provides dramatic examples of the relationship between safety and human factors. In 1977, two Boeing 747s collided on a runway at Tenerife in the Canary Islands, the worst commercial aircraft disaster in history. As with any major accident, several factors were involved, but a critical one was the misunderstanding in voice communications between the controller and the captain of one of the aircraft. As a consequence of this disaster, major efforts were made to standardize communications procedures in international airspace.

Examples do not have to be large scale or sensational to be convincing. Every industry has modest but compelling instances of discomfort, injuries, illnesses, or accidents that could be prevented with greater attention to human factors. An example is the large number of slips and falls that happen on the ground under ordinary circumstances.

Human factors experts not only must be able to identify particular areas where safety improvements could be made, but also must be prepared to demonstrate, in clear and specific terms, how their involvement will appreciably improve the existing situation. They must take into account both the human side of the equation—a healthier, safer, happier workforce—and the monetary side, such as cost savings due to fewer absences, lower medical fees, reduced insurance and workers' compensation costs, and fewer lawsuits.

Human factors practitioners confront the fact that human characteristics among individuals are variable. These characteristics include physical dimensions; personality states and traits; knowledge, skills, and aptitudes; cognitive schema and style; motivation; and a host of behavioral attributes—which collectively contribute to variability in human performance. Maximizing system reliability and performance requires effectively addressing the most variable component—the human.

Some human factors practitioners consider human variability the Achilles' heel of human factors. But many consider the challenge of managing human variability a core competency of human factors that should be highlighted during discussions of organizational strategic planning. Management of human variability requires the application of human factors principles,