HYPOXIA
Hypoxia results when the body lacks oxygen. Hypoxia tends to be associated with flights at altitudes. However, many other factors such as alcohol abuse, heavy smoking, & various medications interfere with the blood’s ability to carry oxygen.
INDIVIDUALS PHYSIOLOGICAL ALTITUDE.
Drugs. Many medications have an unexpected effect when combined with high altitudes. Never self-medicate, even w/ over the counter drugs.
Alcohol. 1 ounce of alcohol can give the body a physiological altitude up to 2000’.
Smoking. The hemoglobin molecule of RBCs has a 200-300 times greater affinity for CO than for O2. Smoking 3 cigarettes in rapid succession or 20 to 30 cigarettes w/ in a 24 hr period gives a physiological altitude of 5000’ at sea level & a 20% reduction of night vision.
CLASSIFICATIONS:
Hypoxic. Occurs when not enough O2 is in the air or when decreasing atmospheric pressures prevent the diffusion of O2 from the lungs to the bloodstream. Typically, Occurs at higher altitudes.
Hypemic. or anemic, hypoxia is caused by a reduction in the oxygen-carrying capacity of the blood. Anemia & blood loss are the most common causes. CO,nitrites, & sulfa drugs also cause this by forming compounds w/ hemoglobin & reducing the hemoglobin that is available to combine w/ O2.
Stagnant. O2 carrying capacity of the blood is adequate, but circulation is inadequate. Conditions as heart failure, arterial spasm, & occlusion of a blood vessel predispose the individuals to stagnant hypoxia. More often, a crew member experiences extreme gravitational forces, causing the blood to be stagnant.
Histotoxic. Results when there is interference with the use of O2 by body tissues. Alcohol, narcotics, & certain poisons-cyanide- interfere the cell’s ability to use an adequate supply of oxygen.
STAGES
Indifferent. (0’ – 10,000’)
Night vision deteriorates at about 4000’. When approaching 10,000’ visual acuity begins to decrease.
Compensatory. (10,000’ – 15,000’)
The circulatory & the respiratory system provide some defense against hypoxia at this stage. The pulse rate, systolic blood pressure, circulation rate, & cardiac output increase. Respiration increases in depth & sometimes in rate. At 12,000’ to 15,000’ the effects of hypoxia on the nervous system become increasingly apparent. After 10-15 min, impaired efficiency is obvious. Crew members may become drowsy & make frequent errors in judgment. May become difficult to do even simple task. Easy to overlook these symptoms.
Disturbance. (15,000’ – 20,000’)
The physiological responses can no longer compensate for the O2 deficiency. Subjective symptoms include fatigue, sleepiness, dizziness, headache, breathlessness, & euphoria. Objective symptoms include:
Senses: peripheral & central vision are impaired, & visual acuity is diminished. Weakness & loss of muscular coordination are experienced. Sensations of touch & pain are diminished or lost. Hearing is one of the last senses lost.
Mental Processes: Intellectual impairment is an early sign that often prevents the individual from recognizing disabilities. Thinking is slow, & calculations are unreliable. Short-term memory is poor, & judgment & reaction time is affected.
Personality Traits: Person may display traits & emotions much the same as with intoxication. Euphoria, aggressiveness, overconfidence, or depression can occur.
Psychomotor Functions: Muscular coordination is decreased, & delicate or fine muscular movements may be impossible. Stammering & illegible handwriting are typical impairments.
Cyanosis: the skin becomes bluish in color. This effect is caused by O2 molecules failing to attach to hemoglobin molecules.
Critical (20,000’ and above)
Within 3 to 5 minutes, judgment, & coordination usually deteriorate. Subsequently, mental confusion, dizziness, incapacitation, & unconsciousness occur.
PREVENTION of HYPOXIC HYPOXIA
Education is the greatest prevention. Hypoxic hypoxia is the type most often encountered in aviation. The other 3 may also present danger to aviators.
HYPERVENTILATION
An excessive rate & depth of respiration leading to abnormal loss of CO2 from the blood. Condition occurs more often among aviators than generally recognized. The human body reacts under conditions of stress & anxiety. Often, a marked increase in breathing occurs. This leads to a significant decrease in the CO2 content of the body & a change in the acid-base balance.
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SIGNS & SYMPTOMS
Dizziness, muscle spasms, unconsciousness, visual impairment, tingling sensations, & hot/cold sensations.
TREATMENT
The most effective method is reduction in the affected individuals rate of respiration. However, an extremely apprehensive person may not respond to directions to breathe more slowly. The normal rate is 12 to 16 breaths per minute. Treat by controlling breathing & go to 100% O2. If symptoms continue & conscious control of respiration is not possible, the individual should talk or sing. It is physiologically impossible to talk & hyperventilate at the same time.
PRESSURE CHANGE EFFECTS
DYSBARISM
The human body can withstand enormous changes in barometric pressure as long as air pressure in the body cavities equals ambient air pressure. Difficulty occurs when expanding gas cannot escape. DYSBARISM- refers to the various manifestations of gas expansions induced by decreased barometric pressures.
Boyle’s Law: states that the volume of a gas is inversely proportional to its pressure, with temperature remaining constant.
Trapped Gas Disorders.
Free gas normally present in various body cavities expands. If the escape of the expanded volume is impeded, pressure builds up and pain is experienced. Greater pressure changes occur from 15,000’ down to 0’ PA, especially 5000’ to 0’ PA.
Gastrointestinal
Gas expansion in digestive tract. Not serious most of the time, unless above altitudes of 25,000’.
☺Preventive measures: avoid eating high gas foods, such as: onions, cabbages, raw apples, radishes, dried beans, cucumbers, & melons. Chewing the food well is important. Avoid carbonated drinks & chewing gum during ascent.
☺Relief: belching or passing flatus, if pain persist, descent to lower altitude is necessary.
Middle Ear Discomforts
The Eustachian tube normally allows air to pass outward from the middle ear. However, with an increase in pressure during descent, the pressure of the external ear is higher than the pressure in the middle ear & the ear drum is forced inward. If the pressure differential increases appreciably, it may be impossible to open the eustachian tube. Very painful & eardrum can rupture if the pressure is not equalized.
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Blocked Eustachian Tube
☺Relief: Normally you can equalize pressure by swallowing, yawning, or tensing the throat muscles. If this fails, perform the valsalva maneuver. If the pain increase with further descent, relief can only be obtained by ascending to an altitude where the pressure can be equalized. Then a slow descent is recommended.
Sinus Pain
Sinus openings may become obstructed when the mucous membrane lining swells as a result of an infection or allegoric reaction. Viscous secretions may also cause the openings to be covered. These conditions may make it impossible to equalize pressure. Change of altitude produces a pressure differential between the inside & the outside of the cavity, sometimes causing severe pain. Unlike, the ears, the sinuses are equally affected by ascent & descent. Could involve any three of areas of the sinuses: ethmoid, frontal, & Maxillary.
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SINSUS AREAS
☺Avoid flying with a cold or congestion & valsalva often during descent.
Evolved Gas Disorders
Occurs inflight as a direct result of a reduction of atmospheric pressure. Also known as decompression sickness. Typically, pressure altitudes over 18,000’.
Henry’s Law: states that the amount of gas dissolved in a solution is directly proportional to the pressure of the gas over the solution.
Bends
At the onset, pain in the joints & related tissues may be mild, but it can become deep, gnawing, penetrating, & eventually intolerable. The pain is progressive & gets worse if ascent is continued.
Chokes
Symptoms occurring in the thorax are caused by innumerable small bubbles that block the smaller pulmonary vessels. At first, a burning sensation is citied under the sternum. As the condition progresses, the pain becomes stabbing & inhalation is markedly deeper. There is almost uncontrollable desire to cough. Finally, there is a sensation of suffocation; breathing becomes more shallow & the skin bluish. An immediate descent is imperative.
Paresthesia
Tingling, itching, cold, & warm sensations that are believed to be caused by bubbles formed locally or in the CNS where they involve nerve tracts leading to the affected areas in the skin.
CNS
In rare cases when aircrews are exposed to high altitude, symptoms may indicate that the brain or the spinal cord is affected by nitrogen bubble formation. The most common symptoms are visual disturbances such as the perception of lights flashing or flickering when they’re actually steady.
STRESS
Stress is the nonspecific response of the body to any demand placed upon it. Stress is a physiological phenomenon involving actual changes in the body’s chemistry & function, and Stress involves some perceived or actual demand for action. Any event which requires you to adjust or adapt in some way is a source of stress, also called a stressor.
TYPES OF STRESSORS
Psychosocial. These stressors may trigger adaptation or change in one’s lifestyle, career, and/or interaction with others. Positive or negative. Job stress: low morale/unit cohesion/boredom/fatigue/over-tasking/poorly defined responsibilities, Illness: organic diseases/fatigue, & Family issues: family commitments/spousal relationships.
Environmental. Those things found in our every day job. Altitude: altitudes below 5000’/ trapped gas causing ear or sinus problems. Speed: associated with speeds > than those experienced in every day life cause a higher degree of alertness & concentration over long periods. Hot or Cold: use proper clothing or equipment. Aircraft Design: cockpit illumination/instrument location/seat comfort/heating & ventilating systems/visibility/noise level. IMC conditions: increased vigilance & accuracy reading, following, monitoring flt instruments are very stressful.
Physiological. Self-imposed stressors or maladaptive behaviors that are potentially debilitating & threaten aviation safety. Acronym DEATH.
- Drugs. Self-medication: may incur unwanted side-effects. Caffeine most commonly ingested. Limit or avoid drugs unless prescribed by a flt surgeon.
- Exhaustion. Lack of rest and poor sleep. Lack of exercise impairs circulatory efficiency, reduces endurance, & increases likelihood of illness.
- Alcohol. Affects of alcohol depend on: the amount of alcohol consumed/the rate of absorption from the stomach & small intestines/the body’s rate of metabolism, 1 oz every 3 hrs.
- Tobacco. Use of any tobacco product is detrimental.
- Hypoglycemia. maintain a well-balanced diet to avoid low blood sugar, which could cause weakness or fainting, , fatigue, & inefficiency’s.
Cognitive. How one perceives a given situation or problem is a potentially significant & frequently overlooked source of stress. Pessimism, obsession, failure to focus on the present, and/or low self-confidence can create a self-fulfilling prophecy that will ensure a negative outcome. Musts & Shoulds: lack of flexibility in thinking causes problems when reality does not accommodate one’s wishes. Failure to accept the possibility that things may happen contrary to one’s wishes leaves one unprepared, frustrated, & dysfunctional. Failure to Focus on the Here & Now: living in the past or future & overemphasizing what should have been or what could be, can increase one’s overall stress.
STRESS RESPONSE
Emotional Responses. Ranges from increased anxiety, irritability, or hostility to depressed mood, loss of ones self-esteem, hopelessness, & inability to enjoy life.
Behavioral Responses. High stress can adversely affect one’s work performance, decrease motivation, & increase the likelihood of conflict, insubordination, & violence in the workplace. Some individuals become socially isolated. Others may abuse drugs or alcohol.
Cognitive Responses. Stress can significantly affect one’s thought processes. It can decrease attention & concentration, interfere with judgment & problem solving, & impair memory.
Simplification Heuristic: under high stress conditions, people tend to oversimplify problem solving & ignore important relevant information, taking the easy way out.
Stress-Related Regression: individuals under high-stress conditions will forget learned procedures & skills & revert to bad habits.
Perceptual Tunneling: individual or an entire crew under high stress becomes focused on one stimulus, & neglects to attend to other important task/information such as flying the aircraft. A similar situation may occur when an aviator realizes during flight that he or she overlooked some aspect of flight such as missing a radio call. The stressed aviator may then overattend to rectifying this problem/become emotionally & mentally fixated on the error & fall “behind the aircraft.”
Physical Responses. involves overall heightened arousal of the body. Increased heart rate, increased blood pressure, more rapid breathing, tensing of the muscles, & the release of sugars & fats into circulation to provide fuel for “fight or flight.” Prolonged stress & its continuous effects: muscle tension & pain, headaches, high blood pressure, decreased immunity to infectious diseases.
Stress Underload. Too little stress may be dysfunctional as having too much stress. A lack of challenges: complacency, boredom, & impulsive risk taking.
STRESS & PERFORMANCE
Physical Characteristics of the Individual. Differences in strength, endurance, & physical health effects stress performance.
Psychological Makeup of the Individual. Individuals with good coping, problem solving, & social skills will cope more efficiently.
Mental Skills Required by the Task or Situation. Attention, concentration, memory, problem solving, or spatial orientation will influence the extent to which stress will degrade performance.
Stress Characteristics of the Individual. Taking a stressful, timed problem-solving test in a quiet comfortable room is much easier & will result in fewer errors than taking the same test in a hot, noisy room.
STRESS MANAGEMENT
Avoiding Stressors. Most powerful mechanism. Avoid with good planning, foresight, realistic training, good time management, & effective problem solving. Stay physically fit & eat right. Good crew coordination & communication.
Changing Your Thinking. Practice positive self-talk, taking responsibility for your actions, avoiding perfectionism & inflexibility in thinking, focusing on the here & now rather than the past or future.
Learning to Relax. Use breathing exercises, meditation, or regularly engaging in a quiet hobby, greatly reduces stress.
FATIGUE
The state of feeling tired, weary, or sleepy that results from prolonged mental or physical work, extended periods of anxiety, exposure to harsh environments, or loss of sleep.
Acute Fatigue. Associated with physical or mental activity between 2 regular sleep periods. Loss of awareness of errors & coordination first to develop. Crew members feel this tiredness at night after being awake for 12 to 15 hrs in a day. Characterized by: inattention, distractibility, errors in timing, neglect of secondary task, loss of accuracy & control, lack of awareness of error accumulation, & irritability.
Chronic Fatigue. Result of inadequate recovery from successive periods of acute fatigue. It may take several weeks of rest to completely eliminate chronic fatigue & there may be underlying social causes, such as family or financial difficulties. Characterized by: insomnia, depressed mood, irritability, weight loss, poor judgment, loss of appetite, slowed reaction time, poor motivation & performance on the job.
Motivational Exhaustion or Burnout. If chronic fatigue proceeds untreated for too long, the individual will eventually “shut down” & cease functioning occupationally & socially.

DIURNAL (CIRCADIAN) RHYTHMS & FATIGUE
We have an intrinsic biological clock with a cycle of roughly 24 to 25 hours, & many important bodily functions such as core body temperature, alertness, heart rate, & sleep cycle occur along these diurnal rhythms.
Circadian Desynchronization (Jet Lag)
Rapid travel from one time zone to another causes the body to resynchronize its diurnal rhythms. Sleep disorders & fatigue will prevail. Resynchronization occurs more rapidly when traveling west.
THE SLEEP CYCLE
The sleeping brain cycles between rapid eye movement & non-REM sleep through five stages. Cycling occurs every 90 minutes. The duration & quality sleep depend on body temperature. It is the timing of sleep, not the amount that matters. A sleep schedule that is inconsistent w / ones circadian rhythm & the light & social cues of the environment will ultimately result in fatigue. Frequent changes in sleep patterns may also result in fatigue. Sleep efficiency deteriorates with age.
SLEEP REQUIREMENTS
During operations in which sleep loss is expected, aircrew members should closely monitor each others behavior for indications of fatigue. Avg person sleeps 7 to 9 hrs per day. Sleep length can be reduced 1-2 hrs without performance decrement over an extended period. As a RULE, five hours of sleep per night are the minimum for continuous operations (for example 14 days).
PREVENTION OF FATIGUE
Control the sleep environment, adjust to shift work, maintain good health & physical fitness, practice good eating habits, practice moderate controlled use of alcohol & caffeine, plan & practice good time management, practice realistic planning, maintain optimal working conditions, & Take naps.
Treatment of Fatigue. The most important action is to get rest & natural (not drug induced) sleep. Alcohol is the number one sleep aid in the U.S., but it suppresses REM sleep. If you find yourself lying awake more than 30 minutes; get out of bed & read a boring book or listen to some relaxing music. When attempting to recover from 24 to 48 hrs of sleep deprivation; do not sleep longer than 10 hrs.
TOXIC HAZARDS IN AVIATION
The greatest toxicological risk during flight is short-term, high level exposure to toxic agents. Ground support personnel may be affected by chronic exposure to toxic agents. These agents can be inhaled, ingested, or absorbed into the body. The two most common entry points are the repiratory tract & the skin.
AIRCRAFT CONTAMINATION
Normally results from exhaust gases, tetraethyl lead, fuel, carbon monoxide, engine lubricants, & oxygen contaminants in the cockpit.
Carbon Monoxide. A colorless, odorless gas that is lighter than air. The effects are subtle & deadly. Results from incomplete combustion. It is the most common gaseous poison in aviation.
ACCELERATION
Change in velocity with respect to time.
Linear. A change in speed without a change in direction/heading.
Radial, or Centripetal. A change in any direction w/ out a change in speed.
Angular. A change in both speed & direction simultaneous. ie..Aircraft in a tight spin.

G-FORCE
Inertial force is = to but opposite acceleraion
Positive G, or +Gz body is accelerated in the headward direction. The inertial force acts in the opposite direction toward the feet, body forced down into seat.
Negative G, or –Gz body is accelerated in the footward direction. Inertial force is toward the head, & the body is lifted out of the seat.
Forward Transverse G, or +Gx accelerative forces acts in a chest-to-back direction. ie..acceleration down a runway.
Backward Transverse G, or –Gx accelerative forces acts in a back-to-chest direction. ie..deceleration, braking on a runway.
Right or Left Lateral G, ±Gy accelerative force impacts across the body from shoulder-to-shoulder direction.
Factors Affecting Accelerative Forces.
Intensity, Duration, Rate of Onset, Body Area & Site, & Impact Direction.
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Inertial Vectors
NOISE

|Frequency (Db) |Effect |
|0 |Threshold of Hearing |
|65 |Avg Human Convsat. |
|85 |Dmg-Risk Limit |
|120 |Threshold of Discomfort |
|140 |Threshold of Pain |
|160 |Eardrum Rupture |

Sound Intensities

|Exposure Duration-Day |Max Exposure Level |
|(hours) |(db) |
|8 |85 |
|4 |90 |
|2 |95 |
|1 |100 |
|1/2 |105 |
|Note: For every 5-db noise intensity increases, the |
|exposure time limit is cut in half. |

Recommended Exposure Levels

|Aircraft |Hearing Protector|Effective |
| | |Exposure Lvl |
|UH-60A |HGU-56 |90.6 |
| |SPH-4B |90.6 |
| |SPH-4 |95.1 |

Est Attenuation Levels

Hearing Loss. Such factors as age, health, & noise environment cause hearing loss. 3 types

Conductive. Occurs when some defect or impediment blocks sound transmission from the ext ear to the inner ear. Ie..wax build-up, middle-ear fluid, & calcification of the ossicles.
Presbycusis. Results from old age. The hair cells of the cochlea become less resistant as people age.
Sensorineural. Hair cells of the cochlea are damaged in the inner ear. Primary cause is noise exposure, but disease or aging can also. Higher freq are lost first.
Mixed. Ear infection can cause hearing loss. Sensorineural hearing loss is not treatable.
SPATIAL DISORIENTATION (SD)
Spatial disorientation is an individuals inability to determine his position, attitude, & motion relative to the surface of the earth. Or significant objects. Ie..trees, poles, or building during a hover. When it occurs, pilots are unable to see, believe, interpret, or prove the information derived from their flt instruments.
Sensory Illusion. is a false perception of reality caused by a conflict of orientation information from 1 or more mechanisms of equilibrium. Sensory illusions are a major cause of Spatial Disorientation.
Vertigo. is a spinning sensation usually caused by a peripheral vestibular abnormality in the middle ear. Pilots often misuse the term vertigo, applying it generically to all forms of spatial disorientation.
TYPES OF SPATIAL DISORIENTATION
TYPE I. (UNRECOGNIZED) A disoriented aviator does not perceive any indication of spatial disorientation, he does not think anything is wrong. THE MOST DANGEROUS TYPE-because he fails to recognize or correct the disorientation, usually resulting in a crash.
☺ SD would be height-/depth perception illusion when the pilot descends into the ground or some obstacle because lack of situational awareness.
TYPE II (RECOGNIZED) The pilot perceives a problem (resulting from SD). The pilot may fail to recognize it as SD.
☺ The pilot may feel that a control is malfunctioning.
☺ The pilot may perceive an instrument failure as in a graveyard spiral.
TYPE III (INCAPACITATING) The pilot experiences such an overwhelming sensation of movement that he cannot orient himself by using visual cues or the acft instruments. Not fatal if pilot can gain control of the aircraft.
EQUILIBRIUM MAINTENANCE

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Equilibrium Systems

Visual System. The visual system is the most important in maintaining equilibrium & orientation. 80% of our orientation information comes from the visual system.
☺ IMC-must rely on instruments for Spatial Orientation. Demands disciplined tng.
Vestibular System. Inner ear contains the vestibular system, which contains the motion- & gravity detecting sense organs. Located in the temporal bone on each side of the head. Each vestibular consist of 2 distinct structures; semicircular canals / vestibule proper, which contain the otolith organs.

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Vestibular System
Vestibule Proper. The otolith organs are small sacs located in the vestibule. Sensory hairs project from each macula into the otolithic membrane, an overlaying gelatinous membrane that contains chalklike crystals, called otoliths. They respond to gravity & linear accelerations/decelerations. Changes in position of the head, relative to the gravitational force, cause the otlithic membrane to shift position on the macula. The sensory hairs bend, signaling a change in head position.
Semicircular Canals. They sense changes in an angular acceleration. The canals will react to any changes in roll, pitch, or yaw attitude.
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The endolymph fluid in the canals move with inertial torque resulting from angular acceleration in one of three planes. The motion of the fluid bends the cupula which moves the hairs of the hair cells situated beneath the cupula. This movement stimulates the vestibular nerve & these impulses are transmitted to the brain where they are interpreted as rotation of the head.
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Cutaway view of Semicircular Canals
Proprioceptive System. The systems reacts to the sensation resulting from pressures on joints, muscles, & skin & from slight changes in the position of internal organs. Forces act upon the seated pilot in flight.

ILLUSIONS
Visual Illusions. (IMC, Day, Night, Tactical flt)
Illusions give false impressions or misconceptions of actual conditions; therefore aircrew members must understand the type of illusions that can occur & the resulting disorientation. Although the visual system is the most reliable of the senses, some illusions can result from misinterpreting what is seen; what is perceived is not always accurate.FFF CRASH SARC
False Horizon. Confusing cloud formations or uneven ground w/ the horizon. This is usually occurs when the aviator looks up after a prolonged period in the cockpit or from poor scanning technique.
Flicker Vertigo. A light flickering at a rate of 4 to 20 cycles per second can produce nausea, vomiting & vertigo. It can be caused by sunlight flickering through the rotor blades or by an anticollision light reflecting against an overcast sky at night. DO NOT CLOSE your eyes, it will intensify the effect.
Fixation. This occurs when aviators ignore orientation cues & fix their attention on a single goal or object without seeing the whole environment. May occur during times of task saturation or target fixation.
Confusion. A common occurrence is to confuse ground lights with stars. A good cross check will prevent this illusion.
Relative Motion. Mistaking the motion of another aircraft or object for that of your own. Could occur during formation flight, hover taxi, or hovering over water or tall grass. The use of proper scanning techniques helps prevent this illusion.
Autokinesis. When a static light is stared at in the dark for 6 to 12 seconds, the light appears to move up too 20 degrees in any direction. Reduce or eliminate by visual scanning, increasing the number of lights, or by varying light intensity.
Structural illusion. The distortion of objects caused by heat waves, rain, snow or other factors that obscure vision. This illusion can be linked to mirages.
Height Perception Illusion. When flying over terrain lacking good contrast (water, desert, snow), crew members may think the aircraft is higher or lower than it actually is. This is due to a lack of visual references. It can be overcome by dropping an object of known size or intensity from the aircraft or by using shadows cast by surrounding objects or the aircraft. At night drop a chem.-stick or flare before landing.
Size-Distance Illusion. Viewing a source of light that is increasing or decreasing in luminance. The aviator may incorrectly interpret the light as approaching or retreating. It also is the false perception of distance from an object or the ground. It occurs when visual cues such as a runway or trees are different size than expected. Montana vs. Alabamas vegetation differences. Shooting an approach to a large runway vs. a small stage field lane. On larger runways an aviator may perceive he is too low when landing.
Altered Planes of Reference The pilot has an inaccurate sense of altitude, attitude, or flt path position in relation to an object so great in size that the object becomes the new plane reference. When approaching a line of mountains or clouds, aviators may feel they need to climb even though their attitude is adequate.
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Reversible Perspective. At night, an aircraft may appear to be going away when it is actually approaching. This illusion often occurs when an aircraft is flying a parallel course. To avoid this illusion observe the lights. Red on right returning.
Crater Illusion. Occurs when aircrew members land at night, under NVG conditions, and the IR searchlight is directed too far under the nose of the aircraft. This will cause the illusion of landing with up-sloping terrain in any directions. Depressing lulls the pilot into continuing to lower the collective. Could result in the aircraft prematurely impacting the ground, causing damage. If observing another aircraft during hover taxi, the aviator may perceive that the crater actually appears to move with the aircraft being observed.
Somatogravic Illusions. are caused from changes in linear acceleration & gravity that stimulate the Otolith Organs.
Oculogravic. Cccurs when an aircraft is accelerated or decelerates in a forward direction. Inertia from linear acceleration causes the otolith organs to sense a nose-high altitude. A pilot correcting for this illusion without cross checking the instruments would most likely dive the aircraft, catastrophic during an approach. This illusion does not occur if adequate references are outside.
Elevator Illusion. This occurs during upward acceleration. Because of inertia, the pilot’s eyes track downward as his body tries, through inputs supplied by the inner ear, to maintain visual fixation on the environment or instrument panel. With the eyes downward, the pilot senses that the nose of the aircraft is rising. Common for aviators flying aircraft that encounter updrafts.
Oculoagravic Illusion. Results from the downward motion of the aircraft. Because of inertia the pilot’s eyes will track upward. This usually results in a sensation that the aircraft is in a nose-low attitude. This illusion is commonly encountered during autorotation.
Somatogyral Illusions. Are caused when angular accelerations & decelerations stimulate the semicircular canals.
Leans. The most common form. The pilot fails to perceive angular motion. During continuous straight-&-level flight, the pilot will correctly perceive that he is straight & level. However, a pilot rolling into or out of bank may experience perceptions that disagree with the reading on the attitude indicator & other instruments. To counter the falsely perceived position, the pilot will lean his body until the false sensation leaves.
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Graveyard Spin. Usually occurs in fixed-wing aircraft. If you enter a spin & remain in it for several seconds, the semicircular canals will reach equilibrium; no motion is perceived. Upon recovering from the spin, you undergo deceleration, which is sensed by the semicircular canals. You then have a strong sensation of being in a spin in the opposite direction even though the flight instruments contradict that perception. If deprived of external references, you may disregard the instruments & make control corrections aginst the falsely perceived spin. The aircraft will then enter a spin in the original direction.
Coriolis Illusion. The most dangerous of all, causing overwhelming disorientation.
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Occurs whenever a prolonged turn is initiated & the pilot makes a head motion in a different geometrical plane. When a pilot enters a turn & then remains in the turn, the semicircular canal corresponding to the yaw axis is equalized. The endolymph fluid no longer deviates, or bends, the cupula. If the pilot initiates a head movement in a geometrical plane other than that of a turn, the yaw axis semicircular canal is moved from the plane of rotation to a new plane of nonrotation. The fluid then slows in that canal, resulting in a sensation of a turn in the direction opposite that of the original turn. Simultaneously, the two other canals are brought within a plane of rotation. The fluid stimulates the other two other cupulas. The combined effect of the coupler deflection in all three canals creates the new perception of motion in three different planes of rotation: yaw, pitch, & roll. The Pilot experiences an overwhelming head-over-heels tumbling sensation.
PREVENTION
These sensations can happen to anyone because they are due to the normal functions & limitations of the senses. Training, instrument proficiency, good health, & aircraft design minimize SD. SD becomes dangerous when pilots become incapable of making their instruments read right. All pilots regardless of experience level can experience of SD.