Fatigue Risk in Maintenance

Fatigue Risk in Maintenance


Aviation maintenance personnel face a particular risk of fatigue due to nighttime work and rotating shift work, the potential for long and unregulated duty times, the sleep disruption that can result from these working conditions, and cumulative sleep deficit. Fatigue can affect maintenance tasks through impaired judgment, difficulty focusing attention, memory lapses, reduced mood and motivation, and other performance effects.

The conditions that produce fatigue originate not only in the workplace but also in the employee’s personal life. Effective fatigue risk management requires a partnership with shared responsibility between the employee and the employer. Workplace factors include the length and time of day of the duty period, staffing levels, task deadlines and the availability of break periods. Personal factors leading to fatigue can include social and family commitments and disruptions, commute time, second jobs, and medical conditions that may reduce the quality or quantity of sleep. The employee has a responsibility to ensure, as much as possible, that he or she is rested and fit for duty before reporting for work. The International Federation of Airworthiness (IFA) has made the following statement in relation to the issue of maintainer fatigue: “Responsibility for the establishment and control of … employees’ duty hours and rest times does not solely rest with the company/employer. Individuals have a responsibility to make use of the opportunities and facilities for rest periods provided. They are also responsible for planning and using their rest periods properly in order to minimize incurring fatigue.”

The three main objectives of fatigue risk management are to:

  • Reduce fatigue - Examples of measures to meet this objective are hours of service (HOS) limits and the re-design of shift schedules.
  • Reduce or capture fatigue-related errors - The intention is to break the link between fatigue and performance decrements. This can be achieved by reducing the probability that a fatigued maintainer will make an error or capturing fatigue-related errors once they have occurred. Work breaks and additional task steps designed to capture errors are examples of such interventions.
  • Minimize the harm caused by errors - An example of this is a policy that prevents a fatigued maintainer from performing the same task on both engines of a twin-engine aircraft. The policy is not intended to reduce fatigue or reduce the probability of error. Rather, it minimizes the operational impact of an error, should one occur.

Because the Fatigue Risk Management System (FRMS) approach originally was developed for pilots, most existing FRMSs focus on the reduction of fatigue. However, the other two objectives deserve special attention in maintenance operations.

Maintenance organizations face a unique set of fatigue-related challenges, but also have access to a unique set of potential solutions:

  • Maintenance tasks tend to be self-paced rather than externally paced. Although much maintenance work is performed under time pressure, a maintainer conscious of impaired performance may be able to pause a task, trade speed for accuracy or repeat a step as necessary.
  • In some cases, there are opportunities to modify methods of task performance in maintenance. In many cases, task cards can be modified, and error-capturing barriers such as secondary inspections or operational/functional, checks can be introduced.
  • Maintenance organisations sometimes have flexibility to choose the time at which certain tasks are performed. In such cases, it may be possible to schedule the most safety-critical tasks, or those most susceptible to fatigue, at times when fatigue will have the least impact.
  • Maintainers are rarely required to travel across time zones while on duty. Consequently, jet lag and travel-related circadian rhythm disruption, which are major considerations for flight crews, are not usually relevant in the maintenance environment. The exception is when maintainers must travel to a remote work site to perform a task.

In recent years, comprehensive fatigue risk management approaches have been adopted in aviation, supplementing, or in some cases replacing, older HOS approaches. FRMSs have been promoted by the International Civil Aviation Organization (ICAO, 2008), the U.S. Federal Aviation Administration (FAA, 2010), the European Union Aviation Safety Agency (EASA, 2009) Transport Canada (2007a), the Civil Aviation Safety Authority of Australia (CASA, 2009a), and others.

U.S. Duty Time Limitations

The U.S. Code of Federal Regulations (Part 121.377, Maintenance and preventive maintenance personnel duty time limitations, states: Within the United States, each certificate holder (or person performing maintenance or preventive maintenance functions for it) shall relieve each person performing maintenance or preventive maintenance from duty for a period of at least 24 consecutive hours during any seven consecutive days, or the equivalent thereof within any one calendar month.

Best Practices

Some examples of fatigue interventions are provided below (the list is not exclusive):

  • HOS limits. Can be mandatory (prescribed by a government regulation) or voluntary (part of a company's rules). These limits can be applied to, for example:
    • Shift duration;
    • Shift extension (beyond the regular shift duration);
    • Number of hours within certain period (72 hours, one week, etc.);
    • Number of shifts within a week or some other specified period.
  • Scientific scheduling. This is an enhancement of the HOS limits in which computer models are used to define working periods based on scientific research (e.g., circadian rhythms).
  • Napping strategies. Short naps (with a duration of 20-40 min) have the potential to greatly improve performance. A potential hazard here is that sleep periods, particularly those lasting more than about 40 minutes, may produce “sleep inertia,” which is a feeling of disorientation that lasts for some time after awakening.
  • Training. If personnel are trained on the specifics of fatigue they can take their part in the implementation of the FRMS.
  • Excused absences. Some FRMSs enable employees to take unplanned leave if they believe their level of fatigue would prevent them from performing their duties. This tool should be used with caution, and the potential disruption caused by an unplanned absence needs to be weighed against the potential harm that could result when an employee reports for duty impaired. The potential for overuse of "fatigue leaves" should also be considered.
  • Medical treatment of sleep disorders, such as insomnia or sleep apnea.
  • Self-assessment of fatigue. This method uses questions (e.g., how much did you sleep in the last 24/48 hours) or scales (e.g., which of the 7 descriptions suits your condition best).
  • Fatigue detection technology. Examples of this are psychomotor tests (measuring the time needed to respond to a stimulus) or systems that detect, for example, blink rate, eye movement, etc.
  • Breaks. A period of exercise, such as a brief walk, can increase alertness and temporarily reverse the impact of fatigue on some psychomotor tasks. This method is not suitable for managing fatigue over long periods of time.
  • Workplace environment. Improvements to the work environment (e.g., bright light, fresh air) may help maintainers cope with fatigue. On the other hand, extreme temperatures, confined spaces, heights and other physically demanding environments can increase the effects of fatigue.
  • Stimulants. If used with moderation, caffeine can be effective against fatigue. Caffeine, followed immediately by a brief nap, has been shown to signifcantly reduce fatigue during the two hours following the nap. When caffeine is used as a fatigue countermeasure, it is generally recommended that the person avoids the routine consumption of caffeinated drinks (routine consumption leads to the development of tolerance).
  • Fatigue-proofing of task procedures. Sometimes it is possible to modify procedures to reduce the task’s susceptibility to fatigue-related errors or to detect the presence of an error by, for example:
    • Close supervision;
    • Working in pairs or teams, depending on the task;
    • Task rotation;
    • Checklists;
    • Support for new personnel by experienced personnel; or,
    • Communication/briefings at shift hand-over
  • Task scheduling interventions. In some cases, maintainers have informal norms concerning the time of day at which tasks are performed. For example, they may have the option to perform the most challenging tasks at the beginning of the shift, leaving less complex tasks until the end of the shift, when they expect to be less alert.
  • Progressive restrictions of work responsibilities. This includes measures to restrict a person from performing certain tasks (carrying out secondary independent inspections) when it is likely that they are fatigued (e.g., after working for 12 hours).

Accidents and Incidents

  • B733, Paris CDG France, 2011 - Poor resource planning caused overstretching of the personnel’s capacities when unexpected extra work turned up. This generated increased time pressure that led to things being forgotten and approximate execution of the work cards. The supervisor had worked for an excessive number of hours over a long period of time, which lowered his performance and his aptitude to carry out checks efficiently.
  • A319, London Heathrow UK, 2013 - ... it was noted that both Technicians were working an overtime shift which was part of a "significant level of planned and overtime working" which was attributable to staff shortage. It was considered that the risk of fatigue when the normal shift pattern was augmented by overtime working "was not (being) accounted for or measured in an objective way".
  • DH8A, en-route, near Bristol UK, 2010 - The Investigation also examined the long working hours recorded by maintenance personnel responsible for overseeing the ‘C’ Check and noted the considerable opportunities for the effects of fatigue to manifest themselves.
  • DH8C, vicinity Abu Dhabi UAE, 2012 - Considerable evidence that fatigue may have played a part in what happened was found. Both the Engineer’s roster and those of other maintenance personnel required them to work on an 8.5-hour shift each day, inclusive of a one-hour break, for 56 consecutive days, alternating between an early start day shift from 0600 to 1430 Local Time and a late shift from 1330 to 2200 Local Time.

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