Fatigue

Description

Fatigue is the general term used to describe physical and/or mental weariness which extends beyond normal tiredness.

Physical fatigue concerns the inability to exert force with ones muscles to the degree that would be expected. It may be an overall tiredness of the whole body, or be confined to particular muscle groups. Physical fatigue most commonly results from physical exercise or loss of sleep. Physical fatigue often leads to mental fatigue.

Mental fatigue, which may include sleepiness, concerns a general decrease of attention and ability to perform complex, or even quite simple tasks with customary efficiency. Mental fatigue often results from loss or interruption of the normal sleep pattern and is therefore of great concern to pilots and ATCOs, who are frequently required to work early in the morning or at night.

Sleep patterns are naturally associated with the body's circadian rhythms. Shift patterns and transit across time zones can interrupt circadian rhythms so that, for example, it may be difficult for flight crew or pilots on duty in the early hours of the morning or flight crew operating long-haul routes through multiple time zones to achieve satisfactory rest prior to commencing duty.

It is important to note that people are not the best evaluators of their own alertness state. They are often sleepier than they report.

Fatigue Types

There are three types of fatigue: transient, cumulative, and circadian:

• Transient fatigue is acute fatigue brought on by extreme sleep restriction or extended hours awake within 1 or 2 days.
• Cumulative fatigue is fatigue brought on by repeated mild sleep restriction or extended hours awake across a series of days.
• Circadian fatigue refers to the reduced performance during nighttime hours, particularly during an individual’s “window of circadian low” (WOCL) (typically between 2:00 a.m. and 05:59 a.m.).

Researches show that the accumulation of "sleep debt", e.g. by having an hour less of sleep for several consecutive days needs a series of days with more-than-usual sleep for a person to fully recover from cumulative fatigue.

Hazards

Fatigue usually results in impaired standards of operation with increased likeliness of error. For example:

• Increased reaction time;

• Reduced attentiveness;

• Impaired memory; and,

• Withdrawn mood.

Typical Scenarios

In a pilot, fatigue may manifest itself by:

• Inaccurate flying;

• Missed radio calls;

• Symptoms of equipment malfunctions being missed;

• Routine tasks being performed inaccurately or even forgotten; and, in extreme cases,

• Falling asleep - either a short "micro-sleep" or for a longer period.

In an ATCO, fatigue may result in:

• Poor decision making;

• Slow reaction to changing situation;

• Failure to notice an impending confliction;

• Loss of situational awareness;

• Forgetfulness.

Contributory Factors

• Circadian adaptation, i.e. adjustment of the body internal clock (e.g. due to the shift pattern, jet lag, etc.)

• Length of previous rest period;

• Time on duty;

• Time awake prior to duty (duties that start in the evening are more likely to cause fatigue than those beginning at e.g. 8 a.m.)

• Sleep/nap opportunities (during the duty but also at layover destinations)

• Physical conditions (temperature, airlessness, noise, comfort, etc.);

• Workload (high or low);

• Emotional stress (in family life or at work);

• Lifestyle (including sleeping, eating, drinking and smoking habits) and fitness; and,

• Health.

Solutions

Employers:

• Ensure that work schedules, including consecutive shift-working patterns, are constructed so as to have the least possible impact on off duty - and, if applicable, on duty rest.

• Seek to provide optimum working conditions;

• Use Crew Resource Management (CRM) or Team Resource Management (TRM) training to promote awareness to fatigue and sleep issues.

• Establish a Fatigue Risk Management System (FRMS), either as a part of the Safety Management System (SMS) or as a standalone system. An effective FRMS is data-driven and routinely collects and analyzes information and reports related to crew alertness as well as operational flight performance data. Computer models can be used to predict average performance capability from sleep/wake history and normal circadian rhythms.

Pilots and ATCOs

Adopt personal strategies which are likely to decrease the effects of fatigue such as the following:

• Planning activities, meals, rest and sleep patterns during off-duty periods;

• Making the most of permitted rest breaks, including naps;

• Advising colleagues if one detects feeling drowsy;

• Alerting colleagues if they appear to be becoming drowsy.

SKYclip

Related Articles

• Pilot Workload
• Controller Workload
• Fatigue Management: Guidance for Air Traffic Controllers and Air Traffic Engineers
• Flight Crew In-Seat Rest

Accidents & Incidents

Events in the SKYbrary database which include fatigue as a contributory factor:

Further Reading

EASA

• Moebus Aviation Final Report: Scientific and Medical Evaluation of Flight Time Limitations;

EUROCONTROL

• Fatigue and Sleep Management Brochure;
• Personal Strategies for Decreasing the Effects of Fatigue in Air Traffic Control;
• Rostering: Fatigue Constraints and Guidelines

UK CAA

• Aircrew Fatigue: A Review of Research Undertaken on Behalf of the UK Civil Aviation Authority.
• EASA Flight Time Limitations (FTL) - Q&A, Aug 2015.

FAA

• Advisory Circular 120-100: Basics of Aviation Fatigue, June 2010
• FAA Advisory Circular 117-3: Fitness for Duty, October 2012

Others

• Fighting Pilot Fatigue, video by Boeing’s Fatigue Risk Management team in partnership with Delta airlines to portray the effects of fatigue on pilots. It describes technologies in the flight deck that can monitor and prevent fatigue-related events.
• Operator's Manual: Human Factors in Aviation Maintenance, FAA, 2014.
• Safety Behaviours: Human Factors Resource Guide for Engineers, CASA (Australia), 2013. Chapter 5 describes the causes and impacts of fatigue, and strategies to manage it (for maintenance personnel).
• Human Performance and Fatigue Research for Controllers, Gawron et al., 2011.
• FAA Fact Sheet – Sleep Apnea in Aviation, Feb 2015.
• Coping with long range flying. Recommendations for crew rest and alertness., Airbus, Cabon, P., et al., Nov 1995.
• Fatigue and Alertness Management in Aviation
• Being Prepared for the Outbound Flight - Checklist
• Being Prepared for the Return Flight in Eastward Rotations - Checklist
• Being Prepared for the Return Flight in North and South Rotations - Checklist
• Being Prepared for the Return Flight in Westward Rotations - Checklist
• CASA Fatigue Risk Management System Handbook, 2013
• CANSO Fatigue Management Expert Group