Dirty Dozen in Aviation

Aircraft · 7 min read · May 27, 2022
dirty dozen aviation

A large number of maintenance-related aviation accidents and incidents occurred in the late 1980s and early 1990s. The Dirty Dozen is a list of twelve of most basic human factors prerequisites or circumstances that can lead to dangerous occurrences. The Dirty Dozen concept developed in 1993 by Gordon Dupont while working for Transport Canada as part of an introductory training course for Human Performance in Maintenance.

It has since become a foundation of Human Factors in Maintenance training classes all over the globe, as demonstrated by the UK CAA CAP715. In most cases, the aircraft maintenance related accident is the result of a series of minor events, many of which can be attributed to the Dirty Dozen human factors. The publication of the Human Factors Dirty Dozen has heightened awareness of human factors in accidents and incidents. With the goal to focus on minimizing and capturing human error.

While the dirty dozen is mainly related to aviation, it is often not just aircraft maintenance. The theory studies human error accident precursors and other common human error preconditions that lead workers to make mistakes in their work. So, the dirty dozen is also a psychological study that can be applied to many industries.

The list of 12 human factors

Lack of communication

Communication is comprised of the transmitter, receptor, and communication channels. Verbal communication mistakes are common, especially when confusing sentences are used or incorrect conclusions are drawn. A lack of communication is a major human factor that can lead to inadequate or poor maintenance procedures.

In spoken conversation, only 30% of information is absorbed and comprehended. Many people only remember the beginning and the end of a conversation. Proper documentation or reliable communication channels are vital to keep the highest information retention.


When a person is interrupted or disturbed while performing a task, they are frequently unaware that an activity or task has been skipped or left unaddressed. As per industry sources, distractions account for approximately 15% of maintenance-related mishaps.

There are various types of distractions. An interrupting micromanaging team leader, unnecessary phone calls and texting, or personal and mental issues. Some of them can be corrected on the spot, such as limiting telephone usage at work, others might need a bigger solution.

An aircraft in an MRO hangar stationed for repairs.

Lack of resources

A lack of appropriate supplies may make it extremely difficult to complete a task. It is also probable that the resources available, notably guidelines, are of poor quality or insufficient for the job. Considering an airplane repair industry example can help to clarify this. The majority of regional and small airlines do not have an appropriate MRO.

Most planes only require minor maintenance that necessitates the use of a specialized tool. If the facility lacks that tool, technicians may attempt to complete the work using nonstandard methods. It has the potential to cause a system failure with disastrous consequences.


Stress is provoked when a situation or occurrence is considered a risk and necessitates activities that exceed a person’s normal operating intensity level. Stress is a biological response to a stimulus that disrupts or conflicts with human physiological equilibrium. Stress is common in the aviation industry and is caused by physiological, psychological, and external factors.

Some stimuli or more commonly known as stressors include major life events such as a family death or a job offer, ongoing frustrations such as a chronic disease or an inflexible work schedule as well as minor annoyances such as traffic congestion, insecurity with coworkers, or exposure to aircraft engine noise and vibration while operating. Personnel is less stressed when they feel safe in the workplace. Moreover, proper equipment and adequate rest prevent mistakes and increase productivity.

Organizations must consider human aspects as well as safety and analyse all the consequences. Some of the first obvious signs of stress are disruptions in personality and emotions, errors in judgment, loss of focus, and impaired memory. People may experience sleeping difficulties, increased tiredness, and stomach problems. Long-term stress symptoms include increased susceptibility to infection, increased use of stimulants and self-medication, absence from work, sickness, and sadness.

Human error in complacency

Complacency is defined as a sense of self-satisfaction combined with a failure to recognize potential threats. This impression is common when performing routine tasks that have become habitual and are perceived to be simple and safe. Things designed to prevent accidents breed complacency. Complacency is influenced by experience, training, and expertise.

Personnel become complacent when they rush through checklists, fail to properly inspect equipment, and fail to use all navigation equipment. This human limitation is frequently encountered in the aviation industry, including aircraft maintenance, air traffic control, and flying.

Complacency or inflated self-confidence can often lead to catastrophic consequences, especially if vital checklists in aviation are overlooked. There are quite a few complacency-related accidents, for example, the Beechcraft B200 Super King Air crash, which could have been prevented if the pilot had not skipped over pre-flight checks.

Lack of teamwork

Teamwork facilitates strong employee connections because more employees work in close proximity. The more they work together, the more they learn to accept one another’s preferences, dislikes, capabilities, and flaws. Collaboration increases productivity, synergy, and innovation.

When employees collaborate to resolve issues, they are more engaged and responsive. Lack of collaboration can have serious consequences for safety. In the aviation industry, jobs are intertwined, which means that being a team player entails being safe, and safety requires teamwork.

Pressure from aviation maintenance tasks

Stress from mental strain can cause human errors. Existing minimal turn-around times place an additional burden on aviation maintenance personnel and make identifying problems and carrying out necessary procedures challenging. Whether a problem is discovered, the technician is under pressure to postpone the flight. 

Consider the distinction between real pressure and self-imposed pressure. The real pressure is obviously the active or passive pressure to complete work within a specific time frame.

Individuals or teams, on the other hand, may experience self-imposed stress in order to complete a task within a specific time frame, even if the time frame is inappropriate or the project is not feasible with the available resources and time frame. The pressure placed on an employee, such as a maintenance crew, to complete pressure aviation maintenance tasks quickly may jeopardize safety.

Actual and self-imposed pressure can both be powerful forces in accelerating any aircraft maintenance task. Conduct a thorough pre-task review to describe job priorities wherever possible.

Constant two-way communication is essential for recognizing and mitigating the effects of pressure on performance and behavior.

An big white multi-engine airplane stationed for repairs in an MRO hangar.

Lack of awareness

Situational awareness is defined as recognizing just about everything about the entire scope of an activity, such as flying, controlling, or maintaining an aircraft, while taking into account all relevant considerations. SA is concerned with an individual’s understanding of specific task-related phenomena in the context of complex operations.

The inability to engage the brain and think a situation through could be interpreted as a lack of awareness. People with a lot of expertise are more likely to be unaware, and they frequently admit that they should have handled it better.

SA is not a lack of information since the remedy is not written in a handbook or legislation. Many people will say they lack common sense, but the Human Factors Dirty Dozen affects many folks who have plenty of it. Lack of awareness leads to poor judgment.

Lack of knowledge

A lack of skill appears to be a growing concern in the aviation industry as airplanes become more complex. This contributor is more prevalent than previously thought due to constantly evolving technologies. Add to that the fact that the average person only remembers about 20% of what they learn, unless they rehearse it regularly.

One of the most effective safeguards against this human error factor is taking maintenance training courses as often as possible. There are many maintenance training courses worldwide that you can take for a specific type of aircraft too.


Fatigue refers to the problems that can arise as a result of long shifts or poorly structured shift patterns. It is commonly defined as a decrease in mental and physical performance caused by prolonged activity, insufficient sleep, or an internal clock disruption. Fatigue can impair a worker’s memory, concentration, reasoning, abnormal mood swings and decision-making abilities.

Unfortunately, many people underestimate the effects of exhaustion or are unaware of their own state of fatigue. Fatigue, if not addressed, can force employees to perform in hazardous work environment, increasing the likelihood of an accident or occupational injuries. While performing a job at height, a fatigued worker may recognize the requirement for a full-body harness but fail to connect to a lifeline.

A fatigued person may also have sluggish reactions and less situational awareness, both of which can lead to a severe injury or an accident. Fatigue is dangerous because people regularly fail to recognize its implications. Organizations can benefit from training by learning to recognize signs of fatigue in their workforce and avoid potentially hazardous situations. Organizations can also reduce the risk of employee fatigue by adjusting work schedules.

Lack of assertiveness

A person is said to be lacking in assertiveness when they lack the confidence to stand up for their interests and beliefs. Failure to express or document concerns about other people’s commands or actions. Many fatal accidents are caused by a lack of assertiveness in failing to warn others when something does not appear to be normal.

Avoiding something that a person knows is bad will only make it worse.


The term “norm” refers to how situations are typically handled. These are unsafe norms that the majority of employees follow or withstand. Adverse norms have the potential to undermine established safety standard and lead to accidents. It is critical to remember that just because something appears to be normal, it is not.

The basic way to complete a task may not be the right choice. It is prevalent in a company to find that some long-standing habits are repeated even by newly hired employees, even if they are not documented in any way.

To ensure the highest level of aviation safety, such “unwritten rules” should be opposed and eliminated by strictly adhering to formal laws.

An aircraft engineer inspecting the landing gear of an aircraft.


Why is the Dirty Dozen important in aviation?

The Dirty Dozen refers to the top twelve most common indications of human error, or elements that can lead to disastrous accidents. These twelve components drive workers to make mistakes. According to the FAA, human factors account for over 80% of maintenance errors, which can waste time, result in injuries, or even result in death.

How do you avoid the Dirty Dozen in aviation?

The Dirty Dozen are the most threatening human limitations that can endanger safety. Human error may be minimized by spreading awareness, providing training, and constantly monitoring activities.

What are the examples of the Dirty Dozen?

The following are the 12 most prevalent reasons for human error in aircraft maintenance: complacency, lack of information, distraction, lack of cooperation, weariness, limited resources, pressure, lack of assertiveness, stress, unawareness, norms.

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Jet pilot @NASA

1 comment

  1. Benjamin R Zielke says:

    How many years in aviation do you have ?

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