The two pilots of Ethiopian Airlines flight ET343 Boeing 737–800, heading from Khartoum, Sudan to Addis Ababa, Ethiopia, fell asleep 37,000 feet in the air and temporarily lost radio communication with Air traffic Control (ATC) controllers and passed the landing airport on 22 August 22, 2022. The pilots woke up after the alarm sounded indicating the autopilot was released, and resumed communication with the ATC controller, landing 25 minutes later. Aviation expert Alex Macheras told the The British Broadcasting Corporation that it is a serious concern and that pilot fatigue is the most threatening factor in aviation safety internationally, requiring continuous management [1].

In order to prevent aircraft accidents that may occur due to fatigue, this paper analyzes fatigue-related accident cases and previous research and suggests ways to improve the management of pilot fatigue.

1. Fatigue and management

1) Definitions

The International Civil Aviation Organization defines fatigue as a physiological state in which mental and physical performance is reduced due to sleep loss, increased waking hours, daily cycles, and heavy workloads [2].

The symptoms and interpersonal effects of fatigue are difficulty in concentrating, decreased attention, decreased memory, failure to deliver important information, difficulty in predicting the seriousness of situations, omission of necessary actions, unnecessary behavior, helplessness, decreased motivation, and irritation [3].

Additional effects of fatigue include inappropriate reactions in emergency situations, symptoms similar to intoxication, decreased reaction time, daydreaming, momentary memory loss, and distraction [4].

2) The influence of fatigue

U.S. Air Force pilot and navigator studies found that mission performance decreased (94%), situational awareness decreased (73%), response time slowed (67%), attentional distraction (43%), forgetfulness (41%), and indifference (33%) as in Table 1. The studies of commercial pilots showed decreased attention (23%), decreased concentration (25%) during flight and, among 80% of short-range pilots decreased judgment during flight. It was found that pilot fatigue leads to heightened emotions and high-dimensional cognitive processing disorders. Fatigue leads to significant visual perceptual impairment and visual neglect. Additional results of fatigue include decreased in the following: communication, reaction time, cognitive flexibility, and eye-hand coordination [5].

3) Importance of fatigue management

Only about 4%–8% of aviation accidents and incidents involve fatigue [6]. Pilot errors caused by fatigue accounted for 15%–20% of aviation casualties. According to a survey of 500 pilots conducted by the British Air Pilots Association, 43% of pilots said they had fallen asleep in the cockpit unconsciously, and 31% of whom said other pilots were also asleep when they woke up. A sleep specialist at the University of Karolinska in Sweden has proven that most people can stay alert during the day but not at night, so if a pilot lands a plane at 5 a.m., the blood alcohol level is 0.08%, exceeding the limit of drunk driving. Flight Global also noted that allowing pilots to be dangerously tired is equivalent to legalizing pilots to fly when they are drunk [7]. These are the reasons why pilot fatigue requires management.

Pilot fatigue has been on the National Transportation Safety Board’s (NTSB) top list of safety priorities since 1990 [8]. Yet, between 2001 and 2012, 23% of major aviation accidents were still attributed to fatigue, above the 21% similarly attributed in 1980 [9].

2. The influence of COVID-19 and changes in air demand

1) The influence of COVID-19

Pilots reported feeling more drowsy in flight and on rest days during the pandemic, citing several causes, such as limited access to nutritional foods during layovers and on duty hours, and reduced access to exercise facilities during layovers [10].

It is reported that fatigue and headaches were the most common symptoms after COVID-19, and muscle pain, cough, changes in smell and taste, fever, chills, and nasal congestion were next in line [11]. The results of COVID-19 Neurological and Molecular Prospective Cohort Study in Georgia showed that fatigue was the most reported symptom (68.5%). 30% of the participants showed hyposmia and 30% showed hypogeusia. In addition, self-reported symptoms were related to depression and anxiety [12].

2) The increase in demand

The demand for the overseas travel has been increasing rapidly as the requirement for Polymerase Chain Reaction tests for entry has been nullified. Korea canceled the requirement from October 1, 2022 [13]. Japan’s visa-free tourism, which had been suspended due to COVID-19, became possible again on October 11th, 2022, and Taiwan, visited by many Koreans before COVID-19, was fully opened on October 13, 2022. Many European countries have also completely lifted entry restrictions related to COVID-19 [14].

3) Pilot fatigue due to increased workload

The Transportation Security Administration said more people were flying in U.S. airports now than before the pandemic. Pilots in the U.S. maid a lot of sacrifices, flying a record amount of time away from their families due to heavy schedules [15].

During the pandemic, the number of pilots decreased, so it takes a long time for new pilots to complete training and attain certification. Experts say that while pilots are trained, the best way to relieve pilots’ fatigue and reduce flight delays and cancellations is for airlines to adjust their schedules. Reducing parts of the route and reducing expectations of how many flights airlines can actually carry out will help avoid last-minute delays and cancellations [16].

The aviation industry is also speeding up the normalization of all-around manpower. Flight attendants are returning and ground operators are increasingly staffed, and airport workers such as carts, cleaning, and security positions are also being staffed [17]. The International Air Travel Association said China's lifting of COVID-19 restrictions led to a 67% surge in global air travel demand in January 2023, maintaining strong passenger traffic, approaching 84% of the level in January 2019, before the pandemic [18].

1. Guantanamo naval base crash

A DC8 aircraft crashed a quarter of a mile before the runway at a Naval Base Guantanamo Bay, Cuba, and burned after the crash in August 1993. The flight was a non-regular flight, and fatigued pilots made inadequate decision-making with poor flight capability. For the first time, the NTSB pointed at pilot fatigue as the cause of the accident. All three flight crew members were experiencing accumulated sleep deprivation, persistent waking hours, and circadian time disruption [19].

2. Little rock plane crash

The MD82 aircraft landed on the runway and then skidded off the runway crashing into the approach light structures, 11 people including the captain were killed and 105 people were injured at Adams Field Airport in Little Rock, Arkansas in June 1999. The NTSB analyzed that the accident was caused by pilot fatigue and misguided decision-making on landing under instrument flight rules conditions [20].

3. Colgan air crash

The Colgan Air Flight 3407, Q400 aircraft with turboprop twin-engine, was approaching Buffalo, New York from Newark, New Jersey. The aircraft suddenly stalled in the night, and the two pilots failed to operate it properly, crashing into a house northeast of the airport, killing 50 people including crew members, passengers, and one person on the ground in February 2009. The pilots who caused the accident did not effectively use available breaks nor manage off-duty hours to ensure that they could arrive at work in top form. Additionally, they did not use the appropriate rest facilities during the time prior to the fatal flight. Colgan Air did not proactively address the pilot fatigue hazards related to commuting. It is highly likely that the performance of the pilots degraded due to fatigue. Following this accident, regulations on flight time and duty periods, to reduce pilot fatigue, were revised in the United States [21].

4. The lessons learned through crashes

There were common threats and errors in the three major accidents involving fatigue as in Table 2. The threats were rostering events, difficult weather, airport threats, and fatigue. The errors were failure to make a missed approach, inadequate communication of the crew, poor aircraft handling, inadequate crew briefing, and callouts. The undesired aircraft states were continued approach, unstable approach, failure of energy management, and incorrect speed.

The accidents occurred when pilots were tired due to extended working hours, aircraft delays, continuous flight schedules, night flights, early-morning flights, and threats such as instrument approaches, airport facilities, airport low-altitude warning equipment, non-precision approaches, offset Distance Measurement Equipment (DME), difficult arrival and landing procedures, terrain, poor training and Standard Operation Procedure (SOP).

The key to accident prevention is to manage the potential fatigue of the pilots proactively by having a rostering committee, fatigue action group, fatigue reporting system, and fatigue risk management in place. Pilots must make missed approaches when the aircraft is out of stable approach criteria. Companies need to train pilots to communicate with each other to be resilient and make effective decision-making even in fatigued conditions.

The airlines need to actively prevent the likelihood of pilots committing errors by managing threats and errors through standard operating procedures and competency-based training including the application of knowledge, application of procedures and compliance with regulation, communication, aero plane flight path management-automation, aero plane flight path management-manual control, leadership and teamwork, problem-solving, decision making, situation awareness, management of information, and workload management [22].

Problems in major fatigue accidents were active communication failure, lack of leadership of the captain, inadequate contingency management and briefing, lack of workload management. The accidents occurred when pilots were operating with extended duty hours, delays, night flights, poor airport facilities such as navaids, malfunctioning Minimum Safe Altitude Warning, non-precision approaches, offset DME (Distance Measurement Equipment), difficult approach and landing procedures, terrain, poor training and SOP in fatigued condition by reviewing the NTSB reports.

In order to prevent accidents related to fatigue, and improve threats and human errors in the environment of pilots, it is fundamentally necessary to identify and analyze the actual threats and errors in the cockpit of the aircraft. Improving and establishing go-around culture in the organization and proactively managing human factors with training and procedures of threat and error management and crew resource management is required.

Previous research related to pilot fatigue and the major accident reports by NTSB were reviewed and suggestions of how these can be used as lessons were derived as follows.

First, it is necessary to improve the overall factors that may decrease the potential fatigue for the pilots such as adjusting schedules and patterns and minimizing fatigue by measuring fatigue with the use of surveys, biomathematical models, and reports of the pilots on the routes associated with long distance, night flight, early morning flights, multi-time zone changes, and multi legs.

Second, the most important accident factors were inadequate decision-making of continuing an unreasonable approach without going around.

Third, implementing Fatigue Risk Management by actively establishing a fatigue reporting system, rostering committee, and fatigue action group is required even before introducing Fatigue Risk Management System to systemically deal with fatigue risk.

Fourth, it is recommended to improve safety culture, such as the manner of go-arounds and reporting culture in the organization.

Lastly, it is necessary to train pilots with competencies according to Competency Based Training or Evidence Based Training to best address contingencies for fatigued conditions.

No potential conflict of interest relevant to this article was reported.