The Dirty Dozen: Common human error factors in aircraft maintenance mishaps

  • Published
  • By Air Education and Training Command Safety Directorate


The Dirty Dozen List

1. Lack of Communication                      2. Complacency                                 3. Lack of Knowledge

4. Distraction                                            5. Lack of Teamwork                         6. Fatigue

7. Lack of Resources                               8. Pressure                                         9. Lack of Assertiveness

10. Stress                                                 11. Lack of Awareness                      12. Norms


Aircraft maintenance saddles the worlds of occupational and aviation safety, which makes for a challenging combination of hazards. In the span of one shift, maintainers may encounter the risks of running a turbine engine at thousands of RPMs, falling from the potentially fatal height of wing, or losing a finger to a hydraulically actuated control surface. In the first half of 2023 alone, Air Education and Training Command experienced more than $23 million in aircraft damage costs associated with maintenance, according to Master Sgt. Clinton Gessler, AETC Safety Directorate flight safety NCO. In the mishaps that occurred, a common theme developed: shortfalls in “back-to-basics maintenance,” or as some would say, “Maintenance 101.”

“In my 16-year career as a tactical aircraft maintenance technician, I can tell you aircraft maintenance isn’t a job that is going to get any less demanding,” Gessler stressed. “We will always have to deal with operational and fiscal constraints leading to aircraft availability challenges resulting in the all too familiar feeling of ‘do more with less.’ Additionally, dealing with an emerging near-peer threat and finding innovative ways to employ airpower will create challenges in both mishap prevention and aircraft maintenance’s mission success.”

To better equip maintainers to combat the risks they encounter daily, AETC Safety is leveraging what one safety expert termed “The Dirty Dozen.” This list identifies 12 of the most common human error factors that lead to aircraft maintenance mishaps. This list is by no means all-inclusive, but it includes some of the most frequent elements that influence people in the maintenance community to make mistakes, and understanding these hazards will enable maintenance personnel to avoid costly and dangerous errors.

Whether maintaining a legacy airframe with decades of “lessons learned” or a 5th generation aircraft with advanced automated aircraft health management and troubleshooting systems, The Dirty Dozen affects everyone.

“When we choose to let these 12 human factors catalyze unnoticed, the probability and severity of mishaps will increase,” Gessler said. “However, when we deliberately allocate time and energy towards accomplishing the basics of maintenance — tool accountability, FOD (foreign object damage) walks, cleaning up spills, following tech data, and paying attention to details — we reduce the likelihood of a mishap occurring.”

Drawing from SKYbrary (, an electronic repository of aviation safety knowledge, this article will identify and define The Dirty Dozen, and provide suggested countermeasures to reduce the risks posed by each of these hazards.



Lack of Communication

Poor communication often appears at the top of contributing and causal factors in accident reports and is, therefore, one of the most critical human factor elements. Communication refers to the transmitter and the receiver, as well as the method of transmission. Transmitted instructions may be unclear or inaccessible. The receiver may make assumptions about the meaning of these instructions, and the transmitter may assume that the message has been received and understood. With verbal communication it is estimated that only 30 percent of a message is received and understood.

Detailed information must be passed before, during and after any task, and especially across the handover of shifts. Therefore, when messages are complex, they should be written down, and organizations should encourage full use of logbooks, worksheets, checklists, etc. Verbal messages can be kept short, with the most critical elements emphasized at the beginning and repeated at the end. Assumptions should be avoided and opportunities for asking questions both given and taken. Furthermore, for critical operations such as towing or jacking an aircraft, or conducting an engine run, ensure all members of the team understand their roles, expectations and what to do if things go wrong. This extra communication may add time to tasks, but even one mishap will cost much more time to sort out, and it may cost someone his or her life.




Complacency can be described as a feeling of familiarity with a task accompanied by a loss of awareness of potential dangers. Such a feeling often arises when conducting routine activities that have become habitual and which may be considered by an individual (sometimes by the whole organization) as easy and safe. With less vigilance, important warning signs can be missed, with the individual only seeing what he, or she, expects to see. Complacency can also occur following a highly intense activity such as recovering from a possible disaster. The relief felt at the time can result in physical relaxation and reduced mental vigilance and awareness.

While too much pressure and demand cause over-stress and reduced human performance, too little results in under-stress, boredom, complacency and reduced human performance. It is therefore important when conducting simple, routine and habitual tasks, and when fatigued, to maintain an adequate, or optimum, level of stress through different stimulation. Always assume you can make a mistake if not careful. Following written instructions and adhering to procedures that increase vigilance, such as inspection routines, can provide suitable stimulus. It is important to avoid working from memory, assuming that something is okay when you haven’t checked it, and signing off work that you are unsure has been completed. Teamwork and mutual cross-checking will provide adequate stimulus when fatigued. If supervising, be actively involved in the activities of your subordinates in a positive, motivating way. Effective leadership is helping our Airmen stay actively engaged with their task by ensuring they perform with excellence, while also teaching them how to do so.



Lack of Knowledge

The regulatory requirements for training and qualification can be comprehensive, and organizations must enforce these requirements. Otherwise, lack of on-the-job experience and specific knowledge can lead workers into misjudging situations and making unsafe decisions. Aircraft systems are so complex and integrated that it is nearly impossible to perform many tasks without substantial technical training, current relevant experience and adequate reference documents. Furthermore, systems and procedures can change substantially, and employees’ knowledge can quickly become out-of-date.

It is important for employees to undertake continuing professional development and for the most experienced workers to share their knowledge with colleagues. Part of this learning process should include the latest knowledge on human error and performance. It should not be taken as a sign of weakness to ask someone for help or for information; in fact, this should be encouraged. Checklists and publications should always be referred to and followed, and never make assumptions or work from memory.

Finally, good leaders will help their subordinates see the value in investing in their own expertise. Encourage intellectual curiosity and independent study of the more technical subjects associated with aircraft maintenance. After all, wise investments in your knowledge of these subjects will better posture you for life after the Air Force as well, and there are many courses available for free such as those found here:




Distraction could be anything that draws a person’s attention away from the task on which they are employed. Some distractions in the workplace are unavoidable, such as loud noises, requests for assistance or advice, and day-to-day safety problems that require immediate solving. Other distractions can be avoided or delayed until more appropriate times, such as messages from home, management decisions concerning non-immediate work (i.e., shift patterns, leave entitlement, meeting dates, administrative tasks, etc.), and social conversations.

Psychologists say that distraction is the number one cause of forgetting things, hence the need to avoid becoming distracted and to avoid distracting others. Humans tend to think ahead. Thus, when returning to a task following a distraction, we have a tendency to think we are further ahead than we actually are.

To reduce errors from distraction, it is best to complete a task before responding. If the task cannot be completed without hurrying, then we can prominently mark (or “lock off”) the incomplete work as a reminder to ourselves and anyone else who may complete the work. When returning to work after being distracted, it is a good idea to commence at least three steps back, so that we retrace some steps before picking up the task again. If necessary, having someone else double-check our work using a checklist may be appropriate and useful.

Management has a role to play in reducing the distractions placed on its employees. This may involve good workspace design, management of the environment, and procedures that create “safety zones,” “circles of safety” or “do not disturb areas” around workers engaged in critical tasks.

Finally, when approached by a co-worker during a critical task, Airmen of all ranks are encouraged to respectfully communicate their need to complete the task before responding. If you need a minute to get to a logical pause in what you’re doing, say so. “Can I get back to you in 3 minutes? I’m on step 2 of 4 on this checklist, and I don’t want to miss anything.” “Sure! I didn’t realize you were in the middle of that. Just come see me when you’re done.”



Lack of Teamwork

In aviation many tasks and operations are team affairs. No single person (or organization) can be responsible for the safe outcomes of all tasks. However, if someone is not contributing to the team effort, this can lead to unsafe outcomes. This means that workers must rely on colleagues and other outside agencies, as well as give others their support. Teamwork consists of many skills that each team member will need to prove their competence.

Some of the key teamwork skills include leadership, followership, effective communication, trust building, motivation of self and others, and praise giving.

To create an effective team, it is necessary that the following issues, as appropriate, are discussed, clarified, agreed and understood by all team members:

  • A clearly defined and maintained aim, or goal(s)
  • Each team member’s roles and responsibilities
  • Communication messages and methods
  • Limitations and boundaries
  • Emergency procedures
  • Individual expectations and concerns
  • What defines a successful outcome
  • Debriefing arrangements
  • Team dismissal arrangements
  • Opportunities for questions and clarification

A team’s effectiveness also can be improved through the selection of team members to reflect a broad range of experience and skill sets, as well as through practice and rehearsal.

If you don’t understand how you fit into the team, or any of the key issues outlined above, speak up! Be that person who asks the obvious question everyone is thinking, and no one else is willing to ask. Good team players will ensure the team is all on the same page before any critical task.




Fatigue is a natural physiological reaction to prolonged physical and/or mental stress. We can become fatigued following long periods of work and following periods of hard work. When fatigue becomes a chronic condition, it may require medical attention; but workers should never self-medicate! As we become more fatigued, our ability to concentrate, remember and make decisions reduces. Therefore, we are more easily distracted, and we lose situational awareness. Fatigue will also affect a person’s mood, often making them more withdrawn and sometimes more irrational and angrier.

It is a human problem that we tend to underestimate our level of fatigue and overestimate our ability to cope with it. Therefore, it is important that workers are aware of the signs and symptoms of fatigue – in themselves and others. Fatigue self-management involves a three-sided program of regular sleep, healthy diet (including reduced use of alcohol and other drugs), and exercise. Work of a critical and complex nature should not be programmed during the low point on the body’s circadian rhythm (usually 3 to 5 a.m.). Additionally, when fatigued, always get someone else to check your work.

Moreover, it is estimated that 80 percent of the body’s calories are burned by the brain as it processes the complex problems we encounter on a daily basis. Some maintenance tasks are physically challenging, but just long hours of problem-solving and intense mental engagement can create fatigue as well.

Finally, if you feel tired, the mission may demand you continue, but it doesn’t mean you don’t communicate it to your team and your supervisor. If your decision-making is suffering, or your fatigue is otherwise making your situation hazardous for you or your teammates, your supervisor needs to know. Unfortunately, manpower and resources are always challenging, so fatigue alone may not result in dismissal from your duties, but it may result in additional help to ensure you don’t hurt yourself or others while you complete a shift. Furthermore, it will enable your supervisor to begin working a plan to adjust your schedule if warranted. If they don’t know, it may not be apparent to them the risks they are asking you to assume by operating in a sleep-deprived state.



Lack of Resources

If all the parts are not available to complete a maintenance task, then there may be pressure on a technician to complete the task using old or inappropriate parts. Regardless of the task, resources also include personnel, time, data, tools, skill, experience, knowledge, etc. A lack of any of these resources can interfere with one’s ability to complete a task. It may also be the case that the resources available, including support, are of a low quality or inadequate for the task.

When the proper resources are available and at hand, there is a greater chance that we will complete a task more effectively, correctly and efficiently. Therefore, forward planning to acquire, store and locate resources is essential. It also will be necessary to properly maintain the available resources. This includes the humans in the organization as well.

Ensure that resource shortfalls are communicated to your supervisor, and if you are a supervisor, ensure they are passed up the chain of command. Commanders may have to assume risk to complete mission tasks without sufficient resources, but they are relying on you to ensure they’re aware of where those gaps are. Don’t assume that someone else has informed leadership about the problem, and guard against cutting corners to “make it happen” without the required resources to complete the mission without unnecessary risk.




Pressure is to be expected when working in a dynamic environment, especially in combat. However, when the pressure to meet a deadline interferes with our ability to complete tasks correctly, then it has become too much. It is the old argument of quantity versus quality; and in aviation, we should never knowingly reduce the quality of our work. Pressure can be created by lack of resources, especially time, and from our own inability to cope with a situation. We may come under direct or indirect pressure from the organization/company, from clients and even our colleagues. However, one of the most common sources of pressure is within us. We put pressure on ourselves by taking on more work than we can handle, especially other people’s problems, by trying to save face and by positively promoting superpowers that we do not possess. These poor judgments are often the result of making assumptions about what is expected of us.

Learning assertiveness skills will allow a worker to say “No! Stop!” and communicate concerns with colleagues, customers and the organization. These skills are essential. When deadlines are critical, then extra resources and help should always be obtained to ensure the task is completed to the required level of quality.

The bottom line is that we need to generate airpower at the right time and place to achieve the desired effects in combat. However, a task done poorly may cause mission failure, and an on-time failure is still just that … failure.



Lack of Assertiveness

Being both unable to express our concerns and not allowing others to express their concerns creates ineffective communications and damages teamwork. Unassertive team members can be forced to go with a majority decision, even when they believe it is wrong and dangerous to do so.

Assertiveness is a communication and behavioral style that allows us to express feelings, opinions, concerns, beliefs and needs in a positive and productive manner. When we are assertive, we also invite and allow others to assert themselves without feeling threatened, undermined or that we’ve lost face. Speaking one’s mind assertively is not to be confused with aggression. It is about communicating directly, honestly and appropriately, giving respect to the opinions and needs of others without compromising our own standards.

Assertiveness techniques can be learned. They focus on keeping calm, being rational, using specific examples rather than generalizations, and inviting feedback. Most importantly, any criticisms should be directed at actions and their consequences rather than people and their personalities. This allows others to maintain their dignity and a productive conclusion to be reached.

Any Airman is empowered to call “Knock it off!” before a mishap occurs. Better to stop, take a breath and ensure critical steps haven’t been overlooked before metal gets bent or people get hurt.




There are many types of stress. Typically, in the aviation environment, there are two distinct types — acute and chronic. Acute stress arises from real-time demands placed on our senses, mental processing and physical body, such as dealing with an emergency or working under time pressure with inadequate resources. Chronic stress is accumulated and results from long-term demands placed on the physiology by life’s demands, such as family relations, finances, illness, bereavement, divorce or even winning the lottery. When we suffer stress from these persistent and long-term life events, it can mean our threshold of reaction to demands and pressure at work can be lowered. Thus, at work, we may overreact inappropriately, too often and too easily.

Some early visible signs of stress include changes in personality and moods, errors of judgment, lack of concentration and poor memory. Individuals may notice difficulty in sleeping and an increase in fatigue, as well as digestive problems. Longer-term signs of stress include susceptibility to infections, increased use of stimulants and self-medication, absence from work, illness, and depression.

It is important to recognize the early signs of stress and to determine whether it is acute or chronic. Coping with daily demands at work can be achieved with simple breathing and relaxation techniques. However, perhaps more effective is having channels of communication readily available through which to discuss the issue and help to rationalize perceptions. It is entirely appropriate that some of these channels involve social interaction with peers. As with fatigue, sleep, diet and exercise are all important factors in helping to reduce stress and build resilience to stressors. If the stress is chronic, then definite lifestyle changes will be required. This must be achieved with support from the organization. Organizations should, therefore, have employee assistance (or wellbeing) policies that include stress reduction programs.

As with many of these factors, communication is key. Let your supervisor know if your personal stressors are affecting you at work. They may not be aware of how factors external to what they see when you’re at work may be adding to your total stress. It may be that certain levels of stress on the job are unavoidable, but if it’s starting to increase the risk of a mishap, you need to let someone know so adjustments can be made wherever possible.



Lack of Awareness

Working in isolation and only considering one’s own responsibilities can lead to tunnel vision, a partial view, and a lack of awareness of how our actions can affect others and the wider task. Such lack of awareness may also result from other human factors, such as stress, fatigue, pressure and distraction.

One problem with “channelized” attention is that it will prevent you from noticing key events happening around you that may affect your task. If you’re so focused on prepping for an engine run that you fail to notice someone else “borrowed” your fire bottle before the start, you may wish you had been aware what was happening so you could intervene at the time, rather than having to delay for 30 minutes to go find the required fire suppression.

Additionally, you may lack awareness how the task you’re doing relates to everything that comes after it. Understanding the “why” will help you remember the “how” to do it correctly and “what” can result if you don’t. It is important to build experience throughout our careers, especially concerning the roles and responsibilities of those we work with and our own place in the wider team. Developing our foresight is essential in pre-empting the effects our actions may have on others. Furthermore, asking others to check our work and challenge our decisions is useful in gaining the relevant experience and expanding our awareness as well as theirs.

Combat lack of awareness through good communication and asking questions. If you don’t know “why” you’re doing something, ask! If your supervisor doesn’t have time to explain it, then hold on to your question and follow up with them once the task at hand is complete. If you are the supervisor, anticipate “why” questions and answer them as thoroughly as time/opportunity will allow. At a minimum, commend your subordinates for their curiosity, and always take advantage of an opportunity to teach. If you don’t know the answer, admit that, ask your supervisor, and follow back up with your Airmen when you do.




Workplace practices develop over time, through experience, and often under the influence of a specific workplace culture. These practices can be both, good and bad, safe and unsafe. They are referred to as “the way we do things round here,” which become norms. Unfortunately, such practices follow unwritten rules or behaviors, which deviate from the required rules, procedures and instructions. These norms can then be enforced through peer pressure and force of habit. It is important to understand that most norms have not been designed to meet all circumstances and, therefore, are not adequately tested against potential threats. They also lack flexibility when the broader situation changes. Norms that were good enough on fourth generation fighters may not work for fifth generation aircraft, especially when every mistake costs much more to repair.

Compliance with regulatory guidance should be the first norm in any maintenance organization. Rules and procedures have been designed and tested and, therefore, ought to be enforced and followed rigorously. Where workers feel pressure to deviate from a procedure, or work around it, then this information should be fed back so the procedure can be reviewed and amended, if necessary.

Norms can be tough to challenge because they are often deeply entrenched in the culture of the organization. However, if a norm is creating a hazardous environment, don’t accept it.  Study the written guidance and respectfully challenge the norm, using factual data wherever possible. This will require assertiveness and good communication, but if you’re new to the unit, you may be the only one who is still outside the culture enough to see the real risk the norm creates. This may mean you stay on the outside a little longer, which can be tough, but you may save a life. Change has to start somewhere with someone bold enough to ask tough questions.

Ultimately, if you have alerted your chain of command to unsafe norms without success, changing norms may require you to go outside of your unit. Consider talking to wing safety or the wing IG if needed rather than accept a hazardous situation.


NOTE: Below is a link to the Airman Safety App (ASAP), which provides Airmen the opportunity to report safety-related risks and close calls using the Airman Safety Action Report. Anyone, anywhere, with almost any device can quickly and easily report safety-related problems involving personnel, equipment or property. Remain anonymous if you wish. Reporting is the first step to obtaining a solution for improvement. Reporting is simple and only takes between 3 and 10 minutes. Click on the link below to start your report. It’s fast and easy!