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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.
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.
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- Withdrawn mood.
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;
- 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,
- 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 or Team Resource Management 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.
- Pilot Workload
- Controller Workload
- Fatigue Management: Guidance for Air Traffic Controllers and Air Traffic Engineers
Accidents & Incidents
Events in the SKYbrary database which include fatigue as a contributory factor:
- A306, vicinity Birmingham AL USA, 2013 (On 14 August 2013, a UPS Airbus A300-600 crashed short of the runway at Birmingham Alabama on a night IMC non-precision approach after the crew failed to go around at 1000ft aal when unstabilised and then continued descent below MDA until terrain impact. The Investigation attributed the accident to the individually poor performance of both pilots, to performance deficiencies previously-exhibited in recurrent training by the Captain and to the First Officer's failure to call in fatigued and unfit to fly after mis-managing her off duty time. A Video was produced by NTSB to further highlight human factors aspects.)
- A319, London Heathrow UK, 2013 (On 24 May 2013 the fan cowl doors on both engines of an Airbus A319 detached as it took off from London Heathrow. Their un-latched status after a routine maintenance input had gone undetected. Extensive structural and system damage resulted and a fire which could not be extinguished until the aircraft was back on the ground began in one engine. Many previously-recorded cases of fan cowl door loss were noted but none involving such significant collateral damage. Safety Recommendations were made on aircraft type certification in general, A320-family aircraft modification, maintenance fatigue risk management and aircrew procedures and training.)
- A320 / A346, en-route, Eastern Indian Ocean, 2012 (On 18 January 2012, ATC error resulted in two aircraft on procedural clearances in oceanic airspace crossing the same waypoint within an estimated 2 minutes of each other without the prescribed 1000 feet vertical separation when the prescribed minimum separation was 15 minutes unless that vertical separation existed. By the time ATC identified the loss of separation and sent a CPDLC message to the A340 to descend in order to restore separation, the crew advised that such action was already being taken. The Investigation identified various organisational deficiencies relating to the provision of procedural service by the ANSP concerned.)
- A320, vicinity Sochi Russia, 2006 (On 3 May 2006, an Airbus 320 crew failed to correctly fly a night IMC go around at Sochi and the aircraft crashed into the sea and was destroyed. The Investigation found that the crew failed to reconfigure the aircraft for the go around and, after having difficulties with the performance of an auto go-around, had disconnected the autopilot. Inappropriate control inputs, including simultaneous (summed) sidestick inputs by both pilots were followed by an EGPWS PULL UP Warning. There was no recovery and about a minute into the go around, a steep descent into the sea at 285 knots occurred.)
- A321, Hurghada Egypt, 2013 (On 28 February 2013, the initial night landing attempt of a Ural Airlines Airbus A321 at Hurghada was mishandled in benign conditions resulting in a tail strike due to over-rotation. The Investigation noted that a stabilised approach had been flown by the First Officer but found that the prescribed recovery from the effects of a misjudged touchdown had not then been followed. It was also concluded that communication between the two pilots had been poor and that the aircraft commander's monitoring role had been ineffective. The possibility of the effects of fatigue was noted.)
- A321, vicinity Singapore, 2010 (On 27 May 2010 an Airbus A321-200 being operated by Australian operator JetStar on a passenger flight from Darwin to Singapore continued an initial approach at destination in day VMC with the aircraft inappropriately configured before a late go around was commenced which was also flown in a configuration contrary to prescribed SOPs. A subsequent second approach proceeded to an uneventful landing. There were no unusual or sudden manoeuvres during the event and no injuries to the occupants.)
- A332 / A333, en-route, North West Australia, 2012 (On 31 March 2012, after the implementation of contingency ATC procedures for a period of 5 hours due to controller shortage, two Garuda A330 aircraft which had been transiting an associated Temporary Restricted Area (TRA) prior to re-entering controlled airspace were separately involved in losses of separation assurance, one when unexpectedly entering adjacent airspace from the TRA, the other when the TRA ceased and controlled airspace was restored. The Investigation did not find that any actual loss of separation had occurred but identified four Safety Issues in relation to the inadequate handling of the TRA activation by ANSP Airservices Australia.)
- A332, vicinity Tripoli Libya, 2010 (On 12 May 2010, an Afriqiyah Airways Airbus A330 making a daylight go around from a non precision approach at Tripoli which had been discontinued after visual reference was not obtained at MDA did not sustain the initially established IMC climb and, following flight crew control inputs attributed to the effects of somatogravic illusion and poor CRM, descended rapidly into the ground with a high vertical and forward speed, The aircraft was destroyed by impact forces and the consequent fire and all but one of the 104 occupants were killed.)
- AS32 / B734, Aberdeen UK, 2000 (For reasons that were not established, a Super Puma helicopter being air tested and in the hover at about 30 feet agl near the active runway at Aberdeen assumed that the departure clearance given by GND was a take off clearance and moved into the hover over the opposite end of the runway at the same time as a Boeing 737 was taking off. The 737 saw the helicopter ahead and made a high speed rejected take off, stopping approximately 100 metres before reaching the position of the helicopter which had by then moved off the runway still hovering.)
- AT43, Lubbock TX USA, 2009 (On 27 January 2009, an ATR 42-300 being operated by Empire Airlines on a scheduled cargo flight from Fort Worth Alliance to Lubbock was making a night ILS approach in IMC to runway 17R at destination when it stalled and crashed short of the runway. The aircraft caught fire and was in any case effectively already destroyed by the impact. Both crew members were injured, one seriously.)
- AT43, vicinity Glasgow, UK 2012 (On 22 February 2012, the crew of an ATR 42 making a radar-vectored ILS approach to runway 23 at Glasgow at night allowed the airspeed of the aircraft to reduce and a stall warning followed. Corrective action then led to an overspeed and further corrective action almost led to a second stall warning. The Investigation concluded that SOPs were not followed, monitoring was ineffective and crew cooperation during recovery was poor. It was considered that crew performance may have been affected by inadequate rest prior to a night flying duty period.)
- AT43, vicinity Pristina Kosovo, 1999 (On 12 November 1999, a French-registered ATR 42-300 being operated by Italian airline Si Fly on a passenger charter flight from Rome to Pristina was positioning for approach at destination in day IMC when it hit terrain and was destroyed, killing all 24 occupants. A post crash fire broke out near the fuel tanks after the impact.)
- Fatigue and Sleep Management Brochure;
- Personal Strategies for Decreasing the Effects of Fatigue in Air Traffic Control;
- Aircrew Fatigue: A Review of Research Undertaken on Behalf of the UK Civil Aviation Authority.
- EASA Flight Time Limitations (FTL) - Q&A, Aug 2015.
- Advisory Circular 120-100: Basics of Aviation Fatigue, June 2010
- FAA Advisory Circular 117-3: Fitness for Duty, October 2012
- IATA Fatigue Risk Management Guide for Airline Operators, 2nd edition, 2015
- 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