Aviation safety: fatigue management

The international civil aviation network carries over four billion passengers around the world annually. In celebrating ICAO's 75th Anniversary Celebrations, we will be highlighting some of the crucial safety achievements that have enabled this. We hope you follow our UnitingAviation.com series throughout the year, and we encourage you to use the #ICAO75 hashtag to share your thoughts and memories with us through social media.


Fatigue is inevitable in a 24/7 industry such as aviation. If we are to remain an ultra-safe industry, fatigue-related risks have to be managed.

In aviation operations, managing fatigue is important because it diminishes an individual’s ability to perform almost all operational tasks.  This clearly has implications for operational efficiency, but in situations where individuals are undertaking safety-critical activities, fatigue-effected performance can also have consequences for safety outcomes. 
Fatigue is a natural consequence of human physiology.

Because fatigue is affected by all waking activities (not only work demands), fatigue management has to be a shared responsibility between the State, service providers and individuals.

A brief history of flight and/or duty limitations

For most workers, hours of work are part of the working conditions and remuneration packages established through industrial agreements or social legislation.  They are not necessarily established from a safety perspective.

However, the need to limit pilots’ flight and duty hours for the purpose of flight safety was recognized in ICAO Standards and Recommended Practices (SARPs) in the first edition of Annex 6 published in 1949.  At that time, ICAO SARPs required the operator to be responsible for establishing flight time limits that ensured that “fatigue, either occurring in a flight or successive flights or accumulating over a period of time, did not endanger the safety of a flight”.  These limits had to be approved by the State.

By 1995, ICAO SARPs required States to establish flight time, flight duty periods and rest periods for international flight and cabin crew.  The onus was on the State to identify “informed boundaries” that aimed to address the general fatigue risk for flight operations nationally.  At no time have ICAO SARPs identified actual flight and duty hours because it had proven impossible to identify global limits that adequately addressed operational contexts in different regions.

While ICAO SARPs apply only to international operations, many States also chose to establish similar flight and duty time limitations for domestic operations.  States generally used the same flight and duty limits for helicopter crew as for airline crew.

The fallacy of flight and/or duty limitations is that staying within them means that operations are always safe.   Buying into this fallacy suggests that scheduling to the limits is enough to manage fatigue-related risks.  However, more recent SARP amendments related to prescriptive limits have highlighted the responsibilities of the operator to manage their particular fatigue-related risks within the limits using their SMS processes.

And then there was FRMS….

Fatigue Risk Management Systems (FRMS) represent an opportunity for operators to use their resources more efficiently and increase operational flexibility outside the prescriptive limits, whilst maintaining or even improving safety. In implementing an FRMS, the onus shifts to the operator to prove to the State that what they propose to do and how they continue to operate under an FRMS, is safe.

In 2011, SARPs enabling FRMS as an alternative means of compliance to prescriptive limitations were developed for aeroplane flight and cabin crew (Annex 6, Part I).  At the time of development, it was necessary to address concerns that airline operators would take this as an opportunity to schedule purely for economic benefits at the cost of safety. Therefore, while often referred to as “performance-based” approach, the FRMS SARPs are nevertheless very prescriptive about the necessary elements of an FRMS and require the explicit approval of an operator’s FRMS by the State.

Since then, similar FRMS SARPs were made applicable for helicopter flight and cabin crew in 2018 (Annex 6, Part III, Section II).

But what about air traffic controllers?

Despite their obvious impact on flight safety outcomes, ICAO SARPs have never required the hours of work to be limited for air traffic controllers even though some States have had hours of duty limitations for air traffic controllers for many years.  This is about to change.  Amendments to Annex 11, becoming applicable in 2020, will require that ICAO States establish duty limits and specify certain scheduling practices for air traffic controllers.  As for international airline and helicopter operations, States will have the option of establishing FRMS regulations for air traffic service providers.

Fatigue Management SARPs today

Today, ICAO’s fatigue management SARPs support both prescriptive and FRMS approaches for managing fatigue such that:

  • Both approaches are based on scientific principles, knowledge and operational experience that take into account:
    • the need for adequate sleep (not just resting while awake) to restore and maintain all aspects of waking function (including alertness, physical and mental performance, and mood);
    • the circadian rhythms that drive changes in the ability to perform mental and physical work, and in sleep propensity (the ability to fall asleep and stay asleep), across the 24h day;
    • interactions between fatigue and workload in their effects on physical and mental performance; and
    • the operational context and the safety risk that a fatigue-impaired individual represents in that context.
  • States continue to be obliged to have flight and duty time limitations but are under no obligation to establish FRMS regulations. Where FRMS regulations are established, the operator/service provider, can manage none, some or all of its operations under an FRMS, once approved to do so.
  • Prescriptive fatigue management regulations now provide the baseline, in terms of safety equivalence, from which an FRMS is assessed.

In practice…

In Airlines:  The Fatigue Management amendments to the Annex 6, Part I, in 2011 led many States  to reviewing their prescriptive limitation regulations for pilots based on scientific principles and knowledge (refer text box) and identifying further requirements for operators to manage their fatigue-related risks within the prescribed limits.  Fewer States have reviewed their prescriptive limitation regulations for cabin crew.

In every case, despite a refocus on providing adequate opportunities for sleep and recovery, altering existing flight and duty limitations remains a very sensitive and difficult task because it impacts income and work conditions as well as the constraints of pre-existing employment agreements. It is made even more challenging for States whose flight and duty time limitations are legislated.

Where States have reviewed their prescribed flight and duty limits, the increased awareness of the relationship between sleep and performance has served to highlight the responsibilities of the individual crew member and the airline to manage fatigue, and in some cases have resulted in the prescribed limits sitting alongside a set of regulations  that make these responsibilities more explicit, e.g. the FAA’s Fatigue Risk Management Program, EASA’s Fatigue Management requirements, CASA’s Fatigue Management requirements and CAA South Africa’s Fatigue Management Program.

The scientific principles of fatigue management

  1. Periods of wake need to be limited.  Getting enough sleep (both quantity and quality) on a regular basis is essential for restoring the brain and body.
  2. Reducing the amount or the quality of sleep, even for a single night, decreases the ability to function and increases sleepiness the next day.
  3. The circadian body-clock affects the timing and quality of sleep and produces daily highs and lows in performance on various tasks.
  4. Workload can contribute to an individual’s level of fatigue.  Low workload may unmask physiological sleepiness while high workload may exceed the capacity of a fatigued individual.

Many States have established, or plan to establish, FRMS regulations, often at the encouragement of their airlines.  The FRMS challenge for States continues to be whether they have the resources to provide the necessary oversight from a scientific and performance-based perspective, particularly when the same regulations usually apply to a variety of domestic flight operations.  While FRMS requirements are onerous and time-consuming, the few airlines who have so far managed to get FRMS approval for particular routes have found the operational flexibility gained to be worth the effort.

General scheduling principles

  1. The perfect schedule for the human body is daytime duties with unrestricted sleep at night. Anything else is a compromise.
  2. The circadian body clock does not adapt fully to altered schedules such as night work.
  3. Whenever a duty period overlaps a crew member’s usual sleep time, it can be expected to restrict sleep. Examples include early duty start times, late duty end times, and night work.
  4. The more that a duty period overlaps a crew member’s usual sleep time, the less sleep the crew member is likely to obtain. Working right through the usual nighttime sleep period is the worst case scenario.
  5. Night duty also requires working through the time in the circadian body clock cycle when self-rated fatigue and mood are worst and additional effort is required to maintain alertness and performance.
  6. The longer a crew member is awake, the worse their alertness and performance become.
  7. Across consecutive duties with restricted sleep, crew members will accumulate a sleep debt and fatigue-related impairment will increase.
  8. To recover from sleep debt, crew members need a minimum of two full nights of sleep in a row. The frequency of recovery breaks should be related to the rate of accumulation of sleep debt.
  9. Keep short notice changes to a minimum, especially where they infringe or overlap the  Window of Circadian Low (WOCL).
  10. Duty periods associated with high workload (such as multiple, challenging landings and in marginal weather conditions) may need to be shortened and extensions avoided where at all possible.

In Helicopter Operations:  For some States, the recent amendments to Annex 6, Part II (Section II) have highlighted the need to establish flight and duty time limits for helicopter crew members that better relate to the context of helicopter operations, rather than using the same limits as for airline pilots.  Within those limits, the helicopter operator is expected to build crew schedules that use both fatigue science and operational knowledge and experience.

A new fatigue management guide for helicopter operators, currently under development in ICAO, identifies general scheduling principles based on fatigue science to guide helicopter operators in building “fatigue-aware” schedules that offer optimum opportunities for sleep and recovery (refer text box).

The particular challenge in helicopter operations, however, is that so many helicopter operations are unscheduled.  While some helicopter operators will be able to operate within prescribed limits and effectively manage fatigue risks using an SMS, many types of helicopter operations, such as those that require unscheduled, immediate responses, possibly in high-risk settings, will benefit from the operational flexibility and safety gains of an FRMS.

In Air Traffic Control Services: Next year, States are expected to have established prescriptive work hour limits for air traffic controllers, while FRMS regulations remain optional and can be established at any time. However, the nature of the relationship between the Air Navigation Services Provider (ANSP) and the State will influence how the implementation of fatigue management regulations will unfold.  In most cases, the State provides oversight of only one ANSP and although there is a current trend for privatisation, many of the ANSPs are fully or partially owned by the State.

In an industry sector that is often largely self-regulated, the distinction between a prescriptive fatigue management approach and FRMS may become blurred.  However, a refocus on safety and not only organisational expediency or personal preference is likely to have substantial effects on the way controllers’ work schedules are built in ANSPs across the world.  This is a “watch this space”.

Fatigue Management Guidance for ICAO States

The Manual for the Oversight of Fatigue Management Approaches (Doc 9966) received another update this year – Version 2 (Revised) – and an unedited version (in English only) will shortly replace the current manual available for download here.  On this website you can also find the following:

  • Fatigue Management Guide for Airline Operators (2nd Edition, 2015)
  • Fatigue Management Guide for General Aviation Operators of Large and Turboject Aeroplane (1st Edition, 2016)
  • Fatigue Management Guide for Air Traffic Service Providers (1st Edition, 2016)
  • The Fatigue Management Guide for Helicopter Operators (1st Edition) is expected to be available later this year.

The Fatigue Management Guide for Helicopter Operators (1st Edition) is expected to be available later this year.

About the author

Dr Michelle Millar is the Technical Officer (Human Factors) and the NGAP Programme Manager at ICAO.  She heads the ICAO FRMS Task Force and has been involved in the development of ICAO fatigue management provisions since 2009.  Her academic background is in sleep, fatigue and performance.