Alan Hobbs

Associations between Errors and Contributing Factors in Aircraft Maintenance

In recent years cognitive error models have provided insights into the unsafe acts that lead to many accidents in safety-critical environments. Most models of accident causation are based on the notion that human errors occur in the context of contributing factors. However, there is a lack of published information on possible links between specific errors and contributing factors. A total of 619 safety occurrences involving aircraft maintenance were reported using a self-completed questionnaire. Of these occurrences, 96% were related to the actions of maintenance personnel. The types of errors that were involved, and the contributing factors associated with those actions, were determined. Each type of error was associated with a particular set of contributing factors and with specific occurrence outcomes. Among the associations were links between memory lapses and fatigue and between rule violations and time pressure. Potential applications of this research include assisting with the design of accident prevention strategies, the estimation of human error probabilities, and the monitoring of organizational safety performance.

Skills, rules and knowledge in aircraft maintenance: errors in context

Automatic or skill-based behaviour is generally considered to be less prone to error than behaviour directed by conscious control. However, researchers who have applied Rasmussens skill-rule-knowledge human error framework to accidents and incidents have sometimes found that skill-based errors appear in significant numbers. It is proposed that this is largely a reflection of the opportunities for error which workplaces present and does not indicate that skill-based behaviour is intrinsically unreliable. In the current study, 99 errors reported by 72 aircraft mechanics were examined in the light of a task analysis based on observations of the work of 25 aircraft mechanics. The task analysis identified the opportunities for error presented at various stages of maintenance work packages and by the job as a whole. Once the frequency of each error type was normalized in terms of the opportunities for error, it became apparent that skill-based performance is more reliable than rule-based performance, which is in turn more reliable than knowledge-based performance. The results reinforce the belief that industrial safety interventions designed to reduce errors would best be directed at those aspects of jobs that involve rule- and knowledge-based performance.

Unsafe acts and unsafe outcomes in aircraft maintenance

Road safety studies using the Driver Behaviour Questionnaire (DBQ) have provided support for a three-way distinction between violations, skill-based errors and mistakes, and have indicated that a tendency to commit driving violations is associated with an increased risk of accident involvement. The aims of this study were to examine whether the three-way distinction of unsafe acts is applicable in the context of aircraft maintenance, and whether involvement in maintenance safety occurrences can be predicted on the basis of self-reported unsafe acts. A Maintenance Behaviour Questionnaire (MBQ) was developed to explore patterns of unsafe acts committed by aircraft maintenance mechanics. The MBQ was completed anonymously by over 1300 Australian aviation mechanics, who also provided information on their involvement in workplace accidents and incidents. Four factors were identified: routine violations, skill-based errors, mistakes and exceptional violations. Violations and mistakes were related significantly to the occurrence of incidents that jeopardized the quality of aircraft maintenance, but were not related to workplace injuries. Skill-based errors, while not related to work quality incidents, were related to workplace injuries. The results are consistent with the three-way typology of unsafe acts described by Reason et al. (1990) and with the DBQ research indicating an association between self-reported violations and accidents. The current findings suggest that interventions addressed at maintenance quality incidents should take into account the role of violations and mistakes, and the factors that promote them. In contrast, interventions directed at reducing workplace injury are likely to require a focus on skill-based errors.

A circadian rhythm in skill-based errors in aviation maintenance.

In workplaces where activity continues around the clock, human error has been observed to exhibit a circadian rhythm, with a characteristic peak in the early hours of the morning. Errors are commonly distinguished by the nature of the underlying cognitive failure, particularly the level of intentionality involved in the erroneous action. The Skill-Rule-Knowledge (SRK) framework of Rasmussen is used widely in the study of industrial errors and accidents. The SRK framework describes three fundamental types of error, according to whether behavior is under the control of practiced sensori-motor skill routines with minimal conscious awareness; is guided by implicit or explicit rules or expertise; or where the planning of actions requires the conscious application of domain knowledge. Up to now, examinations of circadian patterns of industrial errors have not distinguished between different types of error. Consequently, it is not clear whether all types of error exhibit the same circadian rhythm. A survey was distributed to aircraft maintenance personnel in Australia. Personnel were invited to anonymously report a safety incident and were prompted to describe, in detail, the human involvement (if any) that contributed to it. A total of 402 airline maintenance personnel reported an incident, providing 369 descriptions of human error in which the time of the incident was reported and sufficient detail was available to analyze the error. Errors were categorized using a modified version of the SRK framework, in which errors are categorized as skill-based, rule-based, or knowledge-based, or as procedure violations. An independent check confirmed that the SRK framework had been applied with sufficient consistency and reliability. Skill-based errors were the most common form of error, followed by procedure violations, rule-based errors, and knowledge-based errors. The frequency of errors was adjusted for the estimated proportion of workers present at work/each hour of the day, and the 24 h pattern of each error type was examined. Skill-based errors exhibited a significant circadian rhythm, being most prevalent in the early hours of the morning. Variation in the frequency of rule-based errors, knowledge-based errors, and procedure violations over the 24 h did not reach statistical significance. The results suggest that during the early hours of the morning, maintenance technicians are at heightened risk of “absent minded” errors involving failures to execute action plans as intended. (Author correspondence: alan.hobbs@nasa.gov)

Human factor determinants of worker safety and work quality outcomes

The circumstances leading up to 619 safety occurrences that occurred during aircraft maintenance were examined. Ninety-six per cent of the occurrences were at least partly attributable to human actions and in most cases, these actions took the form of errors. The most frequent errors were memory lapses, rule violations and skill-based slips. Worker safety occurrences tended to be preceded by skill-based slips, whereas work quality occurrences tended to be preceded by memory lapses. It is apparent that safety interventions must take into account the associations between error forms and outcomes.

Unmanned Aircraft Systems

Publisher Summary Unmanned aviation may appear to be a recent development, but its history stretches back to the beginnings of aviation. The first unmanned glider flew a century before the Wright Flyer, and unpiloted, powered aircraft made their appearance in the first decades of the 20th century. Over the last 100 years, a series of technological innovations have expanded the capabilities of unmanned aircraft to the point where they now fulfill an increasing range of civilian and military roles. The central message of this chapter is that the further development of unmanned aviation may be held back more by a lack of attention to human factors than by technological hurdles. This chapter begins with a brief overview of unmanned aircraft systems (UAS), from their historical beginnings to the present. Next, the accident record of unmanned aviation is reviewed. The emerging human factors of UAS operation are then examined under the broad headings of teleoperation, design of the ground control station (GCS), transfer of control, airspace issues, and maintenance. If unmanned systems are to reach their full potential, it will be necessary to address each of these issues.

Defining Reliability and Robustness from a Human Factors Perspective

A human factors team was tasked with assessing best practices for developing a crewed space vehicle that is both reliable and robust. The team identified two broad dimensions of human factors relevant to reliability and robustness, namely, the attributes of the product, and the processes used to develop the product. The “product” includes hardware, software, documentation, training systems, and procedures throughout all phases of the system life, including construction, testing, operation and maintenance. Three key attributes of the product are the extent to which task demands are within human capabilities, the capacity of the system to cope with human error, and the ability of the system to make use of unique human capabilities during non-routine situations. The “process” dimension of human factors relates to the human systems engineering program that starts in the early stages of design, and continues throughout the life of the system. There are, of course, no guarantees that a formal consideration of human factors throughout the design process will identify all the relevant human issues. However, in the absence of such a consideration, problems are virtually assured.