12 Human Factors for Aircraft Maintenance Proficiency | Dirty Dozen

12 Human Factors

The dirty dozen of human factors is another model used to describe the most common causes of human factors errors that lead to aviation accidents and incidents.


In the late 1980s and the early 1990s, a large number of aviation maintenance-related accidents and incidents has occurred. Due to the contribution of human factors errors in the aviation accidents and incidents that time, Gordon During -who was working for transport of Canada- developed dirty dozen model in 1993. 

He identifies twelve human factors which degrade people's performance and lead to human errors.


The twelve human factors are lack of communication, lack of teamwork, lack of assertiveness, complacency, fatigue, stress, lack of knowledge, lack of resources, lack of awareness, distraction, pressure, and norms.



1- Lack of Communication

2- Lack of teamwork

3- Norms

4- lack of assertiveness

5- complacency

6- Fatigue

7- stress

8- lack of knowledge

9- lack of resources

10- lack of awareness

11- distraction

12- Pressure




In the previous week, I published my article which was titled pear model human factors. In this article, I will explain another human factor model which affects your performance and suggested some simple mitigating strategies. 

Note : you may like reading SHELL model human factor

I hope you find my website a rich source of aviation articles and you share my articles with your friends. 


The Dirty Dozen Human Factors | aviation maintenance

As I mentioned before, these twelve human factors are known as the dirty dozen. It was adopted by the aviation industry as a simple model to discuss aircraft maintenance errors that occurred by aircraft maintenance technicians.


It is important to know the dirty dozen human factors, recognize their symptoms and avoid them.  


Aircraft maintenance technicians must learn from the errors caused by dirty dozen.


Note: You may not know the federal aviation administration dirty dozen. Click here.


1- Lack of Communication

Communications occur between aircraft maintenance technicians and many people (such as management, pilots, parts suppliers, aircraft servicers). Through the daily communication process, it may be a potential for misunderstanding or omission. For example, the maintenance department may participate in a lack of communication by inadequate/ineffective communication of new roles, maintenance procedures, etc. 


But communication between aircraft maintenance technicians may be more important than all kinds of communications. Lack of communication between aircraft technicians could lead to a maintenance error and result in aircraft accidents and incidents. Errors may happen where the maintenance procedures - related to aircraft- are performed by more than one maintenance technician.



  •  Maintenance technicians must properly use maintenance logbooks and worksheets to communicate with one another and explain what work has and has not been completed. Because errors may happen during changing shifts with poorly written communication logs. 
  • Maintenance technicians must discuss exactly what had been and needs to be completed for the next shift. 
  • Maintenance technicians must not assume that the work had been completed. They must use the maintenance instructions and work tasks cards. 


2- Lack of teamwork

Teamwork makes the dream work, in the aviation industry work tasks and operations are team affairs. The large an aviation organization becomes, the more common this contributing factor is. 


Teamwork is associated with improved safety in the workplace. teamwork in the workplace involves every Aircraft maintenance technician understanding and gearing on actions to be taken. 


Lack of teamwork is a failure to work together to accomplish a shared goal. Personality differences in the workplace no it is let outside the workplace, and aviation organizations should emphasize that a lack of teamwork can ultimately affect aviation safety.


In this factor, I should impress its importance. it is boring if we work alone. even if there are some individuals with less experience, we should lead, teach, and inspire. But if you, have I sleepy manager it is terrible, keep working with your team. Bad managers will be changed one day. the change will be a huge one. 



Let us back to our subject, lack of teamwork makes all jobs within an aviation organization more difficult and, in aviation maintenance, could result in a miscommunication that affects the airworthiness of the aircraft.



  Discuss how a task should be done.

  Make sure everyone understands and agrees.

  Trust your teammates

  Always look out for co-workers with safety in mind.


3- Norms

Norms are unwritten rules or tolerated by most of the Aircraft maintenance technicians’ groups “shifts”. Norms in workplaces develop over time, through experience, and often under the influence of specific organizational culture.  


Norms are short of “normal”, or the way things are done around and organization. It can be good or bad.


Good norms, that support workplace safety, and the bad norms that lead to not compliance with standard operating procedures and maintenance workshop manuals.  


For example, not using work checklists by Aircraft maintenance technicians during an aircraft maintenance repair.


To reduce maintenance errors occurred due to norms, aviation organizations must provide a work environment that is resistant to human factors errors, it is a role of the safety management system (SMS), of which human factors training in aviation is a part.  



    Everyone must follow the same approved standard

    Many actions may seem normal, make sure it is correct.

    The easiest way to repair things, or to accomplish something may not be the standard.

    Identify and eliminate negative norms.

    Write a voluntary safety report to alert the safety management system manager, make sure your SMS manual supports a voluntary reporting system.  


4- Lack of assertiveness

Assertiveness is the ability to express your feelings, opinions, beliefs, and needs in a positive, productive manner and should not be confused with being aggressive. 


You may believe something is wrong and dangerous to do so, be confident, lack of assertiveness occurs when an aircraft maintenance technician is not self-confident enough to speak up for their right and ideas. 


Failure to speak up or document concerns about work instructions, supervisors’ orders, or the actions of others may lead to violations of maintenance documented procedures. 


Lack of assertiveness in failing to alert others when something is going wrong can result in many fatal accidents. 



  Improve your skills of learning, communication and expressing safety concerns, and offering positive solutions

   Do not let something that you know is wrong continue by ignoring it. 

   Provide clear feedback when a risk or danger is perceived.

   Allow co-workers to give their opinion and always accept corrective criticisms. 


5- complacency

This insidious case of maintenance error usually occurred as aircraft maintenance technicians become overconfident and rely on pattern recognition for maintenance failures interpretation. Overconfidence leads to complacency. 


For example, repeating tasks such as inspections can be ignored or skipped because maintenance technicians have performed a task several times without ever finding fault. 



       Never sign for any work that has not been performed by yourself. 

       Do not take yourself for granted, whatever your experience.

       Communicate when in doubt. 

       Always double-check your work.





6- Fatigue

Fatigue is a feeling of tiredness, reduced energy, and increased effort to perform tasks effectively and without error. It is a major human factor that has contributed to many maintenance errors as a result of the accident. 




    • Be aware of the symptoms and look for them in yourself and co-workers. 

    • Forfeit complex tasks if you know you are exhausted. 



7- Stress

Stress is the subconscious response to the demands placed upon us. This does not only relate to the work environment but our personal lives also. Furthermore, it can be a physical, chemical, or emotional factor that causes physical, or mental tension.


Stress can lead to maintenance errors when it is excessive as it acts as a distraction and reduces concentrations levels when performing complex maintenance tasks. 




  A positive and strong persona helps build confidence and better control over our reactions.

   Take a short break when needed

   Discuss with a co-worker and ask them to monitor your work.

   Eat healthy food and do exercises.


8- Lack of knowledge

In aviation maintenance, technology is changing every time, this contributor to aviation maintenance error is more common than we think. Lack of knowledge means a shortage of training, information, and/or ability to perform the tasks successfully. 


Lack of knowledge when performing aircraft maintenance can result in a faulty repair that can have catastrophic results. 



   Only fix aircraft parts that you are trained to fix.

   Use an up-to-date maintenance manual.

  If you don’t know how to fix something, ask for help from an aircraft maintenance technician who does.


9- Lack of resources

The fact is when the proper resources – such as enough manpower, equipment, documentation, time, parts, etc.- are available and to hand, there is a great chance that aircraft maintenance technicians will complete a task more effectively, correctly, and efficiently.


Lack of resources to safely carry out a maintenance task has caused many fatal accidents. For example, an aircraft is dispatched without a functioning system that normally would not be a problem, suddenly, encounters circumstances where it does become a major problem. 



    • Order parts before they are required.

    • Have a plan for pooling or loaning parts

    • Preserve all equipment through proper maintenance. 


10- Lack of awareness

Lack of awareness is a failure to recognize a situation, understand what it is, and predict the possible results. In other meaning, it is a failure to recognize all the consequences of an action or lack of foresight. 


In aviation maintenance, it is not unusual to perform the same maintenance tasks repeatedly.


After completing the same task multiple times, it is easy for aircraft maintenance technicians to become less vigilant and develop a lack of awareness for what they are doing and what is around them. Each time a task is completed it must be treated as if it were the first time.



    • Fully understand the maintenance procedures needed to complete a task.

    • Even if you are highly proficient in a task, ask co-workers to check your work.

    • Make sure there are no conflicts with an existing repair or modifications.




11- Distraction

This is anything that takes your mind off the task at hand for an instant. When work resumes, the technician may skip over a detail -forgetting things, including what has or has not been done in a maintenance task - that needs attention.


This contributing factor is known to be responsible for at least 15 percent of all aviation accidents. 



    • Use a detailed checklist.

    • Go back 3 steps when restarting the work.

    • Never leave tools or parts lying around. Secure them before leaving the area.


12- Pressure

Pressure - to fix things - to be on time is ever-present in aviation maintenance. Aircraft maintenance technicians are very time-sensitive and many maintenances decisions center around that fact.


Aircraft maintenance technicians should not allow time pressure to get in the way of finishing aircraft maintenance safely. 



    • Ensure that the pressure is not self-induced.

    • Communicate concerns.

    • Ask for extra help.

    • Put safety first.




It is vital to know the dirty dozen, how to perceive their side effects,

furthermore, above all, know how to stay away from or contain blunders created by the dirty dozen. Understanding the cooperation between authoritative, work gathering, and individual factors that might prompt blunders and mishaps, aircraft maintenance technicians can figure out how to forestall or oversee them proactively later on.


I hope I have simply conveyed the information. I'm so glad you're sharing this article now. Many thanks in advance.





1- FAA, Chapter 14, Human Factor [ AMT Handbook Addendum Human Factors]

Maged Saeed AL-Hadabi

I’m Instructor / Maged Saeed Al-Hadabi. ​ Air Cargo / IATA Dangerous Goods Regulations / Safety Management System Senior Instructor, Auditor [ Yemen Airways] . Approved IATA DGR/ SMS Instructor by Yemen Civil Aviation Authority.

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