A commonly used statistic is that 70% of aviation accidents are a result of human error. This statistic has been commonly accepted for the past few decades but conceals a more troubling truth. If 70% of aviation accidents are caused by human error, what are the other 30% caused by?

The most common answer is that these are down to technical failures. However, machines don’t fail by themselves. If part of an aircraft breaks it is either because it has been designed incorrectly (the design is insufficient for its intended purpose), it has been built or maintained incorrectly or has been used in the wrong way. When you probe into the “technical accidents”, human error will be involved somewhere. With the possible exception of a completely freak accident that no one could possibly predict (e.g. a plane being hit by a falling meteorite), every accident, incident and near miss will have some element of human involvement in the sequence of events leading up to it.

If human error is everywhere, why do we insist on classifying accidents and incidents as human related or technical related?

The short answer is that this classification is something of a fallacy. Once an accident cause has been determined as human error (especially when it is so called “pilot error”), the reaction of the people with a stake in determining its cause is that an isolated, one-off, human mediated event has occurred and that this can be easily corrected by dealing with the human, perhaps by firing them or by retraining them. Nothing could be further from the truth. The quality and success of the complex interactions between humans and other humans, humans and machines and the associated procedures that are used to achieve this are at the root of aviation safety.

We have mentioned humans, machines and procedures. Within organisations, these components come together to form systems. Systems are groups of components working together towards a common goal. During the 1970s, this idea of systems was expanded to cover human factors in the aviation industry and led to the development of the SHEL model, SHEL being the acronym of its 4 component types as shown below:

The environment refers to the physical environment, the liveware refers to the human components, hardware refers to the machine components and software refers to any procedures. As you can see from the diagram, there is liveware at the centre of the model. This liveware is the human operators whose job we are looking at. That human operator will need to interact with machines (hardware), with procedures (software) and with other people (liveware). All of this is done in some sort of environment. Aside from the teasing out the individual component types that are present within most systems, the real insight that the original designers of this model had was to highlight the interfaces between components, i.e. the points where the squares touch. As well as wanting to optimise the components themselves, we also need to consider how we can optimise the interfaces between components.

Although the SHEL model can serve as the foundation for our understanding of human factors, in order to make it more relevant to aviation, it can be adapted in a few ways:

1) Firstly, to give us a point of focus, lets make the human in the centre of the model more prominent

2) The environment affects all the components of the model

3) The software (procedures) is also used by the central liveware to interact with the other liveware and hardware

4) There can also be direct, non-procedural interaction between the central liveware and the other other liveware and hardware.

These adaptations give us an aviation-specific SHEL model as shown below:

Human factors in aviation is about optimising the pilot, optimising the direct interaction between the pilot and the other pilot (and any other humans), optimising the interaction between the pilot and the aircraft and, finally, optimising the procedures through which the pilot can interact with the other pilot (or other humans) and the aircraft. Doing this requires expertise and up-to-date scientific research about how best to achieve this optimisation and it is down to the human factors practitioners and instructors to make sure they have the resources to do this effectively.

About the Author:

Captain David Moriarty is founder of Zeroharms Solutions, a company that specializes in the science of safety. Dr. Moriarty was a medical doctor prior to becoming an airline captain and Crew Resource Management Instructor. As well as a medical degree, he also holds degrees in Neuroscience (BSc) and Human Factors (MSc), is a Member of the Royal Aeronautical Society and the Resilience Engineering Association and also has extensive instructional experienceCapt.  You can follow him on Twitter @zeroharmHF

About the Book:

Practical Human Factors for Pilots bridges the divide between human factors research and one of the key industries that this research is meant to benefit—civil aviation. Human factors are now recognized as being at the core of aviation safety and the training syllabus that flight crew trainees have to follow reflects that. This book will help student pilots pass exams in human performance and limitations, successfully undergo multi-crew cooperation training and crew resource management (CRM) training, and prepare them for assessment in non-technical skills during operator and license proficiency checks in the simulator, and during line checks when operating flights.

Each chapter begins with an explanation of the relevant science behind that particular subject, along with mini-case studies that demonstrate its relevance to commercial flight operations. Of particular focus are practical tools and techniques that students can learn in order to improve their performance as well as “training tips” for the instructor.

You can purchase you very own copy of Practical Human Factors for Pilots on the Elsevier Store. Apply discount code STC215 for up to 30% off the list price and free global shipping.