Human Systems Integration Division @ NASA Ames

Accident statistics for the worldwide commercial jet transport industry show maintenance as the "primary cause factor" in a relatively low 4% of hull-loss accidents, compared with flight crew actions that are implicated as a "primary cause factor" in more than 60% of accidents. Yet such statistics may understate the significance of maintenance as a contributing factor in accidents. When safety issues are presented alongside the fatalities that have resulted from them on worldwide airline operations,
deficient maintenance and inspection emerges as the second-most-serious safety threat after controlled flight into terrain. According to former NTSB Board member John Goglia, maintenance has been implicated in 7 of 14 recent U.S. airline accidents.

While it may be tempting to consider that the lessons learned about human performance in other areas of aviation will translate readily to maintenance, some of the challenges facing maintenance personnel are unique. Maintenance technicians work in an environment that is more hazardous than all but a few other jobs in thelabor force. The work may be carried out at heights, in confined spaces, in numbing cold, or sweltering heat. Hangars, like hospitals, can be dangerous places. We know from medicine that iatrogenic injury (unwanted consequences of treatment) can be a significant threat to patient health. In maintenance, as in surgery, instruments are occasionally left behind, problems are sometimes misdiagnosed, and operations are occasionally performed on the wrong part of the "patient." Aircraft and human patients also have another common feature in that many systems are not designed for easy access or maintainability.

To understand maintenance deficiencies, we need to understand the nature of the work performed by maintenance personnel, and the potential for error that exists in maintenance operations. It is relatively easy to describe the work of maintenance personnel at a physical level: They inspect systems; remove, repair, and install components; and deal with documentation. Yet, like virtually every human in the aviation system, maintenance personnel are not employed merely to provide muscle power. They are needed to process information, sometimes in ways that are not immediately apparent. In order to uncover latent failures in aviation maintenance, we must recognize the invisible cognitive demands and pressures that confront maintenance personnel.