SHELL Model Aviation (the name being derived from the initial letters of its components, Software, Hardware, Environment, Livewire) was first developed by Edwards in 1972, with a modified diagram to illustrate the model developed by Hawkins in 1975.
The term "human factor" is used in many different ways in the aviation industry. Most people have known it in the context of aircraft cockpit design and Crew Resource Management(CRM).
However, those activities are only a small part of aviation-related human factors, as broadly speaking it covers all aspects of human involvement in aviation.
Human Factors cover a range of
issues including perceptual, physical, and mental capabilities, the interaction
and effects on individuals of their job and working environments, the influence
of equipment and system design on human performance, and finally the organizational
characteristics which influence safety-related behavior at work.
In addition, Human Factors is the
practice of applying scientific knowledge with the intention of reducing humanerror.
Human factors in aviation are very interesting subject because it is one of the most significant opportunity to make aviation both safer and more efficient. It is not easy to explain all human factors components because it is comprised of many disciplines and diversity in approach by researchers.
In this article, I will
explain a conceptual model of human factors [ the SHELL concept].
Human Factors Definition
(FAA), is defined Human Factors as
a “multidisciplinary effort to generate and compile information about human
capabilities and limitations and apply that information to equipment, systems,
facilities, procedures, jobs, environments, training, staffing, and personnel
management for safe, comfortable, and effective human performance”.
After reading my introduction, I am sure that you clearly understand the definition of human factors and why it is important to improve aviation safety.
During writing this article from many
references I found that it is important to explain to you about the human error because human factors tools aimed at reducing human error.
Why Humans Make Errors?
Human error is defined as a human
action with unintended consequences. Humans make errors for a large number of
reasons. For examples, they make errors:
- because they have not been
adequately trained to perform tasks.
- because they do not have the basic ability to
perform the task even if they were trained.
- because the task is beyond
normal human abilities.
- because they misinterpret
information important to the performance of the task.
- because some event occurring during the
performance of the task changes the nature of the task in a way that they have
never encountered.
- because of influences such
as stress, distraction, fatigue, illness, visual illusions, spatial
disorientation, old age, immaturity, cultural beliefs, and the list goes on and
on.
Many human factors can affect
human performance and work performance in aviation. They encompass a wide range
of challenges that influence people very differently as humans do not all have
the same capabilities, strengths, weaknesses, or limitations.
The study and application of humanfactors are complex because there is not just one simple answer to fix or
change how people are affected by certain conditions or situations.
Understanding SHELL Model Aviation
It is helpful to use a model to aid in the
understanding of Human Factors, as this allows a gradual approach to
comprehension. In the SHELL model, the following interpretations are
suggested: [ L] liveware (human), [ H] hardware (machine) and [
S] software (procedures, symbology, etc.), [ E] environment (the
situation in which the L-H-S system must function).
 |
| A modified diagram to illustrate the SHEL model developed by Hawkins |
The SHELL concept diagram does not
cover the interfaces which are outside Human Factors (hardware-hardware;
hardware-environment; software-hardware) and is only intended as a basic
aid to understanding Human Factors.
[ L] – Liveware (Humans)
Humans, the " [ L] - Liveware,"
can perform a wide range of activities. However, humans have limitations. Since
[ L]- Liveware is at the center of the model [SHELL], all other aspects
(Software, Hardware, and Environment) must be designed or adapted to assist
human performance and respect human limitations. If these two aspects are
ignored, the human - in this case the aviation professionals - will not perform
to the best of their abilities, may make errors and may compromise safety.
To achieve this matching, an
understanding of the characteristics of this central component is essential.
Some of the more important characteristics are the following:
a) Physical size and shape
In the design of any workplace and most equipment, a vital role is played by body measurements and movements, which will vary according to age and ethnic, and gender groups. Decisions must be made at an early stage in the design process.
b)
Physical needs
People’s requirements for food, water, and oxygen, etc.
c)
Input characteristics
Humans
have been provided with a sensory system for collecting information from the
world around them, enabling them to enable to respond to external events and to
carry out the required task. But all senses are subject to degradation for one
reason or another.
d)
Information processing
These human capabilities have severe limitations. Poor instrument and warning system design have frequently resulted from a failure to take into account the capabilities and limitations of the human information processing system. Short- and long-term memory are involved, as well as motivation and stress.
e)
Output characteristics
Once information is sensed and processed, messages are sent to the muscles to initiate the desired response, whether it be a physical control movement or the initiation of some form of communication. Acceptable control forces and direction of movement have to be known.
f)
Environmental tolerances
Temperature,
pressure, humidity, noise, time of day, light, and darkness can all be
reflected in performance and also in well-being. Heights, enclosed spaces, and
a boring or stressful working environment can also be expected to influence behavior
and performance.
Adapting and matching remaining components [S, H, E, L] to [ L] – Liveware (Humans) the central component.
1-
Liveware-Hardware
2-
Liveware-Software
3-
Liveware-Environment
4- Liveware-Liveware
I will start with
1-
Liveware-Hardware
This
interface is the one most commonly considered when speaking of human-machine
systems: design of seats to fit the sitting characteristics of the human body,
of displays to match the sensory and information processing characteristics of
the user, of controls with proper movement, coding, and location.
2-
Liveware-Software
This encompasses humans and the non-physical aspects of the system such as procedures, manual and checklist layout, symbology, and computer programs.
3-
Liveware-Environment
The
human-environment interface was one of the earliest recognized in flying.
Initially, the measures taken all aimed at adapting the human to the
environment.
L-E interface must consider perceptual errors induced by environmental conditions, for example, illusions during approach and landing phases.
4-
Liveware-Liveware
This is
the interface between people (leadership, crew co-operation, teamwork, and
personality interactions).
Quiz
I will assume that you read this article and
understand a conceptual Model of Human Factors [The SHELL concept].
Which component of [SHELL Model] may involve these safety deficiencies:
- Relationships with other
people.
- shortage of manpower,
- lack of supervision,
- lack of support from
managers
Please write your answer in the
comments section.
Summary
Human Factors is the practice of
applying scientific knowledge with the intention of reducing human error. A
model which is often used is the SHELL model aviation, a name derived from the initial
letters of its components:
- [ S] software (e.g., work
procedures, operational manuals, checklist layout, etc.)
- [ H] hardware (e.g.,
tools, test equipment, the physical structure of aircraft, design of flight
decks, positioning and operating sense of controls and instruments, etc.)
- [ E] environment (e.g.,
physical environment such as conditions in the hangar, conditions on the line, etc.,
and work environment such as work patterns, management structures, public
perception of the industry, etc.)
- [ L] liveware - (i.e.,
the person or people at the center of the model, including pilots, maintenancetechnicians, supervisors, planners, managers, etc.).
Humans, the " [ L] - Liveware,"
can perform a wide range of activities. However, humans have limitations. Since
[ L]- Liveware is at the center of the model [SHELL], all other aspects
(Software, Hardware, and Environment) must be designed or adapted to assist
human performance and respect human limitations.
Human factors awareness can lead
to improved quality, an environment that ensures continuing worker and aircraft safety, and a more involved and responsible workforce. More specifically, the
reduction of even minor errors can provide measurable benefits including cost
reductions, reduction in work-related injuries, and reduction in more
significant events that can be traced back to human error.
Thank you for reading.
Further reading:
1- UK CAA, CAP 719, Fundamental Human Factors Concepts.