CONSIDERING BOTH ERRORS AND VIOLATIONS
Because errors have been the focus of much research, there are many more theories about why errors occur than why violations occur. However, errors and violations often occur together to produce an unwanted outcome. Data from the U.S. Navy suggests that:
- Approximately 60 percent of maintenance events are caused by an error only.
- Approximately 20 percent of these events are caused by a violation only.
- Approximately 20 percent of these events are caused by an error and a violation
(see fig. 2 and fig. 3).
In this example, a mechanic does not use a torque wrench (violation), which leads to an engine in-flight shutdown (event). There are reasons why (contributing factors) the violation occurred (e.g., unavailable torque wrench or work group norm is not to use a torque wrench).
In this example, the mechanic mistakenly misses a step in the airplane maintenance manual (contributing factor), which leads to an incomplete installation (error). The mechanic decides not to carry out the operational check (violation), thereby missing the fact that the task was not done correctly. Because an error was made and this was not caught by the operational check, an engine in-flight shutdown (event) occurs.