Dirty Dozen in Aviation Maintenance: The 12 Human Factors

The dirty dozen in aviation maintenance are twelve human factors that degrade a technician’s ability to work effectively and safely and can lead to maintenance errors: Lack of Communication, Complacency, Lack of Knowledge, Distraction, Lack of Teamwork, Fatigue, Lack of Resources, Pressure, Lack of Assertiveness, Stress, Lack of Awareness and Norms (Aviation Maintenance Technician Handbook - General, FAA-H-8083-30B, ch. 14, pp. 14-13 to 14-27). Transport Canada identified them after a large number of maintenance-related accidents and incidents in the late 1980s and early 1990s, and the aviation industry adopted them as a straightforward way to discuss human error in maintenance (p. 14-13). They are part of the Human Factors subject on the A&P General written test.

The 12 human factors in aviation maintenance, one by one

The names below are exactly as the handbook gives them, in the order its text covers them. Each has the handbook’s meaning, a short example we made up to show what it looks like in a hangar, and the safety net from the handbook’s “Mitigating the risk” box for that factor. Page and figure numbers are from FAA-H-8083-30B, chapter 14.

1. Lack of Communication

What it is: Missing or unclear information between people, which can lead to incorrect or faulty maintenance. Shift change is the classic risk point (pp. 14-13 to 14-14).

Shop example (made up): The night shift reconnects a fuel line but runs out of time before torquing the fitting. Nobody mentions it at handover, and the day shift closes the panel.

Safety net: Use logbooks and worksheets to communicate what was done, never assume work has been completed, and tell the next shift exactly what still needs doing (Figure 14-18). Continue someone else’s job only after a face-to-face meeting, or a phone call if you cannot meet (p. 14-14).

2. Complacency

What it is: False confidence that builds with experience, so a repetitive inspection item gets skipped because it has never had a fault. Working without documentation, or documenting work not performed, are signs of it (p. 14-14).

Shop example (made up): A mechanic has checked the same control cable pulley on many inspections without finding wear, so this time they initial it without opening the panel.

Safety net: Go in expecting to find a fault, check your own work a second time, and never sign for an item you have not fully inspected (Figure 14-19). Read the item and confirm it was done before you sign (p. 14-14).

3. Lack of Knowledge

What it is: Doing a job without the training or current data it needs, which can lead to a faulty repair. Differences between aircraft and updated procedures make this easy to fall into (p. 14-14).

Shop example (made up): A technician who knows one model well uses a familiar rigging value on a similar-looking model without opening that model’s manual.

Safety net: Work only on what you are trained for, get help from someone who knows the job, and confirm the manual you are using is current (Figure 14-20). If needed, contact the manufacturer’s technical representative: it is better to delay a procedure than do it incorrectly (p. 14-15).

4. Distraction

What it is: Anything, mental or physical, that pulls your attention off the task, so a step gets skipped when work resumes. The handbook estimates that 15 percent of maintenance-related errors are caused by distractions (p. 14-15).

Shop example (made up): A mechanic is safety wiring a row of bolts when the phone rings. They come back sure the last bolt was already wired. It was not.

Safety net: Go back three steps from where the distraction happened and resume from there, tag incomplete work, and lock wire or torque fasteners right after each step (p. 14-16). Secure tools and parts before leaving the area and use a detailed checklist (Figure 14-21).

5. Lack of Teamwork

What it is: People not working together toward one outcome. Teamwork means everyone understands and agrees on the actions to be taken, as in a gear swing or other operational check (p. 14-16).

Shop example (made up): Two technicians do a gear swing. Each assumes the other watched the downlock indication, so nobody did.

Safety net: Keep people talking, watch out for each other’s safety, and agree who does what before any job that needs more than one person (Figure 14-22).

6. Fatigue

What it is: A reduction in cognitive ability, decision-making, reaction time, coordination, speed, strength or balance. The primary cause is lack of sleep, and a fatigued person may still feel wide awake (p. 14-16).

Shop example (made up): At the end of a double shift, a technician starts a complex rigging job alone because “it will only take an hour.”

Safety net: Look for the symptoms in yourself and co-workers, keep regular eating, exercise and sleep patterns, and give up complex tasks if you know you are exhausted (Figure 14-23). Have others check your work. The handbook recommends eight to nine hours of sleep a day (p. 14-17).

7. Lack of Resources

What it is: Not having the parts, tools, technical documentation or support to do the job properly (pp. 14-18 to 14-21). The handbook’s own example: an aircraft weighed without the proper load cells slipped off one, and the jack point creased the spar (p. 14-20).

Shop example (made up): The shop has no bearing puller, so someone levers the bearing off with a pry bar.

Safety net: Order anticipated parts early, maintain your equipment, never fit an incompatible part to get the job done, and stop the work until the proper parts are available (Figure 14-25).

8. Pressure

What it is: Constant pressure to work faster without mistakes, from schedules and costs, or self-induced when you take ownership of a situation that was not of your doing (p. 14-22).

Shop example (made up): A charter flight is due out in 40 minutes, so the mechanic rushes a brake job and skips the final check.

Safety net: Check that the pressure is not coming from you, get extra help when time is short, and speak up early if a repair needs more time instead of rushing it (Figure 14-27). Raise unrealistic or unsafe time limits with management (p. 14-22).

9. Lack of Assertiveness

What it is: Not voicing concerns when something is wrong. Assertiveness means expressing your feelings, opinions, beliefs and needs in a positive, productive way, and is not the same as being aggressive (p. 14-22).

Shop example (made up): A new technician sees a senior mechanic skip a torque check but says nothing.

Safety net: State the problem directly, explain the consequences, propose solutions and ask for feedback (pp. 14-22 to 14-23). Give clear feedback when you see a risk, accept correction from co-workers, and hold to your standards (Figure 14-28).

10. Stress

What it is: The subconscious response to the demands placed on a person (Figure 14-29). Stressors are physical (temperature, noise, lighting, confined spaces), psychological (work, money, relationships) or physiological (fatigue, poor physical condition, hunger, disease) (pp. 14-24 to 14-25).

Shop example (made up): A technician works in a cramped, poorly lit tail cone in a hot hangar while worrying about a family problem.

Safety net: Take time off or a short break, eat well, exercise and rest, and ask a co-worker to monitor your work (Figure 14-29).

11. Lack of Awareness

What it is: A failure to recognize all the consequences of an action, or a lack of foresight. It grows after doing the same task many times, so treat each task as if it were the first time (p. 14-26).

Shop example (made up): A technician installs a new antenna doubler without noticing it overlaps an earlier repair on the same skin panel.

Safety net: Look for any earlier modification or repair your work could clash with, and have a co-worker check your work however experienced you are (Figure 14-30).

12. Norms

What it is: Short for “normal,” the way things are normally done: unwritten rules followed or tolerated by most of an organization. Taking shortcuts, working from memory and not following procedures are unsafe norms, and newcomers spot them more easily than long-standing members (pp. 14-26 to 14-27).

Shop example (made up): “We never torque those clamps, hand tight is fine.” Everyone does it, so the new hire does too.

Safety net: Hold everyone to one standard, remember the easiest way is not always the approved way, and do not treat a habit as correct just because it feels normal (Figure 14-31).

Why the dirty dozen matters in aviation

The handbook says that, historically, 20 percent of all accidents are caused by machine failure and 80 percent by human factors, and that breaking the chain of events at the maintenance level can drastically reduce the chance of an accident (p. 14-29).