The medicine definition of ‘Fatigue’ refers to: “A condition characterized by a lessened capacity for work and reduced efficiency of accomplishment, usually accompanied by a feeling of weariness and tiredness. Fatigue can be acute and come on suddenly or chronic and persist” [Medicine Net (2008 9)].

Author Hawkins [7] defines fatigue as “a source of difficulty which has tended to generate confusion and retarded progress.

Medicine Health [8] defines ‘Fatigue’ as: “Fatigue, also known as weariness, tiredness, exhaustion, or lethargy, is generally defined as a feeling of lack of energy.”

Theoretical frame

Fatigue have a varied range of interpretations with a wide concept which may defers from one person to another [Medicine Net (2008 9)]. Fatigue can be interpreted in four ways. Firstly, it may reflect on inadequate rest, sleep, the symptoms of being disturbed, by stressors or sufferer such as jetlag, excessive physical activity disturbance or excessive cognitive work being undertaken [Hawkins (1988 7)]. Fatigue can be said to be like ‘stress’ which is an umbrella term which encompasses many different perspective [Green, Muir, James, Gradwell, & Green (1996 6)]. Fatigue causes can be also group as Acute Fatigue (immediate) or Chronic Fatigue (long term build-up).

Fatigue is a major risk in aviation, and implementation of countermeasures, both organisational and individual, are need to minimise this risk. Fatigue is a condition that is hard to determine, its effects are very widespread and contribute more to aviation risk than actually perceived. As aviators, an understanding of the causes of fatigue is helpful in avoiding this syndrome. Circadian desynchrony, sleep debt, hypoxia, zietgeber shifts and workload contribute significantly to fatigue. However, careful planning by the organisation, technical advances and individual responsibility may reduce the risk of fatigue in the aviation industry.

The reduced state of physical and mental function associated with tiredness is known as fatigue (Caldwell & Caldwell, 2003). Deprivations of rest, circadian desynchrony or zeitgeber shifts (i.e. light or temperature cues for time) increase the rate of fatigue in an individual. Kirsch (1996) writes that 4-7% of aviation accidents can be attributed to fatigue, however this is not an accurate representation of the problem. The actual extent of its effects is extremely hard to determine, as there are no testing methods available that can accurately measure the level of fatigue in an individual (Petrilli, Roach, Dawson & Lamond, 2006). The effects of fatigue, however, can be observed from an individual’s behaviour (Caldwell & Caldwell, 2003). According to research (Pilcher & Huffcutt, 1996 as cited in Passer & Smith, 2008), fatigue has negative effects on mood, cognitive and physical performance. Adversely affecting mood causes irritation, poor decision making and therefore increase miscommunication between flight crew. Likewise, an aircraft technician might also find it difficult to assemble complicated aircraft components due to cognitive and physical impairment. In addition, fatigued individuals incorrectly perceived an increase in performance although their cognitive and physical had been impaired by sleep deprivation (Passer & Smith, 2008). Hence, individuals often lay blame of an incident on other confounding factors such as complicated displays or un-cooperative team members, although the root cause may be fatigue. It can be assumed that fatigue contributes to more aircraft accidents than statistically reported.

Heinrich illustrated in his safety pyramid that for each major accident there are an estimated 300 near misses. In addition, further research indicates that an estimated 600 incidents without mishap go unreported (Phimister, Oktem, Kleindorfer, Kunreuther and Yen, 2000). Therefore, even though a small number if accidents can be directly attributed to fatigue, the actual number may be in fact much larger, signalling an urgent need for the aviation industry to take steps in reduce fatigue related risks. Suitable countermeasures should be adopted on the organisational as well as the personal level to combat the root causes of fatigue. Unfortunately, with the improvement of the aviation industry and the onset of new low cost carriers, (International Air Transport Association, 2007), pilots are made to fly multiple sectors while maximising the limits on flight duration allowed by the Airline Operators Certificate (Fatigue Managment, n.d.). Commute time and other personal necessities also reduce the amount of time available for sleep. In a single international pattern around the world, international pilots experience many difficulties; they cross many time zones, work long shifts, Experience early flights and flying at night. However, the human body is unable to re-adjust its sleep wake cycles to the new time zones immediately, causing circadian desynchrony or otherwise known as jet lag (Petrilli et al, 2006). Caldwell and Caldwell (2003) noted that normal recovery from jet lag takes 2 to 3 days, and that the effect is more pronounced on an eastward followed by a westward route than vice versa.

Pilot’s fatigue increases as they fly an international pattern with many sectors (Petrilli et al, 2006), a situation aggravated by the loss of sleep credits (Passer & Smith, 2008). According to Passer and Smith, 1 sleep credit is equivalent to 1 hour, therefore sleeping 7 hours a day instead of 8 results in a loss of 1 sleep credit. Caldwell and Caldwell (2003) wrote that organisations often plan shifts without taking into account their worker’s commute time and time for other necessities, assuming that all time spent off work is spent resting. Hence, international patterns with many ports of call are planned with layovers too short for pilots to rest. The loss of sleep credits forces the brain to sleep involuntarily, and this often goes unnoticed(Petrilli et al, 2006). This effect, known as microsleep, compromises safety as pilots are effectively not in control of the aircraft during that short period Caldwell and Caldwell (2003). Our brain is a complex organ that runs on oxygen. However, the external air pressure decreases as an aircraft climbs; an individual’s respiratory system absorbs less oxygen at higher altitude than at seal level and this causes a condition known as hypoxia (Whitt, n.d.). Although hypoxia has many symptoms such as dizziness, shortness of breath, etc. Whitt writes that these symptoms of hypoxia contribute significantly to aviation fatigue. Smoking also aggravates this situation by reducing oxygen absorption into the lungs, therefore, even if an airplane is pressurised to a certain cabin altitude, the smoker would feel as if he is breathing at an altitude of much higher, increasing the rate of fatigue (Nesthus, Garner & Mills, 1997).

Our circadian rhythm is influenced and controlled by external cues or zeitgeber. Temperature and light fluctuate during the day and our bodies match our sleep/wake cycles to match these changing patterns (Green, Muir James, Gradwell & Green, 1996). It was found out that 59% of surveyed pilots responded that night flying was a major cause of fatigue (Bourgeois-Bougrine et al., 2003 as cited in Petrilli et al., 2006). This occurs when the human body increases melatonin production in the body, lowering heart rate and body temperature in preparation for sleep (Passer & Smith, 2006). The amount of workload is also a factor that determines the rate of fatigue. Pilots are constantly faced with the responsibility of monitoring multiple cockpit instruments, radio communications, surrounding traffic, aircraft heading and many other aspects of flying including the actual control of the aircraft (Hancock & Desmond, 2001). According to Hancock and Desmond, the cockpit workload fluctuates with the progression of the flight peaking prior to take-off and landing, increasing the rate of fatigue in aircrew. Therefore, while increasing workload also increases fatigue risk, decreasing workload decreases, however, organisational efficiency a constant balance that the aviation industry maintain.

The effects of fatigue are often grossly underestimated; it affects almost every human factor involved and may have accounted for more accidents in aviation that actually perceived. However, organisations can help counter the effects of fatigue in their staff by planning duties according to the circadian rhythm. Technology assists relieving fatigue through ergonomics, environment simulation and automation. Most importantly, the individual has the responsibility to increase their resistance to fatigue, and take steps to reduce it if they are on duty.

Classification of Fatigue

There are mainly three types of fatigues.

Physical Fatigue
Physical fatigue refers to various physical issues such as muscle soreness, lack of oxygen, poor nutrition, tiredness caused by lack of sleep or illness [Stokes & Kites (1994 13)].

Mental Fatigue
It is associated with task demanding intense concentration, cognitive information processing or other high cognitive skills. Such metal fatigue can be seen in examples such as single pilot flying in Instrument Flight Rules (IFR) during night. Mental fatigue can be arise from prolong activity as well [Stokes & Kites (1994 13)].

Emotional Fatigue
Emotional fatigue can be also known as ‘burnout’ which simply refers to the wearying effect of working under psychological disagreeable task. This type of fatigue can be seen when individual starts complaining saying its tired, bored, routine or from consistent arguing in workplace or domestically [Stokes & Kites (1994 13)].

Causes of Fatigue

Internal Drive for Sleep
Sleep duration or the amount of sleep obtained will influence the level of fatigue. Author Dijk and Czeisler [3] stated that the ‘sleep homeostat’ or the bodies demand for sleep will increase throughout the day of wakefulness will contribute to the amount and quality of sleep at night. Thus if sleep has been prevented or shorten, it will result in physical fatigue for an individual.

Circadian Biological Clock
Our bodies sleep clock that influences the sleep duration and quality is critical in the level of fatigue one will experience. As the circadian system helps to maintain our wakefulness during the day, with sleep rarely being initiated during the day. If this system gets distorted, fatigue level will increase as sleep will be consistently being initiated at the wrong time, creating a decrease in individual’s performance [Dijk & Czeisler (1995 3)].

Jet Lag
After travelling to and fro from time zones, individuals circadian clock will be out of its ‘preset’ local day-night cycle. Thus the circadian clock can adapt the time of both physiological and behavioural variables [Signal, Ratieta, & Gander (2006 12)]. Thus consistent jetlag will eventually distorts ones’ bio clock which will increase the probability of fatigue causing, slower reactions, degrading performance, and defective memory which inevitably increases the outcome of human error in any situation [Hawkins (1988 7)].

Shift Work
Shift work schedules are referring to working hours’ distortion which requires sleep to be displaced from its normal night time slot. Thus this distorting inevitably affects the characteristics of circadian rhythm, which might be a source for fatigue [Signal, Ratieta, & Gander (2006 12)]. The symptoms are similar to jetlag as their cues for sleeping are often disturbed from their different shift working rosters. Thus the consistent changing of sleep rhythm will affect ones performance as fatigue due to the lack of sleep or the irregularities of sleep cycle from disturbance of the bio clock will result in degrading human performances.

Consequences of Fatigue

The precise nature of fatigue can be said to be diverse and insidious. As fatigue level in one individual increases, accuracy and timing degrade with lower performance level which are unconsciously accepted without self-detection [Signal, Ratieta, & Gander (2006 12)]. Narrowing of attention (similar to stress) occurs thus increasing the risk of human errors in any situations. As sleepiness increases, performance decreases and the effects of such relationships worsens during night hours [Dinges & Kribbs (1991 4)]. Problem solving and reasoning skills are slower then normal while psychomotor skills are degrading with an increase rate of false responses [Caldwell (1997 1)]. Furthermore, fatigue will reduce social interaction with others and eventually loses group or team performance level. This is extremely critical for pilots operating an aircraft.

Biological limitations imposed by fatigue will impair performance of even the most highly skilled or motivated individuals [Caldwell (1997 1)]. In addition, the effects of fatigue cannot be overcome either by training or experience, or negated by monetary or other incentives [Signal, Ratieta, & Gander (2006 12)].

Prevention of Fatigue

Here are a few ways to prevent fatigue as recommended FAA and ICAO for pilots. Total prevention of fatigue is impossible, thus the recommendations will significantly reduced fatigue only.

•First, to ensure restful, quality sleep, the sleep environment should be cool, dark, and quiet. It is also best to avoid working or reading in bed, as this may actually contribute to problems in falling asleep. The bed should be associated only with sleeping and sexual activity. If you desire to read before going to bed, do this in a chair outside the bedroom and then go to bed

•Adjustment of shift work to prevent circadian dis-synchronization. This can be accomplished by maintaining a consistent sleep/wake schedule even on days off. It is also important, when on the night shift, to avoid exposure to daylight from dawn to 1000. Wear sunglasses if you cannot go to sleep before the sun rises (as long as this does not pose a safety hazard), and while asleep consider wearing a sleep mask to avoid any exposure to light. Exposure to light before you go to sleep will interfere with the quality of your sleep. You may eat a light snack before going to sleep, but do not go to sleep too full or too hungry. Also avoid caffeine consumption for about 6 hours prior to going to sleep. Napping is a good strategy for coping with sleep deprivation during continuous operations or other times when it is difficult to get a good night’s sleep

•Maintain good physical health with regular fitness programmes which will enable the body to resist the effects of fatigue.

•Get plenty of natural sleep. It is also important when treating fatigue to maintain a reasonable work schedule during waking hours. It makes no sense to try to catch up on sleep and then exhaust oneself during the day. Also ensure that you eat properly to give your body the fuel it needs to recuperate.

•After 24 - 48 hours of sleep deprivation DO NOT sleep overly long during the recovery period. This could interfere with your normal sleep/wake cycle and cause sleeping problems the next night.

•When trying to sleep outside your normal bedtime, prepare for sleep as you normally would have - wear the clothes to bed that you would normally wear, darken the room, and keep noise to a minimum.

Supporting evidence

The accident report compiled by the NTSB (2000 [10]) on Korean Air Flight 801 suggests a classical example and evidence of fatigue in aviation. After the investigation and experimentation, investigators were able to identify the fatigue factor of the captain. The accident occured at 00:42 hours in the flight crew's home time zone on 6 August 1997. According to most of the research, pilots are vulnerable to poor alertness and higher possibility of errors during midnight. More importantly, captain must have been sleeping if he were on his usual flight schedule. He was suffering from fatigue and was preoccupied with glidesope and lost the position of the aircraft. Consecuently he was too late to execute a "go around" approach, resulting into crash of aircraft at a hill near Guam International Airport killing 228 of 254 people.

A research carried out by Powell, Spencer, Holland and Petrie (2008 [11]) on fatigue levels on two-pilot operations found an interesting result. For 12 weeks several pilots having 3-12 hours flight timings were allowed to complete Samn-Perelli fatigue ratings just before their descent at the end of their flights. Total of 3023 usable ratings, including 74 per cent of double sector pilots and 26 per cent of single sector pilots, were collected. The results showed that highest levels of fatigue were observed in the night between 2 am to 6 am. It was found the fatigue is correlated to length of the duty. Moreover, fatigue levels were higher at end of two-sector duties that single sector duty.

Refuting evidence

Way forward (to do list)

Refer to Stress, Stress Management, Stress Coping Strategies

1. Caldwell, J. A. (1997). Fatigue in Aviation Environment: An Overview of Cause and Effects as well as Recommended Countermeasures. Aviation, Space and Environmental Medicine. Vol: 68 No: 10.
2. Campbell, R. D. & Bagshaw, M. (1999). Human Performance and Limitations in Aviation. England: Blackwell Science.
3. Dijk, D. J & Czeisler, C.A. (1995). Contribution of the circadian pacemaker and the sleep homeostat to sleep propensity, sleep structure, electroencephalographic slow waves, and sleep spindle activity in humans The Journal of Neuroscience, vol. 15 no. 5, pp. 3526-3538.
4. Dinges, DF & Kribbs, NB (1991). Performing while sleepy: Effects of Experimentally-induced Sleepiness. In MONK, T. H. (Eds). Sleep, Sleepiness and Performance. John Wiley and Sons, New York.
5. Federal Aviation Administration (FAA). (2007). //Instrument Flying Handbook USA: Jeppesen, Boeing Company.
6. Green, R. G. Muir, H. James, M. Gradwell, D. & Green, R. L. (1996).Human Factors for Pilots (2nd Ed). U.K: Ashgate.
7. Hawkins, F. H. (1988). Human Factors in Flight. USA: Ashgate
8. Medicine Health. (2008). Definition of Fatigue. Information retrieved on 2nd October 2008 on Medicine Health Official website: http://www.emedicinehealth.com/fatigue/article_em.htm
9. Medicine Net. (2008). Definition of Fatigue. Information retrieved on 2nd October 2008 on Medicine Net Official website: http://www.medterms.com/script/main/art.asp?articlekey=9879
10. National Transport Safety Board (NTSB). (2000). Controlled flight into terrain, Korean Air Flight 801. Washington DC: US.
11. Powell, D., Spencer, M, B., Holland, D. and Petrie, K, J. (2008). Fatigue in two-pilot operations: Implications for flight and duty time limitations. Aviation Space and Environmental Medicine, 79, 11, 1047-1050.
12. Signal, L. Ratieta, D & Gander, P. (2006). Fatigue Management in New Zealand Aviation Industry. ATSB RESEARCH AND ANALYSIS REPORT: Sleep/Wake Research Centre, Research School of Public Health, Massey University April 2006.
13. Stokes, A & Kites, K. (1994).Stress. Fatigue and Performance in Aviation. Avebury, Aviation.
14. Wickens, C. D. & Hollands, J. G. (2000).Engineering Psychology and Human Performance. Upper Saddle River, USA: Prentice-Hall Inc.
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