Human Factors in Aviation Maintenance
Colin G. Drury State University of New York at Buffalo
Before human factors techniques can be applied appropriately in any system, the system itself must be well understood by the human factors engineers. The following description of aviation maintenance and inspection emphasizes the philosophy behind the system design, and the points where there is potential for operator error.
An aircraft structure is designed to be used indefinitely provided that any defects arising over time are repaired correctly. Most structural components do not have a design life, but rely on periodic inspection and repair for their integrity. There are standard systems for ensuring structural safety (e.g., Goranson & Miller, 1989), but the one that most concerns us is that which uses engineering knowledge of defect types and their time histories to specify appropriate inspection intervals. The primary defects are cracks and corrosion (which can interact destructively at times), arising respectively from repeated stretching of the structure from air or pressure loads, and from weathering or harmful chemicals. Known growth rates of both defect types allow the analyst to choose intervals for inspection at which the defects will be both visible and safe. Typically, more than one such inspection is called for between the visibility level and the safety level to ensure some redundancy in the inspection process. As the inspection system is a human/machine system, continuing airworthiness has thus been redefined by the design process from a mechanical engineering problem to a human factors one. Inspection, like maintenance in general, is regulated by the Federal Aviation Administration (FAA) in the United States, the Civil Aviation Authority (CAA) in the United Kingdom, and equivalent bodies in other countries. However, enforcement can only be of following procedures (e.g., hours of training and record keeping to show that tasks have been completed), not of the effectiveness of each inspector. Inspection is also a complex sociotechnical system ( Taylor, 1990), and as such, can be expected to exert stresses on the inspectors and on other organizational players ( Drury, 1985).
Maintenance and inspection are scheduled on a regular basis for each aircraft, with the schedule eventually being translated into a set of workcards for the aircraft when it arrives at the maintenance site. Equipment that impedes access is removed (e.g. seats, galleys).