Introduction

Annotation.

This course addresses the core problem of human limitations in the aviation environment where technology has advanced far beyond the design limits of the human body and mind. Modern aircraft reliability has shifted the dominant accident cause from mechanical failure to human factors, accounting for roughly 73 percent of events since the 1950s. Professional pilots preparing for the EASA ATPL theoretical knowledge examination must master both physiological constraints such as hypoxia and psychological processes such as threat and error management. The material fills the critical gap between textbook knowledge and practical flight-deck application by converting regulatory syllabus content into actionable self-study sequences that reduce error rates and improve decision quality under operational pressure.

Course goal.

After completing this course you will be able to identify, explain and mitigate the principal human performance limitations that affect flight safety, correctly apply the relevant ICAO and EASA standards, and demonstrate competence in threat and error management, hypoxia recognition and crew resource practices required for the ATPL 040 examination and subsequent line operations.

Who this course is for.

This course is designed for student pilots enrolled on an EASA ATPL theoretical knowledge course, licensed pilots preparing for licence conversion or recurrent examinations, and flight instructors who need a structured reference for human factors teaching. It is equally useful for cabin crew and operations staff who require a solid grounding in the physiological and psychological factors that influence flight safety.

It is not intended for recreational pilots seeking only a light overview, nor for medical professionals who already possess specialist aeromedical knowledge. Readers without basic secondary-school biology may need supplementary anatomical references before tackling the circulation and respiration modules.

Module 1. Basic Concepts of Human Performance in Aviation

Human Factors is defined by ICAO as the study of people in their working and living environments, their relationship with equipment, procedures and other people, and the overall performance of human beings within the aviation system. The twin objectives are safety and efficiency. In practice this means optimising the interface between the pilot and the aircraft through systematic application of human sciences within system engineering. The modern pilot must treat Human Factors as a continuous operational tool rather than a theoretical subject. A practical starting point is to review every flight against the five elements of safety culture: informed, reporting, learning, just and flexible. When an undesired aircraft state appears, ask which defensive layer failed and which countermeasure of the Avoid-Trap-Mitigate sequence could have prevented the progression. This habit converts abstract ICAO definitions into daily cockpit discipline and directly reduces the probability that latent organisational threats will align with active pilot errors.

The history of aviation accidents shows a clear shift. Early aircraft suffered primarily from mechanical failure; after the 1950s human factors became the dominant cause, remaining at approximately 73 percent of all accidents. Controlled Flight Into Terrain remains the single most common accident category. The five most frequent pilot-induced causes, in order, are loss of directional control, poor judgement, airspeed not maintained, poor pre-flight planning and decision making, and failure to maintain ground clearance. The phases of flight most exposed are intermediate and final approach, landing, take-off and descent. When reviewing any accident report, map the event onto Reason’s Swiss Cheese Model: identify the latent organisational failures, the active unsafe acts, and the final alignment of holes that allowed the hazard to reach the aircraft. This structured analysis turns statistical knowledge into a personal risk-reduction checklist that can be applied before every sector.

A competent pilot combines a high sense of responsibility, academic and handling ability, motivation, communication skill, flexibility, physical fitness, reliability, a balanced personality, team orientation, calmness under stress, attention to detail, and competence in risk assessment plus stress and crew management. Training must be relevant, regular, clear, time-efficient, participative and supported by readable revision material. Self-training is mandatory: after every flight perform a personal debrief that asks what threats were present, which errors occurred, and which undesired aircraft states developed. Maintain a personal log of these items and cross-reference them against company threat and error management data. Over time this self-monitoring builds the automatic pattern recognition that distinguishes an average pilot from a consistently safe one. Airlines increasingly reject applicants who smoke; the same discipline that stops smoking supports the wider self-management required for long-term career health.

Safety culture is the enduring value and prioritisation of safety by every member of every group at every level of an organisation. An open culture encourages active participation in improvement; a closed culture withholds information on threats and errors. National culture, both governmental and ethnic, further shapes attitudes. Leadership, visible commitment and consistent example are the three factors that most reliably promote a healthy safety culture. In daily operations this translates into immediate reporting of any latent threat, refusal to accept pressure that compromises minimum equipment list compliance, and active support for colleagues who raise safety concerns. When a policy change is introduced, verify that the ripple effects on rostering, maintenance schedules and crew duty times have been assessed; otherwise a well-intentioned commercial decision can quietly degrade the defensive barriers that protect the flight.

Reason’s Swiss Cheese Model represents organisational defences as successive slices of Swiss cheese. Each slice contains holes that represent latent or active weaknesses; the holes continuously change size and position. An accident occurs only when the holes momentarily align, allowing a hazard trajectory to pass through every defensive layer. In the cockpit the practical application is to treat standard operating procedures, checklists, briefings and training as the hard slices, and personal vigilance plus crew cross-checking as the soft slices. When an error is trapped, the system has succeeded; mitigation after an undesired aircraft state has already developed still counts as success because safety margins have been restored. Never regard successful mitigation as failure. Record the event, share it through the company reporting system, and adjust personal scan patterns so that the same hole is less likely to open on the next flight.

Threat and Error Management comprises three components: threats, errors and undesired aircraft states. Latent threats include poor equipment design or visual illusions; environmental threats include weather, terrain and ATC; organisational threats include operational pressure and documentation deficiencies. Errors are classified as aircraft handling, procedural or communication. Undesired aircraft states are flight-crew-induced deviations in speed, position, configuration or system status that reduce safety margins. The universal countermeasure sequence is Avoid-Trap-Mitigate. Avoidance is performed at low workload by forecasting problems; trapping occurs in real time by detecting and correcting threats or errors before they propagate; mitigation deals with the consequences after an error has already produced an undesired state. Practise the sequence deliberately on every simulator detail and every line flight until the three verbs become automatic responses rather than conscious recall.

Module 2. The Circulation System and Its Operational Implications

The circulatory system consists of the pulmonary circuit that oxygenates blood in the lungs and the systemic circuit that delivers oxygenated blood to all tissues. Blood comprises plasma, red cells containing haemoglobin, white cells that defend against infection, and platelets that enable clotting. Oxygen is carried almost entirely by haemoglobin forming oxyhaemoglobin; a small amount dissolves in plasma. Carbon dioxide is transported mainly as carbonic acid. Cardiac output is the product of stroke volume and heart rate; at rest it averages 5.0 to 5.5 litres per minute and can increase linearly with pulse rate up to approximately 180 beats per minute. Above that rate the heart cannot fill adequately and output declines. In flight the practical implication is that any factor raising heart rate—exercise, altitude, temperature, emotion or the fight-or-flight response—increases oxygen demand and therefore shortens time of useful consciousness if cabin altitude is elevated. Monitor personal pulse during high-workload phases and treat an unexplained rise as an early indicator that physiological reserves are being consumed.

Carbon monoxide binds to haemoglobin with an affinity 210 to 250 times greater than oxygen, forming bright-pink carboxyhaemoglobin. Sources include leaking exhausts and combustion heaters. Symptoms begin with headache or tightness across the forehead, followed by nausea, dizziness, impaired vision, lethargy, impaired judgement, personality change, memory loss, slowing of breathing and pulse, loss of muscular power, flushed cheeks, cherry-red lips, convulsions and death. Effects are cumulative; repeated exposure on successive days can produce serious poisoning even if each individual dose is small. Treatment requires immediate shut-down of cabin heat, cessation of all smoking, administration of 100 percent oxygen if available, maximum fresh-air ventilation, and landing as soon as practicable. Carbon monoxide detectors must be checked regularly in flight and maintained by engineering. A practical cockpit habit is to open a fresh-air vent whenever cabin heat is selected; the slight temperature penalty is far preferable to undetected poisoning.

Smoking elevates carboxyhaemoglobin by approximately 7 percent in a twenty-cigarette-per-day smoker, equivalent to a physiological altitude increase of 4000 to 5000 feet. Combined with a typical cabin altitude of 6000 to 8000 feet the smoker experiences the effects of 10 000 to 12 000 feet and therefore develops anaemic hypoxia earlier than a non-smoker. Additional consequences include lung cancer, breathing and circulatory problems, reduced g-tolerance, elevated heart-attack risk, degradation of night vision, and nicotine-driven addiction. Many airlines refuse to train smokers. The only effective operational rule is absolute: if you smoke, stop; if you do not smoke, never start. Night-vision loss is particularly insidious because it begins at altitudes as low as 5000 feet and is rarely noticed by the pilot until instrument or external visual performance has already degraded.

Blood pressure is recorded as systolic over diastolic values in millimetres of mercury. A healthy young adult typically shows 120/80. Hypertension of 160/95 or higher is assessed as unfit under JAR-FCL 3. Causes include stress, smoking, excessive dietary fat or salt, age, obesity, lack of exercise and arterial hardening. Symptoms may be absent until a stroke or heart attack occurs; screening therefore remains essential. Hypotension normally presents little risk but extreme low pressure reduces g-tolerance, resistance to shock and overall alertness. Pressoreceptors in the carotid sinus detect pressure changes and trigger compensatory adjustments in heart rate and vessel tone to maintain cerebral blood flow. Under high positive g the system is overwhelmed and grey-out or black-out occurs; under negative g the reverse produces red-out and possible vessel rupture. After blood donation aircrew must rest supine for 15–20 minutes, drink freely, and remain grounded for a minimum of 24 hours. Pulmonary embolism risk rises on long-haul flights; regular cabin walking and leg exercises reduce clot formation in the lower limbs.

Module 3. Oxygen, Respiration and Altitude Physiology

Oxygen intake occurs through external respiration driven by the intercostal muscles and diaphragm. Air travels via the trachea and bronchi to the alveoli where gas exchange takes place by diffusion according to Fick’s Law. Tidal volume is approximately 500 ml, inspiratory reserve 3000 ml, expiratory reserve 1100 ml and residual volume 1200 ml in the average male; female values are 20–25 percent lower. The brain, although only 2 percent of body mass, consumes 20 percent of total oxygen; brain cells die after roughly two minutes without oxygen. Carbon dioxide concentration in blood is the primary trigger for breathing rate: elevated CO₂ increases ventilation until the acid-base balance is restored. In the cockpit the practical consequence is that any condition raising metabolic demand—exercise, cold-induced shivering, illness or anxiety—shortens the time available before hypoxia becomes critical. Always brief passengers on oxygen equipment before flight above 10 000 feet and verify that supplementary oxygen is serviceable and correctly configured.

The ICAO standard atmosphere is defined by a mean-sea-level temperature of +15 °C, pressure of 1013.25 hPa (760 mm Hg), density of 1225 g m⁻³ and a lapse rate of 1.98 °C per 1000 ft up to 36 090 ft. Atmospheric composition remains essentially constant to 70 000 ft: 21 percent oxygen, 78 percent nitrogen, 0.93 percent argon, 0.03 percent carbon dioxide and 0.04 percent rare gases. Dalton’s Law states that total pressure equals the sum of partial pressures; therefore the partial pressure of oxygen falls in exact proportion to total pressure. At sea level alveolar oxygen partial pressure is approximately 103 mm Hg; the minimum acceptable value for normal operations is 55 mm Hg, reached at a cabin altitude of about 10 000 ft. Boyle’s Law governs volume changes with pressure and explains otic and gastrointestinal barotrauma. Henry’s Law governs the amount of gas dissolved in liquid and underpins decompression sickness. Charles’ Law and the combined gas law complete the set required for quantitative understanding of cabin altitude effects.

Oxygen requirements by altitude are summarised as follows: air only up to 10 000 ft; oxygen-air mixture from 10 000 ft to 33 700 ft; 100 percent oxygen from 33 700 ft to 40 000 ft; and 100 percent oxygen under positive pressure above 40 000 ft. These thresholds maintain alveolar partial pressure at or above the sea-level equivalent of 103 mm Hg or, at the absolute limit, the 55 mm Hg minimum. Hypoxic hypoxia develops when inspired oxygen partial pressure is insufficient. Stages progress from the indifferent zone (surface to 10 000 ft) through compensatory (10–15 000 ft), disturbance (15–20 000 ft) to critical (20–23 000 ft). Symptoms include personality change, impaired judgement, headache, tingling, hyperventilation, muscular impairment, short-term memory loss, visual degradation (especially night vision from 5000 ft), tunnel vision, cyanosis, formication, unconsciousness and ultimately death. Factors that accelerate onset are higher altitude, longer exposure, exercise, temperature extremes, illness, fatigue, alcohol and drugs. Treatment is immediate oxygen and descent to a safe altitude or minimum safe altitude, whichever is higher.

Time of useful consciousness is the interval from loss of adequate oxygen until the pilot can no longer take corrective action. Typical values at rest are 30 minutes at 20 000 ft, 1–2 minutes at 30 000 ft, 30–90 seconds at 35 000 ft and 15–20 seconds at 40 000 ft; moderate activity shortens these times dramatically. Effective performance time is always shorter and highly individual. Hyperventilation is over-breathing that reduces blood carbon dioxide and therefore the acidity needed for haemoglobin to release oxygen. Causes include anxiety, motion sickness, shock, vibration, heat, high g and pressure breathing. Symptoms overlap those of hypoxia: dizziness, tingling, visual disturbance, temperature sensations, anxiety, muscular incoordination and eventual unconsciousness. Below 10 000 ft assume hyperventilation and slow the breathing rate; above 10 000 ft assume hypoxia and execute oxygen drills. After unconsciousness from hyperventilation recovery is automatic; after hypoxia without oxygen the outcome is death. Never reverse the assumption.

Cabin pressurisation normally maintains an equivalent altitude of 6000–8000 ft with a maximum differential of 8–9 psi. Rate of change is limited to 500 ft min⁻¹ ascent and 300 ft min⁻¹ descent to protect the middle ear. Rapid decompression exposes occupants to hypoxia, cold and decompression sickness; the aircraft must descend immediately to 10 000 ft or minimum safe altitude. Crew must don and check oxygen masks before assisting others. Decompression sickness arises when nitrogen comes out of solution as bubbles, producing the bends (joint pain), creeps (skin sensation), chokes (respiratory distress) and staggers (neurological impairment). Risk rises above 18 000 ft and is greatly increased by recent scuba diving. The strict rule is no flying within 12 hours of any compressed-air dive and no flying within 24 hours if depth exceeded 30 ft. Treatment of in-flight DCS is immediate descent, 100 percent oxygen, warmth, rest and urgent medical care on landing. Pre-oxygenation before high-altitude exposure reduces body nitrogen stores and therefore DCS probability.

Module 4. The Nervous System, Ear, Hearing and Balance Foundations

The nervous system comprises the central nervous system (brain and spinal cord), the peripheral nervous system (sensory and motor nerves) and the autonomic nervous system that regulates involuntary functions including arterial pressure, gastrointestinal activity, sweating, body temperature and the general adaptation (fight-or-flight) syndrome. Nerve impulses travel electrically along neurons and chemically across synapses. Reflex arcs can operate at spinal level without brain involvement, providing rapid protective responses. In aviation the autonomic system is especially relevant because it mediates the physiological reactions to stress, hypoxia and acceleration. Understanding that breathing, heart rate and vessel tone are largely automatic explains why conscious control is limited once hypoxia or hyperventilation has begun; the only reliable intervention is restoration of the correct inspired gas mixture or removal of the initiating stressor. Continuous self-monitoring of autonomic signs—pulse, breathing pattern, peripheral temperature—supplies early warning that homeostatic reserves are being taxed.

The ear performs two distinct functions: sound reception and spatial orientation. The outer ear collects sound via the pinna and auditory canal; the middle ear transmits vibrations through the ossicles (malleus, incus, stapes) to the oval window; the inner ear converts fluid motion in the cochlea into nerve impulses. The eustachian tube equalises pressure across the tympanic membrane; failure produces otic barotrauma. Audible range for a young person is roughly 20–20 000 Hz, with speech occupying 500–3000 Hz. Sound intensity is measured in decibels; permanent damage begins above continuous exposure to 90 dB and is accelerated by high-frequency noise. Conductive deafness results from damage to the conducting pathway; noise-induced hearing loss damages the cochlear hair cells, beginning with high frequencies; presbycusis is age-related deterioration. Aviation noise routinely exceeds safe levels; consistent use of hearing protection whenever exposed to high-intensity sound is a non-negotiable professional habit that preserves both medical fitness and long-term quality of life.

Balance and linear acceleration are detected by the vestibular apparatus. Three semicircular canals oriented at right angles sense angular accelerations greater than 0.5 ° s⁻²; otoliths in the utricle and saccule detect linear acceleration and head tilt greater than 0.1 m s⁻². Signals are processed by the cerebellum, which also predicts balance loss and initiates compensatory muscle action. In flight these sensors can generate somatogyral and somatogravic illusions when visual references are absent or misleading. Because the vestibular system evolved for terrestrial motion, its outputs under prolonged or unusual accelerations must always be subordinated to instrument indications. A practical cockpit rule is never to manoeuvre on the basis of bodily sensation alone when outside visual cues are degraded; cross-check attitude, heading and vertical speed immediately. Alcohol further impairs vestibular function and prolongs recovery from spatial disorientation; the only safe policy is zero alcohol within the regulated pre-flight period and preferably longer.

Module 5. Spatial Disorientation, Vestibular Illusions and Motion Sickness

Spatial disorientation remains a contributory factor in 37 percent of general-aviation accidents and 12 percent of commercial-transport accidents; more than 80 percent of accidents caused directly by disorientation are fatal. The most common manifestation is the leans, also called the somatogyral illusion. It arises whenever the vestibular apparatus fails to register a slow angular acceleration or adapts to a sustained turn. In the first case a gentle bank goes undetected; when the aircraft is later rolled level the semicircular-canal hairs bend and the pilot senses a false turn in the opposite direction. In the second case a prolonged turn allows the endolymph to settle so that the hairs erect; the subsequent roll-out again displaces the hairs and produces an identical false sensation. The conflict between visual and vestibular signals can persist for up to an hour. The practical countermeasure is absolute: in IMC believe the instruments; in VMC look at the true horizon. Never attempt to recover by «seat-of-the-pants» sensation. After any unusual attitude or prolonged turn, force a deliberate instrument cross-check before making control inputs.

The somatogyral illusion is the sensation of turning in the opposite direction that occurs when the body undergoes angular deceleration from sustained angular velocity. The classic operational expression is the graveyard spin. During a prolonged spin the endolymph settles and the sensing hairs erect; when recovery is initiated the hairs are again displaced, producing a strong sensation of spinning in the opposite direction. If the pilot follows that false cue the aircraft re-enters the original spin. The somatogravic illusion is the false sensation of pitch caused by linear acceleration acting on the otoliths. On take-off the resultant of thrust and gravity is interpreted as a nose-up attitude; on deceleration the opposite occurs. An air-driven artificial horizon can reinforce the error by displaying its own acceleration-induced climb or descent. The only reliable defence is continuous instrument monitoring during the acceleration phase and a pre-briefed decision never to pitch solely on bodily sensation. Both illusions illustrate why the visual system must always be treated as the primary spatial-orientation channel.

Coriolis effect is produced when a pilot maintains a steady turn and then moves the head at more than approximately three degrees per second. The sudden head motion cross-couples the semicircular canals and generates an erroneous sensation of change in turn rate. The practical implication is that any head movement during instrument manoeuvres must be slow and deliberate. Vertigo, a rotating or tumbling sensation, can be triggered by blocked eustachian tubes, sudden middle-ear pressure changes, high g-loadings or residual alcohol in the otolith stalks. Alcohol has a lower specific gravity than water; even after blood alcohol has returned to zero the substance can remain in the otoliths for up to three days and provoke disorientation or motion sickness with small head movements. The operational rule is therefore zero alcohol for at least 24 hours before flight and preferably longer whenever complex instrument work is expected.

Motion sickness is a normal response of a healthy vestibular system to unfamiliar real or apparent motion. It results from mismatch between visual and vestibular signals and produces nausea, hyperventilation, vomiting, pallor, cold sweating, headache and depression. Up to 8 percent of passengers on modern aircraft experience symptoms. The condition can appear even in a static simulator when expected motion does not occur. Training progression must therefore be gradual: gentle turns before steep turns, no aerobatics in early stages. After any prolonged break the same gradual re-exposure is required. Coping strategies include keeping the head as still as possible, reducing look-out head movements by concentrating on instrument flying, opening air vents, and, only after aviation-medical consultation, the use of hyoscine. Chronic sufferers must be referred to the organisation’s aviation medical specialist; self-medication is never acceptable.

Module 6. Structure and Function of the Eye

The eye functions as a biological camera. Light enters through the cornea, which provides 70–80 percent of the total focusing power by its fixed curvature. The iris, acting as a diaphragm, rapidly adjusts pupil diameter over a five-to-one range to control the amount of light reaching the retina. Final fine focus is achieved by the lens, whose shape is altered by the ciliary muscles—a process called accommodation. Near objects require a thickened lens; distant objects require a flattened lens. The inverted image formed on the retina is reinterpreted by the brain as upright. Fatigue or ageing reduces accommodative power and produces blurred near vision. In the cockpit the practical consequence is that instrument scanning distance and external visual range must both be considered when setting seat position and lighting; any sudden onset of blurred near vision after prolonged instrument work is an early fatigue warning that should trigger a rest break or oxygen check.

The retina contains two types of photoreceptor. Cones, concentrated at the fovea, provide high-acuity photopic (daylight) colour vision; each cone has its own neurone, allowing discrimination of approximately one thousand colour shades. Rods, densest about ten degrees from the fovea, provide scotopic (night) black-and-white vision and are highly sensitive to movement; several rods share a single neurone. Mesopic vision occurs when both systems operate. Only the fovea achieves 20/20 or 6/6 acuity; at five degrees eccentricity acuity already falls to 20/40 and at twenty-five degrees to 20/200. Alphanumeric information is therefore usable only when imaged on the fovea. Night scanning must deliberately use peripheral rod vision by looking ten to fifteen degrees off the target. Both rods and cones are direct extensions of the brain and are therefore highly vulnerable to hypoxia, alcohol, drugs and smoking—factors that must be eliminated before any night or high-altitude sector.

Light adaptation to sudden high illumination occurs in about ten seconds, but prolonged bright exposure depletes photochemicals and temporarily impairs subsequent dark vision. Full dark adaptation requires approximately seven minutes for cones and thirty minutes for rods; even a brief flash of bright light restarts the process. Night-vision degradation without supplemental oxygen reaches 5 percent at 1 100 m, 18 percent at 2 800 m, 35 percent at 4 000 m and 50 percent at 5 000 m. Additional degraders include age, mild hypoxia, cabin altitudes above 5 000 ft, smoking (20 cigarettes per day costs roughly 20 percent night vision), alcohol, minor illness and vitamin-A deficiency. Standard airmanship therefore includes avoiding bright light for thirty minutes before night flight, raising cockpit lighting when thunderstorms are forecast, and treating any unexplained loss of night acuity as a possible early hypoxia cue.

The optic-nerve head creates a physiological blind spot devoid of photoreceptors. An aircraft on a constant collision bearing can remain inside this spot until very late if the observer stares fixedly ahead. Safe visual look-out therefore demands continuous eye movement with minimal dwell time in any single direction. When both eyes are open the contralateral eye normally covers the blind spot; however an intervening cockpit structure can still hide the threat. Empty-field myopia is the tendency of the relaxed eye to focus at 1–1.5 m rather than infinity when no visual detail is present. In cloudless high-altitude skies, total darkness or uniform overcast the eyes therefore miss distant traffic. The countermeasure is deliberate periodic refocusing on known distant objects or wing-tips. Stereopsis, the depth cue derived from binocular disparity, is useful only within approximately 60 m and is irrelevant for most en-route traffic avoidance.

Module 7. Visual Performance Limits, Protective Measures and Pathology

High-altitude flight exposes the eye to elevated levels of high-energy blue and ultraviolet light that can produce cumulative retinal and lenticular damage. Suitable sunglasses must therefore be impact-resistant, thin-metal-framed, polycarbonate-coated, optically high-quality, with 10–15 percent luminous transmittance and appropriate spectral filtration. Cheap sunglasses that over-diffuse light, polarising lenses that interact with laminated windscreens, and photochromic lenses whose dark-to-clear transition is too slow are all operationally unacceptable. The practical selection rule is to purchase only after consultation with an aviation-knowledgeable optician and to carry a spare clear pair at all times. Polarising lenses additionally distort cloud appearance and suppress ground reflections useful for VFR navigation; they are therefore discouraged for professional flight.

Refractive errors are corrected by appropriate lenses. Hypermetropia (long-sightedness) results from a shorter eyeball and is corrected by a convex lens; myopia (short-sightedness) results from a longer eyeball and is corrected by a concave lens. Presbyopia, the age-related loss of lens elasticity, appears after approximately forty years and is managed with weak convex reading lenses or bifocals. Astigmatism caused by corneal irregularity is corrected by cylindrical (toric) lenses or modern laser reshaping. Licence retention requires corrected acuity of at least 6/9 in each eye and 6/6 binocular, plus the ability to read normal small print at 30 cm. Any pilot required to wear corrective spectacles must carry an easily accessible spare pair. Contact lenses improve peripheral vision and eliminate misting but introduce risks of corneal hypoxia, dehydration and bubble formation under decompression; bifocal contact lenses remain prohibited. Medical clearance for contact-lens use always includes the requirement to carry ordinary spectacles as back-up.

Cataracts produce progressive clouding of the lens and marked loss of vision; modern outpatient surgery with local anaesthesia and intraocular-lens replacement normally restores flying status. Glaucoma is a rise in intraocular pressure (normal range 10–20 mm Hg) that damages the optic nerve and can cause irreversible blindness if untreated. Symptoms include acute eye pain, blurred vision, photophobia, visual-field loss and red discoloration. Screening forms part of every Class 1 medical; treatment is by topical beta-blockers such as timolol or by surgical creation of a drainage channel. Colour vision is essential for navigation lights, runway lighting, charts, cockpit displays and light signals. Total colour blindness is disqualifying; the common red-green defect, while not affecting acuity, must be disclosed and assessed. High-speed low-level flight (greater than 450 kt below 500 ft) extends total reaction time because the visual-perception cascade itself can stretch beyond the ideal one second when atmospheric conditions, darkness, object size or angular approach are unfavourable. Monocular pilots may retain Class 2 medicals after adaptation, but EASA Class 1 requires binocular vision.

Module 8. Acceleration Forces and G-Tolerance in Flight

Acceleration is classified as linear, radial or angular. Positive Gz pools blood in the lower body, reduces cerebral and ocular perfusion and produces greying-out above 3–4 g then G-LOC above 5 g. Negative G forces blood into the head, causes red-out and facial vessel rupture. Tolerance is reduced by hypoxia, fatigue, heat, alcohol and obesity. Anti-g straining and suits raise positive tolerance by 1.5–2 g.

Short-duration impact forces are limited by skeletal strength: 25 g vertical and 45 g fore-aft. Five-point harnesses with anti-submarining straps give best protection. Lap straps alone allow jack-knifing and internal injury. Always verify harness tension before take-off and after any significant attitude change.

Long-duration positive G tolerance for a relaxed subject is about +3.5 g. Raising knees, tensing legs and rhythmic anti-g straining can raise this to +7–8 g. Negative G tolerance is only –3 g for a few seconds. Body position (prone or supine) can tolerate up to 12 g by eliminating hydrostatic gradients.

Susceptibility to G rises with smoking, low blood sugar, hypotension and stress. Practical tip: never commence high-G manoeuvres when dehydrated or after a heavy meal. Monitor for early visual tunnelling and reduce G immediately if greying occurs.

Module 9. Barotrauma and Pressure Equalisation

Otic barotrauma occurs mainly on descent when the Eustachian tube fails to re-open. Symptoms include pain, temporary deafness, tinnitus and pressure vertigo. Clearing techniques are Frenzel, gentle Valsalva, swallowing or jaw movement. Never force a violent Valsalva as it can induce vertigo.

Sinus barotrauma produces severe peri-orbital pain that can disable the pilot. Unlike otic problems it may be equally acute on climb or descent. Immediate action is to return to the altitude of onset and descend slowly. Never fly with an active upper-respiratory infection.

Aerodontalgia is tooth pain from expanding gas trapped under fillings or in abscesses, most common on ascent. Prevention is regular dental care. Gastrointestinal gas in the small intestine expands and can cause incapacitating pain; avoid gas-producing foods and chewing gum before flight.