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Investigating Human Factors

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Maintenance mishaps are increasing around the world in the aviation community on a regular basis. It is all too common to think that the first cause of an aircraft accident was the result of maintenance. Human factors affect the lives of maintainers on a daily basis to the point that human factors in maintenance can be blamed for mishaps that involve maintainers. This research paper focuses on the human factors that are incorporated into maintenance mishaps of major airlines. Through this investigation of human factors in maintenance mishaps, the goal is to educate on the importance of decreasing human factors in maintenance by utilizing proper training and resource management. Throughout the research being conducted examples of major airline accidents due to maintenance mishaps will be conducted and broken down to where human factors played a role into the mishap. Human factors in maintenance is a real epidemic that stems from many different sources such as environmental, mental and physical, but education and training are the keys to success.

Investigating Human Factors in Maintenance Mishaps of Major Airlines

Human factors are also known as ergonomics to many individuals. The definition that is given to ergonomics according to Merriam-Webster is “An applied science concerned with designing and arranging things people use so that the people and things interact most efficiently and safely” (“Definition of Ergonomics,” n.d.). Throughout the conducted research it has been apparent that human factors in maintenance mishaps have been very prevalent when it has happened to major airlines. Maintenance mishaps caused by human factors have been examined in the research conducted such as Southwest Airlines flight 1380 where a woman was killed due to an engine explosion (Kitroeff, Negroni, & Wichter, 2018 p.1). Many human factors will be discussed and explored to educate on how important the issue is towards maintenance workers and how they are geared toward the major airline industries.

In the aviation industry, it is becoming a concern that maintenance mishaps are increasing at an alarming rate due to human factors being the cause by about 70% (Hobbs & Williamson, 2003, p.1). The goal in the research being conducted is to help educate those in the maintenance field and management of maintenance workers that there are ways to increase the effectiveness of workers and there are ways to decrease maintenance mishaps which are caused by human factors. Ways to decrease maintenance mishaps has been researched and expressed throughout the research paper as a way that the reader can educate one’s self. This research paper discusses many human factors such as the environment which includes management and the working area. The paper also looks strongly into the mental aspect of human factors as well as the physical part of human factors in maintenance. In the conclusion of the research being conducted the reader will understand exactly why it is important to improve human factors for the maintainer due to them being such as an integral part in the daily demands of major airlines and the aviation community.

Human Factors in Maintenance

Maintenance in the aeronautical field is extremely important in every aspect of how a worker conducts maintaining aircraft. According to, (Atak & Kingma, 2011, p.268) “Aviation is closely associated with safety culture, not so much because of a high rate of incidents but rather because of the severe consequences in case something goes wrong. Travel at high speeds and high altitude in complex traffic systems means that even small human and technical errors can quickly lead to disasters.” Human factors play a major role in maintainers and their organization due to the seriousness that various maintenance tasks entail. In the summer of 2010 the Office of Aviation Safety held a two day workshop which consisted of representatives from The Office of Aviation Safety, the aviation industry of the United States, the National Transportation Board, and Transport Canada in which the main topic was human factors in maintenance and the goal was to improve on maintenance human factors (Bedell Avers, Johnson, Banks, & Nei, 2011, p.9).

From the research being conducted a person must understand the human factors that are the most common when it comes to maintenance. These human factors that play a major role in maintenance mishaps are widely known as the “Dirty Dozen” a name in which many maintenance organizations in Canada has given the most common human factors according to Bedell Avers, Johnson, Banks, & Nei (2011). The twelve most common human factors are lack of communication, complacency, lack of knowledge, distraction, lack of teamwork, fatigue, lack of resources, pressure, lack of assertiveness, stress, lack of awareness, and norms (Patankar & Taylor, 2008, p.3). Those are the most common factors but in the research that is discussed about maintenance mishaps, only the factors that have the most impact have been researched due to it being the root cause of the given maintenance mishaps.

Major airlines in the past have faced a lot of scrutinies when a mishap due to maintenance occurs. Southwest Airlines faced scrutiny due to an accident that was caused by engine failure which was because of maintenance. ‘Investigators say a routine visual inspection might not have been sufficient to uncover problems in the engine. Two years ago, the manufacturer of the engine said the flaws suspected in the Southwest accident could be detected only with more thorough, ultrasound inspections’ Kitroeff, Negroni, & Wichter (2018). The accident mentioned above was Southwest Airlines first fatality in 51 years which could have been prevented if ultrasound inspections were required for United States airline carriers. The inspection was recommended due to a previous accident by the engine manufacturer stated in Kitroeff, Negroni, & Wichter (2018).

Human factors that directly impacted the Southwest accident due to maintenance can be attributed to a lack of assertiveness, lack of communication and lack of knowledge which could have prevented the mishap if at least 2 of the 3 factors were utilized. Kitroeff, Negroni, & Wichter (2018) will be revisited throughout the research as it is a prime example of a maintenance mishap due to human factors that could have been prevented by performing one inspection.

The effect that human factors play in the maintenance system is tremendous due to the capabilities and limitations that humans may encounter according to Gramopadhye & Drury (2000). In (Bao & Ding, 2014 p. 294) it is expressed that stress and fatigue plays a big part on a maintainer when they are working alone which may cause them to not fully install a part. It is also addressed in Bao & Ding (2014) that management plays a key role when maintenance errors happen due to many different types of conflicts such as communication, scheduling, and planning. Limitations and capabilities for maintenance workers are endless due to the fact that they are all human but since maintainers are the center of the maintenance world we researched how a mishap due to maintenance has affected major airlines and how can a major airline recover from a maintenance mishap.

The Effect on Major Airlines

Maintenance mishaps carry a major effect on airlines and it can especially affect major airlines to the point that criminal charges can be brought forth to a senior airline executive which shows how big a mishap can affect an airline company if it is determined to be a criminal act. In (Lawrenson & Braithwaite, 2018, p. 258) it is noted that criminalization of aircraft accidents can affect everyone associated with an aircraft that has incurred a mishap or accident that have become a criminal act deemed by the criminal justice system. In the case of ValuJet Flight 592 which crashed in the Florida Everglades and killed 110 people on board.

ValuJet used temporary fixes to fix major issues and also the airlines had around 100 safety-related issues which show that safety was not practiced and ultimately was a factor in the Federal Air Administration (FAA) deciding to shut down the airlines after the crash of Flight 592 (Matthews & Kauzlarich, 2000, p.12). The direct disregard that ValuJet showed towards maintenance ultimately is what caused the FAA to shut the airlines down and later ValuJet became known as AirTran and was purchased by Southwest Airlines where it merged into the Southwest brand completely ending AirTran formerly known as ValuJet (“AirTran plane crashes since 1993,” n.d.).

Alaska Airlines Flight 261 was a prime example of how an aircraft crash would affect the airlines from an economical and emotional standpoint. Flight 261’s crash was determined by the National Safety Transportation Board (NTSB) that the aircraft crashed due to insufficient lubrication of the jackscrew assembly with contributing factors from having an extended lubrication interval along with not having a mechanism that would help in case of a total acme nut thread loss which occurred (National Transportation Safety Board, 2002). It is expressed in Zotova (2017) that airlines that have suffered a crash lose market value immediately after a crash occurs and that is from stock prices alone. “The change of fares and passenger counts post-crash directly lead to an impact on airline profits, and thus, stock value” (Zotova, 2017, p.1). According to Hobbs (2008), a flight cancellation can cost an airline up to $140,000 and $17,000 an hour just by experiencing a flight delay. Both of those numbers can be attributed to maintenance sometimes and especially human factors depending on the situation that occurred for a flight to get canceled if it was not weather related.

Airline customers tend to stay away from airlines that have just suffered a crash due to safety concerns. Flight 261 crashed due to a maintenance mishap but overall in an industry that supplies transportation to millions of travelers on a daily basis the effect that a crash has on an airline is tremendous especially when the airline can’t fly due to impending inspections and investigations. The above examples from Flight 592 and Flight 261 are prime examples of human factors and how mishaps can affect an airline. The result of ValuJet shutting down was more than just an airline closing its doors, the shutdown left thousands of employees without a job and also impacted families with emotional distress. Ultimately disregard for safety led to the closure of ValuJet and shows the importance of improving human factors in aviation.

Lack of situation awareness. Situation awareness is a vital part of the maintenance world due to the importance of fixing aircraft and the dangers that mechanics go through on an everyday basis in order to make sure planes can fly. Every maintenance mishap has happened due to a lack of situational awareness that was always present when a mishap has occurred at some point during the task. ‘Situation awareness has been found to be important in a wide variety of systems operations, including piloting, air traffic control, and maintenance operations. Maintenance crews need support and training in ascertaining the current state of the aircraft system in addition to current training programs that concentrate on technical skills” (Endsley & M. Robertson, 2000, p. 302). Situation Awareness is classified into three levels in which the Aviation Safety Reporting System (ASRS) uses for situation awareness. Level 1 is noted as a failure to correctly perceive the information. Level 2 is the failure to comprehend the situation, and level 3 being the failure to project the situation into the future (Jones & Endsley, 1996).

The lack of situational awareness was present in ValuJet Flight 592 concerning the oxygen generators and the generator caps especially amongst all the maintenance crews that were involved in the incident. Maintenance workers all had conflicting stories from both ValuJet and SabreTech (National Transportation Safety Board, 1997). In the accident report for ValuJet Flight 592 according to the National Transportation Safety Board (1997), it was noted that in the recommendations that the FAA never performed a complete inspection on ValuJet’s repair site and that the FAA should have responded to the company’s maintenance functions.

The FAA played a huge part in the Flight 592 accident in which they could have prevented the accident from happening by performing proper inspections on the company. “Had ValuJet implemented a program to ensure that its subcontractor maintenance facility employees were trained on the company’s lack of authority to transport hazardous materials and had received hazardous materials recognition training, SabreTech might not have mishandled the packaging and shipment of the chemical oxygen generators that were loaded on flight 592” (National Transportation Safety Board, 1997, p. 136). The levels of situation awareness in the accident of ValuJet were all represented in some form in the accident investigation conducted by the NTSB.

Lack of situational awareness is also evident throughout maintenance that mechanics perform on a daily basis. In Latorella & Prabhu (2017) it is mentioned that in 1991 Boeing 747’s had to conduct in-flight engine shutdowns due to maintenance errors which can be attributed to situational awareness. Among these errors were items such as B-nuts not being safety wired, incorrect installation of parts, not tightening oil-tank caps, and dropping foreign objects into engines to name a few. All of the practices of maintenance above should have been prevented but are a result of lack of awareness by a mechanic. It is important in maintenance that maintainers double check their work or obtain another mechanic to look over their work to avoid mishaps.

Stress. In Hobbs (2008) he expresses how maintainers are kind of like doctors in the way that they have to diagnose and fix aircraft and their parts. Furthermore in the research that he conducted Hobbs (2008) explains why maintainers have a lot of stress when it comes down to their work. ‘When maintenance personnel leave work at the end of their shift, they know that the work they performed will be relied on by crew and passengers for months or years into the future. The emotional burden on maintenance personnel whose work has been involved in accidents is largely unrecognized outside the maintenance fraternity. On more than one occasion, maintenance personnel has taken their own lives following aircraft accidents caused by maintenance error” (Hobbs, 2008, p. 11).

In the case of Alaska Airlines Flight 261, stress played a huge factor on the maintenance accident due to mechanics having to get aircraft off the inspection line in a timely manner in order to fly when it needs to. According to Yazgan & Kavsaoglu (2017) stress is caused by many things such as fatigue and time pressure which ultimately played a factor in the lack of lubrication of the jackscrew assembly for flight 261. In tough economic times often maintenance centers are pressured to cut costs in order to keep aircraft in the air as a way to make money in which at times maintenance companies will push out an inspection to be more cost efficient in which Yazgan & Kavsaoglu (2017) researched. Stress has always been around in the maintenance world due to the amount it costs for an aircraft to fly but it costs even more for aircraft companies to not fly but human factors directly impact the amount of stress that is placed on a maintainer depending on the overall given situation the mechanic is in. Often times many mechanics may also have personal stress from home and family issues.

Lack of knowledge. Experience as a mechanic matures over time by learning on the job and by doing sufficient training in order to gain the knowledge needed to make decisions on how to fix future solutions in maintenance. “Lack of on-the-job experience and specific knowledge can lead workers into misjudging situations and making unsafe decisions” (“Human Factors “Dirty Dozen” – SKYbrary Aviation Safety,” n.d.). In Wiegmann & Shappell, (2001) lack of knowledge is described as a decision and skill-based error which basically will cause an unsafe act to happen. Decision-based errors are from improper choices or just not understanding the given information. On the other hand, skill-based errors can be documented as forgotten intention which is still knowledge based which shows a lack of knowledge.

Maintainers need to have the ability to understand the job that they are working on and by doing so a mechanic must be able to understand a maintenance manual in order to perform the specific task at hand. In Knezevic (2015) it is emphasized that maintenance manuals are basically not being understood by the maintainers and that is the reason for maintenance mishaps in which will affect every other aspect of maintenance from reliability to costs. According to Knezevic maintenance documentation has three main functions which are as followed: correct execution of the maintenance task, training personnel and the legal process such as aircraft forms. Having the ability to complete these three things should increase a maintainer’s lack of knowledge.

Maintenance mishaps have happened on numerous occasions due to lack of knowledge in many aviation accidents such as Flight 592 which showed a lack of knowledge from numerous parties involved with the incident. In the accident report for Flight 592, the National Transportation Safety Board (1997) made many different findings that were due to a lack of knowledge which could have possibly stopped an accident if parties would have known what was going on. The findings that were discovered were that if a warning label would have been attached to the generator which stated the dangers it proposed it could have helped workers prepare them for shipment the correct way.

“Because of the lack of information regarding products approved for transportation by the Bureau of Explosives, Research and Special Programs Administration cannot adequately ensure that these products are being packaged and shipped safely in the transportation environment” (National Transportation Safety Board, 1997, p.137). The above finding from the NTSB basically could have prevented the whole accident of ValuJet and shows how lack of knowledge affects everyone especially those who work maintenance.

Southwest Airlines Flight 1380 was another example of lack of knowledge displayed which caused a horrific accident. In Kitroeff, Negroni, & Witcher (2018) it was found that visual inspections for fan blades in the engine were no longer enough and that it needed to be inspected via ultrasound instead to find the crack on the interior side of the fan blade. Not performing the inspection using ultrasound techniques caused the accident to happen and a person to lose their life. Before the above incident happened Southwest had another incident happen two years prior to the same accident. This case could be lack of communication from management to the mechanics and just lack of knowledge from the mechanics that the FAA sent a directive for airlines to perform the inspections. On top of that the engine manufacturer also sent out a recommendation for the inspections to be accomplished but airline companies in the United States do not have to follow manufacturer guidelines (Kitroeff, Negroni, & Witcher, 2018).

Fatigue. Fatigue is a major factor in maintenance for all aviation workers in the United States, however, there is an increase in fatigue amongst maintenance personnel. Shifts workers on the flight line often experience fatigue at a faster pace due to shift work and their circadian rhythms being disrupted as noted by Wang & Chuang (2014). Maintainers often become affected with both mental and physical fatigue which begins to set in on them from being overworked, shift work such as swing shift or mid-shift and by experiencing a lack of resources which will cause them to work longer hours and work harder. Fatigue is also an onset of increased stress as noted in Yazgan & Kavsaoglu (2017).

Lack of communication. Probably the most important human factor in maintenance is communication mainly because maintenance tasks carry over to another shift many times and that shift must know what to repair or what inspection needs to get performed before an aircraft is deemed airworthy again. Lack of communication is not good for maintenance “Not only are accidents related to shift turnovers, but errors occur disproportionately after shift turnover in dynamic industries” (Parke & Kanke, 2008, p.73). In aviation maintenance, re-accomplishing tasks that have already been completed causes airlines to lose money and delays begin to happen.

Once companies add on pressure for tasks to get completed more human factors begin to fail and a maintenance mishap is more likely to happen which was started from a lack of communication. ‘Authorities on shift handover recommend face-to-face handovers by the people doing the work, instead of verbal briefings filtered through a shift lead, as is currently the case in many maintenance facilities’ (Hobbs, 2008, p. 21). Maintenance personnel should fully communicate with each other when shift turnovers happen if there are questions regarding tasks it should be asked and it should be answered. Shift turnovers should also be reflected in a logbook and other applicable maintenance documentation.

Valujet Flight 592 was the result of failed communication which had catastrophic results. In Matthews & Kauzlarich (2000) they go into great detail on how all of the individuals were questioned and how they replied. Some inspectors admitted about knowing caps and claimed that they told others about it while many admitted that caps were never mentioned for the oxygen generators (Matthews & Kauzlarich, 2000). According to the National Transportation Safety Board (1997) individuals that worked in the shipping department was never told about the generators being in the department and SaberTech never had a system in place to identify items which would have helped in screening what is hazardous and what is not. The lack of communications failed on so many levels with the ValuJet incident from the organizational heads all the way down to the maintainers and inspectors. In the exchange between the stock clerk and the logistics director, it shows a clear lack of communication when the clerk believed he got the go-ahead to ship the generators out and the logistics director denied doing so (National Transportation Safety Board, 1997).

Another incident which highlighted a lack of communication took place on Eastern Airlines on a flight from Miami to Nassau in which the aircraft had to divert back to Miami to make an emergency landing (Hobbs, 2008). The issue which caused the emergency landing was that chip detectors were installed without using the O rings which help stops oil leaks from happening. According to Hobbs (2018), Easter airlines had a bigger problem on their hands with chip detector installation because they have faced other times in the past when they had to perform engine shutdowns in-flight. Lack of communication and documentation affected Eastern Airlines when it came to inspection and maintenance of chip detectors. Mechanics would remove O rings from them and forget to install a new one and complacency happens due to mechanics always performing the task so they fully do not inspect the part (Hobbs, 2008). Directives should have been made by Eastern Airlines for more clear procedures regarding chip detectors and O rings that would end the confusion. “Rather than addressing the wider system problems such as poor procedures and undocumented norms, the incidents resulted in individual disciplinary action and training” (Hobs, 2018, p. 5).

How Do We Improve Human Factors

Human factors in maintenance must always be improved to keep up with timelines that aircraft must achieve in order to fly. In the aviation industry there are always new methods and technologies that mechanics must get trained to do but in order for maintainers to do their jobs correctly, human factors must be improved on. “Most airlines, and even some third-party repair stations, now have active human factors programs. These programs train maintenance and inspection personnel, analyze incidents, change equipment, and apply information technology solutions to many of the operational issues we raise here” (Gramopadhye & Drury, 2000, p. 130). Hobbs (2018) mentions about risk controls and how they have the ability to manage hazards in the working environment. “There are two main types of risk controls related to maintenance error – preventative controls and recovery risk controls” (Hobbs, 2018, p. 26). The purposes of preventative risk controls are to lessen the chance of events that are not planned such as a human error event. The recovery risk control main purpose is to recover when a dangerous situation has started (Hobbs, 2018).

In Latorella & Prabhu (2017) Human reliability analysis (HRA) is seen as a way to examine all risk factors that a system is exposed to especially human errors. Utilizing HRA can be seen as a great way to improve human factors related to maintenance mishaps caused by human error by actually keeping track and identifying the error within a certain amount of time. HRA also has the ability to recognize how and why a human error was committed which would improve some organizations in combating the human error (Latorella & Prabhu, 2017). Organizations may also improve on human factors by incorporating the SHELL model into their organizations as it focuses on human factors as seen below in Fig 1, SHELL model of aircraft maintenance (Shanmugam & Paul Robert, 2015, p. 411). [image: ]

Understanding the Needs of Your Workers

Organizations need to understand how hard maintainers work to get aircraft in the sky because working in maintenance is not an easy career. The SHELL model lists human factors within its framework as seen in Shanmugam & Paul Robert (2015). Maintenance data and records need to be clear and updated in job tasks so that mechanics can properly understand directions in order for them to succeed. Maintenance records should be kept good and accurate with up to date data and information concerning all work that has been accomplished. It is very important that organization groom their mechanics on how important documentation is and their mechanics need to see that their organization supports good documentation in case of a mishap or accident occurs (Shanmugam & Paul Robert, 2015).

Facilities that are used to perform maintenance are often lacking in good lighting for maintainers to effectively perform their job. On top of that many maintenance facilities lack comfortable conditions and at times lack ventilation especially when workers are working around fumes (Hobbs, 2008). Tools are extremely important to mechanics because in order to get tasks done mechanics need tools that are not worn out. According to Shanmugam & Paul Robert (2015), the environment plays a big part of human error due to physical conditions that a mechanic must work in these conditions can be directly affected due from temperature and lighting. Maintenance workers should be able to work in clean safe conditions where they do not have to battle outside elements if they are in a closed hangar.

Training. Every maintenance worker should undergo training regularly in order to keep up with trends that are changing or just for a refresher in safety. Training is emphasized in Latorella & Prabhu (2017) maintenance technicians undergo computer based training (CBT) and often perform refresher training on various maintenance items which are computer-based. ‘Results from an evaluation study demonstrated that students trained with the CBT system showed the same level of post-training knowledge as those trained in the traditional instructor-led method” (Latorella & Prabhu, 2017, p.153).

On the job training is important for mechanics because it gives them experience on maintenance procedures and gets them acquainted with what they will be working on and the tasks that they will be performing. “Training sessions and on the job training improve maintenance skills and knowledge” (Sheikhalishahi, Pintelon, & Azadeh, 2016, p. 228). Maintenance resource management (MRM) is annual training that maintainers attend in order to reacquaint themselves with safety issues (Hobbs, 2018). MRM’s criteria are based on stress management, assertiveness, decision-making skills, and conflict resolution to name a few.

The environment. As stated earlier in the research conducted maintenance workers should be able to work in a maintenance facility that will give them proper lighting and shield them from the outside temperatures while supplying good ventilation in order for them to do their jobs. Management and supervision of an organization are part of the maintenance environment that mechanics work in and it is important that they supply their workers with confidence to get the job done in a stress-free zone. Organizations should focus on three things for the work environment which consists of wise leadership, excellent communication, and an understanding of human factors that are involved (Sheikhalishahi, Pintelon, & Azadeh, 2016).

Often at times, maintainers will work in a team environment which means that teamwork will have to be utilized to get the job done. It is important that mechanics learn to put differences and personal agendas aside in order to get maintenance jobs fulfilled (Hobbs, 2008). Lack of teamwork and poor communication among a team can disrupt an organization and also cause mishaps to happen during maintenance operations. The goal of a maintenance organization should be workers working together and exhibiting communication skills to get tasks accomplished along with demonstrating organizational values.


Through the research conducted it has become evident on the need to improve on human factors in aviation maintenance. Human factors played major roles in the accidents that were researched. Alaska Airlines Flight 261 (National Transportation Safety Board, 2002) stress played a factor and also fatigue. Southwest Airlines Flight 1380’s accident stemmed from a lack of knowledge by not performing the ultrasound inspection on the fan blades to see if there were cracks on the interior side. The human factors that were involved with ValuJet Flight 592 (National Transportation Safety Board, 1997) ranged from lack of knowledge to lack of communication and quite honestly that ValuJet accident was a total breakdown of all human factors which were involved at some point.

The research that was conducted also showed how airlines are affected from an economic standpoint and as a business standpoint by noting how stocks are affected when an aircraft has an accident that is maintenance related. The price it costs an airline to cancel and delay a flight was also noted due to maintenance in the research that was conducted. The researched showed how an airline can ultimately get shut down and later bought out in which was the case with ValuJet becoming AirTran and then being bought out by Southwest Airlines. All of the scenarios mentioned above were directly related to human factors in maintenance mishaps.

Human factors were explained in the research on how they can be improved on to better a maintenance organization and how it would help in avoiding a mishap. The research conducted also highlighted many items that would help in improving human factors such as maintenance resource management which is very big on teaching the safety aspects and decision making processing of human factors. The importance of on the job training was expressed and how it helps with building confidence and knowledge in maintainers that once suffered from a lack of knowledge and how that can improve maintenance practices and avoids mishaps.

The needs of maintenance workers were discussed in the researched and how better maintenance facilities would help decrease the risk of a mishap. Other factors such as improving the organization and teamwork would also help in decreasing the chance of a mishap. It was expressed on how organizations need to improve their maintenance areas in order to provide a better place to perform maintenance job tasks. The importance of communication was discussed in the research and how a lack of communication increases the chances of maintenance mishaps to happen. In closing the main goal of the research that was conducted was to give the reader an in-depth overview on why it is important to improve human factors in maintenance and the direct effect that maintenance mishaps have on the airline industry and maintenance as a whole.

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