1. 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

2. 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

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

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

5. 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.

6. 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

7. 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

8. 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

9. 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

10. The end