Are mistakes Repeated?
One question that human-factors professionals are often asked is whether a mechanic will make the same mistake a second, third, or fourth time while performing a task. For instance, if a mechanic adds oil to the right engine and forgets to secure the oil cap, will this same mechanic be less likely to secure the oil cap on the left engine after adding oil to the left engine? In addition, if the mechanic remembers to secure the cap on the left engine, will he or she then remember that the oil cap cover on the right engine was not secured?

According to the Boeing Commercial Airplanes Maintenance Human Factors organization, the question has multiple results that can be affected by various factors called performance-shaping factors (PSF). External PSFs are such things as lack of positive-lock feedback or task sequence interruption. Internal PSFs are such things as distraction due to multitasking. In a sample scenario, a mechanic does not secure an oil cap on engine no. 1. If the same external PSF that caused the mechanic to not secure the cap on engine no. 1 is present on the remaining engines, and if no other factors are present, then the mechanic probably will not secure the cap correctly on the other engine. However, if a mechanic fails to secure an oil cap on engine no. 1 because of either external or internal PSFs (for example, distraction caused by multitasking), then the mechanic may or may not do the task correctly on engine no. 2. The difference is in the sequence in which the task is performed, and the relative impact that each PSF has in causing the mechanic to make decisions at the time. In the example of the BAe 146 cited in the main story, maintenance was performed on all four engines: On three of the engines, the oil seals were left off; on the remaining engine, the seals were installed.

Because it appears that cues play an important role in how a maintenance task is ultimately accomplished, operators should consider the cues that the mechanics are likely to encounter when they perform a task. These cues can be explicit (such as written on a task card) or implicit (cues that are assumed to be present).

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