Vision and Hearing 9.2.1-2 PDF

Vision and Hearing (9.2.1-2) Learning Objectives 9.2.1 Explain the importance of vision to aircraft maintenance workers and how vision may be affected in individuals and under certain conditions (Level 2). 9.2.2.1 Explain the importance of hearing to aircraft maintenance workers and how...

Vision and Hearing (9.2.1-2) Learning Objectives 9.2.1 Explain the importance of vision to aircraft maintenance workers and how vision may be affected in individuals and under certain conditions (Level 2). 9.2.2.1 Explain the importance of hearing to aircraft maintenance workers and how hearing may be affected in individuals and under certain conditions (Level 2). 9.2.2.2 Describe strategies for protecting hearing in an aircraft maintenance environment (Level 2). 2023-01-12 B-09 Human Factors Page 41 of 340 CASA Part 66 - Training Materials Only  Introduction Summary Humans are very capable animals, yet our capability has limitations. We perform poorly at night and in the cold. We are sometimes not strong enough, or our vision is not sharp enough and we need tools to assist us. We often cannot remember things and our brain does not work well when we are under stress or dealing with competing priorities. The intention of this chapter is to provide an overview of those key physical and mental human performance characteristics which are likely to affect an aircraft maintenance engineer in their working environment, such as vision, hearing, information processing, attention and perception, memory, judgement and decision-making. 2023-01-12 B-09 Human Factors Page 42 of 340 CASA Part 66 - Training Materials Only  Human Performance Limitations Must be Taken into Account Humans are an integral part of the maintenance engineering system, so human performance limitations must be taken into account when considering aircraft maintenance and workplace safety. Just as certain mechanical components used in aircraft maintenance engineering have limitations, engineers themselves have certain capabilities and limitations that must be considered when looking at the maintenance engineering system. Rivets will eventually fail if enough force is applied to them. The same principles apply to human performance, which is likely to degrade and eventually ‘fail’ under certain conditions (e.g., stress). Humans are limited by our physiology and psychology. Humans need tools, vehicles, clothes, air conditioning, computers and Personal Protective Equipment (PPE) all because we lack physical or mental characteristics that are needed to do certain tasks. People can also fail to function properly in certain situations. Physically, humans become fatigued, are affected by the cold, can break bones in workplace accidents and suffer other physical ailments. Mentally, humans can make errors, have limited perceptual powers and can exhibit poor judgement due to lack of skills and knowledge. Unlike mechanical components, human performance is also affected by social and emotional factors. Failure by aircraft maintenance personnel will likely be to the detriment of aircraft safety. Image by Herry Sutanto on Unsplash Humans are limited by our physiology and psychology 2023-01-12 B-09 Human Factors Page 43 of 340 CASA Part 66 - Training Materials Only  The AME is the central part of the aircraft maintenance system. It is therefore very useful to have an understanding of how various parts of their body and mental processes function and how performance limitations can in uence their effectiveness at work. Image by Maria Teneva on Unsplash People can also fail to function properly in certain situations 2023-01-12 B-09 Human Factors Page 44 of 340 CASA Part 66 - Training Materials Only  Vision Factors Affecting Clarity of Sight The eye is very sensitive in the right conditions (e.g. clear air, good light). The eye has approximately 1.2 million nerve cells leading from the retinas to the area of the brain responsible for vision, while there are only about 50 000 from the inner ears, making the human eye about 24 times more sensitive than the ear. Visual acuity is the ability of the eye to discriminate sharp detail at varying distances. Various factors can affect and limit the visual acuity of the eye. These include: Physical factors, such as: Physical imperfections in one or both eyes (short sightedness, long sightedness) Age. Environmental factors, such as: Amount of light available Clarity of the air (e.g., dust, mist, rain, etc.). Nature of the object being viewed, such as: Size and contours of the object Contrast of the object with its surroundings Relative motion of the object Vibration of the object Distance of the object from the viewer. The angle of the object from the viewer. The ingestion of foreign substances, such as: Drugs Medication Alcohol Cigarettes. 2023-01-12 B-09 Human Factors Page 45 of 340 CASA Part 66 - Training Materials Only  Image by Peter Heeling from Skitterphoto Various factors can affect and limit the visual acuity of the eye 2023-01-12 B-09 Human Factors Page 46 of 340 CASA Part 66 - Training Materials Only  Physical Factors Lens Imperfections Long sightedness is caused by a shorter than normal eyeball which means that the image is focused behind the retina. If the cornea and the lens cannot use their combined focusing ability to compensate for this, blurred vision will result when looking at close objects. A convex lens overcomes long sightedness by bending light inwards before it reaches the cornea. Short sightedness occurs when the eyeball is longer than normal, causing the image to be formed in front of the retina. If the accommodation of the lens cannot counteract this then distant objects are blurred. A concave lens overcomes short-sightedness by bending light outwards before it reaches the cornea. Image by Dani Link from Pixabay A concave lens overcomes short-sightedness by bending light outwards before it reaches the cornea 2023-01-12 B-09 Human Factors Page 47 of 340 CASA Part 66 - Training Materials Only  Ageing As a person grows older, the lens becomes less exible meaning it is unable to adjust suf ciently. This is known as presbyopia and is a form of long sightedness. Consequently, after the age of 40, spectacles may be required for near vision, especially in poor light conditions. Fatigue can also temporarily affect the lens’ ability to accommodate, causing blurred vision for close work. Blind Spot The blind spot is a normal visual de ciency at the point where the optic nerve enters the retina (between the rods and cones). At this point the retina is not sensitive to any light shining on it. Facial features such as the nose can also contribute to this problem. Other Visual Imperfections include: Cataracts - clouding of the lens usually associated with exposure to UV light and ageing; Astigmatism - a misshapen cornea causing objects to appear irregularly shaped; Glaucoma - a build-up in pressure of the uid within the eye which can cause damage to the optic nerve and even blindness; Migraine - severe headaches that can cause visual disturbances. 2023-01-12 B-09 Human Factors Page 48 of 340 CASA Part 66 - Training Materials Only  Environmental Factors Light Vision can be improved by increasing the lighting level, but only up to a point. Increased illumination often causes increased glare. Older people are more affected by the glare of re ected light than younger people. Moving from an extremely bright environment to a dimmer one has the effect of reducing vision being reduced until the eyes get used to less light being available. This is because the eyes become adapted to ambient light. Moving from a bright hangar, or from inside an aircraft, to a dark apron area at night can mean that maintenance workers must wait for their eyes to adapt to the lower ambient light. In low light conditions, it is often easier to focus if you look slightly to one side of an object. This allows the image to fall onto the part of the retina that has many rods. Image by Mihai Paraschiv from Pixabay Environmental factors like poor lighting can affect vision Airborne Particles Any particles in the air such as dust, rain or mist can interfere with the transmission of light through the air, distorting what is seen. This can be even worse when spectacles are worn, as they are susceptible to getting dirty, wet, misted up or scratched. 2023-01-12 B-09 Human Factors Page 49 of 340 CASA Part 66 - Training Materials Only  Contact Lenses in Dry and Dusty Atmospheric Conditions The maximum wear time for contact lenses is usually 8 to 12 hours. Extended wear may have adverse effects on the eyes, such as dryness and irritation. This is particularly important if working in an environment which is excessively dry or dusty, as airborne particles may also affect contact lens wear. Goggles should be worn where necessary to exclude dust from the eyes. 2023-01-12 B-09 Human Factors Page 50 of 340 CASA Part 66 - Training Materials Only  The Nature and Angle of the Object Being Viewed Size Visual cues often refer to the comparison of objects of known size to those of objects of unknown size. An example of this is that we learn as a child to associate small objects with being further away. In general terms, larger objects are more easily seen than smaller objects, but it is no use moving too close. There needs to be an appreciation of the micro and macro view. Contrast Similarly, if an object does not stand out well from its background (poor contrast with its surroundings), it is harder to distinguish its edges and hence its shape. Movement and Vibration Movement and relative motion of an object, as well as distance and angle of the object from the viewer, can increase visual demands. If the object, or the viewer is vibrating, then the view of the object will not be clear. Image by Johannes Rapprich from Pexels Movement and relative motion of an object can increase visual demands 2023-01-12 B-09 Human Factors Page 51 of 340 CASA Part 66 - Training Materials Only  Colour Although not directly affecting visual acuity, inability to see particular colours can be a problem for the aircraft maintenance engineer. Among other things, good colour vision for maintenance engineers is important for: Recognising components Distinguishing between electrical wires Using various diagnostic tools Recognising various lights on the air eld (e.g., warning lights). The most common type is colour vision de ciency is distinguishing between red and green. More rarely, it is possible to confuse blues and yellows. Ageing also causes changes in colour vision. This is a result of progressive yellowing of the lens, resulting in reduced colour discrimination in the blue-yellow range. Image by MichaelGaida from Pixabay Good colour vision for maintenance engineers is important for recognising tarmac markings 2023-01-12 B-09 Human Factors Page 52 of 340 CASA Part 66 - Training Materials Only  Colour Loss at Night Central vision is poor at night or with low illumination. Better results are obtained by looking slightly to one side of an object, rather than directly at it. This effect can be demonstrated by counting a group of faint lights in the distance when looking directly at them, then by looking some 10 degrees to one side. It will be possible to see more lights. Some people who have perfect day vision may be myopic (short-sighted) at night. Night myopia is often not recognised well by people who have it, but can present a signi cant hazard, particularly because of the false con dence instilled from having good vision by day. Image by skeeze from Pixabay Central vision is poor at night or with low illumination 2023-01-12 B-09 Human Factors Page 53 of 340 CASA Part 66 - Training Materials Only  The Angle of the Object from the Viewer Objects are never as clear when they are looked at from an angle, compared to front-on. In addition, the background behind an object may change if the observer changes position. This may affect the clarity of the object. ‘Parallax' refers to the way an object seems to change its position when your own point of observation changes. Instrument reading can suffer from parallax error if the instrument is not read from directly in front. Older instruments are particularly susceptible to this, as there is often a physical gap between the instrument pointer/needle and the face of the dial. Tel-Tru Parallax error 2023-01-12 B-09 Human Factors Page 54 of 340 CASA Part 66 - Training Materials Only  Ingestion of Foreign Substances that Affect Eyesight Vision can be adversely affected by using certain drugs and medications, drinking alcohol, and smoking cigarettes. With smoking, carbon monoxide builds up in the bloodstream allowing less oxygen to be carried in the blood to the eyes. This is known as hypoxia and can rapidly impair the sensitivity of the rods. Alcohol can have similar effects, even hours after the last drink. Image by Karolina Grabowska from Pexels Vision can be adversely affected by using certain drugs and medications 2023-01-12 B-09 Human Factors Page 55 of 340 CASA Part 66 - Training Materials Only  Vision for Aircraft Maintenance Vision is critical for aircraft maintenance, especially when conducting inspection tasks. It is important for maintenance workers, particularly those who are involved in inspection tasks, to have adequate vision to meet the task requirements. As discussed previously, age and problems developing in the eye itself can gradually affect vision. Without regular vision testing, AMEs may not notice that their vision is deteriorating. Often, airline companies or airports will set the eyesight standards for reasons other than aircraft maintenance safety, for insurance purposes, or for driving on the air eld. It is important for the individual to recognise when their vision is adversely affected, either temporarily or permanently, and to consider carefully the possible consequences should they continue to work if the task requires good vision. Photo by Adrian Smith on Unsplash It is important for the individual to recognise when their vision is adversely affected 2023-01-12 B-09 Human Factors Page 56 of 340 CASA Part 66 - Training Materials Only  Ambient and Task Lighting A maintenance organisation must provide a well-lit area for aircraft inspection tasks or provide supplementary lighting if the ambient lighting is not suf cient. Individual maintenance workers must ensure that illumination is adequate for the inspection tasks they must perform. Western Technology Task lighting 2023-01-12 B-09 Human Factors Page 57 of 340 CASA Part 66 - Training Materials Only  Hearing Performance and Limitations of the Ear The performance of the ear is associated with the range of sounds that can be heard, both in terms of the pitch (frequency) and the volume of the sound. The audible frequency range that a young person can hear is typically between 20 and 20 000 cycles per second or (Hertz), with greatest sensitivity at about 3000 Hz. Volume (or intensity) of sound is measured in decibels (dB). The audible frequency range that a young person can hear is typically between 20 and 20 000Hz 2023-01-12 B-09 Human Factors Page 58 of 340 CASA Part 66 - Training Materials Only  Impact of Noise on Hearing Noise can have various negative effects in the workplace. It can: Be annoying (e.g. sudden sounds, constant loud sound). Interfere with verbal communication between individuals in the workplace. Cause accidents by masking warning signals or messages. Be fatiguing and affect concentration, decision-making. Damage workers’ hearing (either temporarily or permanently). Intermittent and sudden noise are generally considered to be more disruptive than continuous noise at the same level. In addition, high frequency noise generally has a more adverse effect on performance than lower frequency. Noise tends to increase errors and variability rather than directly affect work rate. Image by @chairulfajar from Unsplash. Noise can damage workers’ hearing (either temporarily or permanently) 2023-01-12 B-09 Human Factors Page 59 of 340 CASA Part 66 - Training Materials Only  Hearing Impairment Hearing loss can result from exposure to noise of even relatively short duration noise. The degree of impairment is in uenced mainly by the intensity of the noise. The hearing loss can be temporary, lasting from a few seconds to a few days, or permanent. Temporary hearing loss may be caused by relatively short exposure to very loud sound. Impact of noise on hearing Within the inner ear, hair-like cells convert the physical pulse of sound in the air to electrical signals that are sent to the brain. With loud sound, the hair-like cells in the inner ear are pushed over and take time to recover and stand upright again. When the hair-like cells are pushed over, hearing performance is reduced and, in some people, this also causes a ringing sound called tinnitus. With additional exposure, the extent of recovery gradually decreases, and hearing loss becomes permanent. Thus, regular exposure to high levels of noise over a long period may permanently damage the hair-like cells in the cochlea, leading to irreversible hearing impairment. Typical workplace health and safety regulations state that an employer must assess the risk to employees’ hearing, tell the employees about the risks provide employees with personal ear protection devices and explain their use. 2023-01-12 B-09 Human Factors Page 60 of 340 CASA Part 66 - Training Materials Only  For especially loud areas, employers must do all that is possible to reduce exposure to the noise and mark zones where noise reaches a dangerous level and post signs to restrict entry. Efforts should be made to exclude people from noisy areas as much as possible by means of physical barriers with speci c signage. Other work areas must also be isolated from the severe noise. Presbycusis Hearing deteriorates naturally as one grows older. This is known as presbycusis. It affects the ability to hear high-pitched sounds rst and may occur gradually from age 30 onwards. When this natural decline is exacerbated by noise-induced hearing loss, it can obviously occur rather sooner. Cochlea.org Hearing is impacted by age 2023-01-12 B-09 Human Factors Page 61 of 340 CASA Part 66 - Training Materials Only  Hearing Protection Hearing protection is available, to a certain extent, by using ear plugs or earmuffs. Noise levels can be reduced (attenuated) by up to 20 dB using ear plugs and 40 dB using earmuffs. However, using ear protection will tend to interfere with verbal communication. Despite this pitfall, it must be used consistently and as instructed to be effective. It is good practice to reduce noise levels at the source or move the noise away from workers. Often this is not a practical option in the aviation maintenance environment. Hearing protection should always be used for noise, of any duration, above 115 dB. This means the aircraft maintenance engineer will almost always need to use some form of hearing protection when in reasonably close proximity (200-300 metres) to aircraft whose engines are running. Image by Cetteup from Unsplash Noise levels can be reduced (attenuated) by up to 20 dB using ear plugs and 40 dB using earmuffs 2023-01-12 B-09 Human Factors Page 62 of 340 CASA Part 66 - Training Materials Only  Hearing Awareness When Conducting Aircraft Maintenance Hearing may be damaged when conducting aircraft maintenance. It is very important that aircraft maintenance workers understand the limited ability of the ears to protect themselves from damage due to excessive noise. Even though engineers should be given appropriate hearing protection and trained in its use, it is up to individuals to ensure that they actually put this to good use. It is a common misconception that the ears get used to constant noise or will always recover from a loud noise exposure. If noise is too loud, it will damage the ears gradually and be irreparable. If noise is too loud, it will damage the ears gradually and insidiously and be irreparable 2023-01-12 B-09 Human Factors Page 63 of 340 CASA Part 66 - Training Materials Only