A total of 1359 questionnaires were returned, representing a response
rate of ∼28%. Of the returned surveys, 945 were from airline maintenance
personnel. The remaining surveys were from non-airline technicians
who worked on general aviation aircraft, typically small private planes
that are usually maintained during standard business hours. Because of
the small number of shiftworkers among the non-airline respondents,
their responses were excluded from further analysis. Some 402 of the
airline maintenance personnel reported maintenance incidents, providing
369 descriptions of errors in which the time of the incident was
reported and sufficient detail was available to classify the error. Of these,
177 were classified as skill-based errors, 68 as rule-based mistakes, 55 as
knowledge-based mistakes, and 69 as procedure violations. In 58% of
cases, the reporter indicated that they had been involved in the incident;
in the remaining cases, the reporters indicated that they had witnessed
the incident. Fifty-six percent of the cases had occurred within the last
year, the remaining cases had occurred prior to this