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ALC-107: Dirty Dozen - Human Error In Aircraft Maintenance
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The human condition is that we make mistakes. Mistakes are not only common they are universal. People make mistakes because they are people, not because they are deficient in some way. Error and success result from the same mental processes so we cannot experience one without the other. Since aviation is terribly unforgiving of human error, we cannot afford to allow mistakes to “escape” and erode the safety of our system. This course covers twelve common error preconditions and the error capture methods that may prevent them from having tragic consequences.

Gordon DuPont while working with Transport Canada developed the “The Dirty Dozen” The Dirty Dozen is a poster series highlighting 12 preconditions for unsafe acts. These twelve preconditions are not a comprehensive list. As illustrated by ICAO’s Circular 240, “Investigation of Human Factors in Accidents and Incidents” which lists over 300 such human error precursors. It is our hope this course will encourage you to openly discuss human error, and those things that influence people to make mistakes.

This course covers the following 12 preconditions for unsafe acts:

  • Fatigue
  • Stress
  • Complacency
  • Communication
  • Awareness 
  • Distraction
  • Lack of knowledge
  • Teamwork
  • Lack of resources 
  • Pressure
  • Lack of assertiveness
  • Norms


Perhaps more important than the 12 examples of preconditions to unsafe acts is the concept of safety nets designed to reduce the possibility an error will cause a problem. The safety nets included in this course are examples of good safety nets. Airmen do the true work of error capture as they account for the hazards of their own workplace, tools and mission.

Click on Chapter 1 above or below to get started. 

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