**5. Human factors analysis and classification system framework**

#### **5.1 HFACS basics**

Although the concept of Swiss-cheese model changed the way aviation and other accident investigators view human error, it did not provide the level of detail necessary to apply in the real world. There was a need to have a comprehensive tool for investigating and analyzing human error associated with accidents and incidents. This necessitated the development of the Human Factors Analysis and Classification System (HFACS) [32].

The HFACS framework adapted from [33] is shown in **Figure 6**. The HFACS framework has a total of 19 causal categories identified within the four levels of human failure. By using the HFACS framework for accident investigation, organizations are able to identify the breakdowns within the entire system that allowed an accident to occur. HFACS can also be used proactively by analyzing historical events to identify recurring trends in human performance and system deficiencies. Both of these methods will allow organizations to identify weak areas and implement targeted, data-driven interventions that will ultimately reduce accident and injury rates.

Most accidents can be traced to one or more levels of failure related to organizational influences (three causal categories), unsafe supervision (four causal categories), preconditions for unsafe acts (seven causal categories), and the unsafe acts themselves (five causal categories).

#### **5.2 Application of human factors knowledge to aviation accidents**

HFACS provides a structure to review and analyze historical accident and safety data. By breaking down the human contribution to performance, it enables the analyst to identify the underlying factors that are associated with an unsafe act. The HFACS framework may also be useful as a tool for guiding future accident investigations in the field and for developing better accident databases, both of which would improve the overall quality and accessibility of human factors accident data. Common trends within an organization can be derived from comparisons of psychological origins of the unsafe acts or from the latent conditions that allowed these acts within

**Figure 6.** *The HFACS framework.*

the organization. Identifying those common trends supports the identification and prioritization of where intervention is needed within an organization.

By using HFACS, an organization can identify where hazards have arisen historically and implement procedures to prevent these hazards resulting in improved human performance and decreased accident and injury rates. The HFACS framework has been successfully applied to analyze accidents in military, commercial, and general aviation sectors [33–39].

An example of analysis using HFACS is shown in **Figure 7** from the data available in [36], considering a total of 1020 aircraft (181 carrier aircraft and 839 commuter aircraft) accidents involving aircrew or supervisory error for the period 1990–2002. Accidents classified as having "undetermined causes" and those that were attributed to sabotage, suicide, or criminal activity are not included in the analysis. Commercial aviation accident data obtained from the NTSB databases were used in the analysis. Numbers 1 through 18 on the abscissa represent the 19 causal categories in the HFACS framework. Note that routine and exceptional violations have not been shown separately, but as a single number represented as 18 on the abscissa.

The HFACS framework has been applied by several researchers to analyze and understand the cause of accidents in aviation and a number of other domains such as rail, maritime, construction, mining, and nuclear power. A consolidated review is available in [40], where the authors conclude that HFCAS can help in analysis to

*Role of Human Factors in Preventing Aviation Accidents: An Insight DOI: http://dx.doi.org/10.5772/intechopen.106899*

**Figure 7.** *Example of HFACS analysis applied to 1020 commercial aviation accidents.*

identify both latent and active factors underpinning accidents. The development history of 29 different accident causation models and a new 24Model that discusses linear as well as nonlinear accident causation methods is presented in [41]. In 24Model, the cause of the accident is attributed at individual and organizational levels to immediate cause, indirect cause, radical cause, and root cause.

#### **6. A relook at human factors**

In this section, we try to look at human factors and their role in the prevention of aviation accidents from a different perspective. Referring to **Figure 8**, the total environment within which aviation accidents happen is marked by the largest circle and represents the overall domain. The seven smaller circles within this domain represent seven possible sources from where the "holes in the cheese" can get triggered or generated. Each of these seven segments also needs to have closely knit coordination with rest of the segments to ensure that human errors are minimized and do not propagate through the system resulting in accidents and fatalities. A brief description of the seven segments is provided in the following paragraphs.

#### **6.1 The seven-segment model**

#### *6.1.1 Design organization*

This segment covers all the activities commencing from conceptual design of an aircraft till its certification. Design drivers are based on market demand, customer preferences, requirement of reduction in carbon emissions, increase in traffic growth, profit margins, and design modifications to existing aircraft as well. Design organization coordinates and interacts mainly with regulatory body and production organization in achieving its objectives.
