The SHEL Model: A Framework for Understanding Environmental Influences

Question 1 

The SHEL model is an ideational model that uses human factors to establish the interrelationship between the human subsystem and the aviation subsystem. The primary purpose of the model is to eliminate blame on humans as being the only cause of air accidents (SESAR Joint Undertaking, 2012). It achieves this purpose by indicating the connectedness of the different aviation factors that influence operator performance. The components of this model are the software, hardware, environment and liveware. The software component comprises of the policies, regulations which create the standard operating procedures. The hardware involves the air traffic controls and displays, and it engages the interface between people and the hardware. Environment considers the vicinity in which the operations occur, including the natural and social environment. The liveware component considers the people to people interactions such as amongst the crew members and the management. 

Question 2 

By involving the liveware-environment interface, the SHEL model takes care of human factors and flight physiology. The environment components considers the different interactions that humans will have with the flight environment. In that consideration, the functioning of the human body is taken into account to ensure that humans are not adversely affected by environmental changes. The physical environmental changes are encompassed with changes in pressure and oxygen which affects human body functions. 

Question 3 

The human body is accustomed to functioning at the ground level, where the atmospheric pressure is constant. However, in a flight environment, there occurs pressure and force changes impacting bodily functions. The respiratory system has to adjust the breathing rates to match the pressure changes (Federal Aviation Administration, n.d.) . The acceleration during flights also makes the heart to readjust its pumping to keep supplying blood to all organs. The drastic change in the environment may also induce a nauseating effect on the gastrointestinal tract. The musculoskeletal also experience strains due to the changes in motion during flights. 

Module 2 Subsections 

Question 1 

The five significant constituents of the atmosphere are nitrogen, oxygen, water, argon, and carbon dioxide at 78.08%, 20.95%, 0 to 4%, 0.93% and 0.0360% respectively. Nitrogen is used in the makeup of body tissues and plant growth. Oxygen is used to support life and in combustions. Water makes up the tissues of organisms and in everyday activities such as washing, plant growth, amongst others. Argon is an inert gas and is utilized in welding. Carbon dioxide is used in respiration and photosynthesis. 

Question 2 

The five constituents of the atmosphere occupy space and create a pressurized space. The components exert pressure to the earth’s surface. The constituents are essential to the flight environment as flying involves overcoming the pressure differences. Oxygen is also used to support life during flights and also in jet fuel combustion. Carbon dioxide is released from the combustion process. 

Question 3 

The atmospheric temperature, pressure and composition are interrelated. The composition of the atmosphere creates a pressure system. When the components are removed pressure is also eliminated. Temperature affects the pressure since an increase in temperature makes gases to expand, reducing the pressure while a decrease in temperature results in compression, which increases the pressure. 

Question 4 

The physiological zones of the atmosphere are, namely, the physiological efficient zone, the physiological deficient zone, and the space equivalent zone (Federal Aviation Administration, n.d.) . At the lower parts of the physiological region, the human body is quite accustomed. It functions properly with only slight problems such as the trapped gas in ears, and the gastrointestinal tract. At its upper layers, dizziness and headaches may be experienced. In the physiological deficient zone, the absence of atmospheric pressure causes complications such as hypoxia. In the space equivalent zone, the harsh conditions can cause boiling of the bodily fluids when one is exposed in an unprotected manner. 

Question 5 

The various types of aircraft pressurization systems are namely the isobaric, isobaric differential and the sealed cabin system (Federal Aviation Administration, n.d.) . The isobaric system involves using a preset cabin altitude for the whole duration of the flight. The isobaric differential system maintains a preset cabin altitude until a particular flight attitude is attained and henceforth a constant pressure differential is used. The sealed cabin system is restricted to space flights only and involves containment of the gases to be used in pressurizing by the craft. The different system can be degraded by decompression which takes three forms, slow, rapid and explosive. 

Module 3 Subsections 

Question 1 

The four types of hypoxia are namely, hypoxic hypoxia which occurs in the lungs, hypemic hypoxia occurring in blood, stagnant hypoxia that interferes with blood transport, and histotoxic hypoxia which affects the cells (Federal Aviation Administration, n.d.) . 

Question2 

The symptoms of hypoxia include nausea, headaches, dizziness, sight impairment, tiredness, air hunger, shivers, euphoria and hot and cold flashes (Federal Aviation Administration, n.d.) . Hypoxia is treated through the administration of 100 per cent oxygen to the patient. The symptoms of trapped gas include bleeding and spinning sensations in case of ear blocks, extreme pain under the cheekbones and eyebrows and the frontal part of the eyes in case of sinus block and elevated pains in the abdominal region when gas is trapped in the gastrointestinal tract (Federal Aviation Administration, n.d.) . The treatment of trapped gas involves attempts to remove the gas such as through ear and sinus-clearing through yawning, Valsalva maneuver, belching and farting. 

Question 3 

Trapped gas interferes with the movement of gases in which a gas is inhibited from leaving a system. This blockage may interfere with body functioning and cause discomfort. Similarly, hypoxia is caused by insufficiency of oxygen in blood, tissues or the cells, which may result from disturbance of bodily functions. Both conditions result in discomfiture. 

Question 4 

Decompression sickness is a medical state in which the inert gases especially nitrogen, usually held in solution form in tissues and body fluids, leave the body and form bubbles (Federal Aviation Administration, n.d.) . The condition is caused by exposure to low atmospheric pressures. Significant changes in altitude make one more susceptible to DCS due to the accompanied barometric pressure changes. Examples include sharp ascent from underground mining and diving. Sharp altitudinal increase accompanied by huge atmospheric pressure difference during flights also makes one vulnerable to the sickness. Other factors are recent joint or limb injuries, scuba diving before flights, longer duration of exposure at higher altitudes and repetitive exposures to high altitudes of over 18,000 feet. 

Question 5 

The purpose of a low-pressure chamber is to simulate a low-pressure environment in pressurized flight chambers. 

Module 4 Subsections 

Question 1 

The ear is made of three parts, the outer, middle and the inner ear (Stanford Children’s Health, n.d.). The outer ear comprises of the auricle and the ear canal. The middle ear is made up of the eardrum, the tympanic cavity and the ossicles. The inner ear comprises of the oval window, cochlea, semi-circular canals and the auditory tube. 

Question 2 

When sound waves get into the ear canal, they cause the vibration of the eardrum. The vibrations are transferred through the ossicles into the middle ear, setting the fluid in the semi-circular canals into motion (National Institute on Deafness and Other Communication Disorders, 2018) . The motion of the fluids causes the bending of the hair-like cells which transfer the vibrations into nerve impulses. 

Question 3 

The different types of hearing loss are conductive, sensorineural and mixed hearing loss. Their symptoms include perception of speeches and sounds as being muffled, habitually requesting persons to be slower and louder in their statements and the need to increase tv or radio volume. (Mayo Foundation for Medical Education and Research (MFMER), n.d.) . Sensorineural hearing loss is treated using hearing aids. Conductive hearing loss is treated through surgical operations and removal of the blockages. 

Question 4 

The anatomical components of the eye comprise of the choroid, ciliary body, cornea, fovea, iris, lens, macula, optic nerve, pupil, retina, sclera, and the vitreous humor (Garrity, 2019). These different components help achieve the primary function of the eye, recognizing visual stimulus. 

Question 5 

There are two types of visions, central and peripheral vision (Federal Aviation Administration, n.d.). The central vision is useful for recognition of objects and interpretation of colors. In flights, it helps pilots to obtain data from flight instruments, and upon its transformation by the brain, they get orientational information. It also helps to make decisions of speed, distance and depth. The peripheral vision is engaged in raising awareness of movements of both self and the immediate environment. It offers peripheral reference reminders that help retain spatial orientation. 

Question 6 

The main visual illusions in the flight environment are, namely, aerial perspective illusions, autokinetic illusion, and false visual reference illusions (Federal Aviation Administration, n.d.). Aerial perspective illusions are caused by the differences in widths of runways and down sloping or the upsloping of the tracks or the ultimate approach terrain. The autokinetic illusion occurs due to an elongated stare at a singular source of light, e.g. star in a somewhat darkened environment; thus, creating the impression that the light source might collide with the aircraft. The false visual reference illusions occur, especially during night flights in which the ground lights and the dark sky create an illusion of a false horizon. 

Module 5 Subsections 

Question 1 

The vestibular system comprises of 3 semi-circular canals and the otolith organs (Meeks and Bell, 2018). The canals contain sensory hair cells at one of their ends involved in nerve impulses. The otolith organs are made up of the utricle and saccule which are engaged in horizontal and vertical movements respectively. 

Question 2 

The semi-circular canals are aligned in an almost perpendicular manner allowing for the perception of angular acceleration in all the three dimensions of flight movement. The movement of the endolymph fluid and the hair cells aids in the perception of the direction. The otolith organs comprising of the utricle and saccule are aligned perpendicular to each other. The utricle is engaged in perception of horizontal movements while the saccule discerns the changes in vertical motion. 

Question 3 

Spatial disorientation (SD) has been classified into three types (Meeks and Bell, 2018). The first is the unrecognized SD in which no remedial input is made since the need is unidentifiable. The second is the recognized SD in which the pilot can identify the perception of confusion and apply the appropriate controls. The third is the incapacitating SD in which the pilot becomes debilitated to such an extreme level that they cannot regain control of the aircraft. It occurs due to conflicting sensory systems. 

Question 4 

Examples of vestibular illusions are the Somatogyral Vestibular, Leans, Graveyard Spiral, Coriolis, and Somatogravic Vestibular illusions amongst others (Meeks and Bell, 2018). The Somatogyral Vestibular illusions create an unfactual sense of turning due to conflict of motion with the semi-circular canal functions. The Leans illusion occurs during a sharp return to level flight following an extended turn. The Graveyard Spiral occurs due to getting into a prolonged turn which, when terminated, feels as if one is moving in the opposite direction. The Coriolis illusion is caused by the tilting of the head during a turn creating a sense of rolling, pitching and yawing of the aircraft. The Somatogravic Vestibular illusion is deciphered as pitch change during linear acceleration. 

Module 6 Subsections 

Question 1 

Linear acceleration occurs along a linear path, while angular occurs on a circular path with both the speed and direction changing. In contrast, radial occurs on a circular path but with the acceleration directed to the center of the circular path and a change in direction occurs but the speed does not change. 

Question 2 

The Gz vector which occurs due to the substantial gravitational force. 

Question 3 

The main +G force that has impacts on the body is the +Gz which is a gravitational force experienced from the head to the foot. It occurs when an aviator gets out of a steep dive or gets into an inside loop. The heart is forced to beat faster to keep blood flowing to the brain due to the G acceleration. If there occurs a physiologic failure, and the cardiovascular system does not keep up with these changes, the aviator’s performance is decreased, and unconsciousness may occur. 

Question 4 

G-LOC is G-Induced Loss of Consciousness which is defined as a condition in which the awareness is lost due to a sharp decrease in blood circulation to the brain (Banks et al., 2008). Continuum represents the sequence of events that precede G-LOC, namely, loss of vision, and possible unconsciousness (Whinnery and Forster, 2013) . The Stoll curve is a graphical representation of G-tolerance and depicts the time from the initiation of acceleration to the loss of consciousness. 

Question 5 

The Anti-G straining maneuver comprises of two components. One involves the contraction of the muscles, including the calves, thighs, arms, abdominal and shoulders muscles. The second component involves forcing air out of the lungs while keeping the glottis closed. 

Question 6 

A G-suit helps to push blood from the feet and legs into the heart and finally into the brain. It helps to keep aviators from falling unconscious. It offers pilots G protection during positive Gzs ( Eiken et al., 2007) . 

Question 7 

According to the Federal Aviation Administration (n.d.), the main factors that degrade a pilot’s G tolerance are alcohol intake, fatigue and dehydration. Although a pilot may not be alcohol intoxicated, alcohol intake causes hangovers which are detrimental in flights. Smokers exhibit reduced performance in high altitudes and high -G vicinities. Absence of a physical exercise routine can also degrade the G-tolerance. 

Module 7 Subsections 

Question 1 

Before the invention of electric lighting, humans depended on the sun’s light to determine if it was working or resting hours. The pattern of events involving daybreak and sunset had created a biological clock in which humans would be quite active during the day, and the body slowed down as the sunset and darkness ensued ( Brainard et al., 2015) . Sleep was naturally generated by the body in accordance with this established pattern of events. Sleeping patterns were well established, and the circadian rhythms were undisturbed. This rhythm enhanced human performance during working hours. 

Question 2 

Disruption of circadian rhythms is detrimental to human health. The significant effect of this disruption is fatigue (Goel et al., 2013). Despite efforts that may be made to prevent this disruption, some limitations hinder any achievements. The limitations include different time zones that an aircraft cruises, the darkened environment in the high skies and working during the sleeping hours. The circadian disturbances are caused by flying for consecutive nights in more than three days, crossing more than four time zones and taking successive trans meridian rotations in opposite directions. 

Question 3 

Different guidelines have been issued concerning sleep hygiene. According to Irish et al., (2015), the various guidelines that enhance individual sleep hygiene include: 

Avoiding caffeine, nicotine, and alcohol. 

Regular physical exercises. 

Effective stress management. 

Ensuring a calm bedroom environment by eliminating noises. 

Regular timing of the sleep patterns. 

Avoiding napping during the daytime. 

In addition to the above guidelines, the National Sleep Foundation (n.d) advocates for the following practices to enhance sleep hygiene: 

Avoiding heavy meals before bedtime and fatty foods and carbonated drinks which can result in indigestion. 

Exposure to the natural lighting to ensure that the circadian rhythms are well established. 

Engaging in relaxing routines before bedtime such as light stretches, a warm bath, or reading a book. 

Module 8 Subsections 

Question one 

Healthy nutrition is essential in ensuring individuals are in good health, thus can excellently execute different functions. In the absence of situations that disturb the bodily balance, individuals can maximize their performance, and the vice versa is also true. Vibrations disturb the normal functioning of body systems such as sound perception. Nutrition, stress and vibration are interrelated, and whenever one of them is poor, human performance deteriorates. 

Question 2 

Whenever humans are faced with a physical, emotional or psychological condition which disturbs the normal body balance (stress), the body readjusts by creating a coping mechanism to unset the nonequilibrium (Harvard Health Publishing, 2011). If the stress response mechanism is not successful, severe health risks may occur including, hypertension, depression, headaches, and anxiety. 

Question 3 

A balanced diet should contain carbohydrates, proteins, fats, vitamins, minerals, fibre and water. Carbohydrates and fats provide energy for different body functions. Proteins are used in body growth and development, including cells, muscles, and organs. Vitamins support the various body systems such as the immune system. Minerals perform structural and regulatory roles. Water makes up the body and helps in body functions such as digestion. Fibres are useful in helping in the absorption of nutrients into the body and helping in bowel movement ( Dhingra et al., 2012) . 

Question 4 

Body Mass Index is used in adults to determine one’s ideal weight for health. By dividing the body weight in kilograms by the height in meters squared, individuals can know whether they are underweight, healthy weight, overweight or obese ( Nuttall, 2015) . Knowledge of one’s BMI is essential in determining the kind of health measures one should take. 

Question 5 

Vibrations create a shock-like motion which the human body is not accustomed to. Consequently, the musculoskeletal organs are likely to become strained and fatigued by this motion. They also cause noise and discomfort, which are likely to reduce a pilot’s performance. 

Module 9 Subsections 

Question1 

Automation is beneficial since it increases the comfortability of the passengers and crew, enhances flight path control and weather detection and frees aviators from some non-rewarding tasks. The drawbacks of automation include failure to diagnose problems in case the automation fails and inability to recognize speed deviations in case of malfunctions as a result of being accustomed to the automation of the process (Flight Safety Foundation, 2020). 

Question 2 

Automation of flight operations has the drawback of making aviators dependent on the automation. Hence, in case of malfunctions, they are unable to take the right corrective procedures. The problem can be solved through a comprehensive aviators training program that incorporates partial automation, to enable the pilots maintain the competence of semi-automatic handling of flight operations in case of malfunctions. 

Question 3 

Situational awareness (SA) is the interpretation of the components in a vicinity with regard to space and time while estimating their status in the immediate future (Flight Safety Foundation, 2019). In flights, SA involves recognition of all the on-going activities during flying, controlling and in maintenance. 

Question 4 

Some of the factors that degrade an individual’s situational awareness include inadequate training, poor decision making, failure to stick to established procedures, poor crew coordination, delayed responses, negligence of appropriate action, poor comprehension of the prevailing conditions amongst other factors (Flight Safety Foundation, 2016). 

Question 5 

The DECIDE model comprises of the following components, detection of problem necessitating an action, estimation of the importance of the action to be taken, choosing a desirable course of action, identification of appropriate steps to execute the course of action, doing the appropriate action and finally evaluating the effects of the action. The components create a sequential decision-making process that is often effective. 

Question 6 

To handle inflight medical emergencies, aircraft should be equipped with appropriate medical equipment. The first step involves making the right diagnosis through proper assessment of the patient if there is a medic onboard. The right treatment should then be administered. In the absence of a medical practitioner and for severe conditions requiring further attention, the pilot should decide whether to divert the flight or proceed to the planned destination. 

References 

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Brainard, J., Gobel, M., Scott, B., Koeppen, M., & Eckle, T. (2015). Health implications of disrupted circadian rhythms and the potential for daylight as therapy. Anesthesiology: The Journal of the American Society of Anesthesiologists , 122 (5), 1170-1175. 

Dhingra, D., Michael, M., Rajput, H., & Patil, R. T. (2012). Dietary fibre in foods: a review. Journal of food science and technology , 49 (3), 255-266. 

Eiken, O., Kölegård, R., Bergsten, E., & Grönkvist, M. (2007). G protection: interaction of straining maneuvers and positive pressure breathing. Aviation, space, and environmental medicine , 78 (4), 392-398. 

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Goel, N., Basner, M., Rao, H., & Dinges, D. F. (2013). Circadian rhythms, sleep deprivation, and human performance. In Progress in molecular biology and translational science (Vol. 119, pp. 155-190). Academic Press. 

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Mayo Foundation for Medical Education and Research (MFMER).  Hearing loss - Diagnosis and treatment - Mayo Clinic . Mayoclinic.org. Retrieved 6 March 2020, from https://www.mayoclinic.org/diseases-conditions/hearing-loss/diagnosis-treatment/drc-20373077 . 

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Whinnery, T., & Forster, E. M. (2013). The+ Gz-induced loss of consciousness curve. Extreme physiology & medicine , 2 (1), 19.