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The Human Factors "Dirty Dozen" Cheat Sheet (DRAFT) by [deleted]

The Human Factors Dirty Dozen

This is a draft cheat sheet. It is a work in progress and is not finished yet.


The Dirty Dozen refers to twelve of the most common human error precon­dit­ions, or conditions that can act as precur­sors, to accidents or incidents. These twelve elements influence people to make mistakes. The Dirty Dozen is a concept developed by Gordon Dupont, in 1993, whilst he was working for Transport Canada, and formed part of an elementary training programme for Human Perfor­mance in Mainte­nance. It has since become a corner­stone of Human Factors in Mainte­nance training courses worldwide, as exempl­ified in UKCAA CAP715[1].

The Dirty Dozen is not a compre­hensive list of human error accident precur­sors, for example, ICAO Circular 240-AN­/144[2] lists over 300 human error precur­sors. However, since 1993 all areas of the aviation industry, not just aircraft mainte­nance, have found the Dirty Dozen a useful introd­uction to open discus­sions into human error in their busine­sses, organi­sations and workpl­aces. So, it may be possible to find Dirty Dozen lists for pilots, ramp workers, air traffic contro­llers and cabin crew.

1 .Count­erm­easures

Whilst The Dirty Dozen list of human factors has increased awareness of how humans can contribute towards accidents and incidents, the aim of the concept was to focus attention and resources towards reducing and capturing human error. Therefore, for each element on The Dirty Dozen list there are examples of typical counte­rme­asures designed to reduce the possib­ility of any human error from causing a problem.

2. 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 common that only 30% 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 organi­sations should encourage full use of logbooks, worksh­eets, and checklists etc. Verbal messages can be kept short, with the most critical elements emphasised at the beginning and repeated at the end. Assump­tions should be avoided and opport­unities for asking questions both given and taken.

3. Compla­cency

Compla­cency can be described as a feeling of self-s­ati­sfa­ction 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 organi­sat­ion), as easy and safe. A general relaxation of vigilance results and important signals will 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. This particular psycho­logical experience is referred to as a Lacuna.

Whilst too much pressure and demand causes 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 expect to find a fault! 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 ok 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.

4. Lack of knowledge

The regulatory requir­ements for training and qualif­ication can be compre­hen­sive, and organi­sations are forced to strictly enforce these requir­ements. However, 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 a 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.

5. Distra­ction

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 (e.g. 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 re-trace 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 have a role to play in reducing the distra­ctions placed on their 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.

7. Lack of teamwork

In aviation many tasks and operations are team affairs; no single person (or organi­sation) 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 can also be improved through the selection of team members to reflect a broad range of experience and skill sets, and also through practice and rehearsal.

8. Fatigue

Fatigue is a natural physio­logical reaction to prolonged physical and/or mental stress. We can become fatigued following long periods of work and also 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, but sometimes more irrational and angry.

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 programme 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 03:00 – 05:00am); and, when fatigued always get someone else to check your work.

9. 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 and 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 to 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 will also be necessary to properly maintain the resources that are available; this includes the humans in the organi­sation as well.

10. Pressure

Pressure is to be expected when working in a dynamic enviro­nment. 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 also from our own inability to cope with a situation. We may come under direct, or indirect, pressure from the Company, from clients and even our collea­gues. However, one of the most common sources of pressure is ourselves. 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 super powers that we do not possess. These poor judgements 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 Company. These skills are essential, and 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.

11. Lack of assert­iveness

Being both unable to express our concerns and not allowing other 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 behavi­oural 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, but honestly and approp­ria­tely; giving respect to the opinions and needs of others, but not compro­mising our own standards.

Assert­iveness techniques can be learnt and they focus on keeping calm, being rational, using specific examples rather than genera­lis­ations, 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.


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.

The situation of stress arising from lack of stimul­ation at work has been covered above under Compla­cency above.

Some early visible signs of stress include changes in person­ality and moods, errors of judgement, 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 recognise 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 ration­alise 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 Company. Companies ought therefore, to have employee assistance (or wellbeing) policies that include stress reduction progra­mmes.

11. 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 the affect our actions can have on others and the wider task. Such lack of awareness may also result from other human factors, such as stress, fatigue, pressure and distra­ction.

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 affects our actions may have on others. This is an attitude of profes­sio­nalism and involves constant questi­oning “what if …?” Asking others to check our work and challenge our decisions is useful in gaining the relevant experience and expanding our awareness. Vigilance is closely related to situat­ional awareness, and workplace proced­ures, such as scanning, two-way commun­ication and use of checklists will help to maintain vigilance.

12. Norms

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” and become Norms. Unfort­unately such practices follow unwritten rules or behavi­ours, 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.

Rules and procedures should 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 that the procedure can be reviewed and amended, if necessary. Developing assert­iveness can allow workers to express their concerns about unsafe Norms, despite peer pressure.