Challenges In Implementing Human Factors In System Design
Challenges in Implementing Human Factors
in System Design
BEng Final Project
Author: Băndilă D. Valentin Ștefan
Supervisor: Zancu Silviu, PhD
Session: July 2016
Anti-Plagiarism Declaration
I the undersigned Băndilă D. Valentin Ștefan student of the University Politehnica of Bucharest, Faculty of Aerospace Engineering declare herewith and certify that this final project is the result of my own, original, individual work. All the external sources of information used were quoted and included in the References. All the figures, diagrams, and tables taken from external sources include a reference to the source
Date: ____________ Signature: _______________________
List of Figures
Figure 2-1 Vitruvian Man by Leonardo da Vinci 10
Figure 3-1 Structure of the Human Eye 11
Figure 3-2 Central/Peripheral Vision – Acuity 12
Figure 3-3 Change in Acuity from Fovea 13
Figure 3-4 Structure of the Human Ear 13
Figure 3-5 Structure of Inner Ear – SemiCircular Canals 15
Figure 3-6 Sequential Process of Information in Memories 20
Figure 3-7 Procedure and Declarative Knowledge in LTM 22
Figure 3-8 Relationship between workload and performance 23
Figure 3-9 Workload performance plot as a function of time 24
Figure 3-10 Most Common Elements of Situational Awareness 25
Figure 3-11 Understanding the Situation by Matching Mental Model and Real World 26
Figure 3-12 Model of Stress and Performance 27
Figure 3-13 Arousal and Performance Curve 28
Figure 3-14 Stress Factors 28
Figure 4-1 Example of Light Pen on TID screen 32
Figure 4-2 Touch Panel Responsive Area 32
Figure 4-3 Example of Keyboard on the Flight Management System 33
Figure 4-4 Airbus A320 Cockpit 34
Figure 4-5 FCU controls for PFD and ND 35
Figure 4-6 Air Traffic Control WorkStation – Tower 36
Figure 4-7 Short Term Conflict Alert (STCA) 37
Figure 4-8 Line of sight 38
Figure 4-9 Optimal vertical and horizontal visual fields 39
Figure 5-1 Example of ATCO Wrap Around Console and Standard Wrap Around Console 47
Figure 5-2 Types of Multiperson Console Arrangements 48
Figure 5-3 ANSPr Operational Room 48
Figure 6-1 Simulink Model of Plane and Pilot 49
Figure 6-2 Pilot Gain 49
Figure 6-3 Components of block Pilot 50
Figure 6-4 Plane Dynamics representation block 50
Figure 6-5 Chteta Block 50
Figure 6-6 L Block 50
Figure 6-7 Pilot Reaction with Time Delay 0.10s 51
Figure 6-8 Pilot Reaction with Time Delay 1s 52
Figure 6-9 Pilot Reaction with Time Delay 2s 52
List of Tables
Table 3.5-1 Typical Factors Involved in Loss of Situational Awareness 26
Table 3.5-2 Typical Factors Involved in Loss of Situational Awareness 26
Table 3.6-1 Symptoms of Stress 29
Table 4.1-1 Advantages and Disadvantages of non – keyboard input devices 30
Table 4.1-2 Mouse Specifications. 31
Table 4.1-3 Joystick Specifications 31
Table 4.1-4 Light Pen Specifications 31
Table 4.1-5 Touch Panel Responsive Area Dimensions 32
Table 4.2-1 Color Code for Boeing and Airbus 34
Table 5.1-1 Static Human physical characteristics (sitting) 42
Table 5.1-2 Static Human Physical Characteristics (sitting) 43
Table 5.1-3 Design Criteria Levels for Arm Strength (Newton) 44
Table 5.2-1 Standard Console Layout 45
Table 5.2-2 Standard Console Illustration and Dimension Key 46
Glossary of terms and acronyms used
Executive Summary in English
Executive Summary in Romanian
Introduction
Human Factors (HF) have always been a part of society since the break of modern industry with multiple defining actions. These actions are destined to fulfill the goals of occupational health, safety and productivity, depending on the needs and demands from a system. But in many cases it has been proved difficult to understand the human in total due to its complex design and how he will react, together with a given system, when met certain factors such as human senses, display and design of information, etc. These may contribute into a certain outcome of an event, be it positive or negative, resulting in a further analysis and development of both human factors and system design.
In order to aid the development of such domains, a scientific discipline concerned with the understanding of interactions among humans and other elements of a system, but also the profession that applies theory, principles, data and methods to design has been formed, namely Human Factors Engineering (HFE). [1]
An important thing to mention is that HFE is the essential link between System Design and End User/Operators. By generating scientific knowledge about human behavior one can specify the design and use of a human-machine system. Using methods to design, a human-system interface will be created that will operate within human performance capabilities, meet functional system requirements, and also accomplish the given objectives.
The application of HFE not only will increase the performance of a system but it is also the basic science of safety. Human factors can also help us understand the human limitations so that the design of the workplace and the equipment will allow the process of adaptability in humans and human performance. By doing so the likelihood of errors occurring, and the impact of errors when they do occur, can be minimized in order to act moderate and limit the risks of incidence or accidents.
Knowing how fatigue, stress, poor communication and inadequate knowledge and skills affect the user is important because it helps us understand predisposing characteristics that may be associated with adverse events and errors.
A crucial element of human factors relates to the issue of how human beings process information. One will acquire information from the world around him, interpret and make sense of it and then respond to it. Errors can occur at each step in this process in aviation where the tasks have become complicated as a result of the increasing complexity.
In this paper, the purpose will be to see some performance characteristics related to HF and how certain guidelines and criteria’s have been developed along the years, regarding the design of a system in relation with the HF. By doing so, the environment and system will be of such caliber that the information presented towards an operator will aid him, reduce the amount of workload, and perform at optimal strength a given task.
In the next chapter we will see a brief history of HF and how certain scientific studies have started to develop, followed by the pure theoretical chapter about the characteristics of the HF. After which, will follow up chapters regarding specific criteria’s and guidelines for the development of a system, together with examples of how these procedures where adapted into a system to aid the operator. And, in the last chapter we shall see result from a simulation regarding the relation pilot – system followed up by the conclusions of this topic.
History of Human Factors
Figure 2-1 Vitruvian Man by Leonardo da Vinci
One of the first men to have studied HF was Leonardo da Vinci in which he drew the Vitruvian man around 1490. By doing so, he detailed the measures of the human body, strength and size, and see if a human has the strength to propel an aircraft. The drawing is based on the correlations of ideal human proportions and so it was the start of a scientific study of the measurements and proportions of the human body, namely anthropometry. Regarding this topic, a more detailed presentation will be available in Chapter 5.
The discipline of human factors and ergonomics is generally considered to have originated during World War II, although advances that contributed to its formation can be traced to the turn of the 20th century. Prior to World War II, the focus was “designing the human to fit the machine” (trial and error), instead of designing machines to fit the human.
Many of the human factors and ergonomic advances originated out of military necessity. With the start of World War I, the first conflict to employ the newly invented airplane in combat, the need arose for methods to rapidly select and train qualified pilots. This prompted the development of aviation psychology and the beginning of aeromedical research.
The outbreak of World War II, witnessed the tipping point where the technological advances had finally outpaced the ability of people to adapt and compensate to poor designs. This was most evident in airplane crashes by highly-trained pilots due to problems with control configurations.
The two decades following the end of World War II saw the continuation of military-sponsored research, driven in large part, by the Cold War. Towards the late 1970s large airline calamities ushered in an era of research focused on crew resource management and command training. In the present day, the technology and automation in the General Aviation cockpit is exceeding that of the airlines.
Human Perceptual, Cognitive and Performance Characteristics
Sensory processes in vision, hearing and balance
Sensory processing is the neurological mechanism that receives stimulus from both an individual's own body and the environment, copes with the resulting sensations and allows a more effective use of the body with an envinronment. This process deals with how the brain processes multiple sensory inputs such as vision, auditory system, tactile, olfactory, vestibular system and taste into usable outputs. [2]
Two of the most important of the human senses, regarding aviation and system design, are the sight and hearing. In this section we will focus more on these primary senses to have a better understanding of them and see how they provide a vast amount of essential information so that we may make sense of our environment, position in space and balance.
The eye and vision
The eye is the organ of vision which reacts towards light from the external world and passes them to the brain for interpretation into an image. The function of the eye resembles that of a simple camera with components such as aperture, lens, and a light sensitive screen called the retina. [3]
Figure 3-1 Structure of the Human Eye
Source: Oxford Aviation Training ATPL Vol. 8
The Cornea
Is the straightforward front part of the eye that covers the iris and pupil which goes about as a focusing gadget, in charge of very nearly 70% to 80% of the aggregate focusing capacity of the eye. The focusing is acquired by the state of the Cornea twisting the approaching light beams.
The Iris and Pupil
Behind the Cornea is the Iris (shaded part of the eye) which goes about as a diaphragm changing the measure of light that enters through the Pupil. The pupil resembles a dark gap, at the focal point of the iris, and it is the opening through which light enters the eye.
The Lens
The Lens is the second part of the eye, after the cornea, that helpes to focus light and images on the Retina. It is composed of transparent, flexible tissue and is located directly behind the Iris and the Pupil. Its shape can be changed by the muscles (ciliary muscles) surrounding it and helps the eye accomodate to the surrounding environment.
The Retina
It is a light sensitive layer at the back of the eye that spreads around 65% of its inside surface. The retina is made out of two sorts of receptors: rods and cones. Cones are corresponded with high visual sharpness and shading vision, however require a measure of light. Rods are associated with colorless vision, poor sharpness, yet higher affectability than cones in faint light conditions.
The distribution of these neural receptors is inhomogeneous. The concentration of cones is maximal at the center point of image focus, the macula, with the fovea at its center, and diminishes rapidly towards the peripheral areas. The concentration of rods peaks at about 20 degrees from the fovea, which is devoid of rods.
Figure 3-2 Central/Peripheral Vision – Acuity
Source: Electronic Flight Instrument System (EFIS) Course
The Fovea
It is the focal part of the Retina made out of firmly stuffed cones. The Fovea is in charge of sharp central vision, which is necessary in humans for activities where visual detail is of primary importance, such as reading vital information from a radar screen in case of an Air Traffic Controller (ATCo) or observing the changes of an aircraft on the Primary Flight Display (PFD) and Navigation Display (ND) in case of a pilot. The rest of the retina fulfils the function of attracting our attention to movement and change.
Visual Acuity
Usually refers to the clarity of vision and it is the capacity to discriminate objects at varying distances. An individual with an acuity of 6/6 meters (20/20feet) vision ought to have the capacity to see at 6 meters which is the so called normal person is capable of seeing at this range.
The power of the Fovea drops quickly as the angular distance from the Fovea increases. For a 5 degree from the Fovea the acuity drops to 6/12 (20/40), that is half as good as at the fovea. At 25 degree acuity decreases to a tenth 6/60 (20/200). [3]
Factors that can have an effect on acuity are: angular distance from the Fovea, age, hypoxia, smoking, alcohol, visibility (dust, mist), amount of light, size and distance of the object, drugs or medication.
Figure 3-3 Change in Acuity from Fovea
Source: Oxford Aviation Training ATPL Vol. 8 / www.skybrary.aero
The Blind Spot
It is a little parcel of the visual field of every eye that compares to the position of the optic nerve inside the retina. Any sort of picture that falls at this point will not be detected due to the fact that there are no Rods or Cones to detect an image. With both eyes open, the blind spot will not be of any problem because the visual fields of both eyes overlap and also the brain has the ability to „fill in” or ignore the missing portion of the image.
The Ear and Balance (Vestibular System)
The main purpose of the ear is to provide us with two essential functions, hearing and balance. The ear is described as having three parts – the Outer ear, Middle ear and the Inner ear as in the figure below.
Figure 3-4 Structure of the Human Ear
The Outer Ear
It is the external structure of the ear, that collects the sound waves, with the help of Pinna in order to be sent down the auditory canal and towards the eardrum which then it will make the eardrum vibrate.
The Middle Ear
It lies between the Outer and Inner ear and the eardrum isolates the Outer from the Middle ear. It is formed by three small bones, the Ossicles (malleus – hammer , incus – anvil and stapes), which assumes the part of transmiting the vibration through the chamber filled with air of the Middle ear towards the Inner ear that is filled with liquid.
The malleus bone receives the vibrations from the sound waves on the eardrum, it then transmits vibrations to the incus, which in turn transmits the vibration to the stapes bone that is attached to the oval window of the Inner ear. As the oval window receives vibrations from the stapes it is causing movement of fluid within the cochlea.
The Middle ear also connects to the upper throat and nose with the Eustachian Tube allowing pressure to equalise across the ear drum.
The Inner Ear
It basically begins at the oval window and contains the corti organ which is the hearing sensor. Inside the cochlea there is a fine membrane covered in hair cells (corti organ) and when they bend, they generate nerve impulses which are then carried to the Cortex of the brain. Due to this actions sounds are heard and interpreted in the auditory areas of the temporal lobes.
Sound Range of the Human Ear and Noise
The Sound Range describes the range of frequencies that can be heard by humans. The common range of the human ear is between 20 to 20,000Hz, but this can variate between individuals and intensity (measured in decibels). The human voice uses the frequency range of 500Hz to 3,000Hz.
Tabel 3.1.2-3-1 Noise level for various sounds
Source: Adapted from www.skybrary.aero
Balance (Vestibular System)
As mention at the beginning of this section, the ear also has the function of providing balance by detecting angular/linear movement and accelerations. It can also provide a secondary system of spatial orientation in case the primary system, which is the sight generated by the eye, is confined.
The Inner ear is composed of a hearing component, the cochlea, and a balance component, the vestibular system. This system consists of three Semi – Circular Canals and the Otoliths which helps in maintaining a stable spatial orientation and sight on the retina.
Semi – Circular Canals
The anterior, posterier, and horizontal semicircular canals are sensitive to angular accelerations of the head. Positioned at 90 degrees to one another, the three semicircular canals detect changes, with the help of hair cells (corti organ), referred to in aviation as pitch (nose up/down), roll (rotation about the longitudinal axis), and yaw (nose right/left).
Figure 3-5 Structure of Inner Ear – SemiCircular Canals
Otholis (Utricles and Saccules)
The Otholis detects linear acceleration and acceleration of the head. Such linear accelerations are experienced, for example, when an aircraft is picking up speed on the runway for takeoff. Due to such acceleration, the Otholis, are moved back or forth giving the impresion of a climb or pitch down.
Cognition, Attention, and Decision-making
Cognition
Is "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses.”[4] This mental action envelopes processes such as attention, decision – making, memory, reasoning, knowledge, etc. Also with the help of cognitive processes the human can use a variaty of existing knowledge in order to generate new knowledge.
A different approach of analysing cognition can be made in the fields of cognitive science. This field does research on intelligence and behaviour, but more importantly one of its main focus is how information is represented, processed, and transformed (in facilities such as attention, memory, etc.) within the nervous systems and machines. A fundamental concept of cognitive science is that "thinking can best be understood in terms of representational structures in the mind and computational procedures that operate on those structures.”[5]
In order to analyse such processes, three levels of analysis have been developed by the neuroscientist and psychologist, David Marr. These levels promotes the ideea that complex systems (human or computer) must be understood at different stages and it is also useful to be aware of them when desinging systems that are increasingly in complexity.
Marr’s three level analysis consist of:[6]
Computational – describe and specify the problems that are faced with in a generic manner;
Algorithmic – the bridge between the computational and implementational level, describing how the identified problem can be solved;
Implementational – the mechanism in which computation if performed
Attention
As mentioned above, attention is a cognitive process, that has been proved to be one of the most important due to daily activity that people perform on a daily basis. In fields, such as cognitive science and neuroscience, it is a vital field of study because with the help of this process, people selectively process the essential information and will discriminate the unimportant information at a specific time. Due to the control, that people have over attention, we are able to maintain vigilant in order to detect and act accordingly to situations that may lead to a incident or accident.
In aviation, due to the growth of automation of modern systems, studies about attention and vigilance have been noted to be important to human factors. Since modern systems and technologies provide less action for the human, by decreasing its workload with various tools, it requires more monitoring and the people must maintain the ability to act in case of a situation. Such monitoring activity, as it is for an Air Traffic Controller or a pilot, it requires a strong attention and vigilance over the system.
Over the years, several concepts regarding attention and vigilance have been studied, that would prove useful to at least be familiar with:
Overt vs Covert attention: Overt, act of directing the senses (vision, hearing, etc.) to the source that is providing information so that we may acknowledge. Covert, internal act of the human to mentally focus on a specific sens in order to stimulate it and enhance the information.
Selective attention: The focus on a specific stimulus while ignoring other. This type of attention can be either conscious or unconscious and can happen to an individual who is an expert in a particular task where attention is required.
Controlled and automatic attention: The Controlled attention is the type of process that requires effort when a new task appears. By introducing training and procedures, attention becomes more automatic, resulting in less effort in completing the task. As an example, after much training, Air Traffic Controllers and pilots are able to exchange information simultaneously while performing their monitoring over their own systems.
Sustained attention: The act of directing and focusing a specific sense for an extended period of time.
Divided attention: It is the highest level of attention and it is also the ability to respond simultaneously to multiple demands.
Disturbing factors that can affect attention and vigilance:
Time on task
Environment
Temperature
Sleep Loss
Noise polution
Motivation
Decision – making
Decision – making is an active cognitive process which selects one out of a set of possible courses of action. One of its requirements is to take into consideration the pros and cons of different alternatives that will determine the influence on task performance. In aviation, aeronautical decision – making (ADM) is of most importance factor due to its safety consequences regarding poor decision.
The choice of every individual, regarding decision – making, will always depend on two key factors:
The aim of the individual that must be achieved
Values and preferences of the individual
In order to achieve the aim, one must face some internal/external variables that can affect one’s values and preferences, such as personality and biases, nature of the aim, strees, emotion, training, motivation, etc. Although these factors can be different from one individual to another, a set of common factors have been identified that have an impact on how decision – making works, regardless of circumstances. Thesecommon factors are:
Certain skill developed and automated through training resulting a quick decision – making
Creativity
Innovativity
Adaptability
Because of its nature, a cognitive process, in order to reach the end of this process every individual must follow a set of natural steps that leads them in achieving their aim. Some may call this as „The Mechanics of Decision – making”
Tabel 3.3.3-1 Mechanics of Decision – making
Source: Adapted from Oxford Aviation Training ATPL Vol. 8
Limitations of Human Decision – making
The way an individual sees a circumstance or objective relies on the nature of various factors and/or biases that can alter his mindset. One method for restricting the nature of the choice is when people tend to place confidence in subjective and personal factors, in a very pinched situation, regardless of the specific decision-making process used. Knowledge of these limiting factors is important in order to avoid their use or to mitigate their consequences on safety. Three types of factors can be described:
Risk perception and management
Situational factors
Biases
Risk perception and management
All decision alternatives entail some level of risk. The choice between alternatives is a tradeoff based on the expected results for each alternative and the risk of failure to achieve these results when adopting the selected alternative. The way risk is perceived and managed can limit some choices.
People have a tendancy to incline towards solutions they are confident of achieving, even if the result will not be as good as might have been achieved with another, less-familiar solution. The likely solution in such situations is the best of the available alternatives that the individual or the team is actually able to implement, even if it is not the optimum solution.
Situational factors
Each circumstance and individual/group have their on qualities. The minute a connection between these qualities emerge we should manage four sorts of situational elements:
Task related factors: degree of task complexity, time available to complete the task, amount of information, ease of acces of the information, human – machine interface design, clarity of goals.
Cognitive factors: human cognitive abilities and information processing (perception, understanding, etc.) have their own limitations and they are based on individual factors such as knowledge, expertise, qualifications, fatigue and stress.
Motivational and personality factors: degree of motivation, personality traits, attitude, emotions, past experience and mood can have an influence in decision – making.
Psycho-social factors: team collaboration, leadership, influence, reputation.
Biases that influence decisions
Biases are a tendency/inclination to think in another way, leading to deviations from a rational and good judgment. Regarding decision – making, biases have been studied and a number of frequent biases have been found that can influence one’s decision:[7]
Anchoring: tendency to rely heavily on one piece of information
Belief: tendency to base judgements on personal beliefs
Status – quo: tendency to let things stay the same
Correlation: tendency to underestimate rare events and overestimate frequent events
Overconfidence effect: human tendency to be more confident in one’s behavious, attributes than one should
Memory
Throughout this chapter we have seen how an individual process certain information and how he makes use of it. But in order to take action and keep the results of one’s actions, the information must be stored and that is when memory is required. Both simple and complex task, such as speaking, reading, decision-making and taking action can be considered efficient only when an individual has the ability to properly process, store, and recall information in the brain.
By making use of this ability, one can store a detailed image of past events that will help him to identify and classify basic sensory stimulations, such as sight, hearing, touch, smell and taste. Another important feature of memory is that we can also store experiences and knowledge so that we can recall them and help us in similar situations in the future.
As useful as this ability is, human memory has its own limitations and can also fail when trying to store or recall information. Depending on the type of information, and also on the state of mind of an individual, some things can be very easily recalled and others are not. As an example, one can remember a phone number but can forget the clearance frequency of an air traffic controller.
With regards to memory, it is a complex procedure that is constantly present in all the steps of information processing (perception, comprehension, decision and action). As every complex system, it is composed of multiple stages where information is processed and stored differently, depending on the amount of time the information stays in every stage. The three basic types of memory are:[8]
Sensory memory
Short – term memory (STM)
Long – term memory (LTM)
Sensory memory
From the moment we sensed and give attention towards the sensed information, it will enter into our sensory memory. This process allows us to retain impressions of sensory information when the stimulus no longer exists. Sensory memory has the ability to retain a quite accurate “picture” of the information that was sensed and it also exists for both visual and auditory senses.
Figure 3-6 Sequential Process of Information in Memories
Source: Adapted from www.skybrary.aero
Sensory memory is described by being outside of conscious control and occurs automatically. Its primary part is to ignite the first steps of perception. These steps consist of extraction and identification of features of a stimulus once a initial reception of information has been stimulated. Another element of the sensory memory is that it has the ability to perceive meaningful patterns of signals in the information.
Although sensory memory is very short in duration, it can contain a large amount of information. Sensory memory can hold all information received, for a short span of time, however it is restricted by our capacity to pay attention and this makes the difference between what goes into the next stages or not. What determines, if the information will make it through, is the active and passive selection process within the memory system:
Active processes: oriented by concepts in which there is an intention to extract useful and expected information. It is guided by the attention mechanisms, focusing on specific portions due to lack of time, and allows us to analyse with great accuracy.
Passive processes: oriented by data where the brain automatically process and analyse information. Most of the processed information is subliminal, and we are not aware of the process taking place, but we are able to respond when needed.
Short – Term Memory
When information has passed through the sensory memory, and afterwards there is more attention devoted towards the information, it shall enter the stage of short – term memory (STM), that has the capacity to store a limited amount of information for a limited amount of time. Usually, the range of which the information is stored, is between seconds to minutes (average 15 – 30 seconds).
The content of STM is different of that from the sensory memory. Where in the sensory memory, the stored information is in a form of a „whole picture”, STM stores information as an interpretation of the events. From this we can conclude that there can be a difference between interpretation of the events that are stored within the STM and the actual observed events originally in sensory memory.
The types of information that can be held in STM are under the form of:
Recently processed by sensory input via sensory memory
Items recently retrieved from long-term memory
The result of recent mental processing.
Limitations and managing STM
The main limitation of STM consists of how easy the information can be forgotten, due to its limited capacity and the short time informations is kept in this stage. The reason we forget information, in the stage of STM, is because of two mechanism:
Interference: occurs when information cannot be proccesed because STM is full. In this process, one of two things can happen: new information replaces the old information, resulting that old information is lost, or old information blocks new information, resulting that new information will not be remembered.
Mnemonic Trace decrease: it is a small piece of the original memory and is the functional unit of memory. By repetition, the trace of the original memory can be maintained in STM, otherwise it will dissappear.
In order to help in managing STM, various strategies can be used to increase the strength of our memory storage process. These strategies include:
Knowing about the limitations of STM and try to anticipate when you will start to forget information. By doing so it can manage more efficiently tasks and reduce the amount of important information that is forgotten.
Using training and experience to know what information to select and focus on. Through this method the ability to know which information must be stored is enhanced.
Using support devices.
Long – Term Memory
It is the phase where all the encounters and knowledge are stored permanently having an unlimited capacity. A big challenge in LTM is that failures can be expected when retreving the correct information when needed. Regarding the information stored in LTM is that it is never lost, but it is extremly difficult to retrieve therefore, it is vital to focus on how to maintain information but also how to retrieve and interpret it correctly.
As a more complex stage, LTM has three main phases:
Encoding phase
Storage phase
Declarative and Procedural Knowledge
Encoding phase
This stage is the procedure in which the information stored in STM is transferred to be stored in LTM. Through this type of process, it offers content to the new transfered information that is then combined with already stored information. The more depth encoded results a less demanding recall later. Links and affiliations permit the organization of information into a system of hierarchies. Stronger links and associations lead to easier retrieval.
Storage phase
Encoded information can be stored in LTM indefinitely. In any case, natural “fading” may occur in the various links and associations. Active processes are required to prevent this fading, such as solidification. Solidification strengthens the mnemonic trace of information and decreases the likelihood of interference. Information is transformed and integrated into stored knowledge. Much of consolidation occurs during sleep. Also, rehearsal is vitally important to the process of consolidation. Both sleep and rehearsal can help prevent loss of information during consolidation. Any information that is lost during the consolidation phase can affect the storage of other information that was associated/linked to the lost information.
Once this process of consolidation is finished, the memory shall be rebuilt based on the new information gained. When rebuild the new and updated memory will be more powerful and easier to remember then the old ones.
Declarative and Procedural Knowledge
Based on the title, we can see that knowledge can be separated into two categories, declarative and procedural. Declarative knowledge includes episodic and semantic memories and it is described as knowledge about facts, methods and other static pieces of information. On the other hand, procedural knowledge is described by the physical and mental skills which are dynamic in nature.
A very important difference between these type of knowledge is that declarative can be very easily described and shared with others, while procedural implies greater effort. For example, in aviation, being able to write down a procedure from a manual is declarative knowledge. Performing the procedure without looking in the manual for hits is procedural knowledge
Figure 3-7 Procedure and Declarative Knowledge in LTM
Source: Baddeley, A.D. (1976). “The Psychology of Memory”
Workload and Situational Awareness
Workload
Since the evolution of system design and increased automation, systems have now incorporated an important management function. From this perspective, mental workload of staff, in aviation, has received increased attention. When mental tasks exceed the capabilities of human operators, errors can arise that can have a critical impact on safety. Therefore, as a response to the increased automation, mental demands imposed by a human – machine interface must be considered.
Workload can be simply defined as the demand placed on the human operator, but this definition is limited because it includes only requirements generated by sources such as task difficulty. From a human factors perspective, workload can be fully defined as “the demand placed on an operator’s mental resources used for attention, perception, reasonable decision – making and action”.
A key aspect about workload is that it is an individual experience, meaning that a certain task will not produce the same workload level for all operators. It depends also on how the operator is trained, what experience he has with the given task and what level of skills does he presents. A task can also produce a different workload depending on the mental, physical and psychological state of the operator and the time (day or night shift).
An easy way to understand how these factors (task demand, performance, and effort) are related, we take the model of Prof. Dr. D. de Waard that includes six regions of task demand (D, A1, A2, A3, B, C) that increase from left to right in the figure bellow.
Figure 3-8 Relationship between workload and performance
Source: de Waard, D. (1996). “ The Measurment of Drivers’ Mental Workload”
In region D we can observe that the performance is affected due to the condition of the operator, even though the task demand is relatively small, resulting an operator that suffers from fatigue or is distracted and incapable of handling minimal task demands.[9]
Region A2 shows where the performance of the operator is optimal and is fully capable to withstand the task requirements and maintain an adequate level of performance. In region A1 and A3, the performance of the operator is stil optimal but in order to maintain it stable he must exert more effort.[9]
Region B shows the start of when the operator starts to fail in keeping his performance, reaching the level of region C where the operator is overloaded and his performance is at its lowest level. In order to regain his optimal performance, the operator must reduce parts of his task so that he may focus his effort and try to reach a performance area for the primary task.[9]
As mentioned in the beginning, the amount of time on the task can also have an impact on the performance and increase of his workload. Workload increases as a function of time and once a threshold of time is reached, resources of the operator have already been worn out, resulting in a breakdown in performance and increased workload.[10]
Figure 3-9 Workload performance plot as a function of time
Source: Andre, A.D. (2001).“The Value of Workload in the Design and Evaluation of Consumer Products”
For a better prediction regarding the performance measures of workload, there are three ways in order to quantify, and these are:
Primary – task measures: it is solely based on main task characteristics in which we want to find and track performance, number of errors, speed and reaction time by doing tests in laboratorys, simulators or field testing.
Secondary – task measures: it is a way in which we add a task, besides the primary task, so that we can track how the operator devotes more of his time and effort to the main task and measure the increase of workload, if the performance is degrading and how could interference occure between the primary and secondary tasks.
Reference tasks: standardized laboratory tasks measure before and after the task under evaluation. By this we want to see the mental load produce by the main tasks, over a period of time, and to see the change of performance.
Situational Awareness
Closely linked with the mental picture of the world is situational awareness. It describes the extent to which the operator has an integrated and detailed understanding of the operational environment, and can be defined as „the perception of the elements in the environment within a volume of time and space, the comprehension of their meaning and the projection of their status in the near future”.[11] (Endsley, M. R. (1988). „Design and evaluation for Situational Awareness enhancement.”)
Figure 3-10 Most Common Elements of Situational Awareness
Also, when we talk about situational awareness, we must be aware of its main components:
Environment awareness: aircraft, communication of air traffic control and other aircraft, weather, terrain, etc.
Mode awareness: aircraft configuration and flight control system modes, such as speed, altitude, heading, holding modes (both pilot and air traffic controller).
Spatial orientation: awareness of geographical position and aircraft attitude (in case of pilots)
System awareness: awareness of aircraft system/radar system
Time horizon: awareness of time with respect to when required procedures or events will occur
Throughout the course of aviation, it has been seen that human factors have contributed to 70% of all incidents and accident where 85% of incidents were based of loss of situational awareness. This means that with the loss of this ability, poor decision making and mistakes can occure.
In order to identify the to loss of situational awareness and how it can be dealt with, we first must understand the three levels of it:[12]
Level 1 – Perception: Scaning and Gathering Data
Level 2 – Representation: Understanding and creating our mental model
Level 3 – Projection: Thinking ahead and updating the model
Levels of situational awareness and how to deal with loss of situational awareness
Level 1 – Perception: Scaning and Gathering Data
It is obtained by using our senses, such as vision, hearing, in order to gather sufficient data and begin to build a mental model. It is an active process and requires significant discipline in order to know, what, when and why we are looking for, so that we may direct our attention to the most important element from our surroundings.
Table 3.5-1 Typical Factors Involved in Loss of Situational Awareness
Source: Adapted from Airbus, „Human Performance – Enhancing Situational Awareness”
Level 2 – Representation: Understanding and creating our mental model
If the observations, together with knowledge and experience, are linked together succesfully, the mental model is finished and it has to be kept updated with inputs from the real world.
Figure 3-11 Understanding the Situation by Matching Mental Model and Real World
Source: www.skybrary.aero
Level 3 – Projection: Thinking ahead and updating the model
Our understanding enables us to think ahead and project the future state of our environment. This step is vital for the pilots and air traffic controller for a good decision-making process and requires that our understanding is based on careful data gathering to be as accurate as possible.
Table 3.5-2 Typical Factors Involved in Loss of Situational Awareness
Source: Adapted from Airbus, „Human Performance – Enhancing Situational Awareness”
Stress and fatigue
Stress
Stress is our response to a disturbing situation or event, be it anticipated or unexpected, when it is evaluated as a threat and an immediate action is required but it is beyond an individual’s normal operational capability. When faced with such events the body attempts to maintain equilibrium, from a physiological point of view, since stress is a normal human reaction and a certain degree of stress is necessary until the point it gets to intense and negative effects start to appear.
Figure 3.6 – 1 represents the mechanism of how stress is perceived and also the feedback mechanism which determines the amount of stress an individual will experience and if that will have a great impact on his performances of the task. If the demanding task is completed, not only it will reduce the perceived demand and increase of perceived ability, but it will also change the evaluation of the situation/event resulting in a reduction of stress or vice versa
Figure 3-12 Model of Stress and Performance
Source: Oxford Aviation Training ATPL Vol. 8
Although the amount of stress that can be handled varies from one individual to another, the level will depend on the person’s inborn and learnt characteristics but also on the amount of experience. By understanding such factors we can significantly enhance an operator’s performance.
Causes of Stress
Any activity, event or other stimulus that causes stress is referred to as a stressor. These can be internal (cognitive or physical) or external (environmental) to the individual and can be generated by:
Too much (or too little) to do
Time pressure
Unclear or conflicting goals
Interruptions
Design of the work environment
Conditions: workplace, environment
Team and people factors
Arousal and Performance
The term “arousal” is a general physiological/psychological activation of the organism that varies from deep sleep to intense excitement. Below, we can see in Figure 3.6 – 2 a theoretical model that shows how the quality of our performance, especially on complex mental or physical tasks, will vary according to our level of arousal. These levels are:
Drowsiness: low arousal where an individual is uncoordinated has no sequential timing.
Relaxed wakefulness: a level of arousal where routine activities can be carried out.
Alertness: optimal level of arousal in which demanding and sequential tasks can be performed in an ideal manner and where an individual has efficient selective and quick reactions.
Excited emotion: or over – arousal, results from a stressful/demanding event which exceeds the coping abilities of an operator. This results in a decline of performance where lack of control, freezing up, and disorganized manners start to appear.
Figure 3-13 Arousal and Performance Curve
Source: Safety Investigation Course
Stress Factors (Stressors) and Symptoms of Stress
A key aspect about stressors, that needs to be taken into account, is that they are cumulative. If an operator is experiencing a minor stressor, the resultant will be an increase of stress. During this process, of solving the first stressor, another minor event appears it will only accumulate one after the other resulting in an exponential increase of stress. Some of these factors can be:
Figure 3-14 Stress Factors
From these we can deduce a multide of symptoms, such as:
Table 3.6-1 Symptoms of Stress
Source: Safety Investigation Course
Fatigue
Fatigue, which has similarities to stress, is a condition characterized by increased discomfort with lessened capacity for work, reduced efficiency and most of the causes to fatigue are:
Lack of sleep
Lack of physical or mental fitness
Excessive physical or mental stress
Anxiety
Jet Lag
Fatigue leads to a decrease in the ability to carry out tasks. Studies have demonstrated significant impairment in a person’s ability to carry out tasks that require manual dexterity, concentration, and higher – order intellectual processing. This condition can happen acutely, meaning it appears in a shot time span, or it may occur gradually over several days/weeks.
Main symptoms of fatigue:
Lack of awareness
Diminished motor skills
Diminished vision
Tiredness
Concentration problems
Increased mistakes
Decrease in communication
Antidote to Fatigue
Obtaining adequate sleep is the best way to prevent or resolve fatigue. Sleep provides the body with a period of rest and recuperation. Insufficient sleep will result in significant physical and psychological problems. On average, a healthy adult does best with eight hours of uninterrupted sleep, but significant personal variations occur. For example, increasing sleep difficulties occur as we age, with significant shortening of nighttime sleep. A variety of medical conditions can influence the quality and duration of sleep. To name a few: depression, stress, insomnia, and chronic pain. Some of the more common social or behavioral issues are: late-night activities, excessive alcohol or caffeine use, travel, interpersonal strife, uncomfortable or unfamiliar surroundings, and shift work.
Display and Control Design
Input Devices
In this section we will see the criteria and guidelines for input devices such as keyboards, pointing devices, and some alternative input devices that have started to be used in aviation more frequently due to their enhancement over the basic devices used by air traffic controllers and pilots. By doing so, we will see the advantages and disadvantages of non – keyboard input devices that can aid in the selection process for appropriate controls for a given tasks.
Table 4.1-1 Advantages and Disadvantages of non – keyboard input devices
Source: Federal Aviation Administration, „Human Factors Design Guide”
Mouse
Commonly used by air traffic controllers, it is a free – moving X – Y controller used on flat surfaces in order to control the position of the pointer on the radar screen. It is used for data pick or for entry of values such as Flight Level (FL), speed, heading, etc, and also for solving arriving conflicts.
The design and placement of the mouse will allow the user to constantly orient the mouse within 10deg of the correct orientation without visual reference to the mouse. The mouse shall have no sharp edges but shall be shaped roughly as a rectangular solid, with limiting dimensions as such:
Table 4.1-2 Mouse Specifications.
Source: Federal Aviation Administration, „Human Factors Design Guide” – Values
Joystick
Joysticks are appropriate to use if precise input functions are required, such as the maneuvering of an aircraft. They are most useful when used to control the roll and pitch axis of an aircraft. The displacement of joysticks are usually spring – loaded in order to return back to their center position thus helping in less fatiguing over long operating periods.
Table 4.1-3 Joystick Specifications
Source: Federal Aviation Administration, „Human Factors Design Guide” – Values
A discrete mechanism shall be provided for the pilots to allow them to activate and deactivate the joystick in case of certain situation when the autopilot is activated.
Light Pen
Most appropriate in case of item selection and input data together with a touch input device (TID) screen. For example, an air traffic controller who uses a display system of electronic strips of the aircrafts in his sectors will use such a device for inputs, organizing the aircraft strips in terms of Estimated Time of Arrival (ETA).
Table 4.1-4 Light Pen Specifications
Source: Federal Aviation Administration, „Human Factors Design Guide” – Values
The light pen must be equipped with a discrete activating and deactivating mechanism such as a push – tip switch, requiring a force between 0.5 – 1.4 N for activation. Also a feedback system must be allocated in order to see if the light pen has been acknowledged by the system and therefore it is ready to be used. Such a system can include a highlighting system on the pen or on the TID screen.[13]
Figure 4-1 Example of Light Pen on TID screen
Touch Screen
A touchscreen is an input device normally layered on the top of an electronic visual display of an information processing system. A user can give input or control the information processing system through simple or multi-touch gestures by touching the screen with a special light pen and/or one or more fingers.
Figure 4-2 Touch Panel Responsive Area
Table 4.1-5 Touch Panel Responsive Area Dimensions
Source: Federal Aviation Administration, „Human Factors Design Guide” – Values
Keyboards
A keyboard is a rapid input device with a large variation in the number and arrangement of keys. Such a device can contain:
Alphanumeric keys: letters of the alphabet, numerals and punctuation symbols
Dedicated formating keys: used for text formatting operations (space bar, tab, enter)
Navigation keys: used for special page navigation
Such a device is strongly used by the pilots in the cockpit on the Flight Management System (FMS) whenever they need to introduce a flight plan, optimize route determination and en – route guidance for the aircraft.
Figure 4-3 Example of Keyboard on the Flight Management System
Control – Display Relationship
This section will serve as an introduction for the last two parts of this chapter and talk about small guidelines regarding:
Obstruction;
Complexity and precision;
Feedback;
Illumination;
Emergency controls and displays;
When it comes down to relationship between control – display, the most important aspect is that the control associated to a certain display must always be possible and obvious to the operator. This can easily be achieved through the use of grouping and arrangement of controls, color coding, insertion of panels.
Obstruction
The controls related to a display must always be situated in such a way that it will not block the vision of the operator towards the display, and also, while managing the controls the hands should also not block its field of vision. This can be achieved by situating the controls of the display on the upper – bottom or left – right side of the display. [13]
Complexity and precision
Althought complexity of a system is a big issue in modern technology one must always try to keep it at a minimum in order for precision to be obtained. From this results that the complexity of the controls must not exceed the ability of the operator to segregate important detailes. Also prior to this aspect, the complexity must not alter the operators dexterity, coordination, and reaction time due to environment in which he must perform his tasks. [13]
Feedback
No matter the type of domain, be it aviation, automotive, etc., whenever a control, that serves as an input towards a display, must provide an instant feedback for the operator.
Illumination
It is an important feature that must be provided towards visual displays and for any other labels/markings of a display/control, and panel in case of operations during night time or darkened conditions. This feature is easily seen in the cockpit of a pilot during night time flights.
Emergency controls and displays
Such controls and display must be provided in areas of quick acces and also have the corresponding color code when displayed before/during a crisis. Such colors can be:
Table 4.2-1 Color Code for Boeing and Airbus
Source: Electronic Flight Instrument System (EFIS) Course
Grouping and Arrangement of Controls
When it comes to grouping and arrangement of controls we must consider first for them to be functional, meaning that related controls and/or displays must be located near one another and arranged in functional groups, for example, power, status, etc.
The location will be based on the order of use and will provide an order of left – to – right, top – to – bottom or both. The arrangement of groups must be placed, based on the frequency of use, and the most important groups of controls should be located in areas of quick access.
Another way to achieve a good aspect in grouping controls is by marking the functional groups created. This can be done by enclosing the group with a line marked on the panel or color coding the group.
Figure 4-4 Airbus A320 Cockpit
As an example, we can see in Figure 4.3 – 1 the Overhead Panel of an Airbus A320 and how controls are grouped based on their usage such as, Hydraulic systems, Electric systems, Fuel system, etc., and marked by lines, colors, and panels.
Based on the name, “overhead”, we can see that the location of these controls is not in an area of quick access due to their frequency of use. Compared to the pedestal (right side of the captain’s chair) and instrument panel (front view of the captain), which are located in areas of quick access due to their importance of use during take – off, flight, and landing.
In case of both pilots and air traffic controllers, the issue of multiple displays must also be discussed. If the operator must handle an action while observing more than one display, the control must be placed as near as possible to all of the related displays, without blocking the view to any other of the displays that the operator is manipulating. As an example, we shall discuss Figure 4.3 -2 and Figure 4.3 – 3 and see the importance of such features.
In the case of Figure 4.3 – 2 we can see the controls, Flight Control Unit (FCU), that operates the two displays of the Electronic Flight Instrument System (EFIS), namely the PFD and ND. While the captain handles the aircraft he will have a direct vision towards the controls and displays in front of him, that will aid his future actions and decision – making.
Figure 4-5 FCU controls for PFD and ND
In Figure 4.2 – 3 below, we can observe a modern arrangement of displays, using touchscreens, and a reduction of the amount of controls needed for operation. The arrangements where done by knowing information, such as presented in Chapter 3 – Figure 3.1 -2 Central Peripheral Vision – Acuity, in which the most vital information must be displayed in the central vision of the operator, in this case the radar screen and the electronic strip system. The lateral screens, also important but having a secondary function of aiding the operator, are displayed in a more peripheral area of the vision and we can see information about airport layout (lateral right), meteorology and commands towards aircraft (lateral left).
Figure 4-6 Air Traffic Control WorkStation – Tower
Information Presentation
Now that general knowledge have been presented, regarding control – display relationship and grouping – arrangement of controls, we must now see the most important aspect that result from such features, and that is how the information is presented towards an operator. This aspect is of crucial importance because most of the operator’s decisions and actions depend upon the information displayed. In order to understand this chapter, general criteria’s and guidelines shall be exposed for visual displays.
General Principles of Display
Visual displays ought to give the operators a reasonable sign of hardware or framework conditions for operations and maintenance under any inevitability similar with the operational and support rationalities of the system under design. For this to be efficient the content and precision of the information displayed towards an operator must be sufficient to allow him to perform the given task and the information shall be displayed within the limits and precision required for specific actions and decisions.
Another aspect, which is a key role in reducing the workload of an operator, is that the information must be directly usable. This means that information should be introduced in a direct usable structure, that is, operators must not transpose, compute, interpolate, or rationally make an interpretation of the information showed into different units. [13]
Accurate data can also be achieved if information is not consolidated inside a solitary presentation unless the content and arrangement of the information are appropriate to combination and the outcome of the combination does not alter the performance of the operator. By doing so, the display duration of such information should be of adequate length to allow dependable identification and use by the operator under the normal workload and environmental conditions.
If appropriate, advisory and alerting displays, that contain more than a single type or piece of information, shall be capable of advising or alerting the operator if one or more of the pieces of information becomes critical, such as in the case of traffic collision between two or more aircrafts.
Visual Warning and Signal Devices
Alerting and warning displays should bring about a more prominent likelihood of an operator’s detecting capabilities and the triggering condition that would be the case in their absence. Such adaptations can be seen in the figure bellow, regarding the Short Term Conflict Alert (STCA), for air traffic controllers. In case of a conflict between two aircrafts, the controller is presented with a visual alert in the form of a red label for the aircrafts in conflict.
Figure 4-7 Short Term Conflict Alert (STCA)
In case of such events, certain factors must be looked upon when designing systems that incorporate alarm devices. Such factors are: [13]
Alarm parameter selection: the limits of an alarm or warning display must be set so that the alarm gives the operator enough time to counter the event before it becomes more serious. As an example, in the case of STCA, the controller is announced, usually, 2 minutes before the conflict.
General alarms: alerts that require an operator to go to an alternate area for particular data must be avoided. In the event that they are utilized, they must permit adequate time for the operator to acquire and utilize the vital data.
Prioritization of alarms: on the off chance that a system or unit of equipment allows several alarms to be visible or capable of being heard at the same time, the alerts might be organized so operators can separate the most essential caution or alerts from those that are less imperative. In the event that two or more systems are in an alert condition, then just the most critical alarm should be capable of being heard; less essential alerts might be suppressed.
Priority levels: levels shall be based on their importance, severity, and time urgency. The number of such events shall not exceed four.
Visual coding of priority levels: visual signs ought to be coded to demonstrate the need level of the sign. Adequate coding techniques incorporate shading, position, shape, flashing, and symbol.
Audible coding of priority levels: if audible signals accompany visual alarms, they too shall be coded by priority. Adequate coding techniques for audible signals incorporate pulse coding, duration, and frequency. intensity might not be utilized as a coding technique. In the event of pulse coding, the number of levels shall not exceed 3. For duration, the maximum number of levels shall not exceed 3 and if frequency is used, the number of levels must not exceed 5.
Emergency conditions. Flashing red should be utilized to indicate crisis conditions that require prompt operator activity to avert serious incidents or accidents. The glimmering rate should be from 3 to 5 flashes for each second, with approximately equal on and off times. If an emergency condition exists and the flasher fails, the light shall illuminate and burn steadily.
Automatic clearing of alarms: when the system that triggers an alarm shall also clear the alarm automatically when the crisis no longer exists.
Location and Arrangement
The location of the displays must be located, in terms of the operator, in such a position where the operator can have an acceptable degree of accuracy of the information, which is required, without unnecessary moves that can either be uncomfortable, awkward, or unsafe position. This orientation of the display will be perpendicular to the line of sight and will not exceed more than 45 degrees from the line of sight, as presented in the figure below.
Figure 4-8 Line of sight
Source: Federal Aviation Administration, „Human Factors Design Guide”
Based on the frequency of use of the display and of its importance, they must be placed together in an optimum visual field. Besides, they should involve a favored position in that field, for instance, the top or left most position, or they might be highlighted in some way. In the case of a control that is associated towards a display, the distance between the eye and the reference point of the display and control shall be as such: [13]
Minimum viewing distance: not less than 330 mm (13 in)
Preferred viewing distance: at least 510 mm (20 in)
Maximum viewing distance: 635 mm (25 in)
Figure 4-9 Optimal vertical and horizontal visual fields
Source: Federal Aviation Administration, „Human Factors Design Guide”
Although these are standard distances towards the reference point of a display, the viewer should be able to move as close as they like.
Workplace, Crew Station, and Facilities Design
Anthropometry
Designers and human factors specialists incorporate scientific information on human physical capacities into the design of a system and equipment. Human physical qualities, unlike those of machines, can’t be outlined. In any case, design oversight can put unnecessary demands and confinements upon the user.
All in all, as a broad definition, anthropometry is the experimental estimation and gathering of information about human physical attributes and the application (engineering anthropometry) of this information in the design and evaluation of systems, equipment, human – made environments and facilities.
Closely related to anthropometry, we have the notion of biomechanics. It is a field of study that describes the mechanical attributes, in this case the human body, in terms of physical measures and mechanical models. Its applications address mechanical structure, strength, and mobility of humans for engineering purposes.
When data of such form is collected it must be used in the design of systems, equipment, workplace, controls, access openings, and tools. The human’s interface with other system components should be dealt as objectively and efficiently as are other interface and hardware component designs. It is not acceptable to guess about human physical characteristics or to use the designer’s own measurements. Utilization of proper anthropometric and biomechanics information is expected for an optimal environmental workspace.
Using Design Limits
When faced with the application of anthropometric and biomechanics data, it is necessary to understand how to approach it and several steps must be considered. The design limits approach involves selecting the most suitable values and applying the proper related data in a design solution.
The design limit approach is a method of applying population or sample statistics and data about human physical characteristics to a design so that a desired portion of the user population is accommodated by the design. The range of users accommodated is a function of limits used in setting the population portion.
To comprehend, as far as possible, the design limits approach it is useful to consider the decisions that design personnel make in applying these human physical data, such as:
Select the right human physical characteristic and its applicable measurement characteristic for the design problem at hand;
Select the suitable population, representative sample, or guideline information on the selected human physical characteristic and measurement description to apply to the design problem;
Incorporate the measurement value as a basis for the design dimension, or in the case of biomechanics data, for the movement or force solution in the design problem;
Static Body Characteristics for Design Purpose
Before we get to see how common measurements have been found, about men and women, which can aid the design of equipment, workplace, etc. we first have to define what and how we select the correct percentile statistic.
By selecting the correct percentile statistic, we denote the design criteria for a human physical integration problem that will be based on the range of a population that must be suited to a certain working environment. For this, the designers and human factors experts must decide the correct statistical points (percentile statistics) keeping in mind the end goal to accommodate an appropriate range of the population for the specific design problem. [13]
The percentile statistic is determined by ranking all information values (human physical characteristics) in the sample and determining the percentage of data that fall at or below a specific datum value. This percentage is known as the percentile value of the selected datum and these percentile values are: [13]
1st percentile
5th percentile
50th percentile
95th percentile
99th percentile
Easily said, the values mentioned above are design clearance dimensions which must accommodate or allow passage of the body or parts of the body in the working environment. Now that the general knowledge has been set, we can move further and present the static human physical characteristics.
Table 5.1-1 Static Human physical characteristics (sitting)
Source: Adapted from Federal Aviation Administration, „Human Factors Design Guide”
Table 5.1-2 Static Human Physical Characteristics (sitting)
Source: Adapted from Federal Aviation Administration, „Human Factors Design Guide”
Exerted Forces
The most extreme measure of power or resistance outlined into a control ought to be dictated by the best measure of power that can be applied by the weakest individual prone to work the control. Control force limits, like most strength design limits, should be based upon the 5th percentile.
When it comes down to the maximum force that must be applied, mostly it will depend on factors such as the type of control, the body member used to operate the control, and the position of the body or body member during control operations.
This section can be highly used as design criteria for pilots and how to design the joystick that controls the aircraft. Knowing what forces a human can exert while in a sitting position, and also depending on the degree of the elbow flexion, can aid the designers and human factors experts to apply engineering methods in reducing the effort needed for such a control. Such forces will be presented in the table below
Table 5.1-3 Design Criteria Levels for Arm Strength (Newton)
Source: Adapted from Federal Aviation Administration, „Human Factors Design Guide”
General Workplace and Layout
The moment designers and human factors experts have concluded their final result when it comes to human physical characteristics, proper procedure can start in defining the workplace of an operator. For this, in this section, we will discuss some criteria’s and guidelines regarding the layout of the workplaces, console designs including arrangements for process control consoles and workstations with visual display.
A workplace, together with its associated equipment, will incorporate the effects of tasks, performance capabilities, physical dimensions, and viewing dimensions (as discussed in Chapter 4 Display and Control Design – Section 4.4.3 Location and Arrangement) so that from the inputs generated by an operator will result an expected human performance outcome.
As a general notion, a workplace is a location where personnel must attend in order to perform its given task on equipment or to control a certain activity. In some situations the maintenance activity will be correlated with the equipment controlled by an operators thus, the workplace must accommodate both maintainers and operators, with the philosophy that controls of an operator must be separated from those that are associated with maintenance activity.
For a workspace, one must think about the physical accommodation of an operator. In this situation, the layout of the workplace and equipment must be in terms with the anthropometric and biomechanical characteristics, discussed in the first section of this chapter, for the specific population of users for whom the system is being designed for.
Standard Console Design
Sit – Stand Consoles
In the following sections, values regarding console design will be presented that can be used in order to gain benefits such as potential cost savings or an optimal working environment for an operator that will aid him in performing his tasks. Their task performance can be influenced by:
Contour and slopes of the console;
The parallax in viewing displays;
Location of displays and controls;
The space to support the console operator;
These values are of standard form but in some situations, unique design solutions can be needed.
Table 5.2-1 Standard Console Layout
Source: Adapted from Federal Aviation Administration, „Human Factors Design Guide”
The table above, regarding standard console layout, is correlated with the following table
Table 5.2-2 Standard Console Illustration and Dimension Key
Source: Adapted from Federal Aviation Administration, „Human Factors Design Guide”
Accommodation that needs to be achieved when selecting a console in term with the given task:
Visibility over the top console (if required)
User mobility
Control and display demand for panel space (accessibility)
Volume of space necessary for leg room and essential equipment beneath the writing surface
Communications device
Horizontal Wrap – Around Console
This type of consoles are required if the task that needs to be generated through the console exceed the recommendation from Table 5.2 – 1 and Table 5.2 – 2. Such consoles and task are commonly seen in the case of air traffic controllers who have multiple displays to manage the information in order to accurately and safely manage aircrafts on radar screens.
Figure 5-1 Example of ATCO Wrap Around Console and Standard Wrap Around Console
Characteristics for Horizontal wrap around consoles: [13]
Panel Width: if the requirements exceed those for standard console design then panels should be within the reach of the 5th percentile users
Panel Angles: left and right panel angles should be measured from the frontal plane of the central segment, and the measurements must be within the reach of the 5th percentile users
Dimensions with vision over the top: width of the central segment shall not exceed 1.12 m, and that of the left – right segment shall not exceed 610 mm;
Width dimensions without vision over the top: width of the central segment shall not exceed 860 mm, and that of the left – right segment shall not exceed 610 mm;
Viewing angle: left to right viewing angle must not exceed 190 degrees. Angle should be reduced whenever possible;
Design and arrangement of multi person consoles
This type of arrangement is meant for task in which teams are formed in order to perform tasks which demand monitor, diagnose, or control ongoing process/operation, such as it is the case for the Operational Room for air traffic controllers.
The main reasons for multi person console arrangement are those that directly involve and affect the ongoing process and mission of the system. Secondary reasons are based on the direct process of monitoring or control. Such factors are:
Necessary team communication interaction;
Great number of personnel needed to handle high workload levels;
Supervisory viewing requirements, ongoing supervisory process control responsibilities, and supervisory information and communications needed;
Illumination, acoustic, and environmental requirements associated with primary tasks
Security requirements;
Also, in order to select a type of console, certain factors must be analyzed for a correct procurement. This selection will be made based on the type of position an operator must have, which was discussed earlier in this chapter, mainly: sit, sit – stand, stand position. A few main factors are:
Visual access required for normal control show zones which may decide the required see-over qualities;
Position communication requirements;
Personnel mobility;
Requirements to share information, displays, controls, or work surfaces with other personnel;
Figure 5-2 Types of Multiperson Console Arrangements
Source: Federal Aviation Administration, „Human Factors Design Guide”
An example of such positions can be seen in the Operational Room of Air Navigation Service Providers (ANSPr). In the example below, we have in the middle the U – Shape arrangement where usually supervisors and air traffic flow management position take place. In the left and right, we can see the so called “Banana Shape” where the consoles for air traffic controllers are placed. This form was obtained for ease of communication between controllers from different sectors when passing down aircrafts.
Figure 5-3 ANSPr Operational Room
Analysis of Airplane plus Pilot as a Closed Loop Control System – JAS 39 Gripen
For this last chapter we shall see a simplistic analysis of the control system for an aircraft JAS 39 Gripen and how the pilot gain (PG) (human factor) plays a role in stabilizing the aircraft. This will serve as a proof of how the human factor is an important aspect when it comes down to the design of a system so that it does not place unnecessary workload, stress or other unwanted strains, in order for the operator to maintain his optimal performance.
The following scheme below has been realized by using Matlab SIMULINK. For this we shall go into details about the main components, such as Pilot, Plane Dynamics, L, chteta.
Figure 6-1 Simulink Model of Plane and Pilot
The following block is one of most interest since it contains the components needed to see the time delay (TD) of the pilot. It takes the brain a finite amount of time between reception of the display situation by the eye nerves and the sending of a signal to the muscles of the arm and leg. Under normal circumstances, for test pilots the time delay is of 0.10 seconds. For most other pilots this time delay can take values between 0.12 to 0.20 seconds.
Figure 6-2 Pilot Gain
The block “Pilot” contains the following elements:
Transport Delay, representing the delay of the pilot in the case of an event
Transfer Function for a Proportional Derivative (PD) Controller, simulating the pilot’s input. The values for PD Controller are standard for simulating pilot’s response.
Figure 6-3 Components of block Pilot
Next in sequence is a state space representation for the plane dynamics, having as components the following matrices:
A – state matrix: a matrix describing the unforced dynamics of the system (plane). „A” can be either time dependent or time independent matrix, the last choice being called an autonomous system. For the case when the system is autonomous, the solution for the free system is given by the fundamental matrix is .
B, is the input matrix controlling the input vector.
C, is the output matrix selecting which states are selected as output
D, is the connection matrix
Figure 6-4 Plane Dynamics representation block
The “Chteta” block selects the components of the input vector, allowing only the theta angle to be output.
Figure 6-5 Chteta Block
And the last block, “L”, resonates the same as the Chteta block in which it allows only theta value to pass through.
Figure 6-6 L Block
When running the simulation, we can see through the scope 3 waves, such as:
Blue wave: this is an “event” having a step input in the system dynamics.
Purple wave: is the pilot’s delayed reaction being characterized by impulse inputs
Yellow wave: is the behavior of the system
The first simulation will be done by having a normal delayed time for the pilot of 0.10 seconds. This represents that the pilot is in top condition and has no unwanted strains.
Figure 6-7 Pilot Reaction with Time Delay 0.10s
We can clearly see that in the case of an “event”, the purple wave that represents the pilot’s reaction towards that event is delayed with 0.10s. With a normal reaction time the pilots adjusts the system, described by the yellow wave, back to its normal stability when it tends to sync with the blue wave.
For the purpose of experimenting and also to conclude how the human factor can influence a system, depending also on his state, be it in top physical/mental condition for optimum performance or in very poor physical/mental condition resulting in unwanted actions, we shall increase the time delay to 1s and 2s and see the results in the figures bellow.
These numbers are strictly fictional and for experimenting purpose only. In the case of both military and civil pilots, delays up to 1 – 2s are not met in real life.
Figure 6-8 Pilot Reaction with Time Delay 1s
Figure 6-9 Pilot Reaction with Time Delay 2s
As a conclusion for this final chapter, we can see from the last 2 figures above how the system overshoots from the stability domain and how extra effort is needed to rectify such mistakes. This happens due to the fact that the pilot can be either stressed, fatigued, or under the influence of psychoactive substances and a note must be made that further studies must be conducted in order to implement properly the human factor with a given system and how the system is designed.
Conclusions
Bibliography
The present paper has been accomplished by using concepts, ideas and guidelines for which I wish to credit the sources below.
Ergonomic principles in the design of work systems “Definition according to IEA (2012) and ISO 6385 (2004)” – http://www.iea.cc/whats/
Adapted from Stein BE, Stanford TR, Rowland BA (December 2009). "The neural basis of multisensory integration in the midbrain: its organization and maturation"
Oxford Aviation Training ATPL Vol. 8
Definition of cognition from Oxford dictionary http://www.oxforddictionaries.com/definition/english/cognition
Thagard, Paul, Cognitive Science, The Stanford Encyclopedia of Philosophy (Fall 2008 Edition), Edward N. Zalta
Marr, D. (1982). Vision: A Computational Investigation into the Human Representation and Processing of Visual Information. W. H. Freeman.
Kahneman, D.; Slovic, P.; Tversky, A. (1982). Judgment Under Uncertainty: Heuristics and Biases. Cambridge University Press, New York.
Baddeley, A.D. (1976). “The Psychology of Memory”
de Waard, D. (1996). “ The Measurment of Drivers’ Mental Workload”
Andre, A.D. (2001).“The Value of Workload in the Design and Evaluation of Consumer Products”
Endsley, M. R. (1988). „Design and evaluation for Situational Awareness enhancement.”
Airbus, „Human Performance – Enhancing Situational Awareness”
Federal Aviation Administration, „Human Factors Design Guide”
Copyright Notice
© Licențiada.org respectă drepturile de proprietate intelectuală și așteaptă ca toți utilizatorii să facă același lucru. Dacă consideri că un conținut de pe site încalcă drepturile tale de autor, te rugăm să trimiți o notificare DMCA.
Acest articol: Challenges In Implementing Human Factors In System Design (ID: 111548)
Dacă considerați că acest conținut vă încalcă drepturile de autor, vă rugăm să depuneți o cerere pe pagina noastră Copyright Takedown.