In recent years, the emergence in mass culture of the phrase “human factors related” indicates that accidents are often not due to a single cause, but almost always to a chain of events triggered by several factors. In most cases, the accident is not the result of major mistakes, but rather a series of events of lesser severity, many of which might be related to the dirty dozen human factors.

Typically, these factors were associated with flight operations, but lately, they have become a major concern also in maintenance operations and air traffic management. It has been discovered that most of the time, supposedly insignificant events lead to tragedies, precisely because they are “less visible” and therefore perceived as not very dangerous.

The methodologies to guarantee that aerospace systems do not incur in hazardous failures are well ingrained in the design and validation phases of aircraft development. In fact, according to Boeing, human error has been documented as a primary contributor to more than 70% of commercial airplane hull-loss accidents. To make advances in preventing human error, it is paramount to analyse in depth the root cause of previous mishaps to avoid future ones.

For this reason, the analysis of the Human Factor based on cognitive-behavioral aspects has been the subject of countless studies that have also led to qualitative methods that have found great success in the research of possible interactions between the Human Being, the Work Environment, and Aeronautical Products and Procedures. To translate the results of these developments into the industry practices guidelines are stablished such as the Dirty Dozen human factors.

One of the first human factor studies was developed by Gordon Dupont, an employee of Transport Canada, in 1993. He compiled a list of the 12 most common factors that, by affecting the individual, lead him to make a mistake. These twelve factors, were called the “Dirty Dozen”, precisely to indicate their negative connotation.

The original twelve-factor list was written for aircraft maintenance, although nowadays it is used as an introductory concept for the human factor field. It does not present order of relevance, since all twelve points are of equal importance and are factors to which the individual may be subjected every day, without even realizing it.

It indicates a failure to transmit or receive information between individuals in the work environment. It must be emphasized that a lack of information, could cause a wrong choice, due to misunderstanding.

This is why it is essential for workers to improve their communication process, expressing the most important information at the beginning and also at the end of the speech, to emphasize the main object of the indication received. Besides, it is highly recommended to use checklists, i.e., lists, rich in information, that if executed in sequence and order, do not allow the employee to get confused or to perform operations that are not indicated in them.

An operator with a lot of experience in a given aeronautical field is likely to perform the same task for many years in a row. The repetitiveness of his work makes him overocnfident in his abilities and he tends to underestimate the importance of the task he is carrying out, sometimes even performing it superficially.

To avoid performing all tasks mechanically, the worker must be aware of the importance of the actions he takes and of the possible consequences. It is therefore important to use checklists to reduce the possibility of error.

A lack of knowledge about the topics you are working on can lead workers to misinterpret certain situations and make unsafe decisions. Checklists and regulations should always be followed to the letter.

Distraction is due to all the possible external stimuli that take attention away from the operator while he is performing his task.

To avoid distractions and get back to concentrating on the job, it is recommended to use checklists and, if interrupted during the task, it is suggested to go back three steps from where the worker left off, to refocus again without incurring any forgetfulness.

Aircraft maintenance includes specialized personnel with different duties, who share a common goal, that of keeping the aircraft airworthy. Each operator is therefore an integral part of a complex organism, which moves together, making teamwork essential.

It must be ensured that everyone in the team understands and agrees, establishing a working relationship of mutual trust.

Fatigue is a physiological reaction to a prolonged state of physical or mental stress, which can occur either after a long period of work or after a short period of intense work.

Each operator must always recognize the first symptoms of fatigue in himself and others, to be able to intervene immediately. For this reason, if he feels fatigued, he should call someone to check the operation he is doing, so that can have verification of the work done.

It is always needed to have as much support as required. In the case of aircraft maintenance, the parts needed must be ordered before they are required, to have them on hand when they need to be fitted.

Regardless of any deadline, it is always important to put safety first. If the employee realizes that the deadline is approaching, he doesn’t have to rush the process, but rather seek help from other colleagues. If any problems mean the deadline cannot be met, instead of speeding up the process, let the firm know that the deadline will not be met.

An important decision must be made unanimously. A colleague who does not allow others to express their concerns about the selected measure is dangerous, as he or she may direct the choice, without everyone being consulted, increasing the possibility that a mistake will be made.

Team members must be listened to calmly and rationally, inviting each interlocutor to give feedback on the information received. Any criticism should always be constructive and never punitive.

Stress is a physical, chemical, and emotional state capable of exerting damage on the organism, with its prolonged action. It is therefore essential to act against stress before it negatively affects the work done.

To avoid mistakes, then, it is useful to face problems with an approach that is always rational and never emotional, to take a break when it is needed, and finally, if the worker is unable to get rid of stress, he should get help from specialized personnel by going to the appropriate centers.

Watching over the work of other colleagues and vice versa, with a collaborative feeling, indicates a greater awareness of the work environment, and this increases the possibility that the final product will be of high quality.

It is important to analyze the cultural context of the workplace, as it can facilitate bad habits as well as more or less safe procedures. In a company, it is normal to find that some habits rooted in time, are repeated even by newly hired workers, even though they have not been written in any standard. These “unwritten rules” should be discouraged and avoided by strictly following official regulations, to ensure the highest level of safety.

According to the 2020 annual safety review by EASA, only 15 of 144 accidents involving commercial air transport airlines and air-taxi airplanes were caused by human error. Furthermore, the report shows that there is a decreasing trend from 2016 to 2019, indicating a slow, but gradual decrease in human factor related accidents.

Although this type of studies may seem obvious or of secondary importance, they represent our best understanding of the human error component behind aviation accidents. Indeed, they provide, through a systematic approach, the basis for the study and development of a field in which only “opinion” previously existed.

It is important to note that the individual’s senses are neither universal nor infallible. They do not pick up all input from their surroundings, and often after too many hours of work they tend to degrade, no longer functioning properly. Human error in any case, there will always be, but the goal is to reduce it to the minimum possible and if it happens to avoid that it leads to catastrophic consequences.

All the factors considered so far have led over time to changes and improvements in the procedures and instructions set out in the official regulations. This has reduced friction due to interactions between parts of the maintenance system, significantly limiting errors over time and consequently reducing accidents due to incorrect or poor maintenance.

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