Human Error Analysis of Commercial Aviation Accidents: Application of the Human Factors Analysis and Classification System (HFACS) Douglas A. Wiegmann, Ph.D. & Scott A. Shappell, Ph.D. Andrew Wright PSYCH 562 Week 10: Forensic Investigation

Main takeaways… Accident investigation process is better for mechanical failures than human factors failures HSACS looks at unsafe acts and their causal factors such as organizational climate Authors conclude that HSACS could provide a good base for more applied / specific human error analysis methods

Process for investigating and preventing aviation accidents involving mechanical failures Start and finish at accidnt

Process for investigating and preventing aviation accidents involving human errors Fad-driven!

Aviation Accidents 70-80% of aviation accidents involve human error The authors have some criticism of accident investigation processes Proposed HFACS as a better way of understanding the human error component of aviation accidents HFACS is based on Reason’s model of active vs. latent failures, the so-called “swiss cheese” model HFACS is based on Reason’s model of active vs. latent failures was originally developed for the military. Reason’s theory gave some emphasis on supervisory facotrs. Swiss cheese model. It likens human systems to multiple slices of swiss cheese, stacked side by side, in which the risk of a threat becoming a reality is mitigated by the differing layers and types of defenses which are "layered" behind each other. the principle behind layered security The Swiss cheese model of accident causation illustrates that, although many layers of defense lie between hazards and accidents, there are flaws in each layer that, if aligned, can allow the accident to occur.

HFACS HFACS is based on Reason’s model of active vs. latent failures Says error taxonomies ignore things like fatigue, attitudes etc. (not any more) Four levels of unsafe acts: Operator, Preconditions, Supervision, and Organizational Active failures encompass the unsafe acts that can be directly linked to an accident, such as (in the case of aircraft accident pilot error. Latent failures include contributory factors that may lie dormant for days, weeks, or months until they contribute to the accident. Latent failures span the first three domains of failure in Reason's model

Overview of HFACS 1 Unsafe acts, (honest) errors, decision, skill-based (unbconscious0, and perceptual, violations routine eg. slightly speeding and exceptional – going super fast 2. Preconditions - Substandard conidtions – fatigue, situational awarenss loss, spatial disorientation, substandard practices 3. Unsafe supervision inadequate, planned Organizational 4. Resource management, safety goals etc A linear model

Accident Data & HFACS categories 1 Unsafe acts, (honest) errors, decision, skill-based (unbconscious0, and perceptual, violations routine eg. slightly speeding and exceptional – going super fast 2. Preconditions - Substandard conidtions – fatigue, situational awarenss loss, spatial disorientation, substandard practices 3. Unsafe supervision inadequate, planned Organizational 4. Resource management, safety goals etc A linear model

Results, discussion & conclusions HFACS could accommodate all 319 causal factors associated with 119 CAF and 135 Scheduled Air Carriers between 1990 and 1996 Had a 76% reliability between coders re agreement of the classifications. This is quite a bit lower than military data Skill-based errors were the highest source. They did drop later in the study, but not clear why or if it was significant CRM and decision errors did not drop (in spite of interventions e.g. trainings to try and reduce) CAF = code of federal regulations, 76% not that high Thy think the military was higher because they had better data They did graph skill vased, decion errors, vilations etc ,.did not need to show that

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