels

Aircraft maintenance is a fast-paced career which demands long, fluctuating hours involving strenuous, complex tasks.  Maintainers are sometimes required to work greater than 12 hours in heavily fatigued states.  The military aircraft maintainer is often exposed to the dangers of working in sleep-deprived states due to frequent changes to duty schedules.  Fatigue can cause an array of health problems ranging from heart rate fluctuations to reductions in cognitive ability.

The military aircraft maintainer has not been the subject of studies involving fatigue; however, other research has been performed that can be applied to the military maintainer.  In a 2011 article, for example, Boeing published a Federal Aviation Administration (FAA) study in which maintainers’ sleep habits were tracked.  The findings concluded that the average maintainer received approximately five hours of sleep per night, three hours less than the eight hours recommended for the average person.  These and other findings provide excellent evidence of the role that fatigue plays in the daily lives of aircraft maintainers and proves that further studies and control techniques are warranted within the Air Force community.

Frequent Schedule Changes and Fatigue

The most consistent element of military aviation may be its ability to consistently change.  Aircraft receive frequent modifications in order to keep up with the requirements of new missions.  Mission changes also lead to flying schedules that are altered numerous times.  Movement of flying hours often results in changes to duty hours for maintainers.  Military service on the flightline is, therefore, a dynamic environment that demands an extreme level of flexibility and often places personnel on duty while fatigued.

The effects of fatigue on humans are well documented.  A fatigued person often behaves similar in nature to someone with a high blood alcohol level, experiencing a notable reduction in cognitive ability.  While carrying out aviation maintenance, airmen must perform complex actions while monitoring numerous lights and gauges that require additional decision making based on system indications.  When fatigue becomes a factor, alertness drops and mistakes are made that can lead to damaged equipment, personal injury, or death.  Discussions will focus on safety mishap trends associated with shift changes and methods for modifying personnel schedules or duties in order to mitigate the effects of fatigue.

Literature Case Studies

Fatigue and Worker Health

Fatigue is an issue for any workforce and can cause an array of health problems, including psychological and physiological ailments.  Bambra, Whitehead, Sowden, Akers, and Petticrew initiated research into the problems caused by fatigue by reviewing 40 studies on the topic.  The researchers compounded existing information and discovered ample evidence that shift work caused social life problems with difficulties maintaining a balance between personal and work lives.

The 40 studies investigated the effects of altering employees’ work hours by introducing a compressed schedule.  An example of the change was allowing employees to work four 10-hour shifts instead of five 8-hour shifts.  While the benefits of these schedule changes were minimal, balancing four workdays with three consecutive days off allowed employees more flexibility and more time to recuperate before returning to work.  Furthermore, the introduction of sports activities into one of the days off resulted in employees reporting improvements in their personal lives.  This research highlighted the benefits of maintaining a balanced shift routine—worker health is linked not only to their time on duty but also to their time off.  Stated differently, a key aspect of worker performance exists in maintaining a balanced life allowing for proper sleep and reduction of fatigue.

Sleep and Cognitive Ability

When fatigue becomes a factor, cognitive ability and reaction times degrade, and decision-making suffers.  Research into these issues has been carried out in two different areas directly related to fatigue and shift work.  To study how fatigue affects a worker’s reaction time, a simple test was developed in which participants were required to press a button when an indicator light appeared.  The test was repeated numerous times, and the results were compared to participant sleep deprivation levels.  The more workers became fatigued, the slower their reaction times became.  Fatigued participants also made more errors in the form of false reactions and took longer to complete the entire test.  This study provided valuable information on a fatigued worker’s ability to maintain situational awareness.

            Further, research on task switching has shown what effect shift work has on a worker’s ability to move from one activity to another.  The goal of this research was to measure an individual’s ability to move from an original task to a secondary task and then back to the original task as compared with participants’ fatigue levels (measured by their circadian phase and melatonin levels).  The research showed that night shift workers had more difficulty with task switching and exhibited a reduction in task efficiency as compared to day shift workers.

Fatigue and Job Performance           

The final literature review for this research is on law enforcement.  In 2000, the United States Department of Justice published findings from a study on police officers and fatigue.  A total of 379 officers from 4 different departments across the United States took part in the study, which analyzed approximately 60,000 workdays.

The research included the FITTM fatigue eye measurement system and interviews.  The test results concluded that fatigue played a role in all personnel’s performance regardless of shift assignments.  One of the most significant findings was related to personnel’s safety immediately after completing night shift duties.  Several accidents occurred when officers were required to attend mandatory daytime appointments after their shifts ended.  The conclusion drawn from this research is that altering the sleep schedule of shift workers has an impact on job safety and increases accident rates.

Summary of Literature Review & Statement of Problem

While carrying out aviation maintenance, airmen must perform complex actions while monitoring numerous systems and ground equipment.  Considering these tasks, it is evident that fatigue in aviation can lead to catastrophic results.

Aircraft maintenance is a physically and mentally demanding career field, involving high risks activities that often result in injuries, including loss of fingers in landing gear, eyes punctured by safety wire, severe burns from hot engine components, and even death.  When either the mission changes or a shortage of qualified personnel occurs, moving maintainers to cover day shift or night shift becomes necessary.  While advanced warning is preferred, the military maintainer often has little or no warning due to the unpredictability of the aircraft maintenance environment.  These no-notice changes and long duty hours put maintainers at high risk of working in states of reduced situational awareness caused by fatigue.


This study relied on two years of archived quality assurance (QA) inspection data compared to shift schedules from the same period.  Therefore, this research is limited to drawing conclusions from these documents and the patterns that arise.  Due to military medical standards, all maintainers are assumed free from sleep disorders that may interfere with duty performance.

In order to complete the study two fiscal years’ worth, 2017 and 2018, of USAF flightline maintenance quality assurance inspections were gathered for analysis from the quality assurance 2000 (QA2000) database.  The sample for this study was a group of aircraft maintainers stationed at a continental USAF base.  All personnel in the sample group have been stationed at the location for more than one year, providing ample time to acclimate to local conditions.  Additionally, the study involved no interaction with personnel and took place by using archived inspection and duty schedule data.

            The sources of data for this study are forms retrieved from official USAF records.  QA2000 is an extensive database which logs official quality assurance inspector results in numerous types of inspections.  USAF duty schedules are developed and maintained by Non-Commissioned Officers (NCO) operating under the authority of the Officer in Charge (OIC).  These schedules are recorded as official records and archived for three years in unit files.  QA2000 archives, coupled with military maintainer duty schedules, offer a valid source of data for analyzing employee performance and shift hours.

The statistical test chosen was the contingency table in statcrunch with the Chi-square and Fisher’s exact test options.  The QA2000 database pulled data into documents organized in several different ways.  The information was organized by shift for initial counting of passes and fails.  After totaling the complete list, 1,935 inspections were analyzed.  Statistical analysis served the purpose of rejecting or accepting the following null hypothesis; no statistical difference exists in the number of quality assurance fails between day and night shift maintainers.  Once the initial analysis was accomplished, each QA inspection was investigated for the type of fail and compared to possible shift fluctuations up to two weeks prior to the event.


Per the QA2000 database, the military unit chosen for this research experienced 1,935 quality assurance inspections during a two year period starting at the beginning of FY17 and ending at the close of FY18 (Tables 1 & 2).  FY17 accounted for 833 inspections and FY18 totaled 1,102 (Tables 1 & 2). An analysis of the results proved the null hypothesis; there is no statistical difference in the number of QA fails between day and night shift maintainers (Table 3).  This analysis alone does not end the discussion of fatigue-induced fails in maintenance shift operations.

The USAF has many mottos, one of which is, “the mission comes first.”  This saying is frequently put into action when personnel are required to make short or no-notice shift changes resulting in the immediate alteration of their sleep schedules.  While investigating each fail for the two year period, it was discovered that detailed shift data was only available for 75 of the 95 total fails (Table 4).  The 75 fails included all inspection types from both day and night shifts (Table 4).  Of the 75 fails, 20 occurred within one week of a shift change while two fails occurred two weeks after a shift change (Table 4).  These data points contributed to 29.3% of the fails occurring within two weeks of a shift change (Table 4).  Analysis of the 29.3% revealed the majority of fails, 26.7%, occurred within one week of a shift change (Table 4). These rates indicate a relatively high percentage of fails associated with changes in sleep patterns of personnel regardless of shift assignment.

Discussion, conclusion, recommendations


While the combined fiscal years fail percentages do not indicate statistical significance, individual fails researched uncovered 22 fails within two weeks of a significant shift change (Table 4).  Further break down of this data revealed 20 fails occurred within one week, and two fails occurred during the second week (Table 4).   Each fail signifies a lack of attention to detail which is similar to mental overload conditions that occur when cognitive ability is reduced by fatigue.  The 22 fails which occurred within two weeks of a shift change are summarized in the paragraphs below.

Two night-shift maintainers received QA fails within one week of having their schedules changed, which altered their sleep routines by 6 hours (Table 5).  Six night-shift maintainers received QA fails all within one week of accommodating mandatory daytime appointments (Table 5) (Figure 1).  Schedule interruptions due to holidays accounted for the highest percentage of the 22 QA fails (Figure 1).  Six night-shift and two day-shift maintainers failed inspections after returning to work following a four day holiday (Table 5).  Six maintainers received QA fails after being reassigned to different shifts with no acclimation period (Table 5) (Figure 1).

This list of 22 failures represents only a portion of the total fails from the two-year period under review.  There is a discernible pattern of fails associated with interruptions in personnel’s normal shift and sleep routines that may be affecting their ability to perform complex tasks.  It seems unlikely that these maintainers altered their schedules to accommodate work requirements rather than their personal lives.  Upon returning to work after schedule interruptions, maintainers missed maintenance steps, committed safety violations, and failed to use tech data (Table 5). These personnel may have been experiencing a reduction in cognitive ability brought on by fatigue induced by alterations in their sleep schedules.


In conclusion, military aircraft flightline maintenance is a complex environment where attention to detail is essential for ensuring safety.  The research question aimed to discover what effect fatigue had on military aircraft maintainers.  To answer this question, this military unit’s 1,935 QA inspections from FY17 and FY18 were analyzed, and it was determined that night shift did not produce a statistically significant higher fail rate than day-shift.  Further investigation of the data uncovered that altering a person’s shift hours did affect job safety and performance.

Previous research has shown that altering a shift worker’s schedule has a negative impact on their ability to maintain vigilant attention due to increased levels of fatigue (Cheng, Tallent, Bender, Tran, & Drake, 2017).  After analysis of this military unit’s QA fails, 29.3% could be contributed to fatigue induced by a change of shift hours (Table 4).  Eliminating fails due to changes in shift hours could significantly increase this unit’s level of safety.  It is concluded that fatigue plays a major role in reducing both situational awareness and safety of military aircraft maintainers operating in a flightline setting. iii


Workers benefit from a stable routine; however, in the military, it cannot be expected that this routine will not be interrupted.  While safety is the responsibility of every unit member, augmenting current regulations would be required to promote and enforce a culture of safety.  Regulations could include granting night shift workers with daytime appointments a minimum of 10 hours off duty prior to their next day’s appointments.  An amended regulation would ensure personnel changing shifts are allowed 48 hours of off-duty time to acclimate to the new shift hours.  In conjunction with time off and acclimation periods, personnel should be assigned to administrative duties, such as aircraft forms reviews, for one shift immediately following a change in their schedules.  This will remove maintainers from safety-critical areas while providing additional time for schedule acclimation.

Finally, when alterations in schedule hours occur due to shift changes or holidays, safety briefings can be utilized to bring awareness to fatigue and its association with quality assurance fails and unsafe conditions in the workplace.  Utilizing these recommendations could have reduced the analyzed military unit’s QA fails by 29.3%.  When used together, updated regulations and awareness can play a large role in the reduction of failures and increase safety and productivity. This study warrants further research into the effects of fatigue in a military aircraft maintenance environment.

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